ELEVATED CYCLIC-AMP INHIBITS NF-KAPPA-B-MEDIATED TRANSCRIPTION IN HUMAN MONOCYTIC CELLS AND ENDOTHELIAL-CELLS

The NF-kappa B/Rel family of transcription factors regulates the induc ible expression of many genes in activated human monocytes and endothe lial cells. In this study, we examined the molecular mechanism by whic h agents that elevate intracellular cAMP inhibit the expression of the tumor necrosis factor alpha (TNF alpha), tissue factor, endothelial l eukocyte adhesion molecule-1, and vascular cell adhesion molecule-1 ge nes. Both forskolin and dibutyryl cAMP, which elevate intracellular cA MP by independent mechanisms, inhibited TNF alpha and tissue factor ex pression at the level of transcription. Induction of NF-kappa B-depend ent gene expression in transiently transfected human monocytic THP-1 c ells and human umbilical vein endothelial cells was inhibited by eleva ted cAMP and by overexpression of the catalytic subunit of protein kin ase A (PKA). Elevated cAMP did not prevent nuclear translocation of p5 0/p65 and c-Rel/p65 heterodimers, decrease nuclear translocation of p6 5, or significantly modify TNF alpha-induced phosphorylation of p65. F unctional studies demonstrated that transcriptional activation of a pl asmid containing multimerized kappa B sites by p65 was inhibited by ag ents that elevate cAMP and by overexpression of the catalytic subunit of PKA. This study indicates that activation of PKA reduces the induct ion of a distinct set of genes in monocytes and endothelial cells by i nhibiting NF-kappa B-mediated transcription.