RESUMO
Presenilins regulate calcium homeostasis in the endoplasmic reticulum, and dysregulation of intracellular calcium has been implicated in the pathogenesis of Alzheimer disease. Elevated presenilin-1 (PS1) holoprotein levels have been detected in postmortem brains of patients carrying familial Alzheimer disease (FAD) PS1 mutations. This study examines the effect of the FAD presenilin mutant that lacks the ninth exon (PS1 ∆E9) and does not undergo endoproteolysis on store-operated calcium (SOC) entry. Significant enhancement of SOC channel activation was detected by electrophysiological measurements in hippocampal neurons with PS1 ∆E9 mutant expression. Here, we show that (i) the hyperactivation of SOC channels is mediated by the STIM1 sensor and can be attenuated by STIM1 knockdown or 2-aminoethoxydiphenyl borate application, (ii) the STIM2 is not involved in pathological changes of SOC entry, (iii) the pathological SOC entry demonstrates properties of both TRPC and Orai subunit composition, and (iiii) transgenic Drosophila flies with PS1 ∆E9 expression in the cholinergic neuron system show short-term memory loss, which can be abolished by 2-aminoethoxydiphenyl borate feeding.
Assuntos
Canais de Cálcio/metabolismo , Hipocampo/citologia , Ativação do Canal Iônico , Mutação/genética , Neurônios/metabolismo , Presenilina-1/genética , Molécula 1 de Interação Estromal/metabolismo , Animais , Animais Geneticamente Modificados , Linhagem Celular Tumoral , Membrana Celular/metabolismo , Neurônios Colinérgicos/metabolismo , Drosophila melanogaster/genética , Técnicas de Silenciamento de Genes , Transtornos da Memória/patologia , Camundongos , Proteínas Mutantes/metabolismo , Proteína ORAI1/metabolismo , Canais de Cátion TRPC/metabolismoRESUMO
Homers are adapter proteins that play a significant role in the organization of calcium signaling protein complexes. Previous functional studies linked Homer proteins to calcium influx in nonexcitable cells. These studies utilized calcium imaging or whole-cell current recordings. Because of limited resolution of these methods, an identity of Homer-modulated ion channels remained unclear. There are several types of plasma membrane calcium influx channels in A431 cells. In the present study, we demonstrated that Homer dissociation resulted in specific activation of I(min) channels but not of I(max) channels in inside-out patches taken from A431 cells. In contrast, inositol 1,4,5-trisphosphate activated both I(min) and I(max) channels in inside-out patches. Short (1a) and long (1c) forms of Homer had different effects on I(min) channel activity. Homer 1a but not Homer 1c activated I(min) in the patches. This study indicates that I(min) channels are specifically regulated by Homer proteins in A431 cells.