passages.id: 18309
passages.type: title and abstract
passages.text: Store-operated Ca2+ Entry (SOCE) Induced by Protease-activated Receptor-1 mediates STIM1 Phosphorylation to inhibit SOCE in Endothelial Cells through AMP-activated Protein Kinase and p38beta Mitogen-activated Protein Kinase.
  The Ca2+ sensor STIM1 is crucial for activation of store-operated Ca2+ entry (SOCE) through TRPC and Orai channels. STIM1 phosphorylation serves as an off-switch for SOCE. However, the signaling pathway for STIM1 phosphorylation is unknown. Here we show that SOCE activates AMP-activated protein kinase (AMPK); its effector p38β mitogen-activated protein kinase (p38β MAPK) phosphorylates STIM1, thus inhibiting SOCE in human lung microvascular endothelial cells (ECs). Activation of AMPK using AICAR resulted in STIM1 phosphorylation on serine residues and prevented PAR-1-induced Ca2+ entry. Further, AICAR pretreatment blocked PAR-1-induced increase in permeability of mouse-lung microvessels. Activation of SOCE with thrombin caused phosphorylation of isoform α1, but not α2 of the AMPK catalytic subunit. Moreover, knockdown of AMPKα1 augmented SOCE induced by thrombin. Interestingly, SB203580, a selective inhibitor of p38 MAPK, blocked STIM1 phosphorylation and led to sustained STIM1-puncta formation and Ca2+ entry. Of the three p38 MAPK isoforms expressed in ECs, p38β knockdown prevented PAR-1-mediated STIM1 phosphorylation and potentiated SOCE. In addition, inhibition of the SOCE downstream target CaMKKβ or knockdown of AMPKα1 suppressed PAR-1-mediated phosphorylation of p38β and hence STIM1. Thus, our findings demonstrate that SOCE activates CaMKKβ-AMPKα1-p38β MAPK signaling to phosphorylate STIM1, thereby suppressing endothelial SOCE and permeability responses.