This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Goode, N. T. Articles by Hart, I. R. Search for Related Content PubMed PubMed Citation Articles by Goode, N. T. Articles by Hart, I. R.

Selection and Preliminary Characterization of Variant Lines of a Murine Macrophage Tumor Resistant to the Antiproliferative Effects of Phorbol Esters

Imperial Cancer Research Fund Laboratories, P. O. Box 123, Lincoln's Inn Fields, London WC2A 3PX [N. T. G., I. R. H.], and Department of Cellular and Molecular Biology, Institute for Cancer Research, Fulham Road, London SW7 [J. P. M.], United Kingdom

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 (TPA^R) and three clonally derived (TPA^R-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 (TPA^R-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 TPA^R-3 cells. Similarly in both cell lines, prolonged culture in phorbol ester produced down-regulation of PKC, as measured by inducible M_r 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 TPA^R-3 cells is a consequence of PKC activation, and the development of resistance to TPA-antiproliferative effects in the TPA^R-3 cell line was not linked causally to alterations in PKC levels or the c-fos mRNA induction response. The malignant capacity of the TPA^R 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.

¹ To whom requests for reprints should be addressed.

Received 5/23/89. Revised 9/ 5/89. Accepted 11/27/89.