In this work, we report that type IV collagen, mainly via alpha2beta1-integrin ligation, was able to induce cyclin expression and G1/S transition in a colic adenocarcinoma cell line (Caco-2) cultured without soluble growth factors or fetal bovine serum. This process involved Erk 1/2 activation and the production of reactive oxygen species (ROS) by a membrane-bound NADPH oxidase. Data presented here show that NADPH oxidase-dependent production of ROS increased following alpha2beta1-integrin ligation with type IV collagen or with a specific monoclonal antibody (Gi9 mAb). NADPH oxidase activation and, therefore, the production of ROS were shown to be involved in the increase of alpha2beta1-integrin plasma membrane expression, p38 MAPK phosphorylation, cyclin expression, and G1/S transition. We thus identified in this work a new integrin-signaling pathway in colon tumor cells involved in cell cycle regulation by the extracellular matrix.