Endothelial-to-mesenchymal transition (EndMT) was first reported in the embryogenesis. Recent studies show that EndMT also occurs in the disease progression of atherosclerosis, cardiac and pulmonary fibrosis, pulmonary hypertension, diabetic nephropathy, and cancer. Although transforming growth factor β (TGFβ) is crucial for EndMT, it is not clear which isoform elicits a predominant effect. The current study aims to directly compare the dose-dependent effects of TGFβ1, TGFβ2, and TGFβ3 on EndMT and characterize the underlying mechanisms. In our results, all three TGFβ isoforms induced EndMT in human microvascular endothelial cells after 72 hr, as evidenced by the increased expression of mesenchymal markers N-cadherin and α-smooth muscle actin as well as the decreased expression of endothelial nitric oxide synthase. Interestingly, the effect of TGFβ2 was the most pronounced. At 1 ng/ml, only TGFβ2 treatment resulted in significantly increased phosphorylation (activation) of Smad2/3 and p38-MAPK and increased expression of mesenchymal transcription factors Snail and FoxC2. Intriguingly, we observed that treatment with 1 ng/ml TGFβ1 and TGFβ3, but not TGFβ2, resulted in an increased expression of TGFβ2, thus indicating that EndMT with TGFβ1 and TGFβ3 treatments was due to the secondary effects through TGFβ2 secretion. Furthermore, silencing TGFβ2 using small interfering RNA blunted the expression of EndMT markers in TGFβ1- and TGFβ3-treated cells. Together, our results indicate that TGFβ2 is the most potent inducer of EndMT and that TGFβ1- and TGFβ3-induced EndMT necessitates a paracrine loop involving TGFβ2.

Akt1 is essential for the oncogenic transformation and tumor growth in various cancers. However, the precise role of Akt1 in advanced cancers is conflicting. Using a neuroendocrine TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model, we first show that the genetic ablation or pharmacological inhibition of Akt1 in mice blunts oncogenic transformation and prostate cancer (PCa) growth. Intriguingly, triciribine (TCBN)-mediated Akt inhibition in 25-week old, tumor-bearing TRAMP mice and Akt1 gene silencing in aggressive PCa cells enhanced epithelial to mesenchymal transition (EMT) and promoted metastasis to the lungs. Mechanistically, Akt1 suppression leads to increased expression of EMT markers such as Snail1 and N-cadherin and decreased expression of epithelial marker E-cadherin in TRAMP prostate, and in PC3 and DU145 cells. Next, we identified that Akt1 knockdown in PCa cells results in increased production of TGFβ1 and its receptor TGFβ RII, associated with a decreased expression of β-catenin. Furthermore, treatment of PCa cells with ICG001 that blocks nuclear translocation of β-catenin promoted EMT and N-cadherin expression. Together, our study demonstrates a novel role of the Akt1-β-catenin-TGFβ1 pathway in advanced PCa.