Tumor Necrosis Factor (TNF)-α Persistently Activates Nuclear Factor-κB Signaling through the Type 2 TNF Receptor in Chromaffin Cells: Implications for Long-Term Regulation of Neuropeptide Gene Expression in Inflammation

Abstract

Chromaffin cells of the adrenal medulla elaborate and secrete catecholamines and neuropeptides for hormonal and paracrine signaling in stress and during inflammation. We have recently documented the action of the cytokine TNF-α on neuropeptide secretion and biosynthesis in isolated bovine chromaffin cells. Here, we demonstrate that the type 2 TNF-α receptor (TNF-R2) mediates TNF-α signaling in chromaffin cells via activation of nuclear factor (NF)-κB. Microarray and suppression subtractive hybridization have been used to identify TNF-α target genes in addition to those encoding the neuropeptides galanin, vasoactive intestinal polypeptide, and secretogranin II in chromaffin cells. TNF-α, acting through the TNF-R2, causes an early up-regulation of NF-κB, long-lasting induction of the NF-κB target gene inhibitor κB (IκB), and persistent stimulation of other NF-κB-associated genes including mitogen-inducible gene-6 (MIG-6), which acts as an IκB signaling antagonist, and butyrate-induced transcript 1. Consistent with long-term activation of the NF-κB signaling pathway, delayed induction of neuropeptide gene transcription by TNF-α in chromaffin cells is blocked by an antagonist of NF-κB signaling. TNF-α-dependent signaling in neuroendocrine cells thus leads to a unique, persistent mode of NF-κB activation that features long-lasting transcription of both IκB and MIG-6, which may play a role in the long-lasting effects of TNF-α in regulating neuropeptide output from the adrenal, a potentially important feedback station for modulating long-term cytokine effects in inflammation.