De Novo Synthesized RelB Mediates TNF-Induced Up-Regulation of the Human Polymeric Ig Receptor

Abstract

Secretory Abs, which operate in a principally noninflammatory fashion, constitute the first line of acquired immune defense of mucosal surfaces. Such Abs are generated by polymeric Ig receptor (pIgR)-mediated export of dimeric IgA and pentameric IgM. TNF activates a proinflammatory gene repertoire in mucosal epithelial cells and also enhances pIgR expression. In this study we show that TNF-induced up-regulation of the human pIgR critically depends on an NF-κB site and flanking sequences within a 204-bp region of the first intron in the pIgR gene, a region largely overlapping with a recently characterized IL-4-responsive enhancer. The intronic NF-κB site was rapidly bound by NF-κB p65/p50 heterodimers present in nuclear extracts after TNF treatment of HT-29 cells, but a more delayed binding of RelB agreed better with the slow, protein synthesis-dependent, transcriptional activation of the pIgR gene. Overexpression of NF-κB p65 caused transient up-regulation of a pIgR-derived reporter gene, whereas overexpression of RelB showed a stronger and more sustained effect. Finally, we demonstrated that inhibition of endogenous RelB by RNA interference severely reduced the TNF responsiveness of our pIgR-derived reporter gene. Thus, TNF-induced signaling pathways required for up-regulated pIgR expression appear to differ from those of the proinflammatory gene repertoire.

Long-Term Exposure of the HT-29 Human Intestinal Epithelial Cell Line to TNF Causes Sustained Up-Regulation of the Polymeric Ig Receptor and Proinflammatory Genes through Transcriptional and Posttranscriptional Mechanisms

“…3). Our results, along with those of Schjerven et al (23,24), suggest that in intestinal epithelial cells TNF may activate proinflammatory gene transcription through the classical NF-B pathway, while activating transcription of the PIGR gene through the alternative NF-B pathway.…”

“…Using reporter gene analyses, Schjerven et al (23) demonstrated that TNF-induced transcription of the PIGR gene was mediated by a novel NF-B/ Rel site in intron 1. Surprisingly, these investigators found that transcriptional activation of the PIGR gene in HT-29 cells required de novo synthesis of RelB and was not stimulated by overexpression of RelA (24). We report here that chronic stimulation of HT-29 cells with TNF leads to continuous up-regulation of RelB mRNA, to levels exceeding those of RelA mRNA (Fig.…”

“…3A). These investigators recently demonstrated that de novo synthesis of the RelB subunit of NF-B was correlated with enhanced PIGR transcription (24). To determine whether chronic exposure to TNF alters expression of these transcription factors, RNA samples from the experiment described in Fig.…”

RelB/p52 NF-κB Complexes Rescue an Early Delay in Mammary Gland Development in Transgenic Mice with Targeted Superrepressor IκB-α Expression and Promote Carcinogenesis of the Mammary Gland

“…Therefore, experiments were performed in Hs578T human breast cancer cells and D3-1 DMBA-transformed mammary epithelial cells, which were both found to express substantial levels of RelB (see below). In order to determine the involvement of RelB in tumor cell proliferation, RelB was repressed in Hs578T breast cancer cells, using stable transfection with pSIREN siRelB expression vector or, as a control, the pSIREN RelB-sense vector (43). Expression of siRelB strongly repressed nuclear RelB compared to the control (Fig.…”

Food fight! Parenteral nutrition, enteral stimulation and gut-derived mucosal immunity

“…In vitro studies show that up-regulation of pIgR expression occurs following exposure to both tumor necrosis factor alpha (TNF-a) and interleukin-1-beta (IL-1β). 75,[94][95][96] Both cytokines are pro-inflammatory cytokines typically elevated during stress and following trauma. This hypothetical relationship between these inflammatory cytokines and pIgR levels was tested in the mouse model by pre-injury administration of antibodies antagonistic to TNF-α and IL-1β.…”