Abstract
Interleukin (IL)-22 is a cytokine that plays a critical role in intestinal epithelial homeostasis. Its downstream functions are mediated through interaction with the heterodimeric IL-22 receptor and subsequent activation of signal transducer and activator of transcription 3 (STAT3). IL-22 signaling can induce transcription of genes necessary for intestinal epithelial cell proliferation, tissue regeneration, tight junction fortification, and antimicrobial production. Recent studies have also implicated IL-22 signaling in the regulation of intestinal epithelial fucosylation in mice. However, whether IL-22 regulates intestinal fucosylation in human intestinal epithelial cells and the molecular mechanisms that govern this process are unknown. Here, in experiments performed in human cell lines and human-derived enteroids, we show that IL-22 signaling regulates expression of the B3GNT7 transcript, which encodes a β1-3-N-acetylglucosaminyltransferase that can participate in the synthesis of poly-N-acetyllactosamine (polyLacNAc) chains. Additionally, we find that IL-22 signaling regulates levels of the α1-3-fucosylated Lewis X (Lex) blood group antigen, and that this glycan epitope is primarily displayed on O-glycosylated intestinal epithelial glycoproteins. Moreover, we show that increased expression of B3GNT7 alone is sufficient to promote increased display of Lex-decorated carbohydrate glycan structures primarily on O-glycosylated intestinal epithelial glycoproteins. Together, these data identify B3GNT7 as an intermediary in IL-22-dependent induction of fucosylation of glycoproteins and uncover a novel role for B3GNT7 in intestinal glycosylation.
Highlights
Unlike observations in the mouse, where IL-22 signaling regulates the synthesis of glycan structures decorated with α1-2- [11] or α1-3-linked fucose (Fig. S3C), IL-22 signaling in human intestinal epithelial cells only led to the enhanced synthesis of α1-3-fucosylated glycan structures (Fig. S3A) including the terminally α1-3fucosylated carbohydrate epitope, Lewis X (Lex) (Fig. 4)
Lex belongs to the human histo-blood group antigen system, and its synthesis is primarily attributed to the expression of FUT4 and FUT9, encoding enzymes that catalyze the transfer of fucose to the acceptor substrate, galactose (Gal) and N-acetylglucosamine (GlcNAc) in an α1-3-linkage [31, 36]
We note that IL-22-dependent induction of β1-3-N-acetylglucosaminyltransferase 7 (B3GNT7) was moderate in Caco-2 BBe1 cells, which are commonly used to model of the small intestine, and more robust in T84 cells, which are morphologically and biochemically more similar to the colon [18]; the mechanism underlying this difference may be worthy of further investigation
Summary
We report that IL-22 signaling in human intestinal epithelial cells modulates expression of the B3GNT7 transcript and induces α1-3-fucosylation of glycoproteins, including those displaying mucosal O-linked glycans. We found that B3GNT7 gene expression is upregulated by IL-22 in differentiated Caco-2 BBe1 cells (approximately fivefold increase; Fig. 1B). To determine whether B3GNT7 gene expression was dependent on STAT3 activation, we incubated differentiated Caco-2 BBe1 cells with 0.5 μM niclosamide, a pharmacological inhibitor of STAT3 signaling [21], or vehicle control.
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