RIPPLY1 suppresses cancer cell stemness via targeting TBX19 in CTNNB1-mutated hepatocellular carcinoma

Background & Aims: CTNNB1 -mutated HCCs exhibit a relatively low stem-like and well-differentiated phenotype. However, the mechanism remains unclear. Ripply transcriptional repressor 1 (RIPPLY1), a transcriptional repressor required for somite segmentation, has hardly been studied in cancer. Here, we aim to unveil the role of RIPPLY1 in the regulation of cancer cell stemness in CTNNB1 -mutated HCCs. Approach and Results: RIPPLY1 was found to be transactivated by the Wnt/β-Catenin signal pathway. Human sample analysis confirmed that RIPPLY1 was significantly upregulated in CTNNB1 -mutated HCC tissues and positively correlated with better prognosis of HCC patients. Hepatocyte-specific deletion of RIPPLY1 promoted tumorigenesis and progression in DEN/PB-induced CTNNB1 -mutated HCC mouse model and hydrodynamic tail-vein injection (HDTVi)-induced CTNNB1 -mutated HCC mouse model. RIPPLY1 knockout tumor cells displayed upregulated levels of stem cell makers and enhanced cancer stem cell properties. Co-IP and MS identified TBX19 as the target protein of RIPPLY1. RIPPLY1 suppressed the transcriptional activity of TBX19 via recruiting TLE1 and promoting proteasome-dependent degradation of TBX19. TBX19 deficiency abolished the effect of RIPPLY1 loss on cancer cell stemness in CTNNB1 -mutated HCCs. Conclusion: Loss of RIPPLY1 promotes cancer cell stemness via facilitating the TBX19 transcriptional activity in CTNNB1 -mutated HCCs.