ER-localized bestrophin 1 activates Ca2+-dependent ion channels TMEM16A and SK4 possibly by acting as a counterion channel
- 669 Downloads
Bestrophins form Ca2+-activated Cl− channels and regulate intracellular Ca2+ signaling. We demonstrate that bestrophin 1 is localized in the endoplasmic reticulum (ER), where it interacts with stromal interacting molecule 1, the ER-Ca2+ sensor. Intracellular Ca2+ transients elicited by stimulation of purinergic P2Y2 receptors in HEK293 cells were augmented by hBest1. The p21-activated protein kinase Pak2 was found to phosphorylate hBest1, thereby enhancing Ca2+ signaling and activation of Ca2+-dependent Cl− (TMEM16A) and K+ (SK4) channels. Lack of bestrophin 1 expression in respiratory epithelial cells of mBest1 knockout mice caused expansion of ER cisterns and induced Ca2+ deposits. hBest1 is, therefore, important for Ca2+ handling of the ER store and may resemble the long-suspected counterion channel to balance transient membrane potentials occurring through inositol triphosphate (IP3)-induced Ca2+ release and store refill. Thus, bestrophin 1 regulates compartmentalized Ca2+ signaling that plays an essential role in Best macular dystrophy, inflammatory diseases such as cystic fibrosis, as well as proliferation.
KeywordsBestrophin Ca2+-activated Cl− currents CaCC Ca2+-activated K+ currents SK4 TMEM16A Pak2 Purinergic receptors Endoplasmic reticulum ER Ca2+ store
human bestrophin 1
Ca2+-activated Cl− channels
small conductance calcium-activated potassium channel type 4
transmembrane protein 16A
p21-activated protein kinase
sarcoendoplasmic reticulum calcium ATPase
stromal interacting molecule 1
This study was supported by the grants DFG SFB699 A6/A7, DFG KU 756/8-2, and Else Kröner-Fresenius-Stiftung P36/05//A44/05. We are grateful for the technical expertise of Caio Toledo, Christine Meese, Karin Schadendorf, Helga Schmidt, and Uwe de Vries in performing the ultrastructural analysis. The Ca2+-sensitive GFP protein G-CaMP2 was kindly provided by Dr. J. Nakai, Wako City Saitama, Japan. We gratefully acknowledge the supply of the vmd2−/− mice by MERCK Research Laboratories (770 Sumneytown Pike, West Point, PA, USA).
- 5.Barro Soria R, Spitzner M, Schreiber R, Kunzelmann K (2006) Bestrophin 1 enables Ca2+ activated Cl− conductance in epithelia. J Biol Chem 281:17460–17467Google Scholar
- 9.Boudes M, Sar C, Menigoz A, Hilaire C, Pequignot MO, Kozlenkov A, Marmorstein AD, Carroll P, Valmier J, Scamps F (2009) Best1 is a gene regulated by nerve injury and required for Ca2+-activated Cl− current expression in axotomized sensory neurons. J Neurosci 29:10063–10071CrossRefPubMedGoogle Scholar
- 24.Marmorstein AD, Marmorstein LY, Rayborn M, Wang X, Hollyfield JG, Petrukhin K (2000) Bestrophin, the product of the Best vitelliform macular dystrophy gene (VMD2), localizes to the basolateral plasma membrane of the retinal pigment epithelium. Proc Natl Acad Sci USA 97:12758–12763CrossRefPubMedGoogle Scholar