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Forms and functions of store-operated calcium entry mediators, STIM and Orai.

ABSTRACT: Calcium signals arise by multiple mechanisms, including mechanisms of release of intracellular stored Ca2+, and the influx of Ca2+ through channels in the plasma membrane. One mechanism that links these two sources of Ca2+ is store-operated Ca2+ entry, the most commonly encountered version of which involves the extensively studied calcium-release-activated Ca2+ (CRAC) channel. The minimal and essential molecular components of the CRAC channel are the STIM proteins that function as Ca2+ sensors in the endoplasmic reticulum, and the Orai proteins that comprise the pore forming subunits of the CRAC channel. CRAC channels are known to play significant roles in a wide variety of physiological functions. This review discusses the multiple forms of STIM and Orai proteins encountered in mammalian cells, and discusses some specific examples of how these proteins modulate or mediate important physiological processes.

SUBMITTER: Putney JW

PROVIDER: S-EPMC5955777 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Forms and functions of store-operated calcium entry mediators, STIM and Orai.

Putney James W JW

Advances in biological regulation 20171122

Calcium signals arise by multiple mechanisms, including mechanisms of release of intracellular stored Ca2+, and the influx of Ca2+ through channels in the plasma membrane. One mechanism that links these two sources of Ca2+ is store-operated Ca2+ entry, the most commonly encountered version of which involves the extensively studied calcium-release-activated Ca2+ (CRAC) channel. The minimal and essential molecular components of the CRAC channe ...[more]

PMID: 29217255

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Project description:The endoplasmic reticulum (ER) is at the epicenter of astrocyte Ca(2+) signaling. We sought to identify the molecular mechanism underlying store-operated calcium entry that replenishes ER stores in mouse Müller cells. Store depletion, induced through blockade of sequestration transporters in Ca(2+)-free saline, induced synergistic activation of canonical transient receptor potential 1 (TRPC1) and Orai channels. Store-operated TRPC1 channels were identified by their electrophysiological properties, pharmacological blockers, and ablation of the Trpc1 gene. Ca(2+) release-activated currents (ICRAC) were identified by ion permeability, voltage dependence, and sensitivity to selective Orai antagonists Synta66 and GSK7975A. Depletion-evoked calcium influx was initiated at the Müller end-foot and apical process, triggering centrifugal propagation of Ca(2+) waves into the cell body. EM analysis of the end-foot compartment showed high-density ER cisternae that shadow retinal ganglion cell (RGC) somata and axons, protoplasmic astrocytes, vascular endothelial cells, and ER-mitochondrial contacts at the vitreal surface of the end-foot. The mouse retina expresses transcripts encoding both Stim and all known Orai genes; Müller glia predominantly express stromal interacting molecule 1 (STIM1), whereas STIM2 is mainly confined to the outer plexiform and RGC layers. Elimination of TRPC1 facilitated Müller gliosis induced by the elevation of intraocular pressure, suggesting that TRPC channels might play a neuroprotective role during mechanical stress. By characterizing the properties of store-operated signaling pathways in Müller cells, these studies expand the current knowledge about the functional roles these cells play in retinal physiology and pathology while also providing further evidence for the complexity of calcium signaling mechanisms in CNS astroglia.Significance statementStore-operated Ca(2+) signaling represents a major signaling pathway and source of cytosolic Ca(2+) in astrocytes. Here, we show that the store-operated response in Müller cells, radial glia that perform key structural, signaling, osmoregulatory, and mechanosensory functions within the retina, is mediated through synergistic activation of transient receptor potential and Orai channels. The end-foot disproportionately expresses the depletion sensor stromal interacting molecule 1, which contains an extraordinarily high density of endoplasmic reticulum cisternae that shadow neuronal, astrocytic, vascular, and axonal structures; interface with mitochondria; but also originate store-operated Ca(2+) entry-induced transcellular Ca(2+) waves that propagate glial excitation into the proximal retina. These results identify a molecular mechanism that underlies complex interactions between the plasma membrane and calcium stores, and contributes to astroglial function, regulation, and response to mechanical stress.

Dataset Information

Forms and functions of store-operated calcium entry mediators, STIM and Orai.

Publications

Forms and functions of store-operated calcium entry mediators, STIM and Orai.

Similar Datasets

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