MCM8 promotes colorectal cancer progression by competitively inhibiting HRD1-mediated CDC42 ubiquitination and degradation.

Abstract

BACKGROUND: Colorectal cancer (CRC) ranks among the top three in both incidence and mortality rates of malignant tumors worldwide. For patients with advanced colon cancer, radical surgery is challenging, and chemotherapy drugs are prone to inducing drug resistance, resulting in a five-year survival rate of only 13.1%. Therefore, in-depth analysis of the occurrence, development, and drug resistance mechanisms of colon cancer is of great clinical significance for optimizing treatment strategies and improving patient prognosis. As one of the homologous recombination repair proteins, minichromosomal maintenance protein 8 (MCM8) not only participates in DNA replication initiation, homologous recombination repair, and genome stability maintenance in normal cells, but also has been reported to be abnormally highly expressed in multiple tumors (e.g. glioblastoma, cholangiocarcinoma, bladder cancer) to promote malignant progression. METHODS: This study focused on the expression and function of MCM8 in colon cancer. The expression level of MCM8 in colon cancer tissues and cells was detected, and its correlation with patients’ clinicopathological features and prognosis was analyzed. Combined with cell function experiments, protein-protein interaction verification assays, and in vivo tumorigenesis experiments, the effects of MCM8 on the biological behaviors of colon cancer cells and the underlying molecular mechanisms were explored. Meanwhile, rescue experiments were conducted to identify the key downstream molecules and pathways mediated by MCM8. Additionally, the relationship between MCM8 and chemoresistance of colon cancer cells was investigated. RESULTS: Our study indicated that MCM8 promotes the transition of the cell cycle from the G1 phase to the S phase in CRC cell lines(SW620, HCT116, CX-1). Moreover, our study showed that MCM8 interacted with Cdc42(Cell Division Cycle 42) and promoted its protein stability by competitively inhibiting the ubiquitination modification of Cdc42‘s E3 ubiquitin ligase HRD1(Hydroxymethylglutaryl Reductase Degradation Protein 1). The rescue experiment showed that MCM8 promoted the proliferation, cell cycle progression, invasion, tumor-forming ability in vivo and resistance to 5-FU of CRC cell lines (SW620FR, HCT15FR) through Cdc42, while inhibiting cell apoptosis. CONCLUSIONS: MCM8 is abnormally highly expressed in CRC and stabilizes Cdc42 protein by competitively inhibiting HRD1, thereby promoting the occurrence and development of CRC and the formation of 5-FU resistance.