8288641

pubmed:Citation

2

Treatment of human myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C (PKC), is associated with induction of monocytic differentiation. Since PKC can act immediately upstream to the cytoplasmic Raf-1 serine/threonine protein kinase, we studied activation of Raf-1 during induction of the differentiated monocytic phenotype. The results demonstrate that Raf-1 is activated during TPA-induced monocytic differentiation of HL-60 cells. In contrast, there was little effect of TPA on this kinase in an HL-60 variant, designated HL-525, which is resistant to TPA-induced differentiation. Treatment of both HL-60 and HL-525 cells with okadaic acid, an inhibitor of serine/threonine protein phosphatases 1 and 2A, was associated with Raf-1 activation and induction of the monocytic phenotype. Since Raf-1 can activate the mitogen-activated protein (MAP) kinases, we also studied the relationship between MAP kinase activation and monocytic differentiation. Treatment of HL-60, but not HL-525, cells with TPA was associated with increased MAP kinase activity as determined by phosphorylation of myelin basic protein and the c-Jun Y peptide. Okadaic acid-induced differentiation of both HL-60 and HL-525 cells was similarly accompanied by increases in MAP kinase activity. These findings indicated that activation of Raf-1/MAP kinase signaling is associated with induction of a differentiated monocytic phenotype and that okadaic acid bypasses a defect in this cascade in TPA-treated HL-525 cells. While recent studies have shown that HL-525 cells are deficient in PKC beta, the present results demonstrate that PKC beta expression is up-regulated in the HL-525 variant by treatment with retinoic acid. The results also demonstrate that retinoic acid-treated HL-525 cells respond to TPA with activation of Raf-1 and MAP kinase, as well as induction of monocytic differentiation. Taken together, the results indicate that activation of Raf-1/MAP kinase signaling is associated with monocytic differentiation and that stimulation of serine/threonine protein phosphorylation by TPA or okadaic acid is sufficient for reversal of the leukemic HL-60 phenotype.

eng

IM

MEDLINE

0021-9258

Print

269

NLM

872-8

pubmed-meshheading:8288641-Amino Acid Sequence, pubmed-meshheading:8288641-Calcium-Calmodulin-Dependent Protein Kinases, pubmed-meshheading:8288641-Cell Differentiation, pubmed-meshheading:8288641-Enzyme Activation, pubmed-meshheading:8288641-Ethers, Cyclic, pubmed-meshheading:8288641-Gene Expression, pubmed-meshheading:8288641-Genes, jun, pubmed-meshheading:8288641-Humans, pubmed-meshheading:8288641-Leukemia, Myeloid, pubmed-meshheading:8288641-Molecular Sequence Data, pubmed-meshheading:8288641-Monocytes, pubmed-meshheading:8288641-Okadaic Acid, pubmed-meshheading:8288641-Protein Kinase C, pubmed-meshheading:8288641-Proto-Oncogene Proteins, pubmed-meshheading:8288641-Proto-Oncogene Proteins c-raf, pubmed-meshheading:8288641-RNA, Messenger, pubmed-meshheading:8288641-Tetradecanoylphorbol Acetate, pubmed-meshheading:8288641-Tretinoin, pubmed-meshheading:8288641-Tumor Cells, Cultured

Activation of Raf-1 and mitogen-activated protein kinases during monocytic differentiation of human myeloid leukemia cells.

Journal Article, In Vitro, Research Support, U.S. Gov't, P.H.S.