Asthma triggers upregulate the expression and directly cleave GSDMB
Ronald Allan M. Panganiban1, Michael O’Sullivan1, Mengyuan Kan2, Blanca Himes2, Jin-ah Park1, and Quan Lu1
1Program in Molecular and Integrative Physiological Sciences, Harvard T.H. Chan School of Public Health, Boston, MA 02115
2Department of Biostatistics, Epidemiology and Informatics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
Asthma is a complex airway disease caused by a poorly understood interplay between environmental and genetic factors. Genome-wide association studies (GWAS) have identified numerous asthma-associated genes including GSDMB, a gasdermin family member that resides in 17q21 locus, the strongest and most replicated asthma GWAS signal. However, the functional role of GSDMB in asthma remains incompletely understood. Our previous work demonstrated that 1) caspase-1 cleaves GSDMB to liberate the N-terminal fragment which induces pyroptosis, a recently characterized mode of pro-inflammatory cell death; 2) a functional splice variant of GSDMB (rs11078928) associated with lower asthma risk abolishes GSDMB’s ability to induce pyroptosis; and 3) GSDMB is highly expressed in the airway epithelium, the airway’s first line of defense against asthma triggers. While these findings strongly implicate GSDMB as a bona fide asthma gene that mediates airway epithelial pyroptosis, it remains unclear how and whether asthma triggers affect GSDMB expression and function. Using in vitro cleavage assay, we show that GSDMB is cleaved directly by house dust mite (HDM), mold, and cockroach extracts. We also show that the GSDMB cleavage site for HDM is different from the cleavage site for caspase-1, which we previously demonstrated to be at Asp236. On the other hand, treatment of human bronchial epithelial cells cultured at the air-liquid interface (HBE-ALI) with rhinovirus A (RVA), but neither mechanical compression nor HDM, induces ~2 fold increase in GSDMB expression compared to untreated control. GSDMB promoter analysis by ContraV3 identifies a GATA-2 consensus binding site within the 1.0 kb promoter region upstream of GSDMB transcription start site suggesting that RVA possibly induces the transcription factor GATA-2 to promote GSDMB expression. Our data provides clues to the effect of different asthma triggers on GSDMB and reveals insights into the possible mechanistic link between asthma triggers and airway epithelial pyroptosis. Future studies are aimed at identifying the specific GSDMB cleavage sites for the asthma triggers, identifying the specific proteases in the asthma trigger extracts capable of cleaving GSDMB, as well as investigating the effects of multiple exposures to asthma triggers (e.g. RVA and HDM extracts) on GSDMB and pyroptosis.