Lysophosphatidic acid inhibits Ca2+ signaling in response to epidermal growth factor receptor stimulation in human astrocytoma cells by a mechanism involving phospholipase C(gamma) and a G(alphai) protein.
The effect of the lysophospholipid mediators lysophosphatidic acid (LPA) and sphingosine 1-phosphate and the polypeptide growth factor epidermal growth factor (EGF) on the human astrocytoma cell line 1321N1 was assessed. These agonists produced a rapid and transient increase of the intracellular Ca(2+) concentration. When LPA was perfused before addition of EGF, the EGF-dependent Ca(2+) transient was abrogated, whereas this was not observed when EGF preceded LPA addition. This inhibitory effect was not found for other EGF-mediated responses, e.g., activation of the mitogen-activated protein kinase cascade and cell proliferation, thus pointing to the existence of cross-talk between LPA and EGF for only a branch of EGF-induced responses. As 1321N1 cells expressed mRNA encoding the LPA receptors endothelial differentiation gene (Edg)-2, Edg-4, and Edg-7 and as sphingosine 1-phosphate did not interfere with LPA signaling, Edg-2, Edg-4, and/or Edg-7 could be considered as the LPA receptors mediating the aforementioned cross-talk. Attempts to address the biochemical mechanism involved in the cross-talk between the receptors were conducted by the immunoprecipitation approach using antibodies reacting with the EGF receptor (EGFR), phosphotyrosine, phospholipase Cgamma (PLCgamma)-1, and G(alphai) protein. LPA was found to induce coupling of PLCgamma-1 to the EGFR by a mechanism involving a G(alphai) protein, in the absence of tyrosine phosphorylation of both PLCgamma and the EGFR. These data show a cross-talk between LPA and EGF limited to a branch of EGFR-mediated signaling, which may be explained by a LPA-induced, G(alphai)-protein-mediated translocation of PLCgamma-1 to EGFR in the absence of detectable tyrosine phosphorylation of both proteins.
Hernández
M
M
Instituto de Biología y Genética Molecular, CSIC-Universidad de Valladolid, Valladolid, Spain.
Barrero
M J
MJ
Crespo
M S
MS
Nieto
M L
ML
D001254:Astrocytoma / Q000378:metabolism* / Q000473:pathology; D020013:Calcium Signaling / Q000187:drug effects*; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D006133:Growth Substances / Q000378:metabolism / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008246:Lysophospholipids / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D009687:Nuclear Proteins / Q000235:genetics; D051966:Phospholipase C gamma; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000235:genetics; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D006133:Growth Substances; D007527:Isoenzymes; D008246:Lysophospholipids; D009687:Nuclear Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D014157:Transcription Factors; D010566:Virulence Factors, Bordetella; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D020962:Heterotrimeric GTP-Binding Proteins