Expression patterns of l-amino acid receptors in the murine STC-1 enteroendocrine cell line
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Regulation of gut function depends on the detection and response to luminal contents. Luminal l-amino acids (l-AA) are detected by several receptors including metabotropic glutamate receptors 1 and 4 (mGluR1 and mGluR4), calcium-sensing receptor (CaSR), GPRC family C group 6 subtype A receptor (GPRC6A) and umami taste receptor heterodimer T1R1/T1R3. Here, we show that murine mucosal homogenates and STC-1 cells, a murine enteroendocrine cell line, express mRNA for all l-AA receptors. Immunohistochemical analysis demonstrated the presence of all l-AA receptors on STC-1 with CaSR being most commonly expressed and T1R1 least expressed (35% versus 15% of cells); mGluRs and GPRC6a were intermediate (~ 20% of cells). Regarding coexpression of l-AA receptors, the mGluRs and T1R1 were similarly coexpressed with CaSR (10–12% of cells) whereas GPRC6a was coexpressed least (7% of cells). mGluR1 was coexpressed with GPRC6a in 11% of cells whereas coexpression between other receptors was less (2–8% of cells). CaSR and mGluR1 were coexpressed with glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) in 20–25% of cells whereas T1R1 and GPRC6a were coexpressed with GLP-1 and PYY less (8–12% of cells). Only mGluR4 showed differential coexpression with GLP-1 (13%) and PYY (21%). l-Phenylalanine (10 mM) caused a 3-fold increase in GLP-1 release, which was strongly inhibited by siRNA to CaSR indicating functional coupling of CaSR to GLP-1 release. The results suggest that not all STC-1 cells express (and coexpress) l-AA receptors to the same extent and that the pattern of response likely depends on the pattern of expression of l-AA receptors.
KeywordsEnteroendocrine cells Taste receptors l-Amino acid receptors STC-1 cells Neurohumoral peptides
This work was supported by the National Institute of Diabetes and Digestive and Kidney Diseases grants DK-15564 (KSM), DK-28300 (KSM) and DK-34153 (JRG). This work was also supported by grants to the Virginia Commonwealth University from the National Center for Advancing Translational Sciences UL1TR002649 (HW) and the Center for Clinical and Translational Research Endowment Fund of Virginia Commonwealth University (HW).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national and institutional guidelines for the care and use of animals were followed. All animal procedures were performed according to a protocol approved by the Institutional Animal Care and Use Committee of Virginia Commonwealth University.
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