Integrin-mediated cell adhesion regulates a multitude of cellular responses, including proliferation, survival and cross-talk between different cellular signalling pathways. So far, integrins have been mainly shown to convey permissive signals enabling anchorage-dependent receptor tyrosine kinase signalling^,,. Here we show that a collagen-binding integrin α₁β₁ functions as a negative regulator of epidermal growth factor receptor (EGFR) signalling through the activation of a protein tyrosine phosphatase. The cytoplasmic tail of α₁ integrin selectively interacts with a ubiquitously expressed protein tyrosine phosphatase TCPTP (T-cell protein tyrosine phosphatase) and activates it after cell adhesion to collagen. The activation results in reduced EGFR phosphorylation after EGF stimulation. Introduction of the α₁ cytoplasmic domain peptide into cells induces phosphatase activation and inhibits EGF-induced cell proliferation and anchorage-independent growth of malignant cells. These data are the first demonstration of the regulation of TCPTP activity in vivo and represent a new molecular paradigm of integrin-mediated negative regulation of receptor tyrosine kinase signalling.