STIM1 regulates store operated calcium entry (SOCE) in human airway smooth muscle

Abstract

Intracellular Ca2+ regulation in human airway smooth muscle (hASM) involves plasma membrane (PM) Ca2+ influx, including that triggered by sarcoplasmic reticulum (SR) Ca2+ depletion, i.e. store‐operated Ca2+ entry (SOCE). While transient receptor potential channels (e.g. TRPC3, TRPC4) are thought to mediate SOCE, the mechanisms triggering or regulating SOCE are being actively investigated. Recent studies suggest that stromal interaction molecule 1 (STIM1) acts as a signaling mediator between PM and SR, potentially regulating Ca2+entry via SOCE. In hASM, fluorescence microscopy and western blot analyses were used to verify the presence of STIM1. SR Ca2+ depletion with 10μM cyclopiazonic acid (CPA) resulted in increased STIM1 expression in the PM fraction, compared to controls. Transfection with 50nM STIM1 siRNA for 48h significantly decreased STIM1 levels. In cells where [Ca2+]i was measured using fura 2‐AM, SOCE was significantly reduced in cells transfected with STIM1 siRNA. Green‐fluorescent protein (GFP)‐tagged STIM1 transfection showed intracellular localization in non‐stimulated cells, with increased PM staining following CPA exposure. Subsequent immunostaining revealed co‐localization of STIM1 with TRPC3 and TRPC4. These results indicate that STIM1 is present in hASM and suggest a role for this protein in regulating SOCE.This work has been supported by NIH grants UL1RR024150‐01(CR to CMP, CR20 and Early Career Development Award to YSP), HL74309 (GCS), and the Department of Anesthesiology (CMP, YSP), Mayo Clinic College of Medicine, Rochester, MN