The downregulation of Mcl-1 via USP9X inhibition sensitizes solid tumors to Bcl-xl inhibition

Abstract

BackgroundIt has been shown in many solid tumors that the overexpression of the pro-survival Bcl-2 family members Bcl-xL and Mcl-1 confers resistance to a variety of chemotherapeutic agents. Mcl-1 is a critical survival protein in a variety of cell lineages and is critically regulated via ubiquitination.MethodsThe Mcl-1, Bcl-xL and USP9X expression patterns in human lung and colon adenocarcinomas were evaluated via immunohistochemistry. Interaction between USP9X and Mcl-1 was demonstrated by immunoprecipitation-western blotting. The protein expression profiles of Mcl-1, Bcl-xL and USP9X in multiple cancer cell lines were determined by western blotting. Annexin-V staining and cleaved PARP western blotting were used to assay for apoptosis. The cellular toxicities after various treatments were measured via the XTT assay.ResultsIn our current analysis of colon and lung cancer samples, we demonstrate that Mcl-1 and Bcl-xL are overexpressed and also co-exist in many tumors and that the expression levels of both genes correlate with the clinical staging. The downregulation of Mcl-1 or Bcl-xL via RNAi was found to increase the sensitivity of the tumor cells to chemotherapy. Furthermore, our analyses revealed that USP9X expression correlates with that of Mcl-1 in human cancer tissue samples. We additionally found that the USP9X inhibitor WP1130 promotes Mcl-1 degradation and increases tumor cell sensitivity to chemotherapies. Moreover, the combination of WP1130 and ABT-737, a well-documented Bcl-xL inhibitor, demonstrated a chemotherapeutic synergy and promoted apoptosis in different tumor cells.ConclusionMcl-1, Bcl-xL and USP9X overexpression are tumor survival mechanisms protective against chemotherapy. USP9X inhibition increases tumor cell sensitivity to various chemotherapeutic agents including Bcl-2/Bcl-xL inhibitors.

Let-7b binding site polymorphism in the B-cell lymphoma-extra large 3′UTR is associated with fluorouracil resistance of hepatocellular carcinoma

“…Identifying SNPs that are associated with cancer and chemosensitivity may therefore be useful in the generation of personalized cancer diagnostic and therapeutic approaches. Numerous studies have shown that Bcl-xl status is associated with the chemosensitivity of cancer cells (32,33). In the present study, it was found that the SNP (rs3208684) A>C variation in the Bcl-xl 3'UTR disrupted the interaction between the let-7 precursor miRNA and Bcl-xl, thus upregulating Bcl-xl expression and Bcl-xl-mediated 5-FU resistance.…”

Targeting deubiquitinase activity with a novel small-molecule inhibitor as therapy for B-cell malignancies

“…5 Usp9x was also recently shown to suppress chemotherapy, radiotherapy, and targeted therapy in several tumor types through its regulation of Mcl-1 and other proteins. 6,7 Mcl-1 is essential for tumor cell survival, and high levels are noted in patients with drug-resistant MM. 8 By using proteomics, ubiquitinated Mcl-1 was recently shown to be bound and deubiquitinated by Usp9x, thus preventing its destruction by the proteasome.…”

Reduced ubiquitin-specific protease 9X expression induced by RNA interference inhibits the bioactivity of hepatocellular carcinoma cells

“…Recently, an increasing number of studies have demonstrated that USP9X is involved with cancer (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). USP9X expression was found to be higher in lung, colon and breast cancer, when compared with normal tissues in vitro (5,10).…”

“…USP9X expression was found to be higher in lung, colon and breast cancer, when compared with normal tissues in vitro (5,10). Furthermore, in lung and colon cancers, decreased USP9X expression resulted in the promotion of cellular apoptosis in vivo (5), which indicated that USP9X expression may be a potential predictor of such cancers.…”

“…Ubiquitin-specific protease 9X (USP9X) is a X-linked ubiquitin specific peptidase which belongs to the ubiquitin-specific protease family (5). USP9X serves as a deubiquitinase and effectively regulates the proliferation, adhesion and signal transduction of cells, therefore is crucial in controlling proteasome activity in organogenesis, transcriptional regulation and tumorigenesis (6)(7)(8)(9).…”