Adhesion of metastatic human mammary carcinoma MDA-MB-435 cells to the basement membrane protein collagen type IV can be activated by treatment with arachidonic acid. We initially observed that this arachidonic acid-mediated adhesion was inhibited by the tyrosine kinase inhibitor genistein. Therefore, we examined the role of the mitogen-activated protein (MAP) kinase family tyrosine phosphorylation-regulated pathways in arachidonic acid-stimulated cell adhesion. Arachidonic acid stimulated the

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... hosphorylation of p38, the activation of MAP kinase-activated protein kinase 2 (MAPKAPK2, a downstream substrate of p38), and the phosphorylation of heat shock protein 27 (a downstream substrate of MAP kinase-activated protein kinase 2). Treatment with the p38 inhibitor PD169316 completely and specifically inhibited arachidonic acid-mediated cell adhesion to collagen type IV. p38 activity was specifically associated with arachidonic acid-stimulated adhesion; this was demonstrated by the observation that 12-O-tetradecanoylphorbol 13-acetate-activated cell adhesion was not blocked by inhibiting p38 activity. Extracellular signal-regulated protein kinases (ERKs) 1 and 2 were also activated by arachidonic acid; however, cell adhesion to collagen type IV was not highly sensitive to PD98059, an inhibitor of MAP kinase kinase/ERK kinase 1 (MEK1) that blocks activation of the ERKs. c-Jun NH 2 -terminal kinase was not activated by arachidonic acid treatment of these cells. Together, these data suggest a novel role for p38 MAP kinase in regulating adhesion of breast cancer cells to collagen type IV. Cell adhesion to extracellular matrix plays a major role in a variety of biological processes, such as embryonic development (1-3), wound healing (4, 5), cell proliferation (6 -8), and disease pathogenesis (9, 10). Among these processes is tumor cell metastasis, during which neoplastic cells interact with other tumor cells, normal endothelial cells, and the extracellular matrix. These interactions are sensitive to regulation by the local microenvironment and are dependent upon cell surface adhesion molecules (11-16). We are interested in identifying factors that influence the adhesive properties of human tumor cells