OTUB1 inhibits the ubiquitination and degradation of FOXM1 in breast cancer and epirubicin resistance

Abstract

The forkhead transcription factor FOXM1 has a key role in DNA damage response, and its deregulated overexpression is associated with genotoxic drug resistance in breast cancer. However, little is known about the posttranslational mechanisms by which FOXM1 expression is regulated by genotoxic agents and how they are deregulated in resistant cells. Initial co-immunoprecipitation studies verified previous proteomic analysis finding that the OTUB1 is a novel FOXM1-interacting protein. Western blot analysis showed that both OTUB1 and FOXM1 expression reduced upon genotoxic agent treatment in MCF-7 cells, but remained relatively constant in resistant cells. FOXM1 expression reduced upon OTUB1 depletion by siRNA and increased with OTUB1 overexpression in MCF-7 cells, arguing that OTUB1 positively regulates FOXM1 expression. In agreement, co-immunoprecipitation experiments demonstrated that FOXM1 expression is associated with OTUB1 binding but inversely correlates with conjugation to the protein degradation-associated Lys-48-linked ubiquitin-chains. Overexpression of wild-type (WT) OTUB1, but not the OTUB1(C91S) mutant, disrupted the formation of Lys48-linked ubiquitin-conjugates on 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. 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 physiological relevance of the regulation of FOXM1 by OTUB1 is further underscored by the significant correlations between FOXM1 and OTUB1 expression in breast cancer patient samples. Cox-regression survival analysis indicates that OTUB1 overexpression is linked to poorer outcome in particular in patients treated with chemotherapy. Collectively, these data suggest that OTUB1 limits the ubiquitination and degradation of FOXM1 in breast cancer and has a key role in genotoxic agent resistance.

OTUB1-catalyzed deubiquitination of FOXM1 facilitates tumor progression and predicts a poor prognosis in ovarian cancer

“…Moreover, elevated expression of OTUB1 predicts poor prognosis in ovarian cancer. Indeed, it has been reported that OTUB1 could enhance breast cancer chemoresistance [35]. Based on the relationship between OTUB1 and FOXM1, and FOXM1's enhancement of ovarian cancer chemoresistance, [36] the effect of OTUB1 and the OTUB1-FOXM1 axis on ovarian cancer chemoresistance is a curious question for future studies.…”

FOXM1 is a therapeutic target for high-risk multiple myeloma

“…Further encouraged by new evidence indicating that FOXM1 (1) drives tumor development and progression 15–19 by virtue of a complex mechanism that includes enhanced cell proliferation, migration and invasion 6 , regulation of the DNA damage response 20 and changes in the cancer epigenome 21 , (2) promotes cancer-cell resistance to ionizing radiation 22 and cytotoxic drugs 23 , (3) governs, in part, the survival and tissue-regenerating capacity of both normal hematopoietic stem cells 24 and malignant stem cell-like cells 25 , (4) links acquired resistance to cancer therapy with cancer stemness 26 and (5) owing to the development of specific small-molecule inhibitors 27 , may soon be targeted more effectively than possible in the past 28 , we here decided to evaluate whether FOXM1 might play an important but heretofore overlooked role in plasma cell myeloma.…”

The non‐coding RNA OTUB1‐isoform2 promotes ovarian tumour progression and predicts poor prognosis

“…OTUB1 is abnormally up‐regulated in somatic malignancies and exerts oncogenic functions 26, 32, 33, 34. We have also previously demonstrated that OTUB1 prompted tumour growth and metastasis in ovarian cancer and gastric carcinoma 25, 29.…”