Trefoil peptide expression and secretion is regulated by neuropeptides and acetylcholine

Trefoil peptides are a family of small proteins expressed by goblet cells that are secreted onto the apical gastrointestinal mucosal surface, where they are present in high concentrations. These peptides appear to both protect the epithelium and promote hearing after injury. However, the factors regulating the expression and secretion of these proteins contributing to mucosal defense have not been characterized. To determine the mechanisms controlling production of trefoil peptides, the human colon cancer-derived model cell line HT-29 was exposed to a variety of potential secretagogues. Expression and secretion of human intestinal trefoil factor (hITF) as well as the intestinal apomucin MUC2 were assessed by Northern and Western blot analysis. Carbachol, an analog of acetylcholine, and the neuroendocrine peptides somatostatin and vasoactive intestinal polypeptide (VIP) stimulated increased expression of hITF mRNA within 5 min. These same factors stimulated parallel secretion of the hITF peptide, with maximal stimulation observed at concentrations ranging from 10^-6 M (carbachol and somatostatin) to 10^-7 M (VIP). Expression and secretion of hITF in response to carbachol, VIP, and somatostatin was independent of production of apomucin. hITF was not regulated by other neuroendocrine transmitters including histamine and substance P. Similarly, hITF expression and secretion was not modulated by peptide growth factors (epidermal growth factor, transforming growth factor- β, and keratinocyte growth factor), cytokines [interleukin (IL)-1β, IL-2, IL-7, and IL-11], or arachidonic acid metabolites (prostaglandin E₁/E₂ and leukotriene B₄). In conclusion, trefoil peptides appear to be integrated into mechanisms of mucosal defense and repair through the enteric neuroendocrine system and independent of the classical mucosal immune cytokine network.