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-α (TGF-α) 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-α 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 α5, β1, and γ1 chains, respectively, indicating that LIM1215 cells secrete laminin-10 (α5β1γ1). In serum-free medium, LIM1215 cells adhere to laminin-10 primarily via α2β1 and α3β1 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 α3 or β1 but not α2, α6, or β4 subunits. Spreading is almost completely inhibited by blocking α3 + α2, α3 + α6, or β1 + β4 integrin chains and results in cell death. Increased spreading in the presence of EGF correlates with up-regulation of α6β4 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 α3β1 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-α and laminin-10 and autocrine induction of appropriate integrins.