The mitogen-activated protein kinase pathway inhibits ceramide-induced terminal differentiation of a human monoblastic leukemia cell line, U937.
This communication describes an extracellular signal-regulated kinase kinase (MEK)-dependent signal transduction pathway that prevents the terminal differentiation of a hemopoietic cell line. Both PMA and the cell-permeable ceramide, C2-ceramide, caused differentiation of U937 cells, but with distinct cell morphology and CD11b/CD14 surface expression. While PMA activated extracellular signal-regulated kinase (ERK), a downstream kinase of Raf-MEK signaling, C2-ceramide activated c-Jun NH2-terminal kinase (JNK), an anchor kinase of stress-induced signaling. Furthermore, only C2-ceramide stimulated an induction of cell cycle arrest that was associated with stable expression of p21CIP1 and retinoblastoma nuclear phosphoprotein dephosphorylation. Expression of p21CIP1 and JNK activation were also observed in sphingosine-treated cells, whereas sphingosine did not induce detectable differentiation. Concomitant stimulation with C2-ceramide and PMA resulted in the PMA phenotype, and cell cycle arrest was absent. ERK activation was enhanced by C2-ceramide plus PMA stimulation, whereas the activation of JNK was aborted. Strikingly, the inhibition of MEK with PD98059 altered the phenotype of C2-ceramide- and PMA-stimulated U937 cells to that of cells treated with C2-ceramide alone. Thus, ERK and JNK pathways deliver distinct signals, and the ERK pathway is dominant to the JNK cascade. Furthermore, differentiation and cell cycle arrest caused by C2-ceramide rely on independent signaling pathways, and JNK is an unlikely signaling element for this differentiation. Importantly, during C2-ceramide and PMA costimulation, the JNK pathway is not simply blocked by ERK activation; rather, cross-talk between these MAP kinase pathways acts to simultaneously augment ERK activity and down-regulate JNK activity.
John P. Robarts Research Institute, University of Western Ontario, London, Canada.
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D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007948:Leukemia, Monocytic, Acute / Q000201:enzymology / Q000473:pathology*; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010641:Phenotype; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; C064769:N-acetylsphingosine; D016160:Retinoblastoma Protein; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate