UBE2S inhibits colorectal cancer proliferation by regulating the PI3K/AKT and MAPK/ERK pathways via TRAF6

Ubiquitin conjugating enzyme UBE2S is an important enzyme in ubiquitin mediated proteolysis. The mechanisms of UBE2S in the colorectal cancer (CRC) proliferation need further exploration for new ubiquitination-related drugs exploitation. Firstly, we performed immunohistochemistry of UBE2S protein on CRC and adjacent tissues and found that UBE2S protein expressed higher in adjacent tissues than in tumor. TCGA and GTEx databases revealed a positive correlation between UBE2S expression and overall survival rate in CRC (P < 0.05). Cell proliferation experiments on HCT116 and RKO cell lines invalidated that UBE2S overexpression inhibited CRC cell proliferation and progression from G0/1 phase to G2 phase while knocking down UBE2S enhanced it. Mechanistically, combined with enrichment analysis based on RNA sequencing, it was identified molecularly that UBE2S simultaneously inhibited the activation of MAPK/ERK and PI3K/AKT pathways through promoting the ubiquitin-mediated degradation of TRAF6 protein, an upstream molecule to activate the both pathways, which can be blocked by inhibitor MG132. Animal experiments demonstrated that knocking down UBE2S resulted in larger transplanted tumor volumes than the control group, while overexpressing UBE2S resulted in the smaller ones in vivo. Summarily, we firstly identified that the UBE2S inhibited CRC proliferation by negatively regulating MAPK/ERK and PI3K/AKT/mTOR pathways through ubiquitinating TRAF6 protein.