Calcium regulates the interaction of amyloid precursor protein with Homer3 protein

Ca2+ dysregulation is an important factor implicated in Alzheimer's disease pathogenesis. The mechanisms mediating the reciprocal regulation of Ca2+ homeostasis and amyloid precursor protein (APP) metabolism, function, and protein interactions are not well known. We have previously shown that APP interacts with Homer proteins, which inhibit APP processing toward amyloid-β. In this study, we investigated the effect of Ca2+ homeostasis alterations on APP/Homer3 interaction. Influx of extracellular Ca2+ upon treatment of HEK293 cells with the ionophore A23187 or addition of extracellular Ca2+ in cells starved of calcium specifically reduced APP/Homer3 but not APP/X11a interaction. Endoplasmic reticulum Ca2+ store depletion by thapsigargin followed by store-operated calcium entry also decreased the interaction. Interestingly, application of a phospholipase C stimulator, which causes inositol 1,4,5-trisphosphate-induced endoplasmic reticulum Ca2+ release, caused dissociation of APP/Homer3 complex. In human neuroblastoma cells, membrane depolarization also disrupted the interaction. This is the first study showing that changes in Ca2+ homeostasis affect APP protein interactions. Our results suggest that Ca2+ and Homers play a significant role in the development of Alzheimer's disease pathology.