Abstract: Background and purpose: As one of RNA-binding protein family member, Musashi1 (Msi1) is the key regulator of translation, whether it is involved in the tumorigenesis and its molecular mechanism are still unclear. This study aimed to investigate the effects of Msi1 gene silencing on the malignant process of colon cancer cell and its mechanism. Methods: The lentiviral vector was used to construct a stable HCT116 cell line with low expression of Msi1. Cell counting kit-8 (CCK-8) was used to test cell proliferative activity. Clone formation assay was conducted to detect the colony forming ability of stable Msi1 gene silencing HCT116 cells, and flow cytometry analysis was used to examine the change of cell cycle. The nude mouse xenograft model was established to observe the effects of Msi1 gene silencing on tumorigenicity in vivo. Real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR) and Western blot were used to examine the mRNA and protein levels of p27 after silencing Msi1 gene, and the binding site of Msi1 gene to p27 3’-untranslated region (3’-UTR) was examined by luciferase reporter assay. Results: After silencing Msi1 gene, the proliferation and colony forming ability of colon cancer HCT116 cells decreased significantly. The number of G ₀ /G ₁ phase cancer cells significantly increased, while the number of S phase cancer cells significantly decreased. The growth of xenograft tumor was significantly inhibited when Msi1 expression was reduced. And after silencing Msi1 gene, the mRNA expression of p27 was not significantly altered, while the protein level of p27 was significantly increased. Luciferase reporter assay showed Msi1 gene directly bound to p27 3’UTR. Conclusion: Silencing Msi1 gene can up-regulate the expression of p27, thereby arrest cancer cells in G ₀ /G ₁ phase, resulting in the inhibition of proliferation of colon cancer HCT116 cells in vitro and in vivo.

Key words: Colon cancer, Musashi1, p27, Proliferation, Cell cycle