Min Pi1, Karan Kapoor2, Ruisong Ye1, Jeremy C Smith2,3, Jerome Baudry2,3, Leigh D Quarles1. 1. Department of Medicine, University of Tennessee Health Science Center, 19 S Manassas St., Memphis, TN, 38163, USA. 2. UT/ORNL Center for Molecular Biophysics, Oak Ridge, TN, 37830, USA. 3. Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA.
Abstract
SCOPE: The molecular mechanisms whereby gallates in green tea exert metabolic effects are poorly understood. METHODS AND RESULTS: We found that GPRC6A, a multi-ligand-sensing G-protein-coupled receptor that regulates energy metabolism, sex hormone production, and prostate cancer progression, is a target for gallates. Sodium gallate (SG), gallic acid (GA) > ethyl gallate (EG) > octyl gallate (OG) dose dependently activated ERK in HEK-293 cells transfected with GPRC6A but not in non-transfected controls. SG also stimulated insulin secretion in β-cells isolated from wild-type mice similar to the endogenous GPRC6A ligands, osteocalcin (Ocn) and testosterone (T). Side-chain additions to create OG resulted in loss of GPRC6A agonist activity. Another component of green tea, epigallocatechin 3-gallate (EGCG), dose-dependently inhibited Ocn activation of GPRC6A in HEK-293 cells transfected with GPRC6A and blocked the effect of Ocn in stimulating glucose production in CH10T1/2 cells. Using structural models of the venus fly trap (VFT) and 7-transmembrane (7-TM) domains of GPRC6A, calculations suggest that l-amino acids and GA bind to the VFT, whereas EGCG is calculated to bind to sites in both the VFT and 7-TM. CONCLUSION: GA and EGCG have offsetting agonist and antagonist effects on GPRC6A that may account for the variable metabolic effect of green tea consumption.
SCOPE: The molecular mechanisms whereby gallates in green tea exert metabolic effects are poorly understood. METHODS AND RESULTS: We found that GPRC6A, a multi-ligand-sensing G-protein-coupled receptor that regulates energy metabolism, sex hormone production, and prostate cancer progression, is a target for gallates. Sodium gallate (SG), gallic acid (GA) > ethyl gallate (EG) > octyl gallate (OG) dose dependently activated ERK in HEK-293 cells transfected with GPRC6A but not in non-transfected controls. SG also stimulated insulin secretion in β-cells isolated from wild-type mice similar to the endogenous GPRC6A ligands, osteocalcin (Ocn) and testosterone (T). Side-chain additions to create OG resulted in loss of GPRC6A agonist activity. Another component of green tea, epigallocatechin 3-gallate (EGCG), dose-dependently inhibited Ocn activation of GPRC6A in HEK-293 cells transfected with GPRC6A and blocked the effect of Ocn in stimulating glucose production in CH10T1/2 cells. Using structural models of the venus fly trap (VFT) and 7-transmembrane (7-TM) domains of GPRC6A, calculations suggest that l-amino acids and GA bind to the VFT, whereas EGCG is calculated to bind to sites in both the VFT and 7-TM. CONCLUSION:GA and EGCG have offsetting agonist and antagonist effects on GPRC6A that may account for the variable metabolic effect of green tea consumption.
Authors: Min Pi; Karan Kapoor; Ruisong Ye; Dong-Jin Hwang; Duane D Miller; Jeremy C Smith; Jerome Baudry; L Darryl Quarles Journal: PLoS One Date: 2018-04-23 Impact factor: 3.240
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