Ric-8A and Ric-8B are positive regulators of heterotrimeric G protein a subunit function. We have recently defined the cellular action of Ric-8 proteins towards Ga subunits. Ric-8 proteins act as molecular chaperones of nucleotide-free Ga conformations during biosynthetic Ga protein folding. In cells in which Ric-8 genes are deleted, cellular abundances of subsets of Ga subunits were reduced by 95%. Ric-8 proteins also exhibit in vitro guanine nucleotide exchange stimulatory activity towards Ga subunits, and we now believe this to be an in vitro phenomenon stemming from the capacity of Ric-8 to induce a partially folded Ga state that has reduced affinity for GDP. We will develop our hypothesis that Ric-8 proteins are Ga subunit molecular chaperones and investigate the mechanisms by which Ric-8 proteins work with other cellular chaperones including the TRiC/CCT (Chaperonin) complex and HSC70/90 systems to fold individual Ga subunits. We have preliminary evidence that there are complex rules and unique chaperone requirements of individual Ga subunits. We will then test a hypothesis that mouse tissue-specific Ric-8A gene deletion can genetically suppress oncogenic G protein or overactive GPCR-driven cancers. Two mouse melanoma models will be used in which GNAQ/11-Q209L (constitutively-active) alleles are the oncogenic driver mutations of metastatic ocular melanoma, and ectopic mGluR5 expression from a melanocyte promoter elicited robust melanoma. We hypothesize that melanocyte mGluR5 inappropriately activates Gq/11 to promote melanoma. Upon proof-of-concept that Ric-8 deletion will suppress the actions of these oncogenes by reducing Gaq/11 cellular abundances, we will perform screens to identify small molecule inhibitors of Ric-8 and G protein interactions. Our goal is to develop Ric-8 inhibitors as a means to indirectly block G protein disease signaling by reducing the abundance of (mutant) Ga subunits folded by Ric-8. Ric-8 inhibitors may prove efficacious against oncogenic G protein diseases and/or as augmentation therapies for existing GPCR therapeutics. We will also conduct a small project to investigate Ric-8A regulation by phosphorylation events and 14-3-3 binding to Ric-8A.

Public Health Relevance

Ric-8 proteins are newly defined regulators of heterotrimeric G protein a subunit biosynthetic production. G proteins transduce drug, hormone, and neurotransmitter influence into physiological cellular actions. The mechanisms by which Ric-8 proteins aid G protein production will be investigated and means of blocking Ric-8 proteins as a way to reduce G protein abundances in pathophysiological states will be explored.

National Institute of Health (NIH)
Research Project (R01)
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Molecular and Integrative Signal Transduction Study Section (MIST)
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Gaillard, Shawn R
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University of Rochester
School of Medicine & Dentistry
United States
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Tall, Gregory G (2013) Ric-8 regulation of heterotrimeric G proteins. J Recept Signal Transduct Res 33:139-43
Oner, Sukru Sadik; Maher, Ellen M; Gabay, Meital et al. (2013) Regulation of the G-protein regulatory-Gýýi signaling complex by nonreceptor guanine nucleotide exchange factors. J Biol Chem 288:3003-15
Thomas, Celestine J; Briknarová, Klára; Hilmer, Jonathan K et al. (2011) The nucleotide exchange factor Ric-8A is a chaperone for the conformationally dynamic nucleotide-free state of G?i1. PLoS One 6:e23197
Chan, PuiYee; Gabay, Meital; Wright, Forrest A et al. (2011) Ric-8B is a GTP-dependent G protein alphas guanine nucleotide exchange factor. J Biol Chem 286:19932-42
Pashkov, Victor; Huang, Jie; Parameswara, Vinay K et al. (2011) Regulator of G protein signaling (RGS16) inhibits hepatic fatty acid oxidation in a carbohydrate response element-binding protein (ChREBP)-dependent manner. J Biol Chem 286:15116-25
Chan, PuiYee; Gabay, Meital; Wright, Forrest A et al. (2011) Purification of heterotrimeric G protein alpha subunits by GST-Ric-8 association: primary characterization of purified G alpha(olf). J Biol Chem 286:2625-35
Vellano, Christopher P; Shu, Feng-Jue; Ramineni, Suneela et al. (2011) Activation of the regulator of G protein signaling 14-G?i1-GDP signaling complex is regulated by resistance to inhibitors of cholinesterase-8A. Biochemistry 50:752-62
Gabay, Meital; Pinter, Mary E; Wright, Forrest A et al. (2011) Ric-8 proteins are molecular chaperones that direct nascent G protein * subunit membrane association. Sci Signal 4:ra79
Woodard, Geoffrey E; Huang, Ning-Na; Cho, Hyeseon et al. (2010) Ric-8A and Gi alpha recruit LGN, NuMA, and dynein to the cell cortex to help orient the mitotic spindle. Mol Cell Biol 30:3519-30