A positive feedback loop between FOSB and miR-133b controls colon cancer cell proliferation

FOSB, a member of the FOS gene family, forms heterodimers with JUN family proteins to engage in diverse cellular processes. Its biological impacts vary among different types of tumors, yet its specific function in colon cancer (CC) remains ambiguous. In this study, quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC) are applied to measure FOSB expression levels, followed by an analysis of the association between FOSB expression and patients' clinical parameters. In vitro experiments are performed to assess cell proliferation, including growth rate, cell cycle distribution, and apoptosis. A subcutaneous xenograft model in nude mice is utilized to monitor tumor growth in vivo. Additionally, chromatin immunoprecipitation (ChIP) and luciferase reporter assays are conducted to dissect the interactions among FOSB, miR-133b, and POU2F1. The results indicate that FOSB expression is downregulated in CC tissues relative to normal controls. Overexpression of FOSB suppresses proliferation and promotes apoptosis in CC cells. Mechanistically, FOSB binds to the promoter region of miR-133b, enhancing its transcription and subsequently repressing POU2F1 expression. Notably, decreased POU2F1 expression also alleviates the transcriptional repression of the FOSB promoter region, establishing a FOSB-miR-133b-POU2F1 feedback loop that inhibits CC proliferation. In summary, our findings suggest that FOSB acts as a tumor suppressor gene in CC and may exert its inhibitory effects on CC growth via the FOSB-miR-133b-POU2F1 feedback loop.