Cross-talk modulation of signal transduction pathways: two mechanisms are involved in the control of tyrosine aminotransferase gene expression by phorbol esters.
Transcription of the rat tyrosine aminotransferase gene (TAT) is stimulated in liver by glucocorticoid hormones or by cAMP-increased protein kinase A activity via enhancers located 2.5 kilobases (kb) and 3.6 kb upstream of the start site of transcription. The proteins mediating induction have been characterized, and protein binding in the two enhancer regions has been analyzed in vivo and in vitro. The TAT gene is therefore a useful model system with which to study cross-talk between different signal transduction pathways. We find that activation of the second messenger pathway leading from protein kinase C to the transcription factor AP-1 by the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) impairs induction of the TAT gene both by glucocorticoid hormones and cAMP. The effects of TPA treatment on chromatin structure of the TAT gene and protein-DNA interactions in vivo were assayed. Under conditions in which TPA impairs glucocorticoid induction of TAT mRNA, the glucocorticoid receptor and other proteins binding within the glucocorticoid-inducible enhancer occupy their binding sites, indicating that inhibition occurs at a later step necessary for transcriptional stimulation. On the other hand, inhibition of cAMP induction correlates with reduced occupancy of the cAMP response element in vivo.
Reik
A
A
Division Molecular Biology of the Cell 1, German Cancer Research Center, Heidelberg.
Stewart
A F
AF
Schütz
G
G
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002843:Chromatin / Q000187:drug effects / Q000648:ultrastructure; D005576:Colforsin / Q000494:pharmacology; D003345:Corticosterone / Q000494:pharmacology*; D000242:Cyclic AMP / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D004790:Enzyme Induction / Q000187:drug effects; D005796:Genes; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000473:pathology; D008969:Molecular Sequence Data; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011987:Receptors, Steroid / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014444:Tyrosine Transaminase / Q000096:biosynthesis / Q000235:genetics*
D002843:Chromatin; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D011987:Receptors, Steroid; C024357:corticosterone receptor; D005576:Colforsin; D004247:DNA; D000242:Cyclic AMP; D014444:Tyrosine Transaminase; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D003345:Corticosterone