Binding of Autotaxin to Integrins Localizes Lysophosphatidic Acid Production to Platelets and Mammalian Cells

Autotaxin (ATX) is a secreted lysophospholipase D that generates the bioactive lipid mediator lysophosphatidic acid (LPA). We and others have reported that ATX binds to integrins, but the function of ATX-integrin interactions is unknown. The recently reported crystal structure of ATX suggests a role for the solvent-exposed surface of the N-terminal tandem somatomedin B-like domains in binding to platelet integrin alpha IIb beta(3). The opposite face of the somatomedin B-like domain interacts with the catalytic phosphodiesterase (PDE) domain to form a hydrophobic channel through which lysophospholipid substrates enter and leave the active site. Based on this structure, we hypothesize that integrin-bound ATX can access cell surface substrates and deliver LPA to cell surface receptors. To test this hypothesis, we investigated the integrin selectivity and signaling pathways that promote ATX binding to platelets. We report that both platelet beta 1 and beta 3 integrins interact in an activation-dependent manner with ATX via the SMB2 domain. ATX increases thrombin-stimulated LPA production by washed platelets similar to 10-fold. When incubated under conditions to promote integrin activation, ATX generates LPA from CHO cellsprimed with bee venom phospholipase A(2), and ATX-mediated LPA production is enhanced more than 2-fold by CHO cell overexpression of integrin beta(3). The effects of ATX on platelet and cell-associated LPA production, but not hydrolysis of small molecule or detergent-solubilized substrates, are attenuated by point mutations in the SMB2 that impair integrin binding. Integrin binding therefore localizes ATX activity to the cell surface, providing a mechanism to generate LPA in the vicinity of its receptors.