PBX3-HMGCR Axis Promotes Hepatocellular Carcinoma Progression Through Enhancing De Novo Cholesterol Biosynthesis

Tumor cells alter lipid metabolic pathways to meet their demands for energy and membrane biosynthesis. Despite its crucial role in tumor cell growth, survival, and metastasis, the mechanisms underlying tumor cell lipid metabolic reprogramming remain poorly understood. Pre-B-cell leukemia transcription factor 3 (PBX3), a member of the PBX family, could promote tumorigenesis; however, whether it is involved in tumor lipid metabolic reprogramming remains unknown. Herein, we found that PBX3 significantly promotes tumor growth by enhancing lipid accumulation in HCC cells. By assessing the effect of PBX3 on the expression levels of lipid metabolism-related genes, we found that PBX3 could positively regulate the expression of 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR), a rate-limiting enzyme in the cholesterol biosynthesis pathway. Mechanistically, we revealed that PBX3 could directly bind to the -167/-151 region of <i>HMGCR</i> promoter, thereby increasing its transcriptional activity and, subsequently, its expression level. This leads to the increase of HCC cell cholesterol biosynthesis and, eventually, to the increase of the in vivo tumorigenic potential. Collectively, our research revealed an unprecedented regulatory mechanism of cholesterol metabolism in HCC cells through PBX3 positive regulation on HMGCR expression levels. These findings provide novel insights into tumor metabolic reprogramming and uncover a previously unknown physiological function for PBX3. Moreover, these results suggest the potential of targeting <i>PBX3</i> as an anti-tumor therapeutic strategy.