SALL1 functions as a tumor suppressor in hepatocellular carcinoma cells

Hepatocyte nuclear factor 4α (HNF4α) is highly expressed in the liver and acts as a master regulator of liver-specific functions and maintenance of differentiated status. Liver-specific Hnf4a-deficient mice (Hnf4a^ΔHep mice) exhibit numerous phenotypes resulting from marked changes in the expression of several hepatic genes. In this study, we found that the mRNA and protein expression of hepatic Spalt-like transcription factor 1 (SALL1), which is important for kidney development, was significantly increased in Hnf4a^ΔHep mice. Protein expression levels of SALL1 were relatively low in control Hnf4a-floxed mice (Hnf4a^f/f mice), whereas SALL1 mRNA was highly expressed in both normal human liver and kidney. SALL1 mRNA expression was negatively regulated by miR-192-5p and miR-194-5p, which are direct targets of HNF4α, via binding sites of both miRNAs in the coding and 3'-untranslated regions, respectively. Transient overexpression of SALL1 suppressed the proliferation of human hepatocellular carcinoma (HCC) cell lines. RNA sequencing of HCC cells with SALL1 knockdown and promoter analysis revealed that SALL1 positively regulates A-kinase anchoring protein 12 and insulin-like growth factor binding protein 1 and negatively regulates phosphoserine aminotransferase 1. Stable expression of SALL1 in HCC cells induced cellular senescence-like features, as evidenced by cell hypertrophy, increased senescence-associated β-galactosidase-positive cells, and cell cycle arrest at the S phase. Furthermore, stable expression of SALL1 in HCC cells induced the expression of certain liver-specific markers, indicating that SALL1 promotes redifferentiation of HCC cells. These findings suggest that SALL1 may function as a tumor suppressor in HCC and contribute to the development of HCC therapies.