Selection and preliminary characterization of variant lines of a murine macrophage tumor resistant to the antiproliferative effects of phorbol esters.
Treatment of M5076 wild-type cells with 50 ng/ml of 12-O-tetradecanoylphorbol-13-acetate (TPA) almost completely inhibited cellular proliferation. Continuous culture in the presence of TPA was used to derive four lines, one polyclonal (TPAR) and three clonally derived (TPAR-1, -2, and -3), which exhibited variable resistance to the antiproliferative effects of phorbol esters. Protein kinase C (PKC) activation and c-fos expression in wild-type cells and the stably resistant line (TPAR-3) were examined after phorbol ester treatment. Both lines exhibited a comparable rapid and transient induction of c-fos mRNA expression, but induction of c-fos protein was reduced markedly in the TPAR-3 cells. Similarly in both cell lines, prolonged culture in phorbol ester produced down-regulation of PKC, as measured by inducible Mr 80,000 phosphorylation and an in vitro PKC assay. This decrease in PKC levels was paralleled by a decrease in c-fos mRNA and protein induction. Thus, c-fos expression in both wild-type and TPAR-3 cells is a consequence of PKC activation, and the development of resistance to TPA-antiproliferative effects in the TPAR-3 cell line was not linked causally to alterations in PKC levels or the c-fos mRNA induction response. The malignant capacity of the TPAR line was not reduced relative to wild-type cells. PKC activation and c-fos mRNA expression do not appear to determine changes in the in vivo or in vitro growth behavior of M5076 cells, whereas variations in c-fos protein expression may determine the anti-proliferative response to tumor-promoting phorbol esters.
Goode
N T
NT
Imperial Cancer Research Fund Laboratories, London, United Kingdom.
Moore
J P
JP
Hart
I R
IR
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D004121:Dimethyl Sulfoxide / Q000494:pharmacology*; D004351:Drug Resistance; D004789:Enzyme Activation / Q000187:drug effects; D008264:Macrophages; D008970:Molecular Weight; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000096:biosynthesis*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger / Q000096:biosynthesis*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000201:enzymology* / Q000473:pathology
D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D004121:Dimethyl Sulfoxide