THE STIM1 REGULATORS SARAF IN CA2+ SIGNALING IN VIVO

Abstract

Store‐Operated Ca2+ influx(SOCs) is mediated by the pore forming channel Orai1, which is activated and regulated by the ER Ca2+ sensor STIM1. In turn, the function of STIM1 is regulated by the SOC‐Associated Regulatory Factor SARAF. SARAF is an ER protein that interacts with STIM1 to mediate the slow Ca2+ dependent inactivation (SCDI) of Orai1 to inhibit SOC and prevent pathological Ca2+ overload. How SARAF functions in vivo is unknown. In the present work, we developed and partially characterized SARAF deficient (SARAF−/−)mice and investigated the role of SARAF in Ca2+ signaling inpancreatic and salivary gland acinar cells. At 8 weeks of age, the body weight of SARAF−/− mice is about 20% lower and the mice show significant cardiac hypertrophy and increased receptor stimulated fluid and electrolyte secretion by the salivary glands. SARAF−/− pancreatic and salivary glands acini have higher resting free cytosolic Ca2+ ([Ca2+]i) levels, increased SOC‐mediated Ca2+ influx and higher agonist‐evoked Ca2+ oscillation frequency. As a consequence, the SARAF−/− cells have higher resting and receptor‐mediated mitochondrial Ca2+ load. The interaction between STIM1 and SARAF in vitro and in vivo is regulated by stimulus intensity. Physiological stimulus intensity increased interaction of SARAF with STIM1, which remains stable for the duration of cell stimulation. At pathological high stimulus intensity interaction of SARAF with STIM1 is transient, accounting for the sustained activation of Ca2+ influx and cell toxicity. These findings suggest that SARAF plays a critical role as a regulator of SOC‐mediated Ca2+ influx in vivo and aberrant SARAF function maybe associated with Ca2+ overload and associated cytotoxicity.Support or Funding InformationNational Institutes of Health, National Institute for Dental and Craniofacial Research