Mechanism of IL-4-Mediated Up-Regulation of the Polymeric Ig Receptor: Role of STAT6 in Cell Type-Specific Delayed Transcriptional Response

Abstract

The polymeric IgR (pIgR) mediates transport of dimeric IgA and pentameric IgM across mucosal epithelia, thereby generating secretory Abs. Its expression is up-regulated at the transcriptional level by IL-4 in HT-29 cells. In this study, we demonstrate that IL-4 mediates up-regulation of human pIgR through a 554-bp IL-4-responsive enhancer in intron 1. Mutation of a binding site for STAT-6 within this region abolished IL-4-induced enhancement, while an adjacent putative C/EBP site was dispensable. IL-4 treatment induced binding of STAT6 to the intronic STAT6 site, but cooperation with nearby upstream and downstream DNA elements was required for IL-4 responsiveness. Furthermore, IL-4-mediated increased transcription of the pIgR-derived enhancer, like the endogenous pIgR gene, required de novo protein synthesis. Interestingly, a conditionally active form of STAT6 sufficed to activate a pIgR-derived enhancer in HT-29 cells, but not in Cos-1 cells, suggesting a requirement for cell type-specific factors. Thus, STAT6 activation mediates a delayed transcriptional enhancement of pIgR by induction of a de novo synthesized protein that cooperates with STAT6 itself bound to its cognate DNA element in intron 1. This mechanism may represent a general strategy for how pleiotropic cytokines elicit cell type-specific transcriptional responses.

Exploitation of the Polymeric Immunoglobulin Receptor for Antibody Targeting to Renal Cyst Lumens in Polycystic Kidney Disease

“…2). Although the results of IL4 treatment are consistent with previous findings in intestinal epithelial cells (23,24,28), importantly, IL13 treatment has a similar or greater effect on pIgR expression, which has not been demonstrated previously. Together, these results indicate that STAT6 regulates the expression of pIgR in renal epithelial cells and that pIgR expression is increased in cyst-lining cells.…”

“…dIgA can be found in urine, suggesting that it can reach the urinary space by pIgR-mediated transcytosis (21). pIgR expression has been shown to be regulated by IL-4, TNF-␣, and IFN-␥ in airway, intestinal, and mammary gland epithelial cells (22), and a STAT6 binding domain has been identified in intron 1 of the pIgR gene (23,24). Altogether, these data suggest that the kidney can use the dIgA/pIgR system and that it can be up-regulated to protect the urinary space against pathogens.…”

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

“…Transient transfections were performed with FuGene 6 reagent (Roche, Indianapolis, IN) as previously described (19). Transfected cells were either left untreated or stimulated with 10 ng/ml recombinant human TNF for 12 h when indicated.…”

“…One microgram of RNA, primed with oligo(dT) and reverse transcribed with Superscript II or III (Invitrogen, Leek, The Netherlands) was used for a 20-l cDNA reaction. Gene-specific primers were designed with Primer3 software (20) as described previously (19). Specific cDNA was quantified by real-time PCR with the Light Cycler (Roche) and LCFast Start DNA Master SYBR Green I reagents (Roche) or with the QuantiTect SYBR Green PCR kit (Qiagen, Valencia, CA), according to the manufacturer's protocol.…”

“…PCR primer sequences are given in Table I. Quantification of specific mRNA levels was performed as previously described (19) or using dilution curves of exogenous standards. Levels of pIgR and RelB mRNA were normalized to GAPDH before fold induction was calculated.…”