title: The role of bestrophin-1 in intracellular Ca(2+) signaling.
abstract: Mutations in the BEST1 gene lead to a variety of retinal degenerations, among them Best's vitelliforme macular degeneration. To clarify the mechanism of the disease, the understanding of the function of BEST1 gene product, bestrophin-1, is mandatory. In overexpression studies bestrophin-1 appeared to function as a Ca(2+)-dependent Cl channel. On the other hand, bestrophin-1 is able to participate in intracellular Ca(2+) signaling. Endogenously expressed bestrophin-1 largely localized to the cytosolic compartment close to the basolateral membrane of the retinal pigment epithelium (RPE) as it can be shown using differential centrifugation, immunohistochemistry, and transmission electron microscopy. To elucidate a cytosolic function of bestrophin-1, we explored the store-operated Ca(2+) entry in short-time cultured porcine RPE cells. Depletion of cytosolic Ca(2+)stores by SERCA inhibition led to activation of Orai-1 Ca(2+) channels. This resulted in an influx of extracellular Ca(2+) into the cell which was reduced when bestrophin-1 expression was knocked down using siRNA techniques. Quantification of Ca(2+) which can be released from cytosolic Ca(2+) stores revealed that after reduction of bestrophin-1 expression less Ca(2+) is stored in ER Ca(2+) stores. Thus, bestrophin-1 functions as an intracellular Cl channel which helps to accumulate and to release Ca(2+) from stores by conducting the counterion for Ca(2+).
authors.affiliation: Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Berlin, Germany, olaf.strauss@charite.de.
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauß
authors.forename: Claudia
authors.initials: C
authors.lastname: Müller
authors.forename: Nadine
authors.initials: N
authors.lastname: Reichhart
authors.forename: Ernst R
authors.initials: ER
authors.lastname: Tamm
authors.forename: Nestor Mas
authors.initials: NM
authors.lastname: Gomez
mesh_terms: D000818:Animals; D000075002:Bestrophins; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D018118:Chloride Channels / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D057826:Vitelliform Macular Dystrophy / Q000235:genetics / Q000378:metabolism*
chemical_list: C113133:BEST1 protein, human; C491856:Best1 protein, mouse; D000075002:Bestrophins; D018118:Chloride Channels; D005136:Eye Proteins; D007473:Ion Channels; D002118:Calcium