c-Myc expression is controlled by the mitogenic cAMP-cascade in thyrocytes.
In dog thyroid epithelial cells in primary culture, thyrotropin (TSH), acting through cAMP, induces proliferation and differentiation expression, whereas epidermal growth factor (EGF) and phorbol esters induce proliferation and dedifferentiation. In these cells, we have detailed the regulation by cAMP of the c-myc protooncogene mRNA and protein. The cAMP signaling pathway induces a biphasic increase of c-myc mRNA and protein. c-Myc protein accumulation follows the abundance and kinetics of its mRNA expression. Using in vitro elongation of nascent transcripts to measure transcription and actinomycin D (AcD) chase experiments to study mRNA stability, we have shown that in the first phase cAMP releases a transcriptional elongation block. No modification of transcriptional initiation was observed. After 30 min of treatment with TSH, c-myc mRNA was also stabilized. During the second phase, cAMP stabilization of the mRNA disappears and transcription is again shut off. Thus, in a tissue in which it stimulates proliferation and specific gene expression, cAMP regulates biphasically c-myc expression by mechanisms operating at the transcriptional and posttranscriptional levels.
Pirson
I
I
Institute of Interdisciplinary Research, School of Medicine, Free University of Brussels, Belgium.
Coulonval
K
K
Lamy
F
F
Dumont
J E
JE
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D004285:Dogs; D005786:Gene Expression Regulation / Q000187:drug effects; D016259:Genes, myc; D017228:Hepatocyte Growth Factor / Q000494:pharmacology; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000494:pharmacology; D014158:Transcription, Genetic
D012333:RNA, Messenger; D005576:Colforsin; D017228:Hepatocyte Growth Factor; D013972:Thyrotropin; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate