αvβ3 integrin interacts with the transforming growth factor β (TGFβ) type II receptor to potentiate the proliferative effects of TGFβ1 in living human lung fibroblasts

Abstract

The αvβ3 integrin is known to cooperate with receptor tyrosine kinases to enhance cellular responses. To determine whether αvβ3 regulates transforming growth factor β (TGFβ) 1-induced responses, we investigated the interaction between αvβ3 and TGFβ type II receptor (TGFβIIR) in primary human lung fibroblasts. We report that TGFβ1 up-regulates cell surface and mRNA expression of αvβ 3 in a time- and dose-dependent manner. Co-immunoprecipitation and confocal microscopy showed that TGFβRII associates and clusters with αvβ3, following TGFβ1 exposure. This association was not observed with αvβ5 or α5β1. We also used a novel molecular proximity assay, bioluminescence resonance energy transfer (BRET), to quantify this dynamic interaction in living cells. TGFβ1 stimulation resulted in a BRET signal within 5 min, whereas tenascin, which binds αvβ 3, did not induce a substantial BRET signal. Co-exposure to tenascin and TGFβ1 produced no further increases in BRET than TGFβ1 alone. Cyclin D1 was rapidly induced in cells co-exposed to TGFβ1 and tenascin, and as a consequence proliferation induced by TGFβ1 was dramatically enhanced in cells co-exposed to tenascin or vitronectin. Cholesterol depletion inhibited the interaction between TGFβRII and αvβ 3 and abrogated the proliferative effect. The cyclic RGD peptide, GpenGRGD-SPCA, which blocks αvβ3, also abolished the synergistic proliferative effect seen. These results indicate a new interaction partner for the αvβ3 integrin, the TGFβIIR, in which TGFβ1-induced responses are potentiated in the presence αvβ3 ligands. Our data provide a novel mechanism by which TGFβ1 may contribute to abnormal wound healing and tissue fibrosis.