Phospholipase Cβ2 Binds to and Inhibits Phospholipase Cδ1

Phospholipase Cβ (PLCβ) isoforms, which are under the control of Gαq and Gβγ subunits, generate Ca2+ signals induced by a broad array of extracellular agonists, whereas PLCδ isoforms depend on a rise in cytosolic Ca2+ for their activation. Here we find that PLCβ2 binds strongly to PLCδ1 and inhibits its catalytic activity in vitro and in living cells. In vitro, this PLC complex can be disrupted by increasing concentrations of free Gβγ subunits. Such competition has consequences for signaling, because in HEK293 cells PLCβ2 suppresses elevated basal [Ca2+] and inositol phosphates levels and the sustained agonist-induced elevation of Ca2+ levels caused by PLCδ1. Also, expression of both PLCs results in a synergistic release of [Ca2+] upon stimulation in A10 cells. These results support a model in which PLCβ2 suppresses the basal catalytic activity of PLCδ1, which is relieved by binding of Gβγ subunits to PLCβ2 allowing for amplified calcium signals. Phospholipase Cβ (PLCβ) isoforms, which are under the control of Gαq and Gβγ subunits, generate Ca2+ signals induced by a broad array of extracellular agonists, whereas PLCδ isoforms depend on a rise in cytosolic Ca2+ for their activation. Here we find that PLCβ2 binds strongly to PLCδ1 and inhibits its catalytic activity in vitro and in living cells. In vitro, this PLC complex can be disrupted by increasing concentrations of free Gβγ subunits. Such competition has consequences for signaling, because in HEK293 cells PLCβ2 suppresses elevated basal [Ca2+] and inositol phosphates levels and the sustained agonist-induced elevation of Ca2+ levels caused by PLCδ1. Also, expression of both PLCs results in a synergistic release of [Ca2+] upon stimulation in A10 cells. These results support a model in which PLCβ2 suppresses the basal catalytic activity of PLCδ1, which is relieved by binding of Gβγ subunits to PLCβ2 allowing for amplified calcium signals. The binding of an agonist to its target G protein-coupled receptor stimulates heterotrimeric G proteins, which in turn can result in an increase in intracellular Ca2+ through the activation of phospholipase Cβ (PLCβ) 1The abbreviations used are: PLC, phospholipase C; PH, pleckstrin homology; PtdIns, phosphatidylinositol; PI(4,5)P2, phosphatidylinositol 4,5-bisphosphate; YFP, yellow fluorescent protein; BiFC, bimolecular fluorescent complex; HBSS, Hanks' balanced salt solution; DEPC, diethyl pyrocarbonate; PBS, phosphate-buffered saline; BSA, bovine serum albumin; PTX, pertussis toxin; HEK, human embryonic kidney; Ins(1,4,5)P3, inositol 1,4,5-trisphosphate; DABCS4L, 4-(dimethylamino)phenylazo-phenyl-4-sulfonyl chloride succinyl ester. (1Rebecchi M.J. Pentyala S.N. Physiol. Rev. 2000; 80: 1291-1335Crossref PubMed Scopus (831) Google Scholar, 2Rhee S.G. Annu. Rev. Biochem. 2001; 70: 281-312Crossref PubMed Scopus (1227) Google Scholar). PLCs catalyze the hydrolysis of a minor lipid component, phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), to release the second messengers diacylglycerol and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). These messengers in turn activate protein kinase C and stimulate the release of Ca2+ from internal stores. All PLCβs (β1–β4) are regulated by Gαq subunits that are coupled to specific sets of G protein-coupled receptors. PLCβ2 and to a lesser extent PLCβ3 can also be stimulated by Gβγ subunits (1Rebecchi M.J. Pentyala S.N. Physiol. Rev. 2000; 80: 1291-1335Crossref PubMed Scopus (831) Google Scholar, 2Rhee S.G. Annu. Rev. Biochem. 2001; 70: 281-312Crossref PubMed Scopus (1227) Google Scholar). Because Gβγ subunits have the potential to be released from all types of Gα-Gβγ heterotrimers, PLCβ2 and -β3 may be activated by a wider range of receptors. In contrast to other mammalian PLC enzymes, the cellular regulation of PLCδ enzymes is unclear. It is known that these enzymes are regulated by an increase in cellular Ca2+ levels because PLCδ is the only PLC family that is not active at basal Ca2+ levels but is strongly activated when cytoplasmic Ca2+ rises above basal levels (1Rebecchi M.J. Pentyala S.N. Physiol. Rev. 2000; 80: 1291-1335Crossref PubMed Scopus (831) Google Scholar, 3Ochocka A.M. Pawelczyk T. Acta Biochim. Pol. 2003; 50: 1097-1110Crossref PubMed Scopus (35) Google Scholar). This behavior suggests that PLCδs function to amplify, rather than initiate, calcium-mobilizing signals. At maximum Ca2+ concentrations, the specific catalytic activity of purified PLCδ1 is typically 50–100-fold greater than that of unstimulated PLCβ or PLCγ. When reconstituted into permeabilized PC12 and HL60 cells, PLCδ1, but not PLCβ1 or PLCγ1, shows substantial activation by physiologic calcium levels (4Allen V. Swigart P. Cheung R. Cockcroft S. Katan M. Biochem. J. 1997; 327: 545-552Crossref PubMed Scopus (175) Google Scholar). Overexpression of PLCδ1 in PC12 and Chinese hamster ovary cells enhances the increase in cellular Ca2+ and soluble inositol phosphate levels produced by bradykinin (5Kim Y-H. Park T.-J. Lee Y.H. Baek K.J. Suh P.-G. Ryu S.H. Kim K.-T. J. Biol. Chem. 1999; 274: 26127-26134Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar) and thrombin (6Banno Y. Okano Y. Nozawa Y. J. Biol. Chem. 1994; 269: 15846-15852Abstract Full Text PDF PubMed Google Scholar). The Ca2+-amplification role of PLCδ1 has been clearly defined in keratinocytes derived from PLCδ1-null mice in which the sustained elevation of cytoplasmic Ca2+ that follows a PLCγ1-stimulated rapid rise does not occur but can be reconstituted when PLCδ1 is introduced (7Nakamura Y. Fukami K. Yu N. Takenaka K. Kataoka Y. Shirakata Y. Nishikawa S-I. Hashimoto K. Yoshida N. Takenawa T. EMBO J. 2003; 22: 2981-2991Crossref PubMed Scopus (89) Google Scholar). Several studies suggest that activation of PLCδ1 is under more complex control than the simple rise in cytoplasmic Ca2+. In frog oocytes expressing thrombin and platelet-derived growth factor receptors, microinjection of PLCδ1 antibody specifically inhibits thrombin but not platelet-derived growth factor-induced calcium mobilization (8Cho Y.S. Han M.K. Chae S.W. Park C.U. Kim U.H. FEBS Lett. 1993; 334: 257-260Crossref PubMed Scopus (9) Google Scholar). In Chinese hamster ovary cells, overexpression of PLCδ1 enhances the amount of inositol phosphates generated by ionomycin, but this increment is much smaller than the increase observed during thrombin stimulation (6Banno Y. Okano Y. Nozawa Y. J. Biol. Chem. 1994; 269: 15846-15852Abstract Full Text PDF PubMed Google Scholar). Similar results are obtained in bradykinin-stimulated PC12 cells expressing high levels of PLCδ1 (5Kim Y-H. Park T.-J. Lee Y.H. Baek K.J. Suh P.-G. Ryu S.H. Kim K.-T. J. Biol. Chem. 1999; 274: 26127-26134Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar). Here, raising calcium with high extracellular potassium, thapsigargin, or ionomycin induces a measurable increase in inositol trisphosphate, yet this increment is substantially less than that observed with a maximum dose of bradykinin. Thus, although these observations support a generalized amplification hypothesis, they suggest that receptor-generated signals other than calcium also contribute to PLCδ1-dependent inositol phosphate generation. Whereas protein regulators of most mammalian PLCs have been identified, those for PLCδ1 have not been well established. A novel form of RhoGAP associates strongly with PLCδ1 in cell lysates (9Homma Y. Emori Y. EMBO J. 1995; 14: 286-291Crossref PubMed Scopus (189) Google Scholar), stimulating its catalytic activity at low levels of calcium (0.1 μm). There is compelling evidence that PLCδ1 is also regulated by an atypical GTP-binding protein, Gh, or transglutaminase (10Im M.J. Russell M.A. Feng J.F. Cell. Signal. 1997; 9: 477-482Crossref PubMed Scopus (96) Google Scholar). Gh is controlled by α1-adrenergic receptor α1b and α1d in heart and liver (11Das T. Baek K.J. Gray C.D. Im M. J. Biol. Chem. 1993; 268: 27398-27405Abstract Full Text PDF PubMed Google Scholar, 12Chen S. Lin S. Lee P. R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S.N. S. 1999; Scholar), well in K.J. Lee Kim P. Im M. Biochem. J. PubMed Scopus Google Scholar). PLCδ1 stimulates on (11Das T. Baek K.J. Gray C.D. Im M. J. Biol. Chem. 1993; 268: 27398-27405Abstract Full Text PDF PubMed Google Scholar, K.J. S. Im M. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar), and Gh PLCδ1 to be stimulated at Ca2+ these studies that to PLCδ1, the of the cellular that this is unclear. regulators of PLCδ1 have been of PLCδ1 to results in a rise in cytoplasmic although is this is because of of PLCδ1 M. R. EMBO J. 2003; 22: PubMed Scopus Google Scholar). The activity of is by a K. Fukami K. T. Y. Takenawa T. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar), but is regulators of other PLCδ PLCβ and PLCδ are with which is the of this is at high levels in cells of this have signaling, through Gβγ released from Lee Y.S. S.G. PubMed Google Scholar). PLCδ1 is the most PLCδ and is most strongly in of the the and (1Rebecchi M.J. Pentyala S.N. Physiol. Rev. 2000; 80: 1291-1335Crossref PubMed Scopus (831) Google Scholar, 3Ochocka A.M. Pawelczyk T. Acta Biochim. Pol. 2003; 50: 1097-1110Crossref PubMed Scopus (35) Google Scholar, Y. Takenawa T. Emori Y. K. Biochem. PubMed Scopus Google Scholar). In the PLCδ1 is in cells M. S.G. Kim Scopus Google Scholar, M. M. S.G. Kim 1993; PubMed Scopus Google its is low in most in has on the regulation of PLCδ1 and Here we that PLCβ2 inhibits PLCδ and that this is relieved upon binding of Gβγ to results suggest a novel in which G protein stimulation has the to Ca2+ signals through activation of PLCδ1 under cellular In subunits and PLCβ2 in cells by a T. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). subunits reconstituted into lipid by simple PubMed Scopus Google Scholar). PLCδ1 and purified P. S. J. M.J. 1997; PubMed Scopus Google Scholar). in of and both PLC enzymes are above lipid not P. R. S. S. S. V. S. M. 1995; PubMed Scopus Google Scholar, J. S. PubMed Scopus Google Scholar). the Y. S. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). with or J. S. PubMed Scopus Google Scholar, S. 1999; PubMed Scopus Google Scholar). The at and from to The from the of the that the of PLCβ2 a substantial and increase upon the of PLCδ1 and a that the in when the of also by and by the and S. 1999; PubMed Scopus Google Scholar). PLC activity by purified and J. S. PubMed Scopus Google Scholar, T. M.J. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). of used to by of These or that can to form a bimolecular fluorescent complex The of human PLCβ2 amplified by with and through into the The and which and PLCβ2 through an into human PLCδ1 amplified by with and which and and through into The and by their and Overexpression of cells and A10 cells in with bovine serum and A10 cells, the with at in HEK293 cells with cells in by calcium phosphate HEK293 cells with or the used in the Ca2+ and inositol phosphate studies both produced A the levels of expression is in In the pertussis cells, HEK293 cells with for of in cells from into from living cells on a of from a of living cells on an expressing in a with at an of at and from to the to the amount of obtained from with only of the which of the from the cells on in in PBS, and permeabilized in in BSA, and The antibody PLCδ1 used the antibody PLCβ2 also used the in in antibody at for This by of in at in PBS, antibody to PLCδ1 and antibody used to antibody of at the cells by at to the cells, and the under the of expressing and at for The with PBS, in and and The at for and the at for at The the cell and the protein to purified Gβγ subunits and PLCβ2 in and to in the Gβγ of with the fluorescent calcium in an cell with Hanks' balanced salt BSA, and the cells by a cells with for at in with cells and in for the cells at a of and in a cell at The of at and of cells to Ca2+ by the of and M. J. Biol. Chem. Full Text PDF PubMed Scopus Google Scholar) the free The is is the at that in and is the in the of and is the and and are the to the and calcium In in the of extracellular Ca2+ by cell with of and in with for in The cells in and for at with and with with agonist the cells with agonist in the of for at All by the and the cells in of the of of and of by at for at The to to phosphate of the and by and the in of and The in The to and into and the by The amount of for protein PLCβ2 and PLCδ1 on with the that PLCβ2 and PLCδ1 form in and on the of PLCβ2 by to the by the in the of the to PLCβ2 and This an increase in and upon the of Gβγ subunits with PLCβ2 and a to that obtained by Y. S. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). In we the increase in when PLCδ1 is in This increase not observed when or PLCβ2 for PLCδ1. These can be to a bimolecular that an of enzymes are of and is that binding increase their because of a in PLCδ1 to under both enzymes Biochem. Full Text PDF PubMed Scopus Google Scholar). these a of observed to the of to a The of PLCδ1 for PLCβ2 on when the free Ca2+ from to Similar studies the of the under which that which by under of Phospholipase by GTP-binding of Scholar), does not at concentrations to PLCδ1 does not at concentrations to to the in the PLC binding Thus, the PLCβ2 and PLCδ1 is not by a of the PLCs to form PLCβ2 the of the PLCβ2 and PLCδ1 their These studies the rather than The for is that the of PLCδ1 this with to activity at concentrations above the of that the catalytic activity of a of PLCβ2 and PLCδ1 much less than the obtained from the enzymes that the inhibits or both of the a of studies to of the enzymes is by the PLCδ1 binds to through a high for in its pleckstrin in to the low catalytic binding for M.J. S. Annu. Rev. PubMed Scopus Google Scholar). This high PLCδ1 is in the and the amount of in the is In the pleckstrin of PLCβ2 binds to with T. Pentyala S. M. S. 1999; PubMed Scopus Google Scholar). of to PLCδ1 its activity because the binding of the to the of for in the catalytic although high levels of are for by this of PLCβ2 only occur at high levels of the of to the and we that the activity of the not This result suggests that the activity of PLCδ1 may be when to which is in the PLCβ2 we PLCδ1 with diethyl This a with or both of the catalytic the Y. PubMed Scopus Google Scholar). of PLCδ1 in of PLCδ1 activity but not its to and the with PLCβ2 on the of its on of PLCδ1 to PLCβ2 to not its of hydrolysis PLCβ2 inhibits PLCδ1 activity by a of This is to the of the phosphate and of the on PLCδ activity M.J. K. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, Katan M. Biochem. J. 1995; PubMed Scopus Google Scholar). find that the activity is and its binding to and Gβγ subunits is to the in At Ca2+ PLCδ1 activity with increasing of with an to the for PLCδ1 These results that PLCβ2 suppresses the catalytic activity of PLCδ1 at levels of Ca2+. Gβγ in PLCβ2 and PLCδ1 both to Gβγ subunits, although binding to the is of and results in activation T. Pentyala S. M. S. 1999; PubMed Scopus Google Scholar). Gβγ subunits with by complex on in the or of Gβγ subunits by the of to in a in the but this by the of of PLCβ2 and PLCδ1 in the PLC in living cells, we used to PLC in cells because these cells both PLCs J. R. S. FEBS Lett. PubMed Scopus Google and of these cells of PLCβ2 and that when the cells stimulated with and although the low of these not an we used the of bimolecular Y. T. Cell. 9: Full Text Full Text PDF PubMed Scopus Google Scholar). In this the of is to a target protein, whereas the the is to a potential binding J. Chem. 2000; Scopus Google Scholar). the the fluorescent in HEK293 cells, which low levels of PLCδ1 and find that although a amount of is most of the reconstituted is to the of HEK293 cells expressing and stimulation with are in yellow which In observed in cells with only of the or with the to the Also, be for the under a of cytosolic T. Cell. Full Text PDF PubMed Scopus Google Scholar), that the not strongly protein In we also a of a cell that stimulated with the G protein-coupled receptor agonist find a in for in the agonist At the of all to the These studies a of the upon G protein the in from specific of we of the cellular of the in HEK293 cells by also that stimulation of the cells the the and the in from the the cytosolic that the of from the the of G protein stimulation on a of cells, we the with a of cells in a In we that of but not the agonist a in the the This which is to that for the cells, a of the complex in to G protein activation. The extent of this from to of the which to be to in the expression of the All to at release activated Gαq and subunits well Gβγ subunits. which in the of we the cells with to activation of because studies have HEK293 cells to be J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar, A.M. S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). which Gβγ release from to the in These results that Gβγ subunits released from are for the in the of Gβγ subunits to from HEK293 cells with the the in Gβγ subunits or PLCβ2 is in in we find that we can by the of PLCβ2 or Gβγ subunits. The of PLCβ2 PLCδ1 on the above that the activity of PLCδ1 be by with This by cellular Ca2+ levels in living HEK293 cells with PLCβ2 or PLCδ1 expression or both by the calcium The results are in of these cells with PLCβ2 does not the basal or stimulated levels of Ca2+. In with PLCδ1 results in a increase in both the basal and stimulated levels of Ca2+. PLCδ1 with PLCβ2 these Ca2+ levels to much to those of control cells. These support the that PLCβ2 binds to PLCδ1 and inhibits its In we also the of elevated Ca2+ stimulation from a of sets in to the of the in elevated cellular Ca2+ find that the of all but cells be to a to and cells not of or to be to an of This in Ca2+ levels to PLCδ1 most results from of levels in the cells. It is that of PLCβ2 with PLCδ1 this to control during the that the enzymes are that their in to or other than PLCβ2 that in cellular Ca2+ in inositol phosphate we in the inositol phosphate in the basal and stimulated in cells with PLCδ1, or The in that cells with PLCβ2 a increase in inositol phosphate whereas with PLCδ1 in much inositol phosphate with both enzymes the inositol phosphate levels to those for PLCβ2 This of increase in inositol phosphate levels be upon stimulation with of the inositol that the basal levels of are in cells with whereas the levels of this lipid are elevated when the cells are with PLCδ1 The in vitro results a synergistic release of Ca2+ upon agonist stimulation that not clearly in HEK293 cells. in these cells may be at the of this we with in HEK293 cells. that overexpression of from an of to to control cells that with Thus, the of Gβγ results in a in Ca2+ release by of PLCβ2 at the protein in of studies A10 cells. has that these cells have high levels of PLCβ2 and only of PLCδ1 J. R. S. FEBS Lett. PubMed Scopus Google Scholar). these cells with of PLCδ1 and observed a increase in Ca2+ release cells with stimulation with of PLCδ1 in basal Ca2+ and a rise in stimulated levels that is not PLCβ2 to control the PLCδ1 is to a synergistic release of Ca2+ with PLCδ1 a range of The studies that PLCβ2 PLCδ1 This control of PLCδ1 through its with PLCβ2 at concentrations of Ca2+. The these PLCs can be in living cells can the of cellular Ca2+ and inositol phosphate levels to overexpression of PLCδ1. These the regulation of PLCδ1 activity with G protein-coupled receptor purified on model we find that PLCβ2 and PLCδ1 and that this is not because of of the These with in and more strongly when to lipid of to a to a more and their have the in in and to and we the in PLCβ2 and PLCδ1 to be PubMed Scopus Google Scholar). PLCβ2 binds strongly and to J. S. PubMed Scopus Google Scholar) in contrast to PLCδ1, which only binds strongly to that are or is P. R. S. S. S. V. S. M. 1995; PubMed Scopus Google Scholar). The for the on PLCβ2 to with PLCδ1 to its activity under It is that the of on is only than that of S. 1999; PubMed Scopus Google Scholar) and may be under The of is not PLCδ1 binds strongly and specifically to PI(4,5)P2, is observed for and is not because of competition of the for or Because the of both enzymes a role in catalytic and because the of both enzymes Gβγ subunits, this is a for Y. S. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Pentyala S. M. S. 1999; PubMed Scopus Google Scholar). that we have evidence that the of PLCδ1 binds to PLCβ2 with an in range of the and M. that the may be to the and the which also to the that the of the and catalytic of PLCδ1 suggest a of the to the catalytic Y. S. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar), to the that the for that this on PLCβ2 which binds strongly to Gβγ subunits S. 1999; PubMed Scopus Google Scholar), is that results be obtained with the PLCβ3 which are also regulated by Gβγ subunits S.G. Google Scholar), and we find the PLCδ1 for PLCβ3 to be to and S. the is under PLCδ1 is activated by in cellular Ca2+ and by a high of that binding T. M.J. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). of PLCδ1 by RhoGAP and transglutaminase (9Homma Y. Emori Y. EMBO J. 1995; 14: 286-291Crossref PubMed Scopus (189) Google Scholar, J.F. S.G. Im M.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar) is through the Ca2+ that induces PLCδ1 activation. find that PLCβ2 of PLCδ1 at high levels of the of regulation is from RhoGAP and PLCδ1 in an PLCβ2 control on this The of Ca2+ to the PLCβ2 complex suggests that only PLCδ1 not with PLCβ2 be activated upon an in Ca2+ through other than those heterotrimeric G this regulation of PLCδ1 only occur in cell that both are of these by in cells A10 and PC12 J. R. S. FEBS Lett. PubMed Scopus Google Scholar, Suh S.G. S. PubMed Scopus Google Scholar, M. M. Kim S. S.G. PubMed Scopus Google Scholar), we that all of these studies the PLCβ2 which may not have high these by and we expression of of both PLCβ2 and PLCδ1 in heart and and in A10 and PC12 cells by These results suggest that cell both It is also that studies that more which is also by Gβγ subunits, inhibits and S. we find that in living cells the PLCβ2 complex is on the with a the studies suggest that G protein stimulation the with the Whereas internal is to phosphatidylinositol lipid hydrolysis at these internal is of the cytoplasmic PLCβ2 although is to be the rise in cytoplasmic free calcium because complex by this The the of free Gβγ subunits at the that the in of PLCβ2 which is by J. V. Y. P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). this is also that cytosolic PLCβ2 is regulated by which may also its with cytoplasmic PLCδ1. in living cells by This has been to in Y. T. Cell. 9: Full Text Full Text PDF PubMed Scopus Google Scholar). which is is to than Because the of the may the to that complex not by the of to that not form under a of is that the not the of protein we that the from HEK293 cells to be by the of purified PLCβ2 or Gβγ subunits. These studies that is an for in cells. The used in these and its are coupled to both Gαq and heterotrimers, which can both release Gβγ subunits Cell. 1995; 80: Full Text PDF PubMed Scopus Google Scholar). Gαq subunits to and activate and that the of the in cells be caused by Gαq or Gβγ subunits. the cells with pertussis that subunits, their with receptor and release of Gβγ subunits Biochem. Full Text PDF PubMed Scopus Google Scholar). of pertussis the in upon that under these of the complex is to release of Gβγ from subunits. The observed for the and the of complex the of and of receptors, which is with the that Gβγ Scholar). Because the specific activity of PLCδ1 for is than the activity of PLCβ2 T. M. S. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar), the of PLCδ1 by PLCβ2 may be in of and Ca2+ The of by Gβγ subunits that cellular stimulation by a G protein agonist for a synergistic PLC through Gβγ activation of PLCβ2 and of PLCδ1 The results in A10 cells that this is the at low PLCδ1 It is that the cellular that control the and of these enzymes are under control because PLCβ2 of PLCδ1 activity is at PLCδ1 expression in HEK293 cells synergistic Ca2+ and inositol phosphate release not A simple is that under the of overexpression of PLCβ2 and PLCδ1, control of second messengers is at the receptor which the amount of Gβγ activation of PLCβ2 and in turn release of PLCδ1. This is by results that overexpression of in HEK293 cells. results suggest the model in PLCβ2 a cellular of PLCδ1 in which its control is to activation of heterotrimeric G proteins, specifically This also amplification of the calcium of PLCδ1 from PLCβ2 also increase the free of PLCδ1 for may for in the enzymes, for in of for the and of for the with