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

• Published in: Biochemical journal 1993-03, Vol.290 (2), p.545-550
• Main Authors: CASILLAS, A. M, AMARAL, K, CHEGINI-FARAHANI, S, NEL, A. E
• Format: Article
• Language: English
• Subjects: B-Lymphocytes - drug effects; B-Lymphocytes - enzymology; Biological and medical sciences; Calcium-Calmodulin-Dependent Protein Kinases - metabolism; Cell Division - drug effects; Cell physiology; Chromatography, Gel; Enzyme Activation; Ethers, Cyclic - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Immunoglobulin M - immunology; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Molecular and cellular biology; Okadaic Acid; Phosphorylation; Protein-Tyrosine Kinases - metabolism; Responses to growth factors, tumor promotors, other factors; Tetradecanoylphorbol Acetate - pharmacology; Tumor Cells, Cultured; Tyrosine - metabolism
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj2900545

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.