STIM2 protein mediates distinct store-dependent and store-independent modes of CRAC channel activation.
STIM1 and CRACM1 (or Orai1) are essential molecular components mediating store-operated Ca2+ entry (SOCE) and Ca2+ release-activated Ca2+ (CRAC) currents. Although STIM1 acts as a luminal Ca2+ sensor in the endoplasmic reticulum (ER), the function of STIM2 remains unclear. Here we reveal that STIM2 has two distinct modes of activating CRAC channels: a store-operated mode that is activated through depletion of ER Ca2+ stores by inositol 1,4,5-trisphosphate (InsP3) and store-independent activation that is mediated by cell dialysis during whole-cell perfusion. Both modes are regulated by calmodulin (CaM). The store-operated mode is transient in intact cells, possibly reflecting recruitment of CaM, whereas loss of CaM in perfused cells accounts for the persistence of the store-independent mode. The inhibition by CaM can be reversed by 2-aminoethoxydiphenyl borate (2-APB), resulting in rapid, store-independent activation of CRAC channels. The aminoglycoside antibiotic G418 is a highly specific and potent inhibitor of STIM2-dependent CRAC channel activation. The results reveal a novel bimodal control of CRAC channels by STIM2, the store dependence and CaM regulation, which indicates that the STIM2/CRACM1 complex may be under the control of both luminal and cytoplasmic Ca2+ levels.
Parvez
Suhel
S
Center for Biomedical Research and John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96813, USA.
Beck
Andreas
A
Peinelt
Christine
C
Soboloff
Jonathan
J
Lis
Annette
A
Monteilh-Zoller
Mahealani
M
Gill
Donald L
DL
Fleig
Andrea
A
Penner
Reinhold
R
D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D002147:Calmodulin / Q000235:genetics / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D003593:Cytoplasm / Q000502:physiology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D000071740:ORAI1 Protein; D000071738:Stromal Interaction Molecule 2; D015854:Up-Regulation
D015220:Calcium Channels; D002147:Calmodulin; D015815:Cell Adhesion Molecules; D008565:Membrane Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C513279:STIM2 protein, human; D000071738:Stromal Interaction Molecule 2; D002118:Calcium