PhosphoCREB and CREM/ICER: Positive and negative regulation of proenkephalin gene expression in the paraventricular nucleus of the hypothalamus

In the hypothalamic paraventricular nucleus (PVN), the proenkephalin gene may be upregulated by lipopolysaccharide (LPS) and downregulated by the GABA-A agonist muscimol. Candidate transcription factors regulating the proenkephalin gene in opposite directions are cAMP-response-element-binding protein (CREB) (when phosphorylated, a positive regulator) and cAMP- responsive modulatory inducible cAMP early repressor (CREM/ICER) (a negative regulator). Our results demonstrate that CREM α,β,γ transcripts and ICER are induced in the PVN by LPS and remain elevated for periods of up to 12 h. PhosphoCREB is elevated after LPS administration, peaking at 8 h, but remaining elevated over control levels at 12 h. PhosphoCREB induction by LPS is also seen in primary hypothalamic cultures. Cotransfection of ICER with ENK-CAT12 into primary hypothalamic cultures produced a decrease in chloramphenicol acetyl transferase (CAT) levels following cAMP or LPS stimulation. PhosphoCREB is downregulated and CREM/ICER is upregulated in the PVN by muscimol, suggesting that the regulation of these transcription factors may underlie the inhibitory effect of muscimol on target genes in the PVN.