SKP1 promotes YAP-mediated colorectal cancer stemness via suppressing RASSF1

Abstract Background: Cancer stem cells (CSCs) have been recognized as an important drug target, however, the underlying mechanisms have not been fully understood. SKP1 is a traditional drug target for cancer therapy, while, whether SKP1 promotes colorectal cancer (CRC) stem cells (CRC-SCs) and the underlying mechanisms have remained elusive.Methods: Human CRC cell lines HCT-116 and HT-29 and primary human colorectal cancer cells were used in this study. Gene manipulation was performed by lentivirus system. The mRNA and protein levels were examined by qRT-PCR and western blot, respectively. Sphere formation and transwell assay were employed for examination of sphere-forming and migration capacities. The self-renewal capacity was determined by limiting dilution assay. The tumorigenicity was examined by xenograft model. The transcriptional activities of the promoters were examined by luciferase reporter assay. Co-immunoprecipitation assay was used to test protein-protein interaction. The transcription and protein-DNA interaction were examined by nuclear run-on and ChIP-PCR assay. The relationship between gene expression and survival was analyzed by Kaplan-meier analysis. The correlation between two genes was analyzed by Spearman analysis. Data are represented as mean ± s.d. and the significance was determined by Student’s t-test.Results: SKP1 is upregulated in colorectal cancer stem cells and predicts poor prognosis of colon cancer patients. Overexpression of SKP1 promotes the sphere-forming and migration capacities as well as self-renewal of CRC cells, and upregulates the expression of CSCs markers. In contrast, SKP1 depletion produces the opposite effects. SKP1 strengthens YAP activity and knockdown of YAP abolished the effect of SKP1 on the stemness of colorectal cancer cells. SKP1 suppresses RASSF1 at both mRNA and protein levels and overexpression of RASSF1 abolished the effect of SKP1.Conclusion: Our results demonstrated that SKP1 suppresses RASSF1 at both mRNA and protein level, attenuates Hippo signaling, activates YAP, and thereby promoting the stemness of CRC cells. Our works thus revealed a novel underlying mechanism of CRC-SCs maintenance and suggested a novel drug target for eradicating CRC-SCs.