NF-kappa B inhibits glucocorticoid and cAMP-mediated expression of the phosphoenolpyruvate carboxykinase gene

Transcription of the phosphoenolpyruvate carboxykinase (PEPCK) gene is regu lated by a variety of agents. Glucocorticoids, retinoic acid, and glucagon (via its second messenger, cAMP) stimulate PEPCK gene transcription, wherea s insulin, phorbol esters, cytokines, and oxidative stress have an opposing effect. Stimulation of PEPCK gene expression has been extensively studied, and a number of important DNA elements and binding proteins that regulate the transcription of this gene have been identified. However, the mechanism s utilized to turn off expression of this gene are not well-defined. Many o f the negative regulators of PEPCK gene transcription also stimulate the nu clear localization and activation of the transcription factor NF-kappa B, s o we hypothesized that this factor could be involved in the repression of P EPCK gene expression. We find that the p65 subunit of NF-kappa B represses the increase of PEPCK gene transcription mediated by glucocorticoids and cA MP in a concentration-dependent manner. The mutation of an NF-kappa B bindi ng element identified in the PEPCK gene promoter fails to abrogate this rep ression. Further analysis suggests that p65 represses PEPCK gene transcript ion through a protein protein interaction with the coactivator, CREB bindin g protein.