The Lysophosphatidic Acid 2 Receptor Mediates Down-regulation of Siva-1 to Promote Cell Survival

Lysophosphatidic acid (LPA) promotes cell survival through the activation of G protein-coupled LPA receptors. However, whether different LPA receptors activate distinct anti-apoptotic signaling pathways is not yet clear. Here we report a novel mechanism by which the LPA2 receptor targets the proapoptotic Siva-1 protein for LPA-dependent degradation, thereby attenuating Siva-1 function in DNA damage response. The carboxyl-terminal tail of the LPA2 receptor, but not LPA1 or LPA3 receptor, specifically associates with the carboxyl cysteine-rich domain of Siva-1. Prolonged LPA stimulation promotes the association of Siva-1 with the LPA2 receptor and targets both proteins for ubiquitination and degradation. As a result, adriamycin-induced Siva-1 protein stabilization is attenuated by LPA in an LPA2-dependent manner, and the function of Siva-1 in promoting DNA damage-induced apoptosis is inhibited by LPA pretreatment. Consistent with this result, inhibition of the LPA2 receptor expression increases Siva-1 protein levels and augments adriamycin-induced caspase-3 cleavage and apoptosis. Together, these findings reveal a critical and specific role for the LPA2 receptor through which LPA directly inactivates a critical component of the death machinery to promote cell survival. Lysophosphatidic acid (LPA) promotes cell survival through the activation of G protein-coupled LPA receptors. However, whether different LPA receptors activate distinct anti-apoptotic signaling pathways is not yet clear. Here we report a novel mechanism by which the LPA2 receptor targets the proapoptotic Siva-1 protein for LPA-dependent degradation, thereby attenuating Siva-1 function in DNA damage response. The carboxyl-terminal tail of the LPA2 receptor, but not LPA1 or LPA3 receptor, specifically associates with the carboxyl cysteine-rich domain of Siva-1. Prolonged LPA stimulation promotes the association of Siva-1 with the LPA2 receptor and targets both proteins for ubiquitination and degradation. As a result, adriamycin-induced Siva-1 protein stabilization is attenuated by LPA in an LPA2-dependent manner, and the function of Siva-1 in promoting DNA damage-induced apoptosis is inhibited by LPA pretreatment. Consistent with this result, inhibition of the LPA2 receptor expression increases Siva-1 protein levels and augments adriamycin-induced caspase-3 cleavage and apoptosis. Together, these findings reveal a critical and specific role for the LPA2 receptor through which LPA directly inactivates a critical component of the death machinery to promote cell survival. Lysophosphatidic acid (LPA) 3The abbreviations used are: LPAlysophosphatidic acidERKextracellular signal-regulated kinaseGFPgreen fluorescent proteinGSTglutathione S-transferasesiRNAsmall interfering RNAaaamino acid(s)MEFmouse embryonic fibroblastHAhemagglutininBSAbovine serum albuminGAPDHglyceraldehyde-3-phosphate dehydrogenaseRTreverse transcription is a growth factor-like phospholipid that mediates diverse biological events such as mitogenesis, differentiation, cell survival, platelet aggregation, inflammation, angiogenesis, and cell migration (1Mills G.B. Moolenaar W.H. Nat. Rev. Cancer. 2003; 3: 582-591Crossref PubMed Scopus (962) Google Scholar). At least five membrane-bound G protein-coupled LPA receptors have been identified. The LPA1, LPA2, and LPA3 receptors belong to the endothelial differentiation gene family, whereas the LPA4 and LPA5 receptors are structurally distinct from the others (2Noguchi K. Ishii S. Shimizu T. J. Biol. Chem. 2003; 278: 25600-25606Abstract Full Text Full Text PDF PubMed Scopus (486) Google Scholar, 3An S. Bleu T. Huang W. Hallmark O.G. Coughlin S.R. Goetzl E.J. FEBS Lett. 1997; 417: 279-282Crossref PubMed Scopus (241) Google Scholar, 4Bandoh K. Aoki J. Hosono H. Kobayashi S. Kobayashi T. Murakami-Murofushi K. Tsujimoto M. Arai H. Inoue K. J. Biol. Chem. 1999; 274: 27776-27785Abstract Full Text Full Text PDF PubMed Scopus (471) Google Scholar, 5Hecht J.H. Weiner J.A. Post S.R. Chun J. J. Cell Biol. 1996; 135: 1071-1083Crossref PubMed Scopus (667) Google Scholar, 6Lee C.W. Rivera R. Gardell S. Dubin A.E. Chun J. J. Biol. Chem. 2006; 281: 23589-23597Abstract Full Text Full Text PDF PubMed Scopus (388) Google Scholar). Substantial evidence has shown that LPA can protect cells from serum deprivation-induced apoptosis, prevent chemotherapeutic agents-induced apoptosis, and block death receptor-mediated apoptosis in a variety of cells, suggesting that LPA is a survival factor (7Fang X. Yu S. LaPushin R. Lu Y. Furui T. Penn L.Z. Stokoe D. Erickson J.R. Bast Jr., R.C. Mills G.B. Biochem. J. 2000; 352: 135-143Crossref PubMed Scopus (105) Google Scholar, 8Radeff-Huang J. Seasholtz T.M. Matteo R.G. Brown J.H. J. Cell Biochem. 2004; 92: 949-966Crossref PubMed Scopus (171) Google Scholar, 9Kang Y.C. Kim K.M. Lee K.S. Namkoong S. Lee S.J. Han J.A. Jeoung D. Ha K.S. Kwon Y.G. Kim Y.M. Cell Death Differ. 2004; 11: 1287-1298Crossref PubMed Scopus (70) Google Scholar). Several LPA-induced signaling pathways have been defined for these protective effects (8Radeff-Huang J. Seasholtz T.M. Matteo R.G. Brown J.H. J. Cell Biochem. 2004; 92: 949-966Crossref PubMed Scopus (171) Google Scholar). For example, the activation of AKT/PKB by LPA stimulation leads to the phosphorylation and inactivation of BAD and procaspase-9, thereby suppressing the apoptotic signaling pathways (10Datta S.R. Dudek H. Tao X. Masters S. Fu H. Gotoh Y. Greenberg M.E. Cell. 1997; 91: 231-241Abstract Full Text Full Text PDF PubMed Scopus (4994) Google Scholar, 11Cardone M.H. Roy N. Stennicke H.R. Salvesen G.S. Franke T.F. Stanbridge E. Frisch S. Reed J.C. Science. 1998; 282: 1318-1321Crossref PubMed Scopus (2746) Google Scholar). In addition, LPA-induced activation of ERKs has been reported to protect fibroblasts from serum deprivation-induced apoptosis (7Fang X. Yu S. LaPushin R. Lu Y. Furui T. Penn L.Z. Stokoe D. Erickson J.R. Bast Jr., R.C. Mills G.B. Biochem. J. 2000; 352: 135-143Crossref PubMed Scopus (105) Google Scholar). LPA also induces gene expression of NF-κB, which activates the transcription of several anti-apoptotic proteins to promote cell survival (12Raj G.V. Sekula J.A. Guo R. Madden J.F. Daaka Y. Prostate. 2004; 61: 105-113Crossref PubMed Scopus (47) Google Scholar). As the levels of LPA are increased in ovarian cancer cells, LPA may contribute to the resistance to apoptosis and tumor progression (13Xu Y. Shen Z. Wiper D.W. Wu M. Morton R.E. Elson P. Kennedy A.W. Belinson J. Markman M. Casey G. J. Am. Med. Assoc. 1998; 280: 719-723Crossref PubMed Scopus (576) Google Scholar). Thus far, the specificity and mechanisms by which different LPA receptors regulate these signaling events are not yet fully understood. lysophosphatidic acid extracellular signal-regulated kinase green fluorescent protein glutathione S-transferase small interfering RNA amino acid(s) mouse embryonic fibroblast hemagglutinin bovine serum albumin glyceraldehyde-3-phosphate dehydrogenase reverse transcription The carboxyl-terminal tails of the LPA1, LPA2, and LPA3 receptors are structurally distinct form each other, suggesting that this region may specifically regulate the unique protein-protein interactions and functions of each receptor. Therefore, we used the carboxyl-terminal tail of the LPA2 receptor as bait in a yeast two-hybrid screen to identify molecules specifically involved in the function of the LPA2 receptor. In addition to TRIP6, a focal adhesion molecule that regulates LPA-induced cell migration (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar), the proapoptotic Siva-1 protein was found to interact with the LPA2 receptor with a high affinity. Siva-1 is a proapoptotic protein originally identified as a CD27-binding protein (15Prasad K.V. Z. Y. Wu M. S. S. 1997; PubMed Scopus Google Scholar). The of Siva-1 protein a death domain region in the and cysteine-rich in the carboxyl (15Prasad K.V. Z. Y. Wu M. S. S. 1997; PubMed Scopus Google Scholar). Several of evidence that Siva-1 is a proapoptotic For example, Siva-1 gene expression is DNA damage and W. Yu J. Y. 2003; Google Scholar, N. N. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar, Lee PubMed Scopus Google Scholar, H. Y. R.G. J. 2000; PubMed Scopus Google Scholar). of a activates Siva-1 transcription in small cell H. Y. R.G. J. 2000; PubMed Scopus Google Scholar), and the transcription and directly to the Siva-1 and activate Siva-1 expression DNA damage N. N. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar). Siva-1 is for cell death S. N. Cell Death Differ. PubMed Scopus Google Scholar). In addition to apoptosis of through a P. S. J. 2004; PubMed Scopus Google Scholar), Siva-1 may regulate in cell receptor-mediated cell death R. J. S. S. Z. K.V. 2006; PubMed Scopus Google Scholar). Siva-1 also to through death domain region and apoptosis Y. X. M. P. Wu M. K.V. S. PubMed Scopus Google Scholar). has been reported that a form of that and of the death domain is apoptotic Y. Z. Y. K.V. 1999; PubMed Scopus Google Scholar). However, a report that of induces apoptosis in P. S. J. 2004; PubMed Scopus Google Scholar). has been shown that phosphorylation of Siva-1 by kinase is for apoptosis X. S. K.V. D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), the mechanisms that regulate Siva-1 function in apoptosis are In this we the of the Siva-1 and the LPA2 receptor. that this association promotes LPA-dependent ubiquitination and of Siva-1 thereby the proapoptotic of Siva-1 DNA damage response. in addition to AKT/PKB and pathways to promote cell survival, LPA directly the proapoptotic function of Siva-1 through specific of the LPA2 receptor to Siva-1. the Siva-1 expression a Siva-1 from a yeast two-hybrid which to the the Siva-1 and of the was for the expression of Siva-1. was also or expression such that these proteins with a a a green fluorescent protein an a glutathione S-transferase or a hemagglutinin amino of Siva-1 by and and The of each by DNA The was used to the expression of a K. J.C. Lin F.T. Lin W.C. J. 2006; PubMed Scopus Google Scholar), a a mouse LPA2 or a mouse Siva-1 that targets the or (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google was used as bait to screen a cell in as (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). and of the LPA receptors with the proteins was as (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). of Siva-1 and the LPA2 receptor mouse embryonic fibroblasts in LPA1 and LPA2 from Ishii N. X. S. Brown J.H. Chun J. Cell Biol. PubMed Scopus Google and with cells with a resistance gene expression and or was to cell the levels with the LPA2 in of from and with or not for and the LPA2 receptor was with The Siva-1 was with an Siva-1 The was with an LPA2 receptor K.S. Roy K. Y. J. Med. PubMed Scopus Google Scholar). Siva-1 and the LPA2 receptor, was with or receptor in The cells and with or for the cells with LPA for and in Siva-1 or LPA2 receptor was with and the was with an to whether Siva-1 is in the cells or with in acid by the with LPA for and for in and The in was also to the which and the cell and to an The was with an and an as a and the of LPA the of Siva-1 and the LPA2 receptor, cells with or receptor by The cells for with for and with LPA for in the cell and the receptor by an The with an or an as a was to the of in cells with LPA and for The cell was from the and with or The to and cell The expression of the LPA2 receptor was by The of LPA the of was as the of the of these cells with for in and the of Siva-1 was in of Siva-1 and the carboxyl-terminal tail of the LPA2 receptor, or was in and by the proteins was with to of Siva-1 was with of or for Siva-1 protein by was with an cells with different expression to LPA or as RNA was as the to five of RNA was to to mouse Siva-1 and Siva-1 or and LPA2 receptor, and K. Lin F.T. Lin W.C. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar), to of the was to for or of the have been to of the of Siva-1 with the LPA2 receptor, was with the receptor or in The cells in and the cells with an by the with a to receptor. The with The of and directly by was to of with or with Siva-1 and cells or not in or with LPA for by the addition of for The cells in and DNA was with The of cells was by in cells a an LPA2 or a Siva-1 that cells with LPA for by the addition of for was to and a an an and an was also by by cell The of the LPA2 with the of Siva-1 an to identify the molecules specifically involved in the of the LPA2 receptor, a protein the carboxyl-terminal tail of the LPA2 receptor and the domain was used as bait to screen a cell (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). the to the the Siva-1 and the region was identified. The has been by growth of yeast cells Siva-1 with but not or and a these Siva-1 was with protein or protein of in As shown in Siva-1 was by but not a Siva-1 and the carboxyl-terminal tail of the LPA2 receptor. we have shown that the carboxyl-terminal tail of the LPA2 receptor directly with the of (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). In with the cysteine-rich of the of the domain with amino of and the of the domain with amino of Siva-1 the the carboxyl cysteine-rich of Siva-1 and TRIP6, we that the of Siva-1 for LPA2 receptor this a of proteins of and several Siva-1 and or with a receptor expression the expression of Siva-1 was the proteins of Siva-1 and Siva-1 to expression levels of each to was to the expression of but not with the receptor that the LPA2 receptor with and In the receptor with or was that the carboxyl cysteine-rich domain of Siva-1 is for this we whether Siva-1 with the LPA2 receptor a LPA2 receptor in both LPA1 and LPA2 receptors and that the LPA2 receptor was as the LPA2 receptor in by found that Siva-1 specifically with the LPA2 receptor in we Siva-1 expression in the of cells Siva-1 was in and we that the of Siva-1 protein different in these cell both cell with for to degradation, levels of Siva-1 protein and this Siva-1 was found to with the LPA2 receptor in we have shown that LPA stimulation to the LPA2 receptor but not LPA receptors (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). whether Siva-1 also to the LPA1 and LPA3 of Siva-1 with different LPA receptors was in cells or with LPA stimulation for As shown in Siva-1 to the LPA2 receptor. In to TRIP6, Siva-1 with the LPA2 receptor in the of and this was not by LPA stimulation for Siva-1 also to the LPA1 receptor with a but with the LPA3 receptor. the carboxyl-terminal tail of the LPA1 receptor not interact with Siva-1 this that the LPA1 receptor may to Siva-1 or through a stimulation with LPA has the association of Siva-1 with the LPA2 receptor, LPA stimulation the expression and of these found that in cells and the receptor, both Siva-1 and the LPA2 receptor levels by serum with and with However, the expression of both proteins was by with LPA for this of Siva-1 with the LPA2 receptor with that in the of serum with may that the association of Siva-1 and LPA2 is increased by LPA also that in Siva-1 was levels by with the LPA2 receptor with serum of LPA Biochem. PubMed Scopus Google Scholar), is that the LPA2 receptor promotes LPA-induced of Siva-1 protein in the of also with the LPA2 receptor, the levels of not by of the LPA2 receptor. also found that LPA stimulation for attenuated the expression of LPA1, LPA2, and LPA3 in cells the LPA1 receptor was to to Siva-1 LPA the expression of Siva-1 Siva-1 was with the LPA2 receptor. these that LPA2, but not LPA1 or specifically regulates the expression of Siva-1 protein in an LPA-dependent The association of Siva-1 with the LPA2 receptor was by of with or with in and by of with LPA stimulation for The that Siva-1 was in the also found in the and and In to the LPA2 receptor was in the or the and the and of Siva-1 was increased in cells the LPA2 receptor, Siva-1 in that with the of the LPA2 receptor and In to the LPA2 receptor, the which the carboxyl-terminal tail to to to Siva-1 in the that the LPA2 receptor to Siva-1 and Siva-1 from the whether Siva-1 is in the cells Siva-1 or with the LPA2 receptor with LPA for and was to and the which and the the that Siva-1 was in the with the LPA2 receptor, the levels of Siva-1 and by The LPA2 LPA-dependent of Siva-1 G protein-coupled receptors are activation 2006; PubMed Scopus Google Scholar). The receptors are to the in a as or the expression of LPA2 receptor and Siva-1 was both by LPA stimulation and we that both proteins LPA-dependent Therefore, we to LPA-induced of the LPA2 receptor and Siva-1 in cells by cells with to protein that the of the receptor was by LPA stimulation in cells Siva-1 was in whereas LPA a of Siva-1 and the of LPA2 Siva-1 we the of a in cells that not LPA1, LPA2, and LPA3 N. Y. Chun J. S. 1998; PubMed Scopus Google and in cells the receptor. In the expression of Siva-1 was in cells in cells of Siva-1 that LPA not the expression of in cells but attenuated expression in cells suggesting that the LPA2 receptor promotes LPA-induced Siva-1 degradation. LPA of Siva-1 and the LPA2 G protein-coupled receptors have been shown to ubiquitination and through the or pathways 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). that Siva-1 ubiquitination and with the LPA2 receptor in to LPA this cells with or and with for stimulation with LPA for that ubiquitination of the LPA2 receptor was found in the of LPA However, the levels of LPA2 increased by which was by LPA stimulation LPA stimulation Siva-1 and the levels of Siva-1 increased by to prevent protein degradation, we found that the Siva-1 and LPA2 receptor in the and this was increased by LPA for Together, these that LPA stimulation promotes the association of Siva-1 with the LPA2 receptor and targets both proteins for ubiquitination and degradation. DNA Siva-1 by LPA in an LPA2 has been shown that transcription of Siva-1 can by with the DNA and N. N. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar, Lee PubMed Scopus Google Scholar). evidence that Siva-1 is a for and N. N. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar). that Siva-1 in this was not by LPA not Siva-1 protein expression but also the in this was attenuated by LPA The role of LPA in Siva-1 was by the of in cells with and LPA can apoptosis in S.J. J. PubMed Google Scholar), we also found that the addition of to protein stabilization of Siva-1 this was attenuated by we the of LPA2 receptor the of Siva-1 DNA damage response. As shown in with and a activation and stabilization of Siva-1 in cells but not cells, suggesting a role for LPA2 in the of Siva-1 DNA damage response. the of Siva-1 protein expression is by LPA2 of the LPA2 receptor not the expression of that the LPA2 domain this or was or with the receptor in cells, and cells with for in the Siva-1 and Siva-1 and proteins with that have these proteins through the of the region of which is LPA2 However, but not was attenuated by LPA2 receptor suggesting that the carboxyl cysteine-rich of Siva-1 mediates LPA2 Siva-1 LPA Siva-1 in has been shown that of Siva-1 in is to activate caspase-3 and apoptosis in several cell (15Prasad K.V. Z. Y. Wu M. S. S. 1997; PubMed Scopus Google Scholar, P. S. J. 2004; PubMed Scopus Google Scholar, Y. X. M. P. Wu M. K.V. S. PubMed Scopus Google Scholar, Y. Z. Y. K.V. 1999; PubMed Scopus Google Scholar, X. S. K.V. D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In LPA fibroblasts from serum apoptosis (7Fang X. Yu S. LaPushin R. Lu Y. Furui T. Penn L.Z. Stokoe D. Erickson J.R. Bast Jr., R.C. Mills G.B. Biochem. J. 2000; 352: 135-143Crossref PubMed Scopus (105) Google Scholar). LPA targets Siva-1 for degradation, block the proapoptotic function of Siva-1 DNA damage response. that inhibition of the LPA2 receptor expression in cells increased Siva-1 levels and attenuated the protective of LPA adriamycin-induced caspase-3 cleavage of Siva-1 adriamycin-induced caspase-3 this was by LPA Consistent with these of an LPA2 or Siva-1 protein promotes adriamycin-induced apoptosis and In LPA cells from apoptosis in of the cells for the LPA2 cells, in which LPA a protective a apoptosis in cells, the expression of Siva-1 not protect cells from adriamycin-induced caspase-3 cleavage and apoptosis or apoptosis these that LPA not as a survival factor but also an anti-apoptotic role by directly the expression and proapoptotic of Siva-1 through a specific of the LPA2 receptor with Siva-1. LPA is a growth factor-like phospholipid that has been shown to cell survival through the activation of and signaling pathways and the of gene expression (7Fang X. Yu S. LaPushin R. Lu Y. Furui T. Penn L.Z. Stokoe D. Erickson J.R. Bast Jr., R.C. Mills G.B. Biochem. J. 2000; 352: 135-143Crossref PubMed Scopus (105) Google Scholar, 8Radeff-Huang J. Seasholtz T.M. Matteo R.G. Brown J.H. J. Cell Biochem. 2004; 92: 949-966Crossref PubMed Scopus (171) Google Scholar, 9Kang Y.C. Kim K.M. Lee K.S. Namkoong S. Lee S.J. Han J.A. Jeoung D. Ha K.S. Kwon Y.G. Kim Y.M. Cell Death Differ. 2004; 11: 1287-1298Crossref PubMed Scopus (70) Google Scholar, G.V. Sekula J.A. Guo R. Madden J.F. Daaka Y. Prostate. 2004; 61: 105-113Crossref PubMed Scopus (47) Google Scholar, X. Ishii Chun J. PubMed Scopus Google Scholar). a novel mechanism by which stimulation with LPA not promotes ubiquitination and of the LPA2 receptor but also Siva-1 the proapoptotic function of Siva-1 in DNA damage is attenuated by a by which the of Siva-1 with the LPA2 receptor promotes LPA-dependent of Siva-1 function DNA damage response. the function of Siva-1 protein is for caspase-3 and apoptosis, an of Siva-1 through LPA-induced Siva-1 protein may as a mechanism for cell has been that in cells in which the LPA1 receptor is LPA cells from apoptosis through an activation of AKT/PKB pathways X. N. D. J. Biol. Chem. 280: Full Text Full Text PDF PubMed Scopus Google Scholar). In in cells that high levels of LPA2 and of LPA1, an cells from apoptosis T. K. K. G. W. G. 2003; PubMed Scopus Google Scholar). LPA2 specifically but not from apoptosis of W. E. R. G. M. G. Full Text Full Text PDF PubMed Scopus Google Scholar). to whether the anti-apoptotic through an LPA2-dependent of Siva-1 Together, these findings that LPA1 and LPA2 may distinct anti-apoptotic signaling mechanisms to promote cell survival. Thus far, a of G protein-coupled receptors such as the receptor, the receptor, the receptor and the receptor have been shown to ubiquitination and stimulation Science. PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar, Z. M. J. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). In several receptors such as the factor receptor, the receptor, and the receptor are in an of or of the receptor Z. M. J. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar, M. S. P. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, 2003; PubMed Scopus Google Scholar). that the LPA2 receptor is in the of in the of LPA stimulation promotes ubiquitination of the LPA2 receptor. Thus far, a of proteins that directly with the G protein-coupled such as and G protein-coupled receptor kinase have been reported to ubiquitination and Science. PubMed Scopus Google Scholar, J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar, P. Jr., J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, Jr., P. J. 2006; PubMed Scopus (105) Google Scholar). Therefore, of G protein-coupled receptor-mediated of proteins through and degradation. LPA targets the LPA2 receptor and Siva-1 to the for ubiquitination to the yeast two-hybrid we have identified Siva-1 and as the LPA2 The carboxyl-terminal cysteine-rich of Siva-1 and the of domain and are both for the with the LPA2 receptor but not LPA receptors. However, are these molecules in LPA specifically with the LPA2 receptor LPA stimulation for association is LPA for induces the of to focal adhesion the LPA2 receptor is not (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar). In Siva-1 to the LPA2 receptor in the of LPA and However, to degradation, we have that LPA stimulation for promotes the of LPA2 receptor and Siva-1 that Siva-1 may to the LPA2 receptor. The of with the LPA2 receptor promotes LPA-dependent association of with several focal adhesion thereby LPA-induced cell migration (14Xu J. Lai Y.J. Lin W.C. Lin F.T. J. Biol. Chem. 2004; 279: 10459-10468Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar), whereas the of Siva-1 with the LPA2 receptor Siva-1 in the region and promotes LPA-dependent of Siva-1. In to LPA stimulation for not promote ubiquitination and of not is to a of with the LPA2 receptor. that not the that LPA may Siva-1 through and mechanisms involved in cell survival and and Siva-1 may by serum in addition to LPA the of Siva-1 with the LPA2 receptor a mechanism to promote LPA-induced Siva-1 degradation. DNA damage such as regulates Siva-1 gene expression through the activation of and N. N. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google and also Siva-1 protein As a result, Siva-1 DNA damage-induced apoptosis and In addition to the LPA2 receptor, Siva-1 has been shown to interact with cell and tumor factor receptor (15Prasad K.V. Z. Y. Wu M. S. S. 1997; PubMed Scopus Google Scholar, S. G. S. R. Cell Death Differ. PubMed Scopus Google Scholar). In to the LPA2 receptor that mediates LPA-induced cell survival and cell and are involved in apoptosis (15Prasad K.V. Z. Y. Wu M. S. S. 1997; PubMed Scopus Google Scholar, G. S. R. G. S. 1997; PubMed Scopus Google Scholar). these receptors may for Siva-1 in different Siva-1 and and is in the receptors are cell receptors. Siva-1 induces apoptosis a the mechanism has yet to Siva-1 an role in apoptosis or has a different function to for the in yeast two-hybrid and for the cell also for the critical of this The LPA2 was a by P.