USP7 accelerates colorectal cancer progression by up-regulating MYO6 through deubiquitination

Ubiquitin-specific protease 7 (USP7) is one of deubiquitinases and has been reported to regulate cancer cell biological processes through removing ubiquitin modifications from protein substrates. Myosins of class VI (MYO6) is shown to be highly expressed in many of cancers, and is associated with tumor progression in several cancers by affecting cell survival. Moreover, USP7 and MYO6 have been revealed to be involved in colorectal cancer (CRC) progression. Here, we aimed to investigate the intricate interplay between MYO6 and USP7 in CRC, and whether their interaction was associated with deubiquitination.

Quantitative real-time PCR and western blot were used to for mRNA and protein detection. Functional analyses were conducted using Cell Counting Kit-8, 5-ethynyl-2-deoxy-uridine, flow cytometry, wound healing and transwell assays in vitro, and murine xenograft models in vivo. M2 macrophage polarization was determined with CD206 antibody using flow cytometry. The protein interaction between MYO6 and USP7 was determined by chromatin immunoprecipitation assay. The deubiquitination effect of USP7 was validated by cellular ubiquitination and immunoprecipitation assay.

CRC tissues and cells showed high expression of MYO6. Functionally, silencing of MYO6 suppressed CRC cell proliferation, migration, invasion, angiogenesis, induced cell apoptosis and negatively affected macrophage M2 polarization in vitro, and impeded CRC growth in vivo. For a mechanism analysis, USP7 could stabilize and up-regulate MYO6 expression by inducing MYO6 deubiquitination. USP7 was also highly expressed in CRC, USP7 silencing repressed CRC cell malignant phenotypes and reduced macrophage M2 polarization, while these effects were reversed by MYO6 overexpression.

MYO6 promoted CRC cell tumorigenesis and macrophage M2 polarization, and the mechanism was associated with USP7-induced MYO6 deubiquitination. These results suggested new targets for the development of epigenetic-based therapy in CRC.