THE STIM1 REGULATORS SARAF IN CA2+ SIGNALING IN VIVO

Store‐Operated Ca 2+ influx(SOCs) is mediated by the pore forming channel Orai1, which is activated and regulated by the ER Ca 2+ 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 Ca 2+ dependent inactivation (SCDI) of Orai1 to inhibit SOC and prevent pathological Ca 2+ 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 Ca 2+ 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 Ca 2+ ([Ca 2+ ] i ) levels, increased SOC‐mediated Ca 2+ influx and higher agonist‐evoked Ca 2+ oscillation frequency. As a consequence, the SARAF −/− cells have higher resting and receptor‐mediated mitochondrial Ca 2+ 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 Ca 2+ influx and cell toxicity. These findings suggest that SARAF plays a critical role as a regulator of SOC‐mediated Ca 2+ influx in vivo and aberrant SARAF function maybe associated with Ca 2+ overload and associated cytotoxicity. Support or Funding Information National Institutes of Health, National Institute for Dental and Craniofacial Research