An immortalization-dependent switch in integrin function up-regulates MMP-9 to enhance tumor cell invasion

Integrins, the major receptors for cell adhesion to the extracellular matrix, play important roles during tumor progression. However, it is still unclear whether genetic lesions that occur during carcinoma development can lead to altered integrin function, and how changes in integrin function contribute to subsequent carcinoma progression. Loss-of-function mutations in p53 and activating mutations in H-Ras, which immortalize and transform epithelial cells, respectively, are common causal events in squamous cell carcinoma (SCC). Phenotypes resulting from these two genetic lesions promote SCC progression and are, therefore, potential targets for anticancer therapies. We developed a model system of keratinocyte transformation that has allowed us to investigate the individual roles of p53 mutation and oncogenic Ras mutation in the acquisition of integrin alpha 3 beta 1-regulated phenotypes that promote SCC progression. Using this model, we show that keratinocyte immortalization by p53-null mutation causes a switch in alpha 2 beta 1 function that induces matrix metalloproteinase (MMP)-9 gene expression in tumorigenic cells. This acquired alpha 3 beta 1-dependent regulation of MMP-9 was maintained during subsequent transformation by oncogenic Ras, and it promoted invasion of tumorigenic keratinocytes. Our results show that loss of p53 function leads to changes in integrinmediated gene regulation that occur during SCC progression and play a critical role in tumor cell invasion.