Ubiquitin-specific peptidase 15 regulates the TFAP4/PCGF1 axis facilitating liver metastasis of colorectal cancer and cell stemness

The tumor recurrence and metastasis of colorectal cancer (CRC) are responsible for most of CRC-linked mortalities. It is an urgent need to deeply investigate the pathogenesis of CRC metastasis and look for novel targets for its treatment. The current study aimed to investigate the effects of ubiquitin-specific peptidase 15 (USP-15) on the CRC progression. In vivo, a mouse model of liver metastasis of CRC tumor was established to investigate the role of USP-15. In vitro, the migrated and invasive abilities of CRC cells were assessed by transwell assay. Cell stemness was evaluated by using sphere formation assay. The underlying mechanism was further explored by employing the co-immunoprecipitation, dual luciferase reporter assay, oligonucleotide pull-down assay, and chromatin immunoprecipitation assay. The results showed that USP-15 was upregulated in CRC patients with liver metastasis and high metastatic potential cell lines of CRC. Loss of USP-15 repressed the epithelial-to-mesenchymal transition (EMT), migration, invasion, and stemness properties of CRC cells in vitro. Downregulation of USP-15 reduced the liver metastasis of mice in vivo. USP-15 upregulation obtained the contrary effects. Subsequently, USP-15 deubiquitinated transcription factor AP-4 (TFAP4) and enhanced its protein stability. TFAP4 could transcriptionally activated polycomb group ring finger 1 (PCGF1). The pro-cancer effects of USP-15 were rescue by the knockdown of TFAP4 or PCGF1. In conclusions: USP-15 facilitated the liver metastasis by the enhancement of cell stemness and EMT in CRC, which was at least partly mediated by the deubiquitination of TFAP4 upon the upregulation of PCGF1.