RESUMEN
Depletion of intracellular calcium stores activates store-operated calcium entry across the plasma membrane in many cells. STIM1, the putative calcium sensor in the endoplasmic reticulum, and the calcium release-activated calcium (CRAC) modulator CRACM1 (also known as Orai1) in the plasma membrane have recently been shown to be essential for controlling the store-operated CRAC current (I(CRAC)). However, individual overexpression of either protein fails to significantly amplify I(CRAC). Here, we show that STIM1 and CRACM1 interact functionally. Overexpression of both proteins greatly potentiates I(CRAC), suggesting that STIM1 and CRACM1 mutually limit store-operated currents and that CRACM1 may be the long-sought CRAC channel.
Asunto(s)
Canales de Calcio/metabolismo , Señalización del Calcio/fisiología , Membrana Celular/metabolismo , Retículo Endoplásmico/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas de Neoplasias/metabolismo , Calcio/deficiencia , Calcio/metabolismo , Canales de Calcio/efectos de los fármacos , Señalización del Calcio/efectos de los fármacos , Membrana Celular/efectos de los fármacos , Quelantes/farmacología , Regulación hacia Abajo/efectos de los fármacos , Regulación hacia Abajo/fisiología , Retículo Endoplásmico/efectos de los fármacos , Expresión Génica/fisiología , Humanos , Inositol 1,4,5-Trifosfato/farmacología , Líquido Intracelular/efectos de los fármacos , Líquido Intracelular/metabolismo , Células Jurkat , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Proteínas de la Membrana/genética , Proteínas de Neoplasias/genética , Proteína ORAI1 , Molécula de Interacción Estromal 1 , Regulación hacia Arriba/efectos de los fármacos , Regulación hacia Arriba/fisiologíaRESUMEN
Receptor-mediated Ca(2+) release from the endoplasmic reticulum (ER) is often followed by Ca(2+) entry through Ca(2+)-release-activated Ca(2+) (CRAC) channels in the plasma membrane . RNAi screens have identified STIM1 as the putative ER Ca(2+) sensor and CRACM1 (Orai1; ) as the putative store-operated Ca(2+) channel. Overexpression of both proteins is required to reconstitute CRAC currents (I(CRAC); ). We show here that CRACM1 forms multimeric assemblies that bind STIM1 and that acidic residues in the transmembrane (TM) and extracellular domains of CRACM1 contribute to the ionic selectivity of the CRAC-channel pore. Replacement of the conserved glutamate in position 106 of the first TM domain of CRACM1 with glutamine (E106Q) acts as a dominant-negative protein, and substitution with aspartate (E106D) enhances Na(+), Ba(2+), and Sr(2+) permeation relative to Ca(2+). Mutating E190Q in TM3 also affects channel selectivity, suggesting that glutamate residues in both TM1 and TM3 face the lumen of the pore. Furthermore, mutating a putative Ca(2+) binding site in the first extracellular loop of CRACM1 (D110/112A) enhances monovalent cation permeation, suggesting that these residues too contribute to the coordination of Ca(2+) ions to the pore. Our data provide unequivocal evidence that CRACM1 multimers form the Ca(2+)-selective CRAC-channel pore.