Role of protein kinase C in the activation of store-operated Ca2+ entry in airway smooth muscle cells

Abstract

Store-operated Ca(2+) channels (SOCs) are plasma membrane Ca(2+) permeable channels activated by depletion of intracellular Ca(2+) store. Ca(2+) entry through SOCs is known as store-operated Ca(2+) entry (SOCE), which plays an important role in the functional regulation of airway smooth muscle cells (ASMCs). Protein kinase C (PKC) has been shown to have an activating or inhibiting effect on SOCE, depending on cell types and PKC isoforms that are involved. In ASMCs, the effect of PKC on SOCE has not been elucidated so far. In this study, the role of PKC in the activation of SOCE in rat ASMCs was examined by using Ca(2+) fluorescence imaging technique. The results showed that acute application of PKC activators PMA and PDBu did not affect SOCE induced by the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitor thapsigargin. The non-selective PKC inhibitor chelerythrine significantly inhibited thapsigargin- and bradykinin-induced SOCE. RT-PCR assay identified PKCα, δ and ɛ isoforms in rat ASMCs. PKCα-selective inhibitor Gö6976 and PKCɛ-inhibiting peptide Epsilon-V1-2 had no effect on SOCE; by contrast, PKCδ-selective inhibitor rottlerin attenuated SOCE dramatically, suggesting that PKCδ was the major PKC isoform involved in the activation of SOCE in ASMCs. Moreover, PKC down-regulation by extended exposure to high doses of PMA or PDBu also reduced SOCE, confirming the essential role of PKC in the activation of SOCE in ASMCs. In addition, PKC down-regulation did not influence the expression of stromal interaction molecule 1 (STIM1) and Orai1, two elementary molecules in the regulation and activation of SOCs. These results identified PKCδ as an essential PKC isoform involved in the activation of SOCE, and confirmed that PKC regulates the function of ASMCs in a SOCE-dependent manner.