Resistance to phorbol ester-induced differentiation of a U-937 myeloid leukemia cell variant with a signaling defect upstream to Raf-1 kinase.
Previous studies have demonstrated that treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with growth arrest and induction of monocytic differentiation. The present work describes the isolation of a U-937 cell variant, designated TUR, which is unresponsive to the growth-inhibitory effects of this agent. The results demonstrate that, in contrast to U-937 cells, the TUR line fails to respond to TPA with induction of the c-jun, junB, c-fos, and EGR-1 early response genes. The finding that these cells also fail to exhibit adherence or induction of the tumor necrosis factor and c-fms genes further supports their resistance to TPA-induced differentiation. In contrast, TUR cells responded to 1,25-dihydroxyvitamin D3, another inducer of monocytic differentiation, with growth arrest and induction of early response gene and c-fms transcripts. TUR cells also responded to okadaic acid, an inhibitor of type 1 and 2A protein phosphatases, with similar changes in gene expression. Further characterization of TUR cells has demonstrated decreased expression of protein kinase C as compared to wild-type U-937 cells. We also demonstrate that although treatment of U-937 cells with TPA is associated with activation of the Raf-1 serine/threonine kinase, there was no detectable decrease in electrophoretic mobility of this protein in TPA-treated TUR cells. Taken together, these findings indicate that the TUR variant is defective in TPA-induced signaling events upstream to activation of Raf-1 kinase.
Hass
R
R
Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
Hirano
M
M
Kharbanda
S
S
Rubin
E
E
Meinhardt
G
G
Kufe
D
D
D002454:Cell Differentiation / Q000187:drug effects; D004351:Drug Resistance; D006801:Humans; D007951:Leukemia, Myeloid / Q000188:drug therapy* / Q000201:enzymology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D011518:Proto-Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D013755:Tetradecanoylphorbol Acetate