Integrins control a variety of signal transduction pathways central to cell survival, proliferation, and differentiation and their functions and expression levels are altered in many types of cancer. Although alpha5beta1 is one of the most studied integrins in cancer, its functions in different aspects of this disease have not been completely elucidated. In particular, controversial data exist on its role in tumor invasion and metastasis. In order to establish mechanisms underlying involvement of alpha5beta1 integrin in invasion, we depleted its expression in MCF-7Dox human breast carcinoma cells via siRNA. We demonstrated that concomitant to alpha5beta1 integrin depletion, was a sharp decrease in MMP-2 collagenase expression and inhibition of the invasiveness of these cells in vitro. Similar reduction of invasion potential was observed upon siRNA-mediated silencing of the MMP-2 gene. Down-regulation of alpha5beta1 integrin was accompanied by a substantial decrease in the amounts of active (phosphorylated) forms of Akt, Erk1/2 kinases and c-Jun oncoprotein. Moreover, in MCF-7Dox cells, blocking the activity of above kinases by specific inhibitors strongly reduced expression of MMP-2 and c-Jun, and suppressed invasion of the cells in vitro. Similar results were observed upon siRNA-mediated silencing of c-Jun expression. Co-immunoprecipitation experiments demonstrated that alpha5beta1 integrin interacts with MMP-2 collagenase on the surface of MCF-7Dox breast carcinoma and SKMel-147 human melanoma cells. Our data suggest that alpha5beta1 integrin controls invasion of the studied cells via regulation of MMP-2 collagenase expression which can occur either through signaling pathways involving PI-3K, Akt, and Erk protein kinases and the c-Jun or via direct recruitment of MMP-2 to the cell surface.