STIM1 phosphorylation at Y316 modulates its interaction with SARAF and the activation of SOCE and ICRAC

Abstract

Stromal interaction molecule 1 (STIM1) is one of the key elements for the activation of store- operated calcium entry (SOCE). Identification of the relevant phosphorylatable STIM1 residues with a possible role in the regulation of STIM1 function and SOCE might be of interest. Using computational analysis, we have identified that the Y316 residue is susceptible to be phosphorylated. Expression of the STIM1-Y316F mutant in HEK293, NG115-401L and MEG-01 cells has resulted in a reduction in STIM1 tyrosine phosphorylation, SOCE and ICRAC. STIM1-Orai1 colocalization was reduced in HEK293 cells transfected with YFP-STIM1-Y316F compared to YFP-STIM1-WT cells. Additionally, Y316F mutation altered the pattern of interaction between STIM1 and SARAF under resting conditions and upon Ca2+ store depletion. Expression of the STIM1 Y316F mutant enhanced slow Ca2+-dependent inactivation (SCDI) as compared to STIM1 WT, an effect that was abolished by SARAF knockdown. Finally, in NG115-401L cells transfected with shSARAF, expression of STIM1 Y316F induced greater SOCE than STIM1 WT. Summarizing, our results provide evidence supporting that phosphorylation of STIM1 at Y316 plays a relevant functional role in the activation and modulation of SOCE.