Lysophosphatidic acid signals through mitogen-activated protein kinase-extracellular signal regulated kinase in ovarian theca cells expressing the LPA1/edg2-receptor: involvement of a nonclassical pathway?
We investigated the mechanism of lysophosphatidic acid (LPA) signaling in ovarian theca cells and observed that stimulation with this bioactive lipid markedly enhanced Thr/Tyr phosphorylation of the MAPK ERK1/2. Activation of ERK was transient, showing a peak at 5 min that declined thereafter, and was not associated with a concomitant nuclear translocation of the enzyme, suggesting that a cytosolic tyrosine phosphatase may be responsible for switching off the signal. Epidermal growth factor (EGF)-induced activation of the enzyme in the same cell system was more rapid (peaking at 1 min), sustainable for at least 60 min, and could be suppressed by prior treatment with either pertussis toxin or a noncompetitive inhibitor of Ras acceptor protein, manumycin A. This functional inhibition of either Gi or Ras failed, however, to affect the LPA-induced ERK-phosphorylation. Surprisingly, functional inhibition of Rho-GTPase, in C3-exotoxin-lipofected cells, markedly reduced LPA-stimulated phosphorylation of ERK, without affecting the EGF-induced stimulation of MAPK. Theca cells labeled with anti-LPA1/edg2-type antibody showed a distinct cell surface labeling, which is reflected in the expression of (LPA1)-type LPA receptors at both mRNA and protein levels. The findings indicate that LPA transiently stimulates MAPK ERK in LPA1/edg2-expressing theca cells and suggest an alternative mechanism regulating the activation of ERK that differs from the canonical EGF-Ras-MAPK kinase pathway.
Budnik
Lygia T
LT
Institute for Hormone and Fertility Research, University of Hamburg, D-20251 Hamburg, Germany. Budnik@IHF.de.
Brunswig-Spickenheier
Bärbel
B
Mukhopadhyay
Amal K
AK
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D006801:Humans; D008246:Lysophospholipids / Q000378:metabolism* / Q000494:pharmacology; D048369:MAP Kinase Kinase 1; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D010766:Phosphorylation; D021381:Protein Transport / Q000187:drug effects; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D049368:Receptors, Lysophosphatidic Acid; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013799:Theca Cells / Q000187:drug effects / Q000378:metabolism*; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
D004791:Enzyme Inhibitors; D008246:Lysophospholipids; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004815:Epidermal Growth Factor; D037342:Pertussis Toxin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate; C032881:lysophosphatidic acid