Cooperative role of NF‐κB signaling and PARP‐1 activity in the TNF‐induced inhibition of PHEX gene expression

Abstract

Reduced bone mass is a common complication in chronic inflammatory diseases, although the mechanisms are not completely understood. Phex gene encodes an osteoblast Zn‐endopeptidase controlling bone mineralization and is inhibited by TNF in chemically‐induced colitis. Here, we confirm its downregulation in CD4+CD45RBhigh T‐cell transfer colitis, and delineate the molecular mechanism involved in TNF‐mediated inhibition of Phex transcription. TNF decreased expression of Phex in UMR106 cells and did not require de novo synthesis of a transrepressor. Transient transfections with Phex promoter constructs identified a region within ‐74nt containing weak putative NF‐κB binding sites. TNF induced recruitment of p65/p50 complex to two of those cis elements. Inhibition of NF‐κB signaling by a proteasome inhibitor increased the basal level of Phex transcription and abrogated the effects of TNF, while overexpression of p65 reduced promoter activity. Proteomic approaches identified poly(ADP‐rybose) polymerase (PARP‐1) constitutively interacting with Phex promoter, and TNF‐induced PARylation of p65 which potentiates its suppression of Phex transcription. TNF‐mediated downregulation of Phex was completely abrogated in PARP‐1 KO mice. NF‐κB signaling and PARP‐1 enzymatic activity are cooperatively involved in constitutive and inducible suppression of Phex.Grant support: R37DK033209 (F.K.G.)