PHENYLETHANOLAMINE N-METHYLTRANSFERASE GENE-EXPRESSION - SYNERGISTIC ACTIVATION BY EGR-1, AP-2 AND THE GLUCOCORTICOID RECEPTOR

The gene encoding the epinephrine synthesizing enzyme, phenylethanolam ine N-methyltransferase (PNMT), is transcriptionally activated by Egr- 1, AP-2, and the glucocorticoid receptor(GR). Stimulation by AP-2 requ ires its synergistic interaction with an activated GR. The present stu dies show that the GR also cooperates with Egr-1 or the combination of Egr-1 and AP-2 to activate the PNMT promoter. Together Egr-1, Ap-2, a nd the GR can induce PNMT promoter-mediated luciferase reporter gene e xpression beyond the sum of their independent contributions as well as synergistically activate the endogenous PNMT gene leading to marked i ncreases in PNMT mRNA. Examination of the effects of mutation of the A P-2 or Egr-1 binding sites on PNMT promoter activation by DEX and the factor binding, to the remaining intact site or by all three transcrip tional activators showed changes in luciferase reporter gene expressio n which suggest that DNA structure may be altered thereby reducing or enhancing synergistic activation. It also appears that the - 165 bp Eg r-1 site may not be critical For the synergism observed between Egr-1, AP-2 and the GR. When the glucocorticoid response element (GRE) withi n the PNMT promoter was mutated, PNMT promoter activation by Egr-1 and DEX, AP-2 and DEX or all three showed bath inhibition and enhancement , even when the GRE was completely eliminated. These observations indi cate that induction of PNMT gene transcription may occur either throug h GR interaction with other transcriptional proteins after binding to its cognate GRE or through direct protein-protein interaction in the a bsence of GRE binding. While the mechanisms by which Egr-1 and the GR and Egr-1, AP-2 and the GR function cooperatively to stimulate PNMT pr omoter activity remain to be elucidated, this synergistic stimulation of the PNMT promoter by these factors may provide important in vivo an d in vitro regulatory control of the PNMT gene. (C) 1998 Elsevier Scie nce B.V. All rights reserved.