Cross-linking of surface IgM stimulates the Ras/Raf-1/MEK/MAPK cascade in human B lymphocytes.
The mechanism by which mitogen-activated protein kinase (MAPK) is activated in human B cells following cross-linking of the antigen receptor was investigated. Following anti-IgM antibody and phorbol 12-myristate 13-acetate (PMA) stimulation, we demonstrate the activation of Ras, Raf-1, and MAPK/ERK kinase (MEK), all of which are thought to participate in an important signaling cascade that leads to MAPK activation. We detected the kinase activities of Raf-1 and MEK toward purified recombinant substrates for each in this pathway (MEK for Raf-1 and MAPK for MEK). Following stimulation with either anti-IgM or PMA, Ras activation was observed, and the ability of Raf-1 to phosphorylate recombinant kinase-inactive MEK was increased by approximately 10-fold. Similarly, MEK activity toward kinase-active or -inactive recombinant MAPK also increased upon anti-IgM or PMA treatment. Furthermore, the activation of both MAPK and p90rsk was demonstrated under identical conditions in the B cells. We conclude that activation of B lymphocytes through the antigen receptor stimulates distinct members of the Ras/Raf-1/MEK cascade and this mechanism is likely to be responsible for MAPK and p90rsk activation in these cells.
Tordai
A
A
Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Franklin
R A
RA
Patel
H
H
Gardner
A M
AM
Johnson
G L
GL
Gelfand
E W
EW
D001402:B-Lymphocytes / Q000201:enzymology / Q000378:metabolism*; D002472:Cell Transformation, Viral; D003432:Cross-Linking Reagents; D004789:Enzyme Activation; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism*; D008213:Lymphocyte Activation; D048369:MAP Kinase Kinase 1; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D015689:Oncogene Protein p21(ras) / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D003432:Cross-Linking Reagents; D007075:Immunoglobulin M; D011518:Proto-Oncogene Proteins; D011947:Receptors, Antigen, B-Cell; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019893:Ribosomal Protein S6 Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D015689:Oncogene Protein p21(ras); D013755:Tetradecanoylphorbol Acetate