Title: Role of Calreticulin in Store-operated Ca entry (SOCE) Authors: Satanay Hubrack, Awab Ibrahim, Hamid Massaeli, Nasrin Mesaeli, Khaled Machaca. Abstract: Calreticulin is a pervasive protein that is mainly found within the ER. It has been linked to many cellular functions including Ca2+ storage and signaling along with protein folding. Here we use mouse embryonic fibroblasts, both wild type (WT) and knockouts (KO) not expressing calreticulin, to investigate the effect of calreticulin on the activation of store-operated Ca entry (SOCE). SOCE is a Ca influx pathway at the cell membrane that is regulated by the Ca content in intracellular stores primarily the endoplasmic reticulum (ER). SOCE is activated through the combined action of two proteins STIM-1, an ER Ca sensor and Orai1 a plasma membrane Ca selective channel. We hypothesized that calerticulin is essential for ORAI-1 folding and chaperoning; therefore, its function is necessary for the activation of SOC. Confocal microscopy of both WT and KO cells showed the presence of Orai1 at the plasma membrane GFP-Orai-1 transfected cells. Following Store depletion using thapsigargin, endogenous puncta were seen in both WT and KO cells. Moreover, calcium imaging using ratiometric measures showed the presence of SOC after store depletion in both cell lines. From our results, we conclude that Calreticulin is not necessary for the activity or function of SOC.


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