Submitted on February 1, 2008
Accepted on June 9, 2008
The luminal regulation of normal and neoplastic human EC cell serotonin release is mediated by bile salts, amines, tastants and olfactants
Mark Kidd1, Irvin M. Modlin2*, Bjorn I Gustafsson3, Ignat Drozdov1, Oyvind Hauso4, and Roswitha Pfragner5
1 Surgery, Yale University School of Medicine, New Haven, Connecticut, United States
2 Surgery, Yale University School of Medicine, New Haven, Connecticut, United States; United States
3 Surgery, Yale University School of Medicine, New Haven, Connecticut, United States; Internal Medicine, Gastroenterology, St Olavs University Hospital HF, Trondheim, Norway
4 Molecular Biology and Cancer Research, NTNU, Trondheim, Norway
5 Institute of Pathophysiology, Centre for Molecular Medicine, Medical University of Graz, Graz, Austria; Institute of Pathophysiology and Immunology, Centre for Molecular Medicine, Medical University of Graz, Graz, Austria
* To whom correspondence should be addressed. E-mail: imodlin{at}optonline.net.
Introduction: Mechanisms by which gut luminal content regulates secretion and motility is ill-understood. We evaluated whether neuroendocrine enterochromaffin (EC) cells act as luminal-sensors for a wide variety of nutrients and defined the secretory mechanisms of this process.
Methods and Results: Pure (98-99%) FACS-sorted human EC cells and neoplastic EC cells (KRJ-I) were studied. RT-PCR identified transcripts for T2R1 (bitter), OR1G1 (class II olfactory) and trace amine (TAR1) GPCRs, and transporters for glutamine (SNAT1/2), glucose (GLUT1/3/SGLT1) and bile salts (ABST). Glutamine and sodium deoxycholate stimulated 5HT release (EC50=0.002-0.2µM; 2-fold release) but were 10-100x more potent in neoplastic EC cells which also secreted 6-13x more 5HT. Tastants (caffeine, tyramine, octopamine) and olfactants (thymol/eugenol), also stimulated normal and neoplastic EC cell 5HT secretion (EC50=1.2nM-2.1µMand 0.05nM-0.1µM release, respectively) while 2-deoxyglucose and the artificial sweetener, sucralose, stimulated (EC50=9.2nM and 0.38nM). 5HT release was associated with ERK phosphorylation (1.5-fold, p<0.02) and could be inhibited by a somatostatin analogue (IC50: 10-12M). Eleven secretory associated genes including the vesicle docking inhibitor, STXBP3, were up-regulated in response to glutamine and bile salt stimulation in neoplastic EC cells. Targeting STXBP3 expression using antisense knockdown significantly (p<0.05) reduced 5HT secretion.
Conclusions: EC cells express GPRCs and transporters for luminal tastants, olfactants, glutamine, glucose and bile salts. Activation includes a panel of secretory genes, ERK phosphorylation and 5HT secretion. Luminal EC cell regulation is likely to be as important as the G cell regulation in gastric acid secretion; development of agents to target EC cell function is a critical therapeutic goal.
