RPL6 interacts with HMGCS1 to stabilize HIF-1a by activating cholesterol biosynthesis in hepatocellular carcinoma II

The identification of predictive markers to determine the premetastatic phase before metastasis is critical for developing effective strategies for early detection and prevention. By applying the dynamic network biomarker (DNB) approach to analyze time-series transcriptomic data from a pulmonary metastasis HCC mouse model, we revealed that the premetastatic phase occurred during the fourth week after implantation. A total of 142 DNB genes were identified as functionally important biomarkers of this critical phase, among which 60S ribosomal protein L6 (RPL6) was a core DNB member. RPL6 was significantly upregulated in HCC tissues with extrahepatic metastasis and was strongly correlated with poor prognosis in HCC patients. RPL6 promoted the invasion and metastasis of HCC cells, both in vitro and in vivo. Mechanistically, RPL6 directly bound to the HMGCS1 mRNA 3'UTR, a rate-limiting enzyme in cholesterol biosynthesis, thus increasing HMGCS1 mRNA stability and protein expression and subsequently elevating intracellular cholesterol level. Elevated cholesterol inhibited of the ubiquitin-dependent degradation of HIF-1a by binding to PHD2 and reducing PHD2-mediated hydroxylation of HIF-1a, which further resulted in HIF-1a signaling pathway activation. Moreover, RPL6, HMGCS1 and HIF-1a were coexpressed in HCC tissues with extrahepatic metastasis. Taken together, this study provides new insights into the dynamic transcriptome profiles of HCC pulmonary metastasis and establishes an important role for the RPL6-HMGCS1-HIF-1a axis in HCC metastasis, suggesting potential prognostic biomarkers and therapeutic targets in HCC. Overall design: To identify the critical state and driving genes during HCC metastasis process, we systematically monitored gene expression profiles at four stages in a pulmonary metastasis HCC mouse model, in which GFP-labeled MHCC97H cells with high metastatic potential were orthotopically transplanted into the livers of nude mice.