AGR2 Is Induced in Asthma and Promotes Allergen-Induced Mucin Overproduction

Abstract

Mucins are gel-forming proteins that are responsible for the characteristic viscoelastic properties of mucus. Mucin overproduction is a hallmark of asthma, but the cellular requirements for airway mucin production are poorly understood. The endoplasmic reticulum (ER) protein anterior gradient homolog 2 (AGR2) is required for production of the intestinal mucin MUC2, but its role in the production of the airway mucins MUC5AC and MUC5B is not established. Microarray data were analyzed to examine the relationship between AGR2 and MUC5AC expression in asthma. Immunofluorescence was used to localize AGR2 in airway cells. Coimmunoprecipitation was used to identify AGR2-immature MUC5AC complexes. Agr2(-/-) mice were used to determine the role of AGR2 in allergic airway disease. AGR2 localized to the ER of MUC5AC- and MUC5B-producing airway cells and formed a complex with immature MUC5AC. AGR2 expression increased together with MUC5AC expression in airway epithelium from "Th2-high" asthmatics. Allergen-challenged Agr2(-/-) mice had greater than 50% reductions in MUC5AC and MUC5B proteins compared with allergen-challenged wild-type mice. Impaired mucin production in Agr2(-/-) mice was accompanied by an increase in the proportion of mucins contained within the ER and by evidence of ER stress in airway epithelium. This study shows that AGR2 increases with mucin overproduction in individuals with asthma and in mouse models of allergic airway disease. AGR2 interacts with immature mucin in the ER and loss of AGR2 impairs allergen-induced MUC5AC and MUC5B overproduction.

Airway epithelial SPDEF integrates goblet cell differentiation and pulmonary Th2 inflammation

“…The present findings support the concept that SPDEF and FOXA3, perhaps in part related to goblet cell differentiation, influence the recruitment and activation of professional immune cells during the adaptation to exposures to aeroallergens and microbes after birth. SPDEF and FOXA3, transcription factors expressed selectively in nonciliated airway epithelial cells, activate a number of genes regulating mucus metaplasia, including MUC5AC, MUC5B, AGR2, and other proteins involved in the synthesis, glycosylation, and packaging of mucus (23,31). While a rare subset of airway epithelial cells in normal mouse lung, goblet cells are relatively abundant in conducting airways of the neonatal mouse, and their numbers increase in the first weeks of life (32).…”

Agr2 Mediates Paracrine Effects on Stromal Fibroblasts That Promote Invasion by Gastric Signet-Ring Carcinoma Cells

“…Agr2 is physiologically localized in endoplasmic reticulum (ER), and it regulates the expression of components of the ER-associated degradation signaling and plays a pivotal role in resistance to ER stress (9)(10)(11). In addition, Agr2 acts as an ER chaperone for the intestinal mucins MUC2, MUC1, and MUC5 (10,12,13). Among them, gastric SRCC cells express MUC1, which is a membrane-bound mucin that stimulates dysregulated cell proliferation by increasing receptor-mediated signal transduction (14)(15)(16).…”

The Endoplasmic Reticulum Resident Protein AGR3. Required for Regulation of Ciliary Beat Frequency in the Airway

“…Recent genomic and proteomic studies have revealed numerous genes that are selectively expressed in airway epithelial cells (5)(6)(7), but the functions of many of these genes remain obscure. We recently showed that the anterior gradient protein 2 homolog (AGR2) is expressed selectively in mucus cells and plays a role in the processing of mucins (8,9). AGR2 is a member of the protein disulfide isomerase (PDI) family.…”

“…TRX domains of some PDI family members have been shown to mediate formation, shuffling, or reduction of disulfide bonds in client secretory proteins transiting through the ER. AGR2, for example, can form mixed disulfide bonds with mucins in the ER, and loss of AGR2 has led to impaired mucin production and the induction of epithelial ER stress (9). In addition to roles in oxidative protein folding, some PDI family members have been shown to participate in ER-associated degradation, trafficking, and calcium homeostasis (11)(12)(13).…”

“…Methods for real-time quantitative PCR and PCR-based analysis of Xbp1 splicing have been previously described (9). Transcript copy number was determined relative to the mean cycle threshold for three housekeeping genes (Actin, GADPH, and Cyclophilin A).…”