CircABCA1 promotes ccRCC by reprogramming cholesterol metabolism and facilitating M2 macrophage polarization through IGF2BP3-mediated stabilization of SCARB1 mRNA.

BACKGROUND The reliance of clear cell renal cell carcinoma (ccRCC) on exogenous cholesterol import implies a metabolic susceptibility. This susceptibility represents a potential avenue that can be exploited as a novel therapeutic approach for ccRCC. Circular RNAs (circRNAs) are emerging regulators in cancer, yet their roles in ccRCC lipid metabolism and tumor microenvironment remodeling remain unclear. This study investigates the tumor-promoting role of circABCA1 in ccRCC cholesterol homeostasis and M2 macrophage polarization. METHODS The expression levels of circABCA1, IGF2BP3, SCARB1, autophagy-related proteins, and the IGF1R/PI3K/AKT/mTOR and ABCA1/ABCG1 pathways were measured using RT-qPCR and western blot. Untargeted metabolomics, RNA- sequencing, and MS2 RNA-pulldown were conducted to identify targets. Interaction analyses included RNA immunoprecipitation, RNA pull-down, and RNA fluorescence in situ hybridization (FISH) assays. Lipid raft measurements, cholesterol uptake/efflux assays, and lipophagy assessments were performed. A co-culture system between M2 macrophages and ccRCC cells was established. In vivo tumorigenesis and metastasis were evaluated using xenograft models and a hepatic metastasis model. Statistical analyses involved Student's t-tests and ANOVA; significance set at P < 0.05. RESULTS We identified a novel lipid metabolism-related circRNA, circABCA1, which was upregulated in ccRCC and positively correlated with tumor stage and distant metastasis. Functionally, circABCA1 enhanced the half-life of SCARB1 mRNA by forming a circABCA1-IGF2BP3-SCARB1 mRNA ternary complex, thereby increasing the expression of SCARB1 and consequent cholesterol uptake. Next, elevated cholesterol caused by circABCA1-SCARB1 axis-maintained lipid rafts, initiated IGF1R/PI3K/AKT/mTOR cascade, and protected lipid droplets from being destructed by lipophagy, leading to decreased cholesterol efflux. CircABCA1 facilitated the proliferation and migration of ccRCC in vitro and in vivo in a SCARB1 depended manner. Moreover, we uncovered that circABCA1 facilitated M2 macrophage polarization and subsequent pro-tumor effect by prompting cholesterol uptake of ccRCC from tumor microenvironment in a SCARB1-dependent manner. CONCLUSIONS CircABCA1 plays a crucial role in promoting ccRCC progression by regulating cholesterol metabolism and facilitating M2 macrophage polarization, representing a potential therapeutic target for ccRCC treatment.