Platelets promote primary hepatocellular carcinoma metastasis through TGF-β1-mediated cancer cell autophagy

Previous research has revealed that platelets promote tumor metastasis by binding to circulating tumor cells (CTCs). However, the role of platelets in epithelial-mesenchymal transition (EMT) of cancer cells at the primary tumor site, the crucial initial step of tumor metastasis, remains to be elucidated. Here, we found that platelet releasate enhanced EMT and motility of hepatocellular carcinoma (HCC) cells via AMPK/mTOR-induced autophagy. RNA-seq indicated that platelet releasate altered TGF-β signaling pathway of cancer cells. Inhibiting TGFBR or deleting platelet TGF-β1 suppressed AMPK/mTOR pathway activation and autophagy induced by platelet releasate. Compared with Pf4cre^-; Tgfb1^fl/fl mice, HCC orthotopic models established on Pf4cre⁺; Tgfb1^fl/fl mice showed reduced TGF-β1 in primary tumors, which corresponded with decreased cancer cell EMT, autophagy, migration ability and tumor metastasis. Inhibition of autophagy via Atg5 knockdown in cancer cells negated EMT and metastasis induced by platelet-released TGF-β1. Clinically, higher platelet count correlated with increased TGF-β1, LC3 and N-cad expression in primary tumors of HCC patients, suggesting a link between platelets and HCC progression. Our study indicates that platelets promote cancer cell EMT in the primary tumor and HCC metastasis through TGF-β1-induced HCC cell autophagy via the AMPK/mTOR pathway. These findings offer novel insights into the role of platelets in HCC metastasis and the potential therapeutic targets for HCC metastasis.