cAMP-mediated growth inhibition in fibroblasts is not mediated via mitogen-activated protein (MAP) kinase (ERK) inhibition. cAMP-dependent protein kinase induces a temporal shift in growth factor-stimulated MAP kinases.
Growth factors stimulate fibroblast cell division by activating the recently identified mitogen-activated protein kinase (MAP kinase) signaling cascade. In contrast to our previous work (Kahan, K., Seuwen, K., Meloche, S. and Pouysségur, J. (1992) J. Biol. Chem. 267, 13369-13375), several reports have suggested that an elevation in intracellular cAMP blocks cell proliferation by attenuating MAP kinase activation. Hence we re-examined the effect of a long term increase in intracellular cAMP and therefore cAMP-dependent protein kinase (PKA) activation on the MAP kinase cascade in CCL39 fibroblasts. The concomitant addition of cAMP-elevating agents prostaglandin E, (PGE1) and IBMX did not inhibit the mitogen-mediated activation of p44 MAP kinase. However, a 5-min PGE1/IBMX pretreatment abolished the MAP kinase response, in a manner correlating with the extent of PKA activity. This inhibition was temporal in nature, and while modifying the time course of growth factor-mediated p44 MAP kinase, activation did not diminish the magnitude of the response. Thus the major peak of MAP kinase activity normally present 5 min after alpha-thrombin addition was now evident at 10 min in the presence of PGE1/IBMX. CCL39 cell proliferation is inhibited by elevated cAMP levels. Such an inhibition could reflect either a reduction in the number of cells entering the cell cycle or a delay in the time required to go through the cycle. Bromodeoxyuridine labeling experiments revealed that the cAMP-mediated inhibition of DNA synthesis in CCL39 cells was not due to a delay in S phase entry, but was due to a reduction in the number of cells entering S phase. Thus we conclude that although PKA activation may slightly modify the time course of MAP kinase activation in response to mitogens in CCL39 cells, the PKA-mediated inhibition of cell division occurs through modulation of an intracellular target, distinct from the p42/p44 MAP kinase cascade.
McKenzie
F R
FR
Centre de Biochimie, CNRS, Parc Valrose, 06108 Nice, France.
Pouysségur
J
J
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000527:Alprostadil / Q000494:pharmacology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D020930:MAP Kinase Kinase Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology
D011994:Recombinant Proteins; D016222:Fibroblast Growth Factor 2; D002217:Carbachol; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; D013917:Thrombin; D000527:Alprostadil; D015056:1-Methyl-3-isobutylxanthine