Functional Requirement for Orai1 in Store-operated TRPC1-STIM1 Channels

Abstract

Orai1 and TRPC1 have been proposed as core components of store-operated calcium release-activated calcium (CRAC) and store-operated calcium (SOC) channels, respectively. STIM1, a Ca2+ sensor protein in the endoplasmic reticulum, interacts with and mediates store-dependent regulation of both channels. We have previously reported that dynamic association of Orai1, TRPC1, and STIM1 is involved in activation of store-operated Ca2+ entry (SOCE) in salivary gland cells. In this study, we have assessed the molecular basis of TRPC1-SOC channels in HEK293 cells. We report that TRPC1+STIM1-dependent SOCE requires functional Orai1. Thapsigargin stimulation of cells expressing Orai1+STIM1 increased Ca2+ entry and activated typical ICRAC current. STIM1 alone did not affect SOCE, whereas expression of Orai1 induced a decrease. Expression of TRPC1 induced a small increase in SOCE, which was greatly enhanced by co-expression of STIM1. Thapsigargin stimulation of cells expressing TRPC1+STIM1 activated a non-selective cation current, ISOC, that was blocked by 1 μm Gd3+ and 2-APB. Knockdown of Orai1 decreased endogenous SOCE as well as SOCE with TRPC1 alone. siOrai1 also significantly reduced SOCE and ISOC in cells expressing TRPC1+STIM1. Expression of R91WOrai1 or E106QOrai1 induced similar attenuation of TRPC1+STIM1-dependent SOCE and ISOC, whereas expression of Orai1 with TRPC1+STIM1 resulted in SOCE that was larger than that with Orai1+STIM1 or TRPC1+STIM1 but not additive. Additionally, Orai1, E106QOrai1, and R91WOrai1 co-immunoprecipitated with similar levels of TRPC1 and STIM1 from HEK293 cells, and endogenous TRPC1, STIM1, and Orai1 were co-immunoprecipitated from salivary glands. Together, these data demonstrate a functional requirement for Orai1 in TRPC1+STIM1-dependent SOCE. Orai1 and TRPC1 have been proposed as core components of store-operated calcium release-activated calcium (CRAC) and store-operated calcium (SOC) channels, respectively. STIM1, a Ca2+ sensor protein in the endoplasmic reticulum, interacts with and mediates store-dependent regulation of both channels. We have previously reported that dynamic association of Orai1, TRPC1, and STIM1 is involved in activation of store-operated Ca2+ entry (SOCE) in salivary gland cells. In this study, we have assessed the molecular basis of TRPC1-SOC channels in HEK293 cells. We report that TRPC1+STIM1-dependent SOCE requires functional Orai1. Thapsigargin stimulation of cells expressing Orai1+STIM1 increased Ca2+ entry and activated typical ICRAC current. STIM1 alone did not affect SOCE, whereas expression of Orai1 induced a decrease. Expression of TRPC1 induced a small increase in SOCE, which was greatly enhanced by co-expression of STIM1. Thapsigargin stimulation of cells expressing TRPC1+STIM1 activated a non-selective cation current, ISOC, that was blocked by 1 μm Gd3+ and 2-APB. Knockdown of Orai1 decreased endogenous SOCE as well as SOCE with TRPC1 alone. siOrai1 also significantly reduced SOCE and ISOC in cells expressing TRPC1+STIM1. Expression of R91WOrai1 or E106QOrai1 induced similar attenuation of TRPC1+STIM1-dependent SOCE and ISOC, whereas expression of Orai1 with TRPC1+STIM1 resulted in SOCE that was larger than that with Orai1+STIM1 or TRPC1+STIM1 but not additive. Additionally, Orai1, E106QOrai1, and R91WOrai1 co-immunoprecipitated with similar levels of TRPC1 and STIM1 from HEK293 cells, and endogenous TRPC1, STIM1, and Orai1 were co-immunoprecipitated from salivary glands. Together, these data demonstrate a functional requirement for Orai1 in TRPC1+STIM1-dependent SOCE. Store-operated Ca2+ entry (SOCE) 3The abbreviations used are: SOC, store-operated calcium; SOCE, store-operated Ca2+ entry; CRAC, calcium release-activated calcium; TRPC, TRP channels; STIM, stromal interaction molecule; SCID, severe combined immunodeficiency; siRNA, small interfering RNA; HEK, human embryonic kidney; IP, immunoprecipitation; Tg, thapsigargin; RBL, rat basophilic leukemia. 3The abbreviations used are: SOC, store-operated calcium; SOCE, store-operated Ca2+ entry; CRAC, calcium release-activated calcium; TRPC, TRP channels; STIM, stromal interaction molecule; SCID, severe combined immunodeficiency; siRNA, small interfering RNA; HEK, human embryonic kidney; IP, immunoprecipitation; Tg, thapsigargin; RBL, rat basophilic leukemia. is mediated via activation of specific plasma membrane channels in response to depletion of Ca2+ from intracellular Ca2+ stores (1Putney Jr., J.W. Cell Calcium. 1986; 7: 1-12Crossref PubMed Scopus (2106) Google Scholar). Neither the mechanism by which the status of Ca2+ in the endoplasmic reticulum is transmitted to the plasma membrane nor the molecular components of the channels have yet been conclusively identified in all cell types. Several reports suggest a diversity in store-operated Ca2+ channels in different cell types (2Beech D.J. Pfluegers Arch. Eur. J. Physiol. 2005; 451: 53-60Crossref PubMed Scopus (145) Google Scholar, 3Liu X. Groschner K. Ambudkar I.S. J. Membr. Biol. 2004; 200: 93-104Crossref PubMed Scopus (55) Google Scholar, 4Parekh A.B. Putney Jr., J.W. Physiol. Rev. 2005; 85: 757-810Crossref PubMed Scopus (1797) Google Scholar). For example, calcium release-activated calcium (CRAC) channel, which is found in T-lymphocytes, RBL, and other hematopoietic cells, is a highly Ca2+-selective channel with unique properties (4Parekh A.B. Putney Jr., J.W. Physiol. Rev. 2005; 85: 757-810Crossref PubMed Scopus (1797) Google Scholar, 5Lewis R.S. Nature. 2007; 446: 284-287Crossref PubMed Scopus (424) Google Scholar). Channels in other cell types, including salivary gland, endothelial, and smooth muscle cells, referred to as SOC channels, range from non-selective to relatively Ca2+-selective (2Beech D.J. Pfluegers Arch. Eur. J. Physiol. 2005; 451: 53-60Crossref PubMed Scopus (145) Google Scholar, 3Liu X. Groschner K. Ambudkar I.S. J. Membr. Biol. 2004; 200: 93-104Crossref PubMed Scopus (55) Google Scholar, 4Parekh A.B. Putney Jr., J.W. Physiol. Rev. 2005; 85: 757-810Crossref PubMed Scopus (1797) Google Scholar, 6Bolotina V.M. Science's STKE. 2004; 2004: pe34PubMed Google Scholar, 7Brueggemann L.I. Markun D.R. Henderson K.K. Cribbs L.L. Byron K.L. J. Pharmacol. Exp. Ther. 2006; 317: 488-499Crossref PubMed Scopus (78) Google Scholar). It is believed that the difference in channel property is due to differences in the channel components. TRPC1 is reported to form SOC channels that range from being relatively selective for Ca2+ to those that are non-selective in various cell types (2Beech D.J. Pfluegers Arch. Eur. J. Physiol. 2005; 451: 53-60Crossref PubMed Scopus (145) Google Scholar, 7Brueggemann L.I. Markun D.R. Henderson K.K. Cribbs L.L. Byron K.L. J. Pharmacol. Exp. Ther. 2006; 317: 488-499Crossref PubMed Scopus (78) Google Scholar, 8Ambudkar I.S. Ong H.L. Liu X. Bandyopadhyay B. Cheng K.T. Cell Calcium. 2007; 42: 213-223Crossref PubMed Scopus (207) Google Scholar, 9Brownlow S.L. Sage S.O. Thromb. Haemostasis. 2005; 94: 839-845PubMed Google Scholar, 10Montell C. Science's STKE. 2005; 2005: re3PubMed Google Scholar, 11Brough G.H. Wu S. Cioffi D. Moore T.M. Li M. Dean N. Stevens T. FASEB J. 2001; 15: 1727-1738Crossref PubMed Scopus (152) Google Scholar, 12Liu X. Bandyopadhyay B.C. Singh B.B. Groschner K. Ambudkar I.S. J. Biol. Chem. 2005; 280: 21600-21606Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Liu X. Wang W. Singh B.B. Lockwich T. Jadlowiec J. O'Connell B. Wellner R. Zhu M.X. Ambudkar I.S. J. Biol. Chem. 2000; 275: 3403-3411Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar, 14Mori Y. Inoue R. Ishii M. Hara Y. Imoto K. Jpn. J. Pharmacol. 2001; 87: 245-252Crossref PubMed Scopus (16) Google Scholar, 15Tiruppathi C. Freichel M. Vogel S.M. Paria B.C. Mehta D. Flockerzi V. Malik A.B. Circ. Res. 2002; 91: 70-76Crossref PubMed Scopus (331) Google Scholar, 16Zagranichnaya T.K. Wu X. Villereal M.L. J. Biol. Chem. 2005; 280: 29559-29569Abstract Full Text Full Text PDF PubMed Scopus (182) Google Scholar). With the exception of a few studies (17Philipp S. Strauss B. Hirnet D. Wissenbach U. Mery L. Flockerzi V. Hoth M. J. Biol. Chem. 2003; 278: 26629-26638Abstract Full Text Full Text PDF PubMed Scopus (124) Google Scholar, 18Tseng P.H. Lin H.P. Hu H. Wang C. Zhu M.X. Chen C.S. Biochemistry. 2004; 43: 11701-11708Crossref PubMed Scopus (80) Google Scholar), TRPCs do not appear to generate ICRAC. Consistent with this, we have shown that TRPC1 does not contribute to the ICRAC in RBL-2H3 cells (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). Two proteins, STIM and Orai, have emerged as candidate components of the CRAC channel (5Lewis R.S. Nature. 2007; 446: 284-287Crossref PubMed Scopus (424) Google Scholar, 20Feske S. Gwack Y. Prakriya M. Srikanth S. Puppel S.H. Tanasa B. Hogan P.G. Lewis R.S. Daly M. Rao A. Nature. 2006; 441: 179-185Crossref PubMed Scopus (1846) Google Scholar). Knockdown of STIM1 expression using siRNA significantly reduced SOCE in a number of cell types (20Feske S. Gwack Y. Prakriya M. Srikanth S. Puppel S.H. Tanasa B. Hogan P.G. Lewis R.S. Daly M. Rao A. Nature. 2006; 441: 179-185Crossref PubMed Scopus (1846) Google Scholar, 21Roos J. DiGregorio P.J. Yeromin A.V. Ohlsen K. Lioudyno M. Zhang S. Safrina O. Kozak J.A. Wagner S.L. Cahalan M.D. Velicelebi G. Stauderman K.A. J. Cell Biol. 2005; 169: 435-445Crossref PubMed Scopus (1513) Google Scholar, 22Williams R.T. Senior P.V. Van Stekelenburg L. Layton J.E. Smith P.J. Dziadek M.A. Biochim. Biophys. Acta. 2002; 1596: 131-137Crossref PubMed Scopus (124) Google Scholar, 23Liou J. Kim M.L. Heo W.D. Jones J.T. Myers J.W. Ferrell Jr., J.E. Meyer T. Curr. Biol. 2005; 15: 1235-1241Abstract Full Text Full Text PDF PubMed Scopus (1744) Google Scholar), whereas overexpression only modestly enhanced SOCE. The second protein Orai1 has four transmembrane domains (5Lewis R.S. Nature. 2007; 446: 284-287Crossref PubMed Scopus (424) Google Scholar, 20Feske S. Gwack Y. Prakriya M. Srikanth S. Puppel S.H. Tanasa B. Hogan P.G. Lewis R.S. Daly M. Rao A. Nature. 2006; 441: 179-185Crossref PubMed Scopus (1846) Google Scholar, 24Wissenbach U. Philipp S.E. Gross S.A. Cavalie A. Flockerzi V. Cell Calcium. 2007; 42: 439-446Crossref PubMed Scopus (52) Google Scholar). Mutations in Orai1 have been genetically linked to severe combined immunodeficiency (SCID), and T-lymphocytes isolated from SCID patients display decreased ICRAC activity (20Feske S. Gwack Y. Prakriya M. Srikanth S. Puppel S.H. Tanasa B. Hogan P.G. Lewis R.S. Daly M. Rao A. Nature. 2006; 441: 179-185Crossref PubMed Scopus (1846) Google Scholar). Although knockdown of Orai1 decreases SOCE, overexpression of the protein attenuates endogenous SOCE. However, coexpression of Orai1 with STIM1 increases SOCE and generates CRAC channel activity in HEK293 cells (25Peinelt C. Vig M. Koomoa D.L. Beck A. Nadler M.J. Koblan-Huberson M. Lis A. Fleig A. Penner R. Kinet J.P. Nat. Cell Biol. 2006; 8: 771-773Crossref PubMed Scopus (514) Google Scholar, 26Soboloff J. Spassova M.A. Tang X.D. Hewavitharana T. Xu W. Gill D.L. J. Biol. Chem. 2006; 281: 20661-20665Abstract Full Text Full Text PDF PubMed Scopus (483) Google Scholar). Further, mutations in the conserved negatively charged residues of Orai1 alter the Ca2+ selectivity of CRAC channel (27Prakriya M. Feske S. Gwack Y. Srikanth S. Rao A. Hogan P.G. Nature. 2006; 443: PubMed Scopus Google Scholar, A.V. Zhang S.L. W. Y. Safrina O. Cahalan M.D. Nature. 2006; 443: PubMed Scopus Google Scholar). has been that Orai1 and STIM1 are for the of CRAC channel and that Orai1 is the The of to SOCE in all cell types is not yet all cells that demonstrate CRAC U. Philipp S.E. Gross S.A. Cavalie A. Flockerzi V. Cell Calcium. 2007; 42: 439-446Crossref PubMed Scopus (52) Google Scholar, J.T. Putney Jr., J.W. J. Biol. Chem. 2007; 282: Full Text Full Text PDF PubMed Scopus Google Scholar, S.A. Wissenbach U. Philipp S.E. Freichel M. Cavalie A. Flockerzi V. J. Biol. Chem. 2007; 282: Full Text Full Text PDF PubMed Scopus Google Scholar). report that Orai1 does not form the CRAC channel in T-lymphocytes M. Wang H. Rao A.B. Putney J.W. Kinet J.P. Nat. PubMed Scopus Google Scholar). has been that and STIM and display different properties in different cell types the molecular of the channel channel of not only different and but also other channel U. Philipp S.E. Gross S.A. Cavalie A. Flockerzi V. Cell Calcium. 2007; 42: 439-446Crossref PubMed Scopus (52) Google Scholar). The of Orai1 being with a larger protein was also B. D.J. L. T. J. Biol. Chem. 2007; 282: Full Text Full Text PDF PubMed Scopus Google Scholar). We have previously reported that dynamic of a is involved in SOCE in salivary gland cells (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). We have shown that endogenous Orai1, STIM1, and TRPC1 SOCE in these cells. Although expression of TRPC1 alone does not increase SOCE, co-expression with STIM1 was reported to increase SOCE and SOC channel in HEK293 cells W. Kim J.P. L. S. Nat. Cell Biol. 2006; 8: PubMed Scopus Google Scholar, J.P. W. S. Nat. Cell Biol. 2007; PubMed Scopus Google Scholar). Further, a has been that Orai1 as a of and store-dependent activation of these channels Y. C. J. D.L. L. U. S. A. 2007; PubMed Scopus Google Scholar). In this study, we have the molecular basis of SOC channels. We report that in to STIM1, is a functional requirement for Orai1 in the of TRPC1-SOC channels. HEK293 Cell and cells were in and with and were to to and with of 1 using and by the Knockdown were by of Orai1 siRNA number or siRNA a of using and by the with cells were to the and with with the The and with the intracellular that the for all the was with to using a cell were in the cell R.T. Senior P.V. Van Stekelenburg L. Layton J.E. Smith P.J. Dziadek M.A. Biochim. Biophys. Acta. 2002; 1596: 131-137Crossref PubMed Scopus (124) Google Scholar, 23Liou J. Kim M.L. Heo W.D. Jones J.T. Myers J.W. Ferrell Jr., J.E. Meyer T. Curr. Biol. 2005; 15: 1235-1241Abstract Full Text Full Text PDF PubMed Scopus (1744) Google Scholar, 24Wissenbach U. Philipp S.E. Gross S.A. Cavalie A. Flockerzi V. Cell Calcium. 2007; 42: 439-446Crossref PubMed Scopus (52) Google Scholar, C. Vig M. Koomoa D.L. Beck A. Nadler M.J. Koblan-Huberson M. Lis A. Fleig A. Penner R. Kinet J.P. Nat. Cell Biol. 2006; 8: 771-773Crossref PubMed Scopus (514) Google using of the was assessed by the from the from to a of 1 was and a of 1 were than and were not and were and For the was used for of the was in cells for in and as was in cells using a and was used to the and membrane was from cells as previously (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar), in and by and of protein were were used for using were by in and by and or as (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar), were used and whereas was used Expression of Orai1+STIM1 SOCE and that expression of Orai1 and STIM1 in HEK293 cells a increase in SOCE Expression of STIM1 alone did not in SOCE, whereas expression of Orai1 induced a of SOCE not Expression of Orai1+STIM1 resulted in activation of typical in response to stimulation of cells and as has been previously reported (25Peinelt C. Vig M. Koomoa D.L. Beck A. Nadler M.J. Koblan-Huberson M. Lis A. Fleig A. Penner R. Kinet J.P. Nat. Cell Biol. 2006; 8: 771-773Crossref PubMed Scopus (514) Google Scholar, 26Soboloff J. Spassova M.A. Tang X.D. Hewavitharana T. Xu W. Gill D.L. J. Biol. Chem. 2006; 281: 20661-20665Abstract Full Text Full Text PDF PubMed Scopus (483) Google Scholar). SOCE STIM1 and Orai1 in HEK293 co-expression of Orai1 and STIM1 in HEK293 cells is reported to generate the CRAC channel (5Lewis R.S. Nature. 2007; 446: 284-287Crossref PubMed Scopus (424) Google Scholar), expression of channels with STIM1 has been shown to generate SOC channels in these cells W. Kim J.P. L. S. Nat. Cell Biol. 2006; 8: PubMed Scopus Google Scholar, J.P. W. S. Nat. Cell Biol. 2007; PubMed Scopus Google Scholar, Y. C. J. D.L. L. U. S. A. 2007; PubMed Scopus Google Scholar). these channels are and endogenous are involved in the is not yet for that siOrai1 induced in endogenous SOCE with siRNA did not affect SOCE with cells, not also significantly reduced SOCE not The in endogenous Orai1 by siOrai1 is shown in the 1 Orai1 in cells for with siRNA, and and the protein of with and of respectively. expression in the is shown as a that of siOrai1 was used in the of TRPC1 induced a increase in SOCE whereas overexpression of TRPC1+STIM1 induced increase in SOCE to that in cells Ca2+ entry in these cells was blocked by 1 μm Gd3+ as well as by μm that TRPC1+STIM1 in SOCE. knockdown of endogenous Orai1 or SOCE by the increase in in TRPC1+STIM1 cells is whereas that in cells is that these the increase in that in cells Ca2+ to cells, due to Ca2+ knockdown of endogenous Orai1 decreased increase in SOCE in cells in TRPC1+STIM1 cells was with in cells expressing TRPC1 the increase due to STIM1 is With expression of siOrai1 in both of cells, this increase was to a endogenous Orai1 is for TRPC1 and STIM1 to increase SOCE. The data also that the increase in TRPC1 by STIM1 is endogenous Orai1. The of TRPC1, STIM1, and Orai1 in SOCE were by store-operated In to the with Orai1+STIM1 and cells expressing TRPC1+STIM1 which blocked by μm and similar was with 1 μm data not that of the cells which in cells increased with In both the was blocked by 1 μm Gd3+ Together, these data demonstrate that TRPC1+STIM1 generate SOC channels that are from CRAC channels in the property of The of TRPC1+STIM1 channels in these cells are similar to those by J.P. W. S. Nat. Cell Biol. 2007; PubMed Scopus Google Scholar). ISOC was significantly reduced by knockdown of endogenous Orai1 and and for TRPC1+STIM1-dependent SOC channel also requires endogenous Orai1. Together, the data shown in 1 demonstrate that TRPC1 requires overexpression of STIM1 to generate SOC channels in HEK293 cells. in studies was increase in with TRPC1 overexpression in these cells (4Parekh A.B. Putney Jr., J.W. Physiol. Rev. 2005; 85: 757-810Crossref PubMed Scopus (1797) Google Scholar). of the is that the of TRPC1 and STIM1 to increase SOCE and generate SOC channels is endogenous Orai1. We a small of TRPC1 to endogenous SOCE in HEK293 cells, and induced decrease. However, did not affect increase in SOCE and ICRAC not Consistent with these we have previously shown that endogenous TRPC1 does not contribute to ICRAC in cells (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). Several studies have also of a for TRPC1 in CRAC channels in HEK293 cells (25Peinelt C. Vig M. Koomoa D.L. Beck A. Nadler M.J. Koblan-Huberson M. Lis A. Fleig A. Penner R. Kinet J.P. Nat. Cell Biol. 2006; 8: 771-773Crossref PubMed Scopus (514) Google Scholar, 26Soboloff J. Spassova M.A. Tang X.D. Hewavitharana T. Xu W. Gill D.L. J. Biol. Chem. 2006; 281: 20661-20665Abstract Full Text Full Text PDF PubMed Scopus (483) Google Scholar). the molecular requirement for of channels to different from those of channels in this cell We have previously association in human gland cells. The data suggest that STIM1 and TRPC1 with endogenous Orai1 to form a functional SOC channel in HEK293 cells. the not due to the of Orai1 Orai1 for TRPC1+STIM1-dependent of ICRAC in T-lymphocytes isolated from SCID patients has been linked to a the of Orai1. The channel has been shown to (20Feske S. Gwack Y. Prakriya M. Srikanth S. Puppel S.H. Tanasa B. Hogan P.G. Lewis R.S. Daly M. Rao A. Nature. 2006; 441: 179-185Crossref PubMed Scopus (1846) Google Scholar). Although this is not functional is not yet is that a conserved in the of Orai1, of the has been to involved in activation of the channel J. Xu X. Chen L. Xu T. J. Biol. Chem. 2007; 282: Full Text Full Text PDF PubMed Scopus Google Scholar). Expression of R91WOrai1 in HEK293 cells induced a in endogenous SOCE not Expression of TRPC1+STIM1 in cells expressing R91WOrai1 resulted in SOCE similar to that in cells expressing and with and of endogenous SOCE not as well as SOCE in cells was by expression of E106QOrai1 and of Orai1 has decreased and has been shown to of endogenous SOCE as well as SOCE in HEK293 cells (27Prakriya M. Feske S. Gwack Y. Srikanth S. Rao A. Hogan P.G. Nature. 2006; 443: PubMed Scopus Google Scholar, A.V. Zhang S.L. W. Y. Safrina O. Cahalan M.D. Nature. 2006; 443: PubMed Scopus Google Scholar). In expression of Orai1 with TRPC1+STIM1 induced SOCE that was larger than that with TRPC1+STIM1 or but not was to SOCE in cells, data shown in Expression of STIM1 did not SOCE not that E106QOrai1, and Orai1 were similar levels and co-immunoprecipitated with levels of STIM1 as well as TRPC1 that of the were in using and of cells, the functional differences in cells expressing the and are not due to differences in expression levels or to with STIM1 or Further, of TRPC1 similar of STIM1 in cells Orai1 was not not that is of association by expression of Orai1 H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). The association the was also in gland cells. of endogenous TRPC1 co-immunoprecipitated endogenous Orai1 and STIM1 data that is association TRPC1, Orai1, and STIM1. The requirement of functional Orai1 was assessed by using Orai1 of R91WOrai1 in SCID or E106QOrai1 with TRPC1+STIM1 induced of ISOC to also for siOrai1 also similar attenuation of TRPC1+STIM1-dependent SOC channel is that for STIM1 for the of the Orai1 In co-expression of Orai1 with TRPC1+STIM1 and induced non-selective in cells, which was larger in than that with TRPC1+STIM1 or Orai1+STIM1 and In cells, the were but relatively that was used was increased of 1 cells non-selective with in the and not The data reported demonstrate that co-expression of STIM1 with TRPC1 is for of SOC channels in HEK293 cells. is similar to the STIM1 requirement reported for the of CRAC channels in HEK293 cells by expression of Orai1 (5Lewis R.S. Nature. 2007; 446: 284-287Crossref PubMed Scopus (424) Google Scholar). Further, we that TRPC1+STIM1 generate channels that display that are from CRAC channels. data are with studies SOC channel activity in HEK293 cells W. Kim J.P. L. S. Nat. Cell Biol. 2006; 8: PubMed Scopus Google Scholar, J.P. W. S. Nat. Cell Biol. 2007; PubMed Scopus Google Scholar). Together, these data also for the previously reported of of TRPC1 SOCE. and of the is that endogenous Orai1 is for SOC channel Further, Orai1 or the E106QOrai1, the of channels, whereas Orai1 increases TRPC1+STIM1-dependent SOCE. Although we do not yet Orai1 to TRPC1+STIM1 channel that proposed are: TRPC1 and Orai1 contribute to the channel, Orai1 and TRPC1 form channels, the of Orai1 TRPC1, and TRPC1 and Orai1 form and channels. Although the data do not the of and previously (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar), suggest that TRPC1 and Orai1 do not form and channels. increase in the as well as Ca2+ entry in cells expressing in is than that Orai1+STIM1 and TRPC1+STIM1 channels the increase in We do not that this is due to a TRPC1 and Orai1 for STIM1 with different of STIM1 similar not of TRPC1 and STIM1 was not by co-expression of Orai1 (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). siOrai1 did not increase SOCE as Orai1 were for a of STIM1. Although studies are to the functional association TRPC1 and Orai1, we that the the SOC Orai1 has been shown to contribute to the of CRAC channel, which has been reported to of TRPC1 and other However, a that cells but do not display ICRAC U. Philipp S.E. Gross S.A. Cavalie A. Flockerzi V. Cell Calcium. 2007; 42: 439-446Crossref PubMed Scopus (52) Google Scholar), and was that with other or with other to form SOC channels. for Orai1 proposed by Y. C. J. D.L. L. U. S. A. 2007; PubMed Scopus Google was that as a for and channels and to the by the regulation by STIM1. a association Orai1 and TRPC1 in cells expressing SOC channels (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). we have shown that functional Orai1 is for of TRPC1-SOC data do not the that Orai1 and TRPC1 form the SOC channel, this is to in channels TRPC1-SOC channels. Although the of Orai1 in SOC channel has yet to we have shown that the are in salivary TRPC1 has a in SOCE (19Ong H.L. Cheng K.T. Liu X. Bandyopadhyay B.C. Paria B.C. Soboloff J. Pani B. Gwack Y. Srikanth S. Singh B.B. Gill D.L. Ambudkar I.S. J. Biol. Chem. 2007; 282: 9105-9116Abstract Full Text Full Text PDF PubMed Scopus (342) Google Scholar). In store-operated Ca2+ entry to mediated via channels in different cell types. Although channels are We reported that salivary gland cells greatly reduced SOCE and ISOC, which was with a and of all were in cells X. Cheng K.T. Bandyopadhyay B.C. Pani B. A. Paria B.C. W.D. D. Singh B.B. L. Ambudkar I.S. U. S. A. 2007; PubMed Scopus Google Scholar). the were to for the of we that TRPC1 generates SOC channels in a and that these channels are from CRAC channels. data demonstrate a functional requirement for Orai1 in SOC STIM1 and Orai1 appear to for the of CRAC as well as SOC channels. Although Orai1+STIM1 appear to for CRAC channels, TRPC1, Orai1, and STIM1 generate SOC channels. studies are to the molecular these that SOCE. We Rao for with for and with