Caveolin‐2 is a negative regulator of anti‐proliferative function and signaling of transforming growth factor beta in endothelial cells

Using a combination of caveolin‐2 (Cav‐2) knockout and retroviral re‐expression approaches, we provide the evidence for the negative role of Cav‐2 in regulating anti‐proliferative function and signaling of transforming growth factor beta (TGF‐beta) in endothelial cells (ECs). Although, TGF‐beta had a modest inhibitory effect on wild type (WT) ECs, it profoundly inhibited proliferation of Cav‐2 knockout ECs. To confirm the specificity of the observed difference in response to TGF‐beta, we have stably re‐expressed Cav‐2 in Cav‐2 knockout ECs using a retroviral approach. Albeit the levels of re‐expressed Cav‐2 were considerably lower than in WT ECs, the anti‐proliferative effect of TGF‐beta was dramatically reduced in the Cav‐2 re‐expressing ECs. The reduced anti‐proliferative effect of TGF‐beta in Cav‐2 re‐expressing cells was evidenced by three independent proliferation assays and correlated with a loss of TGF‐beta mediated upregulation of p27 and reduction of the levels of phosphorylated form of the retinoblastoma protein in Cav‐2 re‐expressing ECs. Mechanistically, Cav‐2 inhibits anti‐proliferative action of TGF‐beta by suppressing Alk5/Smad2/3 pathway, manifested by reduced magnitude and length of TGF‐beta induced Smad2 phosphorylation as well as activation of Alk5/Smad2 target genes plasminogen activator inhibitor‐1 and collagen type I in Cav‐2 re‐expressing ECs.