DR5 Governs Compound Exocytosis in Colonic Goblet Cells via TATA-Box Binding Protein-Dependent Bestrophin-2 Transcriptional Regulation.

The colonic mucus barrier, dependent on goblet cell-secreted mucin2 (Muc2), prevents microbial invasion. Compound exocytosis enables the rapid, high-volume release of mucus from goblet cells; its underlying mechanisms, however, remain unclear. Here, death receptor 5 (DR5) is identified as a critical regulator of this process. Knockout of DR5 exhibits a thinner mucus layer despite elevated Muc2 and enlarged granules, causing mild dysbiosis and enhances susceptibility to Citrobacter rodentium. DR5 knockout and its ligand TRAIL knockdown inhibits carbachol-triggered goblet cell compound exocytosis, while DR5-activator Bioymifi potentiates it. DR5 modulates intracellular pH through the colonic goblet cell-expressed HCO3 - channel Bestrophin-2 (Best2). TRAIL/DR5/Best2 co-localize in goblet cells, and Best2 knockdown abolishes DR5's pro-exocytosis effect. Proteomics and bioinformatic analyses implicate TATA-box binding protein (TBP) in the death domain-dependent transcriptional regulation of Best2 by DR5. This is supported by TBP-BEST2 promoter binding, as well as enhanced BEST2 mRNA expression and promoter activity upon TBP overexpression. DR5 knockout suppresses TBP expression in colonic goblet cells, while activation increases it. Moreover, TBP knockdown abrogates Bioymifi-enhanced Best2 expression and compound exocytosis. The findings demonstrate that disruption of the DR5-TBP-Best2 axis in goblet cells perturbs goblet cell compound exocytosis and mucus layer formation, resulting in dysbiosis and heightened infection susceptibility.