Okadaic acid activates p42 mitogen-activated protein kinase (MAP kinase; ERK-2) in B-lymphocytes but inhibits rather than augments cellular proliferation: contrast with phorbol 12-myristate 13-acetate.
Ligation of the membrane immunoglobulin M receptor as well as stimulation with the protein kinase C agonist phorbol 12-myristate 13-acetate leads to a B-lymphocyte proliferation and differentiation. Both stimuli activate p42 mitogen-activated protein (MAP) kinase in human B-lymphocytes [Casillas, Hanekom, Williams, Katz and Nel (1991) J. Biol. Chem. 266, 19088-19094]. MAP kinase activation is dependent on tyrosine as well as threonine phosphorylation of the kinase and its activity is inhibited by tyrosine as well as threonine/serine phosphatases. Okadaic acid, a specific inhibitor of type 1 and 2A serine/threonine phosphatases, induced MAP kinase activity in a potent and dose-dependent fashion, but failed to induce [3H]thymidine incorporation into normal human tonsil B-cells. Moreover, in combination with membrane immunoglobulin M ligation, okadaic acid decreased rather than increased [3H]thymidine incorporation. The kinetics of MAP kinase activation by okadaic acid differed from phorbol 12-myristate 13-acetate and anti-membrane immunoglobulin M stimulation. Okadaic acid induced tyrosine phosphorylation of 42 kDa and 44 kDa proteins which co-electrophoresed and co-chromatographed with ERK-2 and ERK-1 respectively. Ramos cells also contained a constitutively active 46 kDa MAP kinase which appeared as a separate peak in chromatography and could be immunoprecipitated by an antiserum against a rat ERK-1 fusion protein.
Casillas
A M
AM
Department of Medicine, UCLA School of Medicine 90024-1680.
Amaral
K
K
Chegini-Farahani
S
S
Nel
A E
AE
D001402:B-Lymphocytes / Q000187:drug effects / Q000201:enzymology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002850:Chromatography, Gel; D004789:Enzyme Activation; D004988:Ethers, Cyclic / Q000494:pharmacology*; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019319:Okadaic Acid; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D004988:Ethers, Cyclic; D007075:Immunoglobulin M; D019319:Okadaic Acid; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate