Integrin-mediated type II TGF-β receptor tyrosine dephosphorylation controls SMAD-dependent profibrotic signaling.

Tubulointerstitial fibrosis underlies all forms of end-stage kidney disease. TGF-β mediates both the development and the progression of kidney fibrosis through binding and activation of the serine/threonine kinase type II TGF-β receptor (TβRII), which in turn promotes a TβRI-mediated SMAD-dependent fibrotic signaling cascade. Autophosphorylation of serine residues within TβRII is considered the principal regulatory mechanism of TβRII-induced signaling; however, there are 5 tyrosine residues within the cytoplasmic tail that could potentially mediate TβRII-dependent SMAD activation. Here, we determined that phosphorylation of tyrosines within the TβRII tail was essential for SMAD-dependent fibrotic signaling within cells of the kidney collecting duct. Conversely, the T cell protein tyrosine phosphatase (TCPTP) dephosphorylated TβRII tail tyrosine residues, resulting in inhibition of TβR-dependent fibrotic signaling. The collagen-binding receptor integrin α1β1 was required for recruitment of TCPTP to the TβRII tail, as mice lacking this integrin exhibited impaired TCPTP-mediated tyrosine dephosphorylation of TβRII that led to severe fibrosis in a unilateral ureteral obstruction model of renal fibrosis. Together, these findings uncover a crosstalk between integrin α1β1 and TβRII that is essential for TβRII-mediated SMAD activation and fibrotic signaling pathways.