Hypoxia Abrogates TGFβ Anti-angiogenesis in Hepatocellular Carcinoma by Modulating miR145 Expression

Background & Objectives: The role of transforming growth factor β (TGFβ) in regulating angiogenesis is controversial. Although TGFβ is abundant in the tumor microenvironment, active angiogenesis still occurs. Here, we aimed to uncover the mechanism by which tumors overcome TGFβ's anti-angiogenesis effect.

Methods: We used mouse xenograft models, transgenic zebrafish models, clinical samples, and cell models.

Results: We found that TGFβ suppressed physiological angiogenesis in zebrafish but not in mouse hepatoma. The anti-angiogenesis effect of TGFβ was abrogated in zebrafish treated with HIF1α stabilizers and recovered in hepatoma xenografts from mice administered with HIF1α inhibitors, indicating that hypoxia attenuates the anti-angiogenesis role of TGFβ. In vitro analyses showed that TGFβ inhibited the migration and tube formation of endothelial cells (EC) in normoxia but not in hypoxia by up-regulating TSP1, a vital anti-angiogenic factor. Moreover, HIF1α induced miR145 expression upon hypoxia, and miR145 abrogated the role of TGFβ in up-regulating TSP1 and repressing angiogenesis by binding to Smad2/3 and inhibiting their expression in EC. Further examination of primary EC isolated from human hepatocellular carcinoma (HCC) tissues (TEC) and their adjacent non-tumor liver (NEC) revealed that Smad2, Smad3, and TSP1 were dramatically decreased, whereas miR145 was significantly elevated in TEC. The decreases of Smad3 and TSP1 were negatively correlated with tumor angiogenesis in hepatocellular carcinoma tissues.

Conclusions: A novel HIF1α-miR145-Smad2/3-TSP1 axis in ECs abrogates the anti-angiogenesis role of TGFβ, highlighting hypoxia as a key factor for tumors to overcome TGFβ's anti-angiogenesis control.

Lay summary: This study provides insights into the complex regulatory network of TGFβ in HCC angiogenesis and demonstrates that hypoxia plays a crucial role in switching the divergent roles of TGFβ in physiological angiogenesis and HCC angiogenesis. These findings may have important implications for precision medicine.