Mitogenic signaling by lysophosphatidic acid (LPA) involves Galpha12.
Lysophosphatidic acid (LPA), a major G protein coupled receptor (GPCR)-activating ligand present in serum, elicits growth factor like responses by stimulating specific GPCRs coupled to heterotrimeric G proteins such as G(i), G(q), and G12/13. Previous studies have shown that the overexpression of wild-type Galpha12 (Galpha12WT) results in the oncogenic transformation of NIH3T3 cells (Galpha12WT-NIH3T3) in a serum-dependent manner. Based on the potent growth-stimulating activity of LPA and the presence of LPA and LPA-like molecules in the serum, we hypothesized that the serum-dependent neoplastic transformation of Galpha12WT-NIH3T3 cells was mediated by the stimulation of LPA-receptors (LPARs) by LPA in the serum. In the present study, using guanine nucleotide exchange assay and GST-TPR binding assay, we show that the treatment of Galpha12WT-NIH3T3 with 2 muM LPA leads to the activation of Galpha12. Stimulation of these cells with LPA promotes JNK-activation, a critical component of Galpha12-response and cell proliferation. We also show that LPA can substitute for serum in stimulating JNK-activity, DNA synthesis, and proliferation of Galpha12WT-NIH3T3 cells. LPA-mediated proliferative response in NIH3T3 cells involves Galpha12, but not the closely related Galpha13. Pretreatment of Galpha12WT-NIH3T3 cells with suramin (100 microM), a receptor-uncoupling agent, inhibited LPA-stimulated proliferation of these cells by 55% demonstrating the signal coupling between cell surface LPAR and Galpha12 in the neoplastic proliferation of NIH3T3 cells. As LPA and LPAR mediated mitogenic pathways have been shown to play a major role in tumor genesis and progression, a mechanistic understanding of the signal coupling between LPAR, Galpha12, and the downstream effectors is likely to unravel additional targets for novel cancer chemotherapies.
Radhika
V
V
Fels Institute for Cancer Research and Molecular Biology, Temple University School Medicine, Philadelphia, PA 19140, USA.
Hee Ha
Ji
J
Jayaraman
Muralidharan
M
Tsim
Siu-Tai
ST
Dhanasekaran
N
N
D016475:3T3 Cells; D000818:Animals; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D004789:Enzyme Activation / Q000187:drug effects; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000187:drug effects / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008246:Lysophospholipids / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D037342:Pertussis Toxin / Q000494:pharmacology; D049368:Receptors, Lysophosphatidic Acid / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction; D013498:Suramin / Q000494:pharmacology
D008246:Lysophospholipids; D049368:Receptors, Lysophosphatidic Acid; D006153:Guanosine Diphosphate; D013498:Suramin; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D048031:JNK Mitogen-Activated Protein Kinases; D044365:GTP-Binding Protein alpha Subunits, G12-G13; C032881:lysophosphatidic acid