A function for phosphoinositide 3-kinase beta lipid products in coupling beta gamma to Ras activation in response to lysophosphatidic acid.
Although Gbetagamma is thought to mediate mitogen-activated protein kinase (MAPK) activation in response to G protein-coupled receptor stimulation, the mechanisms involved in this pathway have not been clearly defined. Phosphoinositide 3-kinase (PI3K) has been proposed as an early intermediate in this process, but its role has remained elusive. We have observed that dominant negative mutants of p110beta, but not of p110gamma, inhibited MAPK stimulation in response to lysophosphatidic acid (LPA). The role of p110beta was located upstream from Ras. To determine which of the lipid or protein kinase activities of p110beta were important for Ras activation, we produced a mutant p110beta lacking the lipid but not the protein kinase activity. This protein displayed a dominant negative activity similar to a kinase-dead mutant, indicating that p110beta lipid kinase activity was essentially involved in Ras activation. In agreement, overexpression of the lipid phosphatase PTEN was found to specifically inhibit Ras stimulation induced by LPA. In addition, we have observed that the PH domain-containing adapter protein Gab1, which is involved in p110beta activation during LPA stimulation, is also implicated in this pathway downstream of p110beta. Indeed, both membrane redistribution and phosphorylation of Gab1 were reduced in the presence of PI3K inhibitors or dominant negative p110beta. Downstream of Gab1, the tyrosine phosphatase SHP2 was found to mediate Ras activation in response to LPA and to be recruited through PI3K and Gab1, because transfection of Gab1 mutant deficient for SHP2 binding inhibited Ras activation without interfering with PI3K activation. We conclude that LPA-induced Ras activation is mediated by a p110beta/Gab1/SHP2 pathway. Moreover, we present data indicating that p110beta is effectively the target of betagamma in this pathway, suggesting that the p110beta/Gab1/SHP2 pathway provides a novel link between betagamma and Ras by integrating two early events of LPA signaling, i.e. Gbetagamma release and tyrosine kinase receptor transactivation.
Yart
Armelle
A
INSERM U326, IFR 30, Hôpital Purpan, Toulouse 31059, France.
Roche
Serge
S
Wetzker
Reinhard
R
Laffargue
Muriel
M
Tonks
Nicholas
N
Mayeux
Patrick
P
Chap
Hugues
H
Raynal
Patrick
P
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D005799:Genes, Dominant; D015801:Helminth Proteins / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D050356:Lipid Metabolism; D008246:Lysophospholipids / Q000378:metabolism*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism* / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection; D014709:Vero Cells; D018631:ras Proteins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D004791:Enzyme Inhibitors; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D015801:Helminth Proteins; D020962:Heterotrimeric GTP-Binding Proteins; D008246:Lysophospholipids; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; D018631:ras Proteins; C118981:G-protein Beta gamma; C490897:Gab1 protein, mouse; C095048:microfilarial sheath protein, Helminth