α2β1 integrin signaling via the mitogen activated protein kinase pathway modulates retinoic acid-dependent tumor cell invasion and transcriptional downregulation of matrix metalloproteinase 9 activity

Tumor cell invasion and metastasis requires precise coordination of adherence to the extracellular matrix (ECM) and controlled degradation of its components. Invasive cells secrete proteolytic enzymes known as matrix metalloproteinases which degrade specific basement membrane molecules. Expression of these enzymes is regulated by multiple signaling mechanisms, including attachment to the extracellular matrix via integrins. All-trans retinoic acid can inhibit tumor cell invasion of ECM by regulating matrix metalloproteinase expression. Using a series of squamous cell carcinoma lines, we investigated the interactions between integrin and retinoic acid signaling in these cells. In a cell line sensitive to RA-mediated inhibition of invasion, this ligand downregulated MMP-9 activity in cells grown on specific ECM molecules but not on plastic. Inhibition of integrin signaling with anti-alpha 2 beta 1 antibodies or MAPK pathway inhibitors abrogated RA mediated down-regulation of MMP-9 activity and invasion. The effects of RA and MARK signaling on MMP-9 activity was mediated at the transcriptional level. These data indicate that crosstalk between RA- and integrin dependent signaling pathways regulate MMP activity and invasion in squamous cell carcinoma lines.