Ubiquitin-specific peptidase 20 affects immune cell infiltration by regulating prostaglandin E2 on intraperitoneal metastasis model of colorectal cancer

BACKGROUND: Ubiquitin-specific peptidase 20 (USP20) acts as oncogene or tumor suppressor gene in different types of cancer. But there are only a few reports about the effect of USP20 on colorectal cancer (CRC). This study aims to further explore the novel molecular mechanisms of USP20 in intraperitoneal metastasis of CRC. METHODS: First, bioinformatics analyses were performed to discover the association between USP20 expression and the clinical characteristics of CRC. Subsequently, the mouse model was constructed using a USP20 knockout (USP20-KO) colon cell line to validate the effects of USP20 on intraperitoneal metastasis and immune cell infiltration. And then metabolomics study was performed on the USP20-KO cells to find the novel mechanisms of USP20. Finally, the relationship of prostaglandin E2 (PGE2) and USP20 was identified by enzyme-linked immunosorbent assay (ELISA) and Western blotting experiments. RESULTS: Bioinformatics analyses showed that the USP20 expression was significantly upregulated in CRC and affected immune cell infiltration. The animal model study revealed that the intraperitoneal metastasis of tumor cell was inhibited by knocking out USP20, and the expression of USP20 could affect the proportions of CD8(+) T cells and myeloid-derived suppressor cells (MDSCs) in tumor tissue and ascites. Metabolomics study found that PGE2 should be the key metabolite regulated by USP20 for affecting immune cell infiltration. Finally, it was validated that the expressions of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) and microsomal prostaglandin E synthase-1 (mPGES-1) were regulated by the USP20 related ubiquitin-proteasome pathway. CONCLUSIONS: The USP20 expression is significantly upregulated in CRC, and can promote tumor metastasis by affecting immune cell infiltration. As an important tumor metabolite which can influence immune cell infiltration, PGE2 is regulated by USP20 through the protein degradation of mPGES-1 and 15-PGDH mediated by proteasome.