Colon cancer cells adhesion and spreading on autocrine laminin-10 is mediated by multiple integrin receptors and modulated by EGF receptor stimulation

Abstract

Epidermal growth factor (EGF) receptor ligands such as EGF and transforming growth factor-alpha (TGF-alpha) play an important role in controlling the proliferation, survival, morphology, and motility of colonic epithelial cells. There is also increasing evidence that growth factors and extracellular matrix (ECM) proteins cooperate to regulate these cellular processes. We have reported previously that autocrine TGF-alpha and an unidentified ECM protein in the serum-free conditioned medium of the human colon carcinoma cell line LIM1215 synergize to induce spreading of these cells in low-density cultures. We have now purified the ECM protein secreted by LIM1215 cells and show that it synergizes with EGF to induce spreading of LIM1215 cells and other human cell lines from the colon and other tissues. The purified ECM migrated as a single protein band with an apparent molecular mass of approximately 800 kDa on SDS-PAGE under nonreducing conditions and, under reducing conditions, as three protein bands of approximately 360, 210, and 200 kDa. Immunoblotting experiments and mass spectrometry analysis of tryptic digests on the purified protein identified the 360-, 210-, and 200-kDa protein bands as laminin alpha5, beta1, and gamma1 chains, respectively, indicating that LIM1215 cells secrete laminin-10 (alpha5 beta1 gamma1). In serum-free medium, LIM1215 cells adhere to laminin-10 primarily via alpha2 beta1 and alpha3 beta1 integrin receptors. EGF-induced spreading of LIM1215 cells on laminin-10 is partially inhibited by pretreatment of the cells with blocking antibodies directed against integrin alpha3 or beta1 but not alpha2, alpha6, or beta4 subunits. Spreading is almost completely inhibited by blocking alpha3 + alpha2, alpha3 + alpha6, or beta1 + beta4 integrin chains and results in cell death. Increased spreading in the presence of EGF correlates with up-regulation of alpha6 beta4 integrins in these cells after exposure to EGF. These results indicate that colon cancer cells attach and spread on laminin-10 via multiple integrin receptors and suggest a critical role for alpha3 beta1 integrins in the spreading response. Together, our results support the concept that the adhesive properties of colon cancer cells are modulated by autocrine production of TGF-alpha and laminin-10 and autocrine induction of appropriate integrins.