Microscopic analysis of Orai-mediated store-operated calcium entry in cells with experimentally altered levels of amyloid precursor protein

Familial Alzheimer's disease (FAD)-causing mutations in presenilins were shown to alter intracellular calcium dynamics, including store-operated calcium entry (SOCE). However, the involvement of FADlinked amyloid precursor protein (APP) in SOCE remains controversial. Here, we used gain-of-function and loss-of-function approaches to shed light on this issue. We found that Jurkat cells, which exhibit prominent SOCE mediated by Orai channels, maintain low APP levels. The ectopic expression of APP, either with wildtype sequence or FAD-causing Swedish mutation, had no effect on SOCE induced by calcium store depletion with cyclopiazonic acid (CPA). The overproduction of C99 fragments, mimicking amyloidogenic processing of APP, also had no effect. Moreover, there was no alteration in the CPA-evoked SOCE upon APP knockdown in HeLa cells, which natively express 100-fold more APP than Jurkat cells. Consistently, we found no evidence for APP-dependent changes in the mRNA or protein levels of main SOCE components. Altogether, these results suggest that APP does not modulate Orai-dependent SOCE following quantitative calcium store depletion.