p38 MAPK activation and STIM1-Orai3 association mediate TRPC6 externalization.

Endothelial cell (EC) migration is critical for the repair of monolayer disruption following angioplasties, but migration is inhibited by lipid oxidation products, including lysophosphatidylcholine (lysoPC), which open canonical transient receptor potential 6 (TRPC6) channels. TRPC6 activation requires an increase in intracellular Ca concentration ([Ca]), the source of which is unknown. LysoPC can activate phospholipase A2 to release arachidonic acid (ArA). ArA can activate arachidonic acid-regulated calcium (ARC) channels that are formed by stromal interaction molecule 1 (STIM1) and Orai1 and Orai3 proteins. Both lysoPC and ArA can activate p38 mitogen-activated protein kinase (MAPK) that induces the phosphorylation required for STIM1-Orai3 association. This is accompanied by an increase in [Ca] and TRPC6 externalization. The effect of lysoPC and ArA is not additive, suggesting activation of the same pathway. The increase in [Ca] activates an Src kinase that leads to TRPC6 activation. Downregulation of Orai3 using siRNA blocks the lysoPC- or ArA-induced increase in [Ca] and TRPC6 externalization and preserves EC migration. These data show that lysoPC induces activation of p38 MAPK, which leads to STIM1-Orai3 association and increased [Ca]. This increase in [Ca] activates an Src kinase leading to TRPC6 externalization, which initiates a cascade of events ending in cytoskeletal changes that disrupt EC migration. Blocking this pathway preserves EC migration in the presence of lipid oxidation products. The major lysophospholipid component in oxidized LDL, lysophosphatidylcholine (lysoPC), can activate p38 MAP kinase, which in turn promotes externalization of Orai3 and STIM1-Orai3 association, suggesting involvement of arachidonic acid-regulated calcium (ARC) channels. The subsequent increase in intracellular calcium activates an Src kinase required for TRPC6 externalization. TRPC6 activation, which has been shown to inhibit endothelial cell migration, is blocked by p38 MAP kinase or Orai3 downregulation, and this partially preserves endothelial migration in lysoPC.