Abstract
Transforming growth factor β (TGF-β) is abundantly present in the tumor microenvironment, contributing to cancer progression. However, the regulatory mechanism by which TGF-β affects vascular endothelial cells (ECs) in the tumor microenvironment is not well understood. Herein, we generated tamoxifen-inducible TGF-β type II receptor (TβRII) knockout mice, specifically targeting ECs (TβRIIiΔEC), by crossbreeding TβRII-floxed mice with Pdgfb-icreER mice. We established tumor-bearing mice by transplanting Lewis lung carcinoma (LLC) cells. TβRIIiΔEC mice exhibited increased tumor angiogenesis with fragile new blood vessels, increased bleeding, and hypoxia compared to control mice. Consequently, the compromised tumor microenvironment precipitated a notable surge in circulating tumor cells. Paradoxically, lung metastasis showed a significant decline. This intriguing discrepancy was explained by a reduction in the engraftment between cancer cells and ECs. Disruption of TGF-β signaling downregulated CD44 on ECs, hindering cancer cell adhesion. These findings highlight TGF-β's role in promoting metastasis by modulating EC function.