title: Distinct kinetic and spatial patterns of protein kinase C (PKC)- and epidermal growth factor receptor (EGFR)-dependent activation of extracellular signal-regulated kinases 1 and 2 by human nicotinic acid receptor GPR109A.
abstract: Nicotinic acid (niacin) has been widely used as a lipid-lowering drug for several decades, and recently, orphan G protein-coupled receptor GPR109A has been identified as a receptor for niacin. Mechanistic investigations have shown that, upon niacin activation, GPR109A couples to a G(i) protein and inhibits adenylate cyclase activity, leading to inhibition of liberation of free fatty acid. However, the underlying molecular mechanisms for GPR109A signaling remain largely unknown. Using CHO-K1 cells stably expressing GPR109A and A431 cells, which are a human epidermoid cell line with high levels of endogenous expression of functional GPR109A receptors, we found that activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) by niacin was rapid, peaking at 5 min, and was significantly blocked by pertussis toxin. Furthermore, time course experiments with different kinase inhibitors demonstrated that GPR109A induced ERK1/2 activation via the matrix metalloproteinase/epidermal growth factor receptor transactivation pathway at both early and later time points (2-5 min); this pathway was distinct from the PKC pathway-mediated ERK1/2 phosphorylation that occurs at early time points (≤2 min) in response to niacin. Overexpression of Gβγ subunit scavengers βARK1-CT and the Gα subunit of transducin led to a significant reduction of ERK1/2 phosphorylation, suggesting a critical role for βγ subunits in GPR109A-activated ERK1/2 phosphorylation. Using arrestin-2/3-specific siRNA and an internalization-deficient GPR109A mutant, we found that arrestin-2 and arrestin-3 were not involved in GPR109A-mediated ERK1/2 activation. In conclusion, our findings demonstrate that upon binding to niacin GPR109A receptors initially activate G(i), leading to dissociation of the Gβγ subunit from activated G(i), and subsequently induce ERK1/2 activation via two distinct pathways, one PKC-dependent pathway occurring at a peak time of ≤2 min and the other matrix metalloproteinase-dependent growth factor receptor transactivation occurring at both early and later time points (2-5 min).
authors.affiliation: Institute of Biochemistry, College of Life Science, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, China.
authors.forename: Guo
authors.initials: G
authors.lastname: Li
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Deng
authors.forename: Chun
authors.initials: C
authors.lastname: Wu
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Linjie
authors.initials: L
authors.lastname: Chen
authors.forename: Ying
authors.initials: Y
authors.lastname: Shi
authors.forename: Haishan
authors.initials: H
authors.lastname: Huang
authors.forename: Naiming
authors.initials: N
authors.lastname: Zhou
mesh_terms: D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D045726:Metalloproteases; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009525:Niacin / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors
chemical_list: C530636:HCAR2 protein, human; D043562:Receptors, G-Protein-Coupled; D011978:Receptors, Nicotinic; D009525:Niacin; D066246:ErbB Receptors; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D045726:Metalloproteases