A function for phosphoinositide 3-kinase beta lipid products in coupling beta gamma to Ras activation in response to lysophosphatidic acid
Authors: Patrick Mayeux
Armelle Yart
Muriel Laffargue
Patrick Raynal
Serge Roche
Reinhard Wetzker
Hugues Chap
Nicholas Tonks
Journal: Journal of Biological Chemistry (2002)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Gbetagamma; mitogen-activated protein kinase (MAPK); phosphoinositide 3-kinase (PI3K); p110beta; p110gamma
Affiliations: INSERM U326, IFR 30, Hôpital Purpan, Toulouse 31059, France.

Abstract:  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. 

Retracted: No

PubPeer comments:
 Mirroring Frullania Sergiae s observation [from another thread] : ![] , 
 Comparing Figs 6C [left] and 3C [right]: ![file] , 
 Figure 4C. Much more similar than you would expect after horizontal stretching, yet the treatments are different. https: imgur.com Z0SURbi , 
 #1 Indeed the same blot for controling Erk expresssion has probably been used in these 2 figures. I guess this is for convenient reasons. I apologize for this. Please note that this does not change the major outcome of each figure, as the images shown are representative of several experiments with similar results. , 
 #2 Sorry, I do not understand where is the issue in these images, since the same protein (Akt and HA-tagged Akt) are shown. , 
 Indeed, there seems to be an issue with the images controlling gel loading in this particular experiment shown in this figure. Please note that the particular images shown in this figure are representative of several expriments with similar results in terms of Gab1 and Sos association, and all of them have been controlled for gel loading, even though perfect images are not always obtained when one performs westerm blotting. , 
 #4 Does that mean that you did not conduct a control on the same blot? #5 I believe the issue is that two lanes showing different conditions are more similar than one would expect, do you have access to the original blots? #6 I would humbly ask that Dr. Raynal provide the original blots here as I don t think anything short will assuage my concerns. If Dr. Raynal would like to consult JBC s requirements on data retention, it should be noted that  If authors refuse or fail to provide requested data after publication, the authors may be asked to withdraw their article or the publisher may retract the article.  ,