Carbachol-induced MUC17 endocytosis is concomitant with NHE3 internalization and CFTR membrane recruitment in...

Area of Science:

• Cell Biology
• Gastroenterology
• Epithelial Biology

Background:

• Transmembrane mucins MUC17, MUC3, and MUC12 contribute to the enterocyte apical glycocalyx.
• MUC17 interacts with PDZ protein PDZK1, anchoring it to the apical surface.
• Goblet cell secretion of gel-forming mucins is triggered by carbachol (CCh) and requires enterocyte ion secretion.

Purpose of the Study:

• To investigate the dynamic behavior of MUC17 in enterocytes upon CCh stimulation.
• To understand the relationship between MUC17 trafficking and ion channel function during mucus secretion.
• To elucidate the role of MUC17 in the apical glycocalyx and its response to physiological stimuli.

Main Methods:

• Surface labeling and confocal microscopy in Caco-2 cells and murine enterocytes.
• Stimulation with carbachol (CCh) to induce physiological responses.
• Analysis of MUC17 colocalization with PDZK1, terminal web, and early endosomes.
• Assessment of ion channel (CFTR, NHE3) localization and activity.

Main Results:

• Apically expressed MUC17 undergoes endocytosis upon CCh stimulation, unlike MUC3 and MUC12.
• MUC17 relocates to the terminal web and early endosomes post-CCh stimulation.
• CCh stimulation leads to internalization of Na+/H+ exchanger 3 (NHE3) and recruitment of CFTR to apical membranes.
• CFTR-mediated bicarbonate secretion is crucial for gel-forming mucin unfolding.

Conclusions:

• CCh stimulation orchestrates a specific trafficking response of MUC17, distinct from other transmembrane mucins.
• The dynamic MUC17 endocytosis may regulate the apical glycocalyx diffusion barrier or facilitate bacterial sampling.
• These findings reveal a coordinated process involving mucus secretion, ion channel dynamics, and MUC17 mucin trafficking in the small intestine.