The Dependency Map (DepMap) is a genome-wide pooled
CRISPR-Cas9 knockout proliferation screen conducted in more than 700 cancer cell lines spanning many
different tumor lineages. Each cell line in the DepMap contains a unique barcode, and each gene
knockout is assigned a “dependency score” on a per cell-line basis which quantifies the rate of
CRISPR-Cas9 guide drop. It has been found that proteins with similar DepMap scores across cell
lines, a phenomenon known as co-dependent genes, have closely related biological functions. This can
include activity in the same or parallel pathways or membership in the same protein complex or the
same pathway.
We identified the strongest seven co-dependent genes (“Symbol”) for DUBs and ran GO enrichment
analysis. We used Biogrid, IntAct, and Pathway Commons PPIDs, and the NURSA protein-protein
interaction databases (PPIDs) to determine whether co-dependent genes interact with one another. The
“Evidence” column contains the PPIDs in which the interaction appears as well as whether there is
support for the association by an INDRA statement. As another approach to identify potential
interactors, we looked at proteomics data from the Broad Institute's Cancer Cell Line Encyclopedia (CCLE) for
proteins whose expression across ~375 cell lines strongly correlated with the abundance of each DUB;
it has previously been observed that proteins in the same complex are frequently significantly
co-expressed. The correlations and associated p-values in the CCLE proteomics dataset are provided.
And, we determined whether co-dependent genes yield similar transcriptomic signatures
in the Broad Institute's Connectivity
Map (CMap). A CMap score greater than 90 is considered significantly similar.
Using the biological processes and other Gene Ontology terms from well characterized DUBs as a
positive control, several gene set enrichment analyses were considered. Threshold-less methods
like GSEA had relatively poor results.
Over-representation analysis with a threshold of of the top 7 highest absolute value Dependency Map
correlations yielded the best results and is reported below.
INDRA was used to automatically assemble known mechanisms
related to OTUB1 from literature and knowledge bases.
The first section shows only DUB activity and the second shows all other results.
Deubiquitinase Activity
psp
cbn
pc
bel_lc
signor
biogrid
lincs_drug
tas
hprd
trrust
ctd
vhn
pe
drugbank
omnipath
conib
crog
dgi
|
rlimsp
isi
tees
geneways
eidos
trips
medscan
sparser
reach
It was also shown that two OTUB deubiquitinating enzyme family members, OTUB1 and OTUB2, can deubiquitinate TRAF3 and TRAF6, leading to the inhibition of virus induced IFN-beta expression and cellular antiviral responses.
OTUB1 and its paralog OTUB2, deubiquitinate TRAF3 and TRAF6 to inhibit virus triggered signaling pathways that ultimately result in IRF3 and NF-kappaB activation [XREF_BIBR].
It was also shown that two OTUB deubiquitinating enzyme family members, OTUB1 and OTUB2, can deubiquitinate TRAF3 and TRAF6, leading to the inhibition of virus-induced IFN-β expression and cellular antiviral responses (53).
Otub1, a DUB from the OTU-domain containing protease family abrogates p53 ubiquitination and stabilizes and activates p53 in cells independent of its deubiquitinating enzyme activity [XREF_BIBR].
Examples for DUBs that might antagonize E4 dependent polyubiquitylation are USP47, a regulator of Base Excision Repair (BER) that controls DNA polymerase beta and OTUB1, which mediates DNA damage dependent deubiquitylation of p53 and MDM2 in the cytoplasm.
For example, USP7 regulates the stability of both p53 and Mdm2 and maintains p53 ubiquitination levels; 120 USP2 mediates the stability of Mdm2; 121 USP10 modulates p53 localization and stability; 122 OTUB1 abrogates p53 ubiquitination and activates p53.
For example, USP7 modulates the stability of both p53 and MDM2, and maintains the level of p53 ubiquitylation; USP2 affects the stability of MDM2; Otub1 inhibits p53 ubiquitination and activates p53 in cells; USP10 regulates the location and stability of p53, and stabilize both mutated and wild-type p53, thereby having a dual role in tumorigenesis.
Consistent with the observation that OTUB1 inhibits RAS ubiquitination, analysis of RAS localization revealed that OTUB1 overexpression augmented the presence of RAS proteins on the plasma membrane (Fig XREF_FIG E and F; XREF_SUPPLEMENTARY).
29 We have shown previously that OTUB1 can specifically limit FOXM1 polyubiquitination and its degradation, through its deubiquitinase enzymatic activity.
Conversely, the invitro deubiquitination assays revealed that both OTUB1 (WT) and OTUB1 (D88A), but not OTUB1 (C91A), could efficiently deubiquitinate FOXM1 (XREF_FIG C, invitro Deub, lanes 5-8), as expected.
Moreover, OTUB1 can deubiquitinate and stabilize the forkhead transcription factor FOXM1, which promotes DNA damage response and genotoxic drug resistance in breast cancer.
These results strongly suggest that OTUB1 blocks MSH2 ubiquitination by inhibiting the E2 ligase activity, rather than by directly deubiquitinating MSH2.
It is possible that OTUB1 prevents MSH2 ubiquitination by inhibiting the E2 activity of HDAC6 or by competing with HDAC6 for the MSH2 residues located in the central domain.
It was also shown that two OTUB deubiquitinating enzyme family members, OTUB1 and OTUB2, can deubiquitinate TRAF3 and TRAF6, leading to the inhibition of virus-induced IFN-β expression and cellular antiviral responses (53).
It was also shown that two OTUB deubiquitinating enzyme family members, OTUB1 and OTUB2, can deubiquitinate TRAF3 and TRAF6, leading to the inhibition of virus induced IFN-beta expression and cellular antiviral responses.
OTUB1 and its paralog OTUB2, deubiquitinate TRAF3 and TRAF6 to inhibit virus triggered signaling pathways that ultimately result in IRF3 and NF-kappaB activation [XREF_BIBR].
Indeed, the ability of OTUB1 to inhibit RNF168 dependent ubiquitylation is independent of its catalytic activity, and is instead mediated by its binding to and inhibition of the E2 UBC13, which cooperates with RNF168, suggesting that E2 regulation could also represent a means to regulate the DDR pathway.
Finally, the DUB OTUB1 inhibits RNF168 mediated ubiquitylation in a non catalytic fashion by binding to UBC13 and inhibiting the formation of Lys63 linked poly-ubiquitin chains [35 **].
It has been reported that OTUB1 suppresses RNF168 dependent poly-ubiquitination by binding to and inhibiting UBC13, but independently of OTUB1 catalytic activity as a deubiquitinating enzyme (Nakada e[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
Remarkably, the ability of OTUB1 to inhibit RNF168 dependent ubiquitylation was independent of its catalytic activity, suggesting an unusual mechanism of action.
Interestingly, it was found that the mechanism is non canonical and non catalytic : instead of OTUB1 directly deubiquitinating SMAD2/3 rather it interacts with the E2 ligases prevents the transfer of [MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
Since, OTUB1 inhibits UBC13 dependent polyubiquitylation but not monoubiquitylation, it may be that a single ubiquitin conjugated to another protein at DSBs is sufficient to be recognized by the MIU d[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
NS1 is the most important IFNs antagonist protein via mechanisms including inhibition of the TRIM25 mediated RIG-I ubiquitination, suppression of protein kinase R (PKR), phosphorylation of IkappaB kinases (IKK) alpha and beta in the NF-kappaB pathway, interruption of the phosphorylation of STAT1, STAT2, and STAT3 [XREF_BIBR, XREF_BIBR], and degradation of OTUB1 [XREF_BIBR].
NS1 is the most important IFNs antagonist protein via mechanisms including inhibition of the TRIM25-mediated RIG-I ubiquitination, suppression of protein kinase R (PKR), phosphorylation of IκB kinases (IKK) α and β in the NF-κB pathway, interruption of the phosphorylation of STAT1, STAT2, and STAT3 [39, 115] , and degradation of OTUB1 [138] .
In contrast, OTU domain, ubiquitin aldehyde binding 1 (OTUB1), B-cell lymphoma-3 (BCL-3), ubiquitin carboxyl-terminal hydrolase 1 (UCHL1), and UCHL5 contribute to the deubiquitination of SMAD2 or SMAD3, making them more stable and less easily degradable and promoting TGF-beta signaling [XREF_BIBR - XREF_BIBR].
In contrast, OTU domain, ubiquitin aldehyde binding 1 (OTUB1), B-cell lymphoma-3 (BCL-3), ubiquitin carboxyl-terminal hydrolase 1 (UCHL1), and UCHL5 contribute to the deubiquitination of SMAD2 or SMAD3, making them more stable and less easily degradable and promoting TGF-beta signaling [XREF_BIBR - XREF_BIBR].
However, the inhibitory effect of OTUB1 is independent of its DUB activity because the catalytically inactive mutant OTUB1 C91S suppresses 53BP1 IRIF and core histone ubiquitination as efficiently as wild-type OTUB1 [XREF_BIBR].
Conversely, the invitro deubiquitination assays revealed that both OTUB1 (WT) and OTUB1 (D88A), but not OTUB1 (C91A), could efficiently deubiquitinate FOXM1 (XREF_FIG C, invitro Deub, lanes 5-8), as expected.
Here, we describe the identification of OTUB1 as a c-IAP-associated deubiquitinating enzyme that regulates c-IAP1 stability. OTUB1 disassembles K48-linked polyubiquitin chains from c-IAP1 in vitro and in vivo within the TWEAK receptor-signalling complex.
Moreover, OTUB1 can deubiquitinate and stabilize the forkhead transcription factor FOXM1, which promotes DNA damage response and genotoxic drug resistance in breast cancer.
Examples for DUBs that might antagonize E4 dependent polyubiquitylation are USP47, a regulator of Base Excision Repair (BER) that controls DNA polymerase beta and OTUB1, which mediates DNA damage dependent deubiquitylation of p53 and MDM2 in the cytoplasm.
Wild-type OTUB1 and the DeltaN mutant, both capable of cleaving K48 linked di- or polyubiquitin chains in vitro, along with all the catalytically inactive mutants (D88A, C91S, H265A, D/H, D/C/H, K71R) were not able to deubiquitylate the polyubiquitylated FLAG and SMAD2/3/4 complex (XREF_FIG).
Furthermore, the OTUB1 knockdown significantly reversed the decreased ubiquitination of E2F1 induced by the overexpression of TMPO-AS1 in RT4 and T24 cells (XREF_FIG).
Conversely, the invitro deubiquitination assays revealed that both OTUB1 (WT) and OTUB1 (D88A), but not OTUB1 (C91A), could efficiently deubiquitinate FOXM1 (XREF_FIG C, invitro Deub, lanes 5-8), as expected.
Whereas the exogenous expression of OTUB1 completely abrogated RNF168 dependent histone ubiquitination, the exogenous expression of OTUB2 did not affect the histone ubiquitination level.
This non canonical mode of regulation was also reported when OTUB1 was shown to stabilize and activate p53 independent of catalytic activity [XREF_BIBR].
For example, USP7 modulates the stability of both p53 and MDM2, and maintains the level of p53 ubiquitylation ( xref , xref ); USP2 affects the stability of MDM2 ( xref ); Otub1 inhibits p53 ubiquitination and activates p53 in cells ( xref ); USP10 regulates the location and stability of p53, and stabilize both mutated and wild-type p53, thereby having a dual role in tumorigenesis ( xref ).
Inhibition of cathepsin K sensitizes oxaliplatin-induced apoptotic cell death by Bax upregulation through OTUB1-mediated p53 stabilization in vitro and in vivo.
Consequently, overexpression of Otub1 induces p53 dependent apoptosis and inhibition of cell proliferation whereas knockdown of Otub1 attenuates p53 activation following DNA damage [XREF_BIBR].
For example, USP7 regulates the stability of both p53 and Mdm2 and maintains p53 ubiquitination levels; xref USP2 mediates the stability of Mdm2; xref USP10 modulates p53 localization and stability; xref OTUB1 abrogates p53 ubiquitination and activates p53. xref Interestingly, USP10 can stabilize both mutated and wild-type p53, with a dual role in tumorigenesis.
In summary, we have found that Otub1 promotes p53 function by stabilizing MDMX, which in turn contributes to the p53 induced mitochondria mediated apoptosis pathway.
This is particularly interesting when considering our observations that in prostate cancer cells, OTUB1 mediates the androgen inhibition of p53 through a mechanism that requires an intact OTUB1 catalytic motif and seems to be independent from MDM2 concentration changes.
Our results demonstrate that cathepsin K inhibition enhances oxaliplatin-induced apoptosis by increasing OTUB1 phosphorylation via CK2 activation, thereby promoting p53 stabilization, and hence upregulating Bax.
As shown in Figure XREF_FIG, cell fractionation assays revealed that Otub1 expression not only significantly induced the nuclear levels of p53 and MDMX, but also induced the levels of cytoplasmic MDMX and p53 (lane 4, Figure XREF_FIG).
On this basis, it has been proposed that OTUB1 inhibits the ability of E2 ~ Ub conjugates to participate in Ub transfer reactions and in building polyUb chains 2.
Further characterization of this mechanism demonstrated that OTUB1 directly binds and consequently inhibits a related subclass of E2 enzymes that include UBC13, the only known E2 that cooperates with RNF168 during the DNA damage response [23], [195].
OTUB1 interacts with UBC13 (UBE2N) and the UBE2D and UBE2E family E2 ubiquitin conjugating enzymes and inhibits their E2 activities in a DUB activity independent manner (Nakada et al., 2010; Sato et a[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
Occlusion of the E3 binding surface, along with the shielding of the Ub ~ UbcH5b ester linkage by OTUB1 likely accounts for the ability of OTUB1 to suppress E2 function.
However, its inhibitory effect was higher than that of an OTUB1 N-terminal deletion mutant that does not inhibit the E2 activity of UBC13 (Nakada et al., 2010).
OTUB1 interacts with UBC13 (UBE2N) and the UBE2D and UBE2E family E2 ubiquitin conjugating enzymes and inhibits their E2 activities in a DUB activity independent manner (Nakada et al., 2010; Sato et a[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
Recently, several studies have described a non canonical mode of OTUB1 action in which OTUB1 inhibits the ubiquitylation of target proteins by binding to and inhibiting the E2 ubiquitin conjugating enzyme UBE2N (also known as UBC13) independent of its catalytic activity XREF_BIBR XREF_BIBR XREF_BIBR XREF_BIBR.
This and other studies have reported that OTUB1 inhibits ubiquitylation by binding to and inhibiting E2 enzymes XREF_BIBR XREF_BIBR XREF_BIBR XREF_BIBR XREF_BIBR.
These results suggest that by binding to E2 ubiquitin conjugating enzymes, OTUB1 appears to inhibit the transfer of ubiquitin from E2-Ub complex onto E3 ubiquitin ligases.
IL-15 mediates membrane recruitment of Otub1, which inhibits ubiquitin dependent activation of AKT, a kinase that is pivotal for T cell activation and metabolism.
The OTUB1 protein interacts directly with the E2 ubiquitin conjugating protein UBC13 and prevents ubiquitin transfer, thereby inhibiting double-strand-break-induced chromatin ubiquitination XREF_BIBR, XREF_BIBR.
This occurs by different molecular mechanisms and requires catalytic activity of USP15, but not that of OTUB1, which rather binds to and inhibits the ubiquitin conjugating activity of the cognate E2 enzyme [XREF_BIBR, XREF_BIBR].
In addition to such enzymatic ubiquitin deconjugation, the DUB OTUB1 limits ubiquitin signaling by direct inhibition of the ubiquitin conjugating enzyme UBC13 [68-70], while the ubiquitin E3 ligase RN[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
OTUB1 binds to a subset of E2 ubiquitin conjugating enzymes and inhibits their activity by trapping the E2 ~ ubiquitin thioester and preventing ubiquitin transfer.
We further showed that OTUB1, by binding to UBE2D1, inhibits the transfer of ubiquitin from E2-Ub conjugate to E3 ubiquitin ligase NEDD4L and subsequently to SMAD3 (XREF_FIG).
However, OTUB1 K71R, a catalytically inactive mutant, does not appear to inhibit the transfer of ubiquitin from the E2-Ub complex to E3 (XREF_FIG cf. bottom line mono-ubiquitin).
Further, UbcH5 in turn mediates Otub1 monoubiquitination and this monoubiquitination facilitates the Otub1 binding to UbcH5 and likely inhibits ubiquitin chain transfer [XREF_BIBR], providing a mechanism underlying the Otub1 inhibition of E2 activity.
OTUB1 has previously been reported to inhibit ubiquitylation of target proteins by interacting with and inhibiting E2 ubiquitin conjugating enzymes XREF_BIBR XREF_BIBR XREF_BIBR XREF_BIBR.
Immunoblot analysis revealed that ubiquitin chains were completely degraded by AMSH but neither by OTUB1 nor the GST control, further supporting our finding that TRIAD3 synthesises K63 linked ubiquitin chains in vitro, full length TRIAD3 protein as well as the TRIAD3-RBR 845 fragment.
For this, heterotypic Ub chains were assembled from 25 mg WT Ub, and the reaction was subsequently treated with OTUB1, which cleaved all Lys48-linkages within the polymers.
OTUB1 binds to a subset of E2 ubiquitin conjugating enzymes and inhibits their activity by trapping the E2 ~ ubiquitin thioester and preventing ubiquitin transfer.
In contrast, only overexpression of mammalian Otubain 1 and Cezanne moderately decreased cellular global Ub conjugate levels, while expression of A20 or Otubain 2 had no effect on total levels of ubiquitinated proteins (Balakirev et al., 2003; Evans et al., 2004; Evans et al., 2003) .
In contrast, only overexpression of Otubain 1 and Cezanne moderately decreased cellular global Ub conjugate levels, while expression of A20 or Otubain 2 had no effect on total levels of ubiquitinated proteins (Balakirev et al., 2003, Evans et al., 2003, Evans et al., 2004).
Consistent with a functional importance of this pocket, the F190S mutation disrupted the ability of OTUB1 to suppress UBC13 activity in vitro (XREF_FIG).
Although human ovarian tumor domain containing ubiquitin aldehyde binding protein 1 (OTUB1) was previously identified as a K48 linkage specific deubiquitinating enzyme that positively regulates p53 stability 22, OTUB1 strongly suppresses E2-ubiquitin-conjugating enzyme UBC13 dependent K63 linked ubiquitination XREF_BIBR, XREF_BIBR.
It is worth noting that OTUB1 inhibits UBE2D/2E family in in vitro experiments as well as UBC13, indicating that deubiquitylating activity independent regulation of E2 might be a common mechanism for [MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
It was reported that Otub1, a deubiquitinase, also negatively regulates the DDR in a catalytically independent manner by regulating the activity of UBC13, an E2 ubiquitin conjugating enzyme for RNF8.
Finally, we carried out GST pull-down assays with the OTUB1 mutants that failed to inhibit UBC13 and found that all had reduced binding to Ub ~ UbcH5b and free Ub (XREF_SUPPLEMENTARY).
This finding was interesting as OTUB1 inhibits the degradation of FOXM1 transcription factor, typically upregulated and overexpressed in aggressive therapy resistant breast cancer.
Our data show that WT OTUB1, but not the OTUB1 (C91S) catalytic dead mutant, can enhance the stability of FOXM1 in response to epirubicin in MCF-7 cells, suggesting that the deubiquitinase activity is required for the degradation of FOXM1.
Our data show that WT OTUB1, but not the OTUB1 (C91S) catalytic dead mutant, can enhance the stability of FOXM1 in response to epirubicin in MCF-7 cells, suggesting that the deubiquitinase activity is required for the degradation of FOXM1.
Importantly, knockdown of OTUB1 by siRNA resulted in an increase in turnover of FOXM1 in MCF-7 cells treated with the protein synthesis inhibitor cycloheximide, whereas overexpression of WT OTUB1, but not the OTUB1 (C91S) mutant, significantly enhances the half-life of FOXM1.
Together, these results suggest that the suppression of FOXM1 degradation by OTUB1 in response to epirubcin requires its deubiquitinating catalytic activity, further confirming that FOXM1 is a novel target of the deubiquitinase OTUB1.
The results showed that in MCF-7 cells OTUB1 depletion culminated in the downregulation of FOXM1, but not vice versa (XREF_FIG), suggesting that OTUB1 positively regulates FOXM1 expression.
To investigate the idea that OTUB1 modulates FOXM1 expression further, we examined the effects of silencing OTUB1 and FOXM1 on the expression of endogenous OTUB1 and FOXM1 protein in MCF-7 cells.
Given our previous finding that genotoxic agents cause FOXM1 SUMOylation, ubiquitination and degradation, these observations led us to hypothesize that OTUB1 promotes FOXM1 expression at the posttranslational level to potentiate genotoxic agent resistance.
FOXM1 expression reduced upon OTUB1 depletion by siRNA and increased with OTUB1 overexpression in MCF-7 cells, arguing that OTUB1 positively regulates FOXM1 expression.
The FOXM1 co-immunoprecipitation analysis showed that overexpression of OTUB1, but not the OTUB1 (C91S) mutant, substantially depleted the levels of K48-polyubiquitin chains and induced FOXM1 expression, particularly following epirubicin treatment (XREF_FIG).
The FOXM1 co-immunoprecipitation analysis showed that overexpression of OTUB1, but not the OTUB1 (C91S) mutant, substantially depleted the levels of K48-polyubiquitin chains and induced FOXM1 expression, particularly following epirubicin treatment (XREF_FIG).
Nevertheless, the correlations between the kinetics of OTUB1 and FOXM1 expression in the sensitive and resistant MCF-7 cells in response to DNA damaging agents support the notion that OTUB1 restricts the downregulation of FOXM1 expression in response to DNA damage and genotoxic agents.
The effect of E2 enzymes in lowering the K M of OTUB1 for substrate suggests that the binding of an E2 partner increases the affinity of OTUB1 for K48 diubiquitin.
Since the N-terminal residues of OTUB1 that precede the OTU domain form a proximal ubiquitin binding helix that plays an essential role in E2 inhibition, we asked whether E2 stimulation of OTUB1 activity similarly requires the OTUB1 N-terminus.
We have shown here that a subset of E2 enzymes markedly stimulate OTUB1 cleavage of Lys48 linked polyubiquitin (XREF_FIG) and that the same set of OTUB1-E2 interactions are required for both OTUB1 non catalytic inhibition of E2 enzymes and E2 stimulation of OTUB1 XREF_BIBR, XREF_BIBR.
No difference in stimulation was observed in cleavage of di-, tri- and tetraubiquitin substrates (XREF_SUPPLEMENTARY), indicating that E2 stimulation of OTUB1 DUB activity is independent of polyubiquitin chain length.
Only the uncharged E2 stimulates OTUB1 DUB activity at physiological concentrations of ubiquitin 37, whereas the charged E2 ~ Ub drives formation of a repressed complex with OTUB1 XREF_BIBR, XREF_BIBR, XREF_BIBR.
Importantly, the fact that a substantial proportion of the E2 partners of OTUB1 are uncharged is consistent with a role for E2 stimulation of OTUB1 in the cell.
The E2 increased the affinity of OTUB1 for K48 diubiquitin, as reflected in a decrease in K d from 84 muM with no E2 to 12 muM in the presence of UBE2D1, 13.2 muM in the presence of UBE2D3, and 22.3 muM in the presence of UBE2N.
Of the E2 enzymes that stimulate OTUB1 (XREF_FIG), UBCH5C (UBE2E3) and UBC13 (UBE2N) have been shown to be the most abundant and in molar excess over OTUB1 20.
The ternary E2 ~ Ub and OTUB1/Ub complex inhibits both ubiquitin discharge from the E2 ~ Ub intermediate and the DUB activity of OTUB1 [XREF_BIBR, XREF_BIBR].
Since only uncharged E2 stimulates OTUB1 DUB activity while charged E2 ~ Ub represses OTUB1 under normal cellular concentrations of free ubiquitin, the relative proportion of charged versus uncharged E2s must be critical determinants of whether OTUB1-E2 complexes function as active DUBs in the cell.
Since estimates of cellular free ubiquitin concentrations range from 4 - 20 microM, this would suggest that E2 ~ Ub conjugates would repress OTUB1 activity unless cellular stresses significantly reduced the availability of free ubiquitin.
The E2 mediated conformational change decreases the K m of OTUB1 for diUb by over 35-fold, thereby enhancing the rate of OTUB1 dependent polyUb degradation 2.
A growing body of literature demonstrates that the DUB Otubain 1 (OTUB1) regulates many cancer associated signaling pathways including MAPK, ERa, epithelial-mesenchymal transition (EMT), RHOa, mTORC1, FOXM1 and P53 to promote tumor cell survival, proliferation, invasiveness and therapeutic resistance.
Activation of mTOR allows selective mRNA translation, including the epistatic regulator of GRAIL, Otubain-1 (Otub1), whose expression results in the degradation of GRAIL and allows T cell proliferation.
18 In here, we not only show that the potent oncogene FOXM1 is a target of OTUB1 but also present evidence to demonstrate that the oncogenic and genotoxic functions of OTUB1 depend on the expression of a functional FOXM1, suggesting that OTUB1 promotes cell proliferation and epirubicin resistance predominantly through targeting FOXM1.
The result showed that overexpression of OTUB1 significantly enhanced MCF-7 cell proliferation, whereas OTUB1 depletion decreased the rates of proliferation of MCF-7 cells (XREF_SUPPLEMENTARY).
Furthermore, addition of IL-2 was able to activate the mTOR pathway, inducing Otubain-1 expression, which mediated GRAIL degradation and improved T cell proliferation.
Conclusions : Our findings reveal the critical role of OTUB1 in PCa, and OTUB1 promotes the proliferation and progression of PCa via deubiquitinating and stabilizing Cyclin E1.
Overexpression of OTUB1, but not the OTUB1 (C91S) mutant, significantly enhanced the cell proliferation as well as the viability of WT MEFs in response to epirubicin (XREF_FIG).
Through in vitro and in vivo experiments, knockdown of OTUB1 suppressed PTC cells growth whereas OTUB1 overexpression enhanced the proliferation ability of PTC cells.
The result showed that overexpression of OTUB1 significantly enhanced MCF-7 cell proliferation, whereas OTUB1 depletion decreased the rates of proliferation of MCF-7 cells (XREF_SUPPLEMENTARY).
Flow cytometry-based analysis of E18.5 lung tissue revealed that Otub1 deletion increased proliferation of major lung parenchymal and mesenchymal/other non-hematopoietic cell types.
Consequently, overexpression of Otub1 induces p53 dependent apoptosis and inhibition of cell proliferation whereas knockdown of Otub1 attenuates p53 activation following DNA damage [XREF_BIBR].
Consequently, overexpression of Otub1 induces p53 dependent apoptosis and inhibition of cell proliferation whereas knockdown of Otub1 attenuates p53 activation following DNA damage [XREF_BIBR].
Together, these results suggest that Otub1 stabilizes MDMX and promotes p53S46P and mitochondria mediated apoptosis, providing an alternative mechanism of Otub1 's role in apoptosis.
Taken together, our findings show that OTUB1 induces apoptosis of melanoma cells in vitro, likely by upregulating TRAIL, and suggest that approaches targeting OTUB1 can be developed to provide novel therapeutic strategies for treating melanoma.
Together, these results suggest that Otub1 also induces mitochondrial mediated apoptosis by stabilizing MDMX and relocalizing it to mitochondria to induce mitochondria mediated apoptosis.
The result showed that AVT drastically reduced the protein level of pro-caspase-3 in both RPMI-8226 and LP1 cells, but it was abolished partly by lentiviral Otub1, suggesting Otub1 expression rescued the apoptosis induced by AVT.
Combined in vivo and in vitro experiments comprising mice lacking OTUB1 specifically in liver parenchymal cells (OTUB1 LPC-KO) and human OTUB1 deficient HepG2 cells revealed that OTUB1 prevented hepatocyte necroptosis but not apoptosis upon infection with Lm and DGal and TNF challenge.
Combined in vivo and in vitro experiments comprising mice lacking OTUB1 specifically in liver parenchymal cells ( OTUB1 LPC-KO ) and human OTUB1-deficient HepG2 cells revealed that OTUB1 prevented hepatocyte necroptosis but not apoptosis upon infection with Lm and DGal / TNF challenge .
While overexpression of WT OTUB1 leads to increased cell invasion, the expression of the OTUB1-C91S variant mimics the effects of OTUB1 siRNA knockdown, leading to reduced cell invasion.
OTUB1 promotes cancer cell invasion and tumorigenesis in various human cancers XREF_BIBR - XREF_BIBR, while the role of OTUB2 in cancer progression remains unknown.
Together, our findings demonstrate that OTUB1 promotes the migration, invasion, and metastasis of CRC cells in vitro and in vivo and acts as a potential metastasis marker and prognostic factor in CRC.
Finally, cell migration and invasion inhibition induced by miR-542-3p overexpression was partially attenuated by co-transfection of recombinant OTUB1 in KYSE150 cells.
Consequently, Otub1 dependent deubiquitination inhibits Tau degradation through the proteasome pathway and prolongs its half-life, leading to accumulation of pathological forms of Tau.
Taken together, our data demonstrate that Otub1, identified as a Tau interacting protein in the Tau interactome mapping, modulates Tau, by increasing Tau seeded Tau aggregation, by formation of a Otub1 induced Tau complex Tau c, and by increasing the concentration of oligomeric Tau forms in primary neurons.
Finally, we demonstrated that expression of Otub1 but not its catalytically inactive form induced pathological Tau forms after 2months in Tau transgenic mice invivo, including AT8 positive Tau and oligomeric Tau forms.
In addition, we found robust induction of a (homo- or heterotypic) Tau complex (Tau c), which was strongly detected in AAV-Otub1-infected neurons but absent in AAV-GFP-infected neurons, indicating clearcut Otub1 induced modulation of Tau in neurons.
Taken together, we conclude that overexpressed Otub1 in primary neurons expressing TauP301S increased total Tau and induced a robust increase in AT8 positive Tau.
We found that Tau degradation was significantly impaired in primary neurons infected with Otub1 WT, but not with catalytically dead mutant C91A, compared with GFP control.
Endogenous Otub1 depletion significantly inhibited Tau aggregation, with the level of inhibition correlating with the level of knockdown efficiency, while use of a control siRNA did not affect levels of Otub1 nor aggregation efficiency.
Taken together, although the precise mechanism by which OTUB1 induces SLC7A11 stabilization requires further elucidation, it is very likely that the binding between OTUB1 and SLC7A11 as well as OTUB1 's ability of inhibiting E2 conjugating enzymes recruited by the unknown E3 ligase contribute to SLC7A11 stabilization induced by OTUB1.
Consistent with the role of a DUB in regulating protein stability, OTUB1 overexpression resulted in reduced SLC7A11 ubiquitination and increased SLC7A11 protein half-life and steady protein levels; conversely, OTUB1 deletion in a variety of cancer cell lines resulted in a significant decrease in SLC7A11 protein levels.
Evidence suggests that the deubiquitinase OTUB1, usually overexpressed in cancers, replicates the ferroptosis process and promotes tumor development by stabilizing the cystine transporter SLC7A11 (Gan, 2019).
For example, in a non neuronal setting, induction of ferroptosis with the small molecule erastin is suppressed by the ubiquitin ligase NEDD4 [XREF_BIBR], whilst the DUBs OTUB1 and USP7 promote ferroptosis by stabilising the mediators SLC7A11 and p53, respectively [XREF_BIBR, XREF_BIBR].
As shown in XREF_FIG, the stability of SLC7A11 was effectively rescued by OTUB1 (C91A) but not by OTUB1 (D88A), suggesting that OTUB1 promotes SLC7A11 stabilization independent of its deubiquitinase activity.
In particular, our results show that (i) OTUB1 is a bona fide binding partner of SLC7A11 both in vitro and in vivo; (ii) OTUB1 acts as a major regulator for SLC7A11 activity in human cancer cells; (iii) OTUB1 inactivation promotes ferroptosis in human cancer cells primarily by down-regulating SLC7A11 levels; (iv) OTUB1 is overexpressed in human cancers and the OTUB1-SLC7A11 interaction is critical for tumor growth; (v) The OTUB1-SLC7A11 interaction is tightly regulated by CD44 in human cancer cells.
As expected in T24 cells, loss of OTUB1 expression diminished the levels of endogenous SLC7A11 (XREF_SUPPLEMENTARY); ROS mediated ferroptosis was significantly enhanced in all clones of OTUB1-null cells (XREF_SUPPLEMENTARY); the same results were observed in OTUB1-null UM-UC-3 cells (XREF_SUPPLEMENTARY, XREF_SUPPLEMENTARY and XREF_SUPPLEMENTARY).
As shown in XREF_FIG, the steady-state levels of SLC7A11 in OTUB1 depleted cells were significantly restored upon treatment with the MG132 proteasome inhibitor (lane 4 vs. lane 2), indicating that OTUB1 depletion promotes SLC7A11 degradation in a proteasome dependent manner.
The steady-state levels of ubiquitinated SLC7A11 were also reduced by OTUB1 expression (XREF_FIG, lane 3 vs. lane 4), suggesting that OTUB1 stabilizes SLC7A11 by directly reducing its ubiquitination levels.
The steady-state levels of ubiquitinated SLC7A11 were also reduced by OTUB1 expression (XREF_FIG, lane 3 vs. lane 4), suggesting that OTUB1 stabilizes SLC7A11 by directly reducing its ubiquitination levels.
Together, our findings demonstrate that OTUB1 promotes the migration, invasion, and metastasis of CRC cells in vitro and in vivo and acts as a potential metastasis marker and prognostic factor in CRC.
We also did not observe OTUB1 induced hyperactivation of the MAPK kinase pathway when we overexpressed a dominant negative KRAS S17N-mutant, indicating that the effect of OTUB1 overexpression is RAS dependent (XREF_SUPPLEMENTARY).
OTUB1 overexpression in the H1993 cell line harboring wt KRAS led to a higher and more sustained activation of ERK1/2 phosphorylation (Fig XREF_FIG A), whereas the introduction of OTUB1 into KRAS-mutant A549 cells only slightly increased the activity of the MAPK pathway (Fig XREF_FIG B).
Consistently with our observation that OTUB1 overexpression induces the MAPK cascade activation in cells with wt RAS, we found that higher levels of OTUB1 significantly correlated with increased levels of ERK1/2 phosphorylation in lung adenocarcinomas harboring wt KRAS (Pearson 's coefficient : 0.352; P-value : 0.013) (Fig XREF_FIG D and E), while mutant KRAS tumors exhibited in general higher levels of ERK1/2 phosphorylation (Fig XREF_FIG D and E).
On the other hand, OTUB1 did not further accelerate anchorage independent colony formation of HEK TE cells overexpressing both a constitutively active MEK1 D218, D222 allele (MEKDD) and myr-AKT, further confirming that OTUB1 overexpression promotes tumorigenic transformation by inducing the MAPK cascade activation.
We observed a similar overactivation of the MAPK pathway, when we overexpressed catalytically inactive OTUB1 C91S-mutant, indicating that catalytic activity of OTUB1 is not necessary to induce the MAPK pathway activation (Fig XREF_FIG F).
Given that OTUB1 overexpression up-regulated the MAPK pathway, but did not affect AKT signaling, we hypothesized that OTUB1 could cooperate with myristoylated (myr) and therefore the constitutively active allele of AKT1 (myr-AKT) to promote cell transformation.
OTUB1 Promotes Progression and Proliferation of Prostate Cancer via Deubiquitinating and Stabling Cyclin E1 Background : Prostate cancer ( PCa ) is currently the most common cancer among males worldwide .
So far , we have a lot of evidence to identify the hypothesis that OTUB1 promotes the progression and proliferation of prostate cancer via mediating and stabling Cyclin E1 .
Conclusions : Our findings reveal the critical role of OTUB1 in PCa , and OTUB1 promotes the proliferation and progression of PCa via deubiquitinating and stabilizing Cyclin E1 .
Discussion In our research , we found that the expression levels of OTUB1 are up-regulated in PCa , OTUB1 could promote the proliferation and progression of PCa via deubiquitinating and stabling the expression of Cyclin E1 protein .
Therefore , this research preliminarily proposed that OTUB1 could promote the progression and proliferation of PCa via regulating the expression of Cyclin E1 , thus the specific internal mechanism will become the main work and direction in the next step .
However, different from USP15, OTUB1 enhances TGF-beta signaling by inhibiting the ubiquitination and degradation of active SMAD2/3 (and not the inactive un phosphorylated form), because the association of OTUB1 to SMAD2/3 is phosphorylation dependent.
In contrast, OTU domain, ubiquitin aldehyde binding 1 (OTUB1), B-cell lymphoma-3 (BCL-3), ubiquitin carboxyl-terminal hydrolase 1 (UCHL1), and UCHL5 contribute to the deubiquitination of SMAD2 or SMAD3, making them more stable and less easily degradable and promoting TGF-beta signaling [XREF_BIBR - XREF_BIBR].
However, we must acknowledge that we did not make a long term follow-up and survival analysis, since most patients accepted varieties of postoperative chemotherapy schemes, including traditional Chine[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
We tested whether the catalytic activity of OTUB1, its ability to inhibit ubiquitylation of SMAD2/3 or its ability to interact with SMAD3 are essential to enhance TGFbeta induced transcription.
We show that both stimulation of OTUB1 by E2 enzymes and noncatalytic inhibition of E2 enzymes by OTUB1 occur at physiologically relevant concentrations of both partners.
Therefore, the association of OTUB1 with phospho-SMAD2/3 would be predicted to prevent SMAD2/3 from being polyubiquitylated and degraded, thereby enhancing TGFbeta signalling.
Interestingly, this non canonical mode of action by OTUB1 was found not to be unique to UBC13, as OTUB1 was also found to interact with and inhibit the E2 enzymes UBE2D2 and UBCH5B and UBE2D3 and UBCH[MISSING/INVALID CREDENTIALS: limited to 200 char for Elsevier]
Competition with E3 binding is likely to be particularly important for OTUB1 inhibition of UBCH5b, which, unlike UBC13, is strictly dependent upon an E3 ligase for activity.
Since OTUB1 also inhibits UBCH5b 4, which does not function with a UEV, we speculate that the OTUB1 N-terminus may also interfere with acceptor ubiquitin binding for other E2s.
Competition with E3 binding is likely to be particularly important for OTUB1 inhibition of UBCH5b, which, unlike UBC13, is strictly dependent upon an E3 ligase for activity.
The OTUB1 double E28A D35A substitution, which affects OTUB1 contacts with UBCH5B, greatly decreased the ability of UBCH5B to stimulate OTUB1 DUB activity without affecting OTUB1 activity in the absence of UBCH5B (XREF_FIG).
Similar interactions could form between OTUB1 and UBE2D2 (UBCH5b) ( xref ), but clashes due to an insertion and a non-conserved lysine would arise with UBE2L3 (UBCH7), consistent with the observation that OTUB1 inhibits UBCH5b but not UBCH7 xref .
Similar interactions could form between OTUB1 and UBE2D2 (UBCH5b) (XREF_FIG), but clashes due to an insertion and a non conserved lysine would arise with UBE2L3 (UBCH7), consistent with the observation that OTUB1 inhibits UBCH5b but not UBCH7 4.
It has been reported that OTUB1 non-catalytically inhibits UBE2D proteins from ubiquitinating p53 xref , xref and SMAD2/3, regulators of TGFβ signaling xref .
Monoubiquitination is critical for ovarian tumor domain containing ubiquitin aldehyde binding protein 1 (Otub1) to suppress UbcH5 enzyme and stabilize p53 protein.
To confirm that the observed stimulation was not assay dependent, we used a gel based assay to verify that UBCH5B stimulates OTUB1 cleavage of native Lys48 linked diubiquitin (XREF_FIG and XREF_SUPPLEMENTARY).
We assayed the ability of UBCH5B ~ Ub to stimulate OTUB1 (XREF_FIG) and found that both charged and uncharged UBCH5B stimulate OTUB1 to a similar degree.
The importance of the OTUB1 N-terminal helix to its ability to be stimulated by UBCH5B, together with the role of these N-terminal residues in forming the proximal ubiquitin binding site of OTUB1 XREF_BIBR, XREF_BIBR, XREF_BIBR, suggested that UBCH5B may increase OTUB1 affinity for Lys48 diubiquitin via the proximal ubiquitin binding site.
However, assays of OTUB1 stimulation by UBCH5B or UBCH5B ~ Ub over a range of ubiquitin concentrations (XREF_FIG) (XREF_SUPPLEMENTARY) showed that stimulation by UBCH5B is relatively insensitive to free ubiquitin, but that stimulation by UBCH5B ~ Ub decreases as a function of increasing concentration of free ubiquitin, dropping to low levels below ~ 1 microM free ubiquitin.
A previous study 37 reported that the binding of UBE2D2 lowered the K M of OTUB1 for K48 diubiquitin by 34-fold, from 120 muM to 3.4 muM, with no significant change in k cat.
Furthermore, addition of IL-2 was able to activate the mTOR pathway, inducing Otubain-1 expression, which mediated GRAIL degradation and improved T cell proliferation.
Thus, our current working model is that Otub 1 promotes GRAIL degradation by de-ubiquitination of ubiquitinated USP8, thereby diminishing USP8 activity (XREF_FIG).
As Otub-1 is controlled by the Akt-mTOR pathway and is a negative regulator of the GRAIL function [XREF_BIBR, XREF_BIBR], this suggests that T. cruzi infection may disrupt the Akt-mTOR pathway resulting in Otub-1 downregulation, which in turn may induce GRAIL.
When mTOR is inhibited by rapamycin treatment during stimulation, although Otub1 mRNA is up-regulated, Otub1 protein is not expressed, allowing GRAIL to be maintained (XREF_FIG, third lane).
Mechanistically, OTUB1 promoted NF-kappaB activity in DCs by K48 linked deubiquitination and stabilization of the E2 conjugating enzyme UBC13, resulting in increased K63 linked ubiquitination of IRAK1 (IL-1 receptor associated kinase 1) and TRAF6 (TNF receptor associated factor 6).
Otub1 deficiency not only promotes signal induced p100 processing and noncanonical NF-kappaB activation but also causes steady-state p100 degradation, leading to aberrant NF-kappaB activation in the canonical pathway.
Recently, it was also observed that OTUB-1 promotes NF-kappaB activation in dendritic cells during stimulated inflammatory conditions by lysine48 deubiquitination of UBC13 [XREF_BIBR].
Overexpression of OTUB1 and OTUB2 inhibited virus induced activation of IRF3 and NF-kappaB, transcription of the IFNB1 gene as well as cellular antiviral response, whereas knockdown of OTUB1 and OTUB2 had opposite effects.
Doxycycline induced expression of Otub1 in T-Rex-U2OS-Flag-Otub1 cells also drastically induced the levels of MDMX, as well as p53 and its target MDM2 in a time dependent manner.
As shown in Figure XREF_FIG, cell fractionation assays revealed that Otub1 expression not only significantly induced the nuclear levels of p53 and MDMX, but also induced the levels of cytoplasmic MDMX and p53 (lane 4, Figure XREF_FIG).
Interestingly, MDMX induced by Otub1 can localize to mitochondria in addition to the cytosol, enhance p53 phosphorylation at S46 (p53S46P) and promote mitochondria mediated apoptotic pathway.
Together, these results suggest that Otub1 also induces mitochondrial mediated apoptosis by stabilizing MDMX and relocalizing it to mitochondria to induce mitochondria mediated apoptosis.
Overexpression of OTUB1, but not the OTUB1 (C91S) mutant, significantly enhanced the cell proliferation as well as the viability of WT MEFs in response to epirubicin (XREF_FIG).
Our data show that WT OTUB1, but not the OTUB1 (C91S) catalytic dead mutant, can enhance the stability of FOXM1 in response to epirubicin in MCF-7 cells, suggesting that the deubiquitinase activity is required for the degradation of FOXM1.
18 In here, we not only show that the potent oncogene FOXM1 is a target of OTUB1 but also present evidence to demonstrate that the oncogenic and genotoxic functions of OTUB1 depend on the expression of a functional FOXM1, suggesting that OTUB1 promotes cell proliferation and epirubicin resistance predominantly through targeting FOXM1.
In addition, proliferative and clonogenic assays also show that OTUB1 can enhance the proliferative rate and epirubicin resistance through targeting FOXM1, as OTUB1 has little effect on FOXM1 deficient cells.
The FOXM1 co-immunoprecipitation analysis showed that overexpression of OTUB1, but not the OTUB1 (C91S) mutant, substantially depleted the levels of K48-polyubiquitin chains and induced FOXM1 expression, particularly following epirubicin treatment (XREF_FIG).
Our data show that WT OTUB1, but not the OTUB1 (C91S) catalytic dead mutant, can enhance the stability of FOXM1 in response to epirubicin in MCF-7 cells, suggesting that the deubiquitinase activity is required for the degradation of FOXM1.
All cell lysates were subjected to WB assays as indicated AVT interferes with the interaction between Otub1 and c-Maf to increase c-Maf polyubiquitination AVT was identified from the Otub1 / c-Maf system , while Otub1 interacts with c-Maf and prevents its polyubiquitination as its deubiquitinase , therefore , we wondered whether AVT can inhibit Otub1 activity toward c-Maf ubiquitination .
As shown in Fig. 5b , Otub1 markedly reduced c-Maf polyubiquitination level but it was reversed by AVT , suggesting AVT inhibited Otub1 activity thus increasing the polyubiquitination level of c-Maf .
AVT was identified from the Otub1 and c-Maf system, while Otub1 interacts with c-Maf and prevents its polyubiquitination as its deubiquitinase, therefore, we wondered whether AVT can inhibit Otub1 activity toward c-Maf ubiquitination.
XREF_FIG d, AVT elicited potent activity to downregulate all these three Dubs in RPMI-8226 and LP1 but not in KMS11, suggesting that AVT might also target other Dubs in addition to Otub1, however, whether these Dubs are associated with c-Maf should be further studied.