The SRC Family Tyrosine Kinase HCK and the ETS Family Transcription Factors SPIB and EHF Regulate Transcytosis across a Human Follicle-associated Epithelium Model

A critical step in the induction of adaptive mucosal immunity is antigen transcytosis, in which luminal antigens are transported to organized lymphoid tissues across the follicle-associated epithelium (FAE) of Peyer's patches. However, virtually nothing is known about intracellular signaling proteins and transcription factors that regulate apical-to-basolateral transcytosis. The FAE can transcytose a variety of luminal contents, including inert particles, in the absence of specific opsonins. Furthermore, it expresses receptors for secretory immunoglobulin A (SIgA), the main antibody in mucosal secretions, and uses them to efficiently transcytose SIgA-opsonized particles present in the lumen. Using a human FAE model, we show that the tyrosine kinase HCK regulates apical-to-basolateral transcytosis of non-opsonized and SIgA-opsonized particles. We also show that, in cultured intestinal epithelial cells, ectopic expression of the transcription factor SPIB or EHF is sufficient to activate HCK-dependent apical-to-basolateral transcytosis of these particles. Our results provide the first molecular insights into the intracellular regulation of antigen sampling at mucosal surfaces. Background: Antigen transcytosis across the follicle-associated epithelium is critical in the induction of adaptive mucosal immunity. Results: The transcription factors SPIB and EHF can independently induce the expression of transcytosis-related proteins, including the SRC family tyrosine kinase HCK. Conclusion: These transcription factors can serve as master regulators of antigen transcytosis. Significance: This is the first molecular characterization of the intracellular mechanism of antigen transcytosis.