β-Catenin (CTNNB1) Promotes Preovulatory Follicular Development but Represses LH-Mediated Ovulation and Luteinization

摘要

Melanocortin-4 receptor (MC4R) is a G protein-coupled receptor expressed in the brain where it controls food intake. Manyobesity-linked MC4R variants are poorly expressed at the plasma membrane and are retained intracellularly. We have studied theintracellular localization of four obesity-linked MC4R variants, P78L, R165W, I316S, and I317T, in immortalized neurons. We findthatthesevariantsareallretainedintheendoplasmicreticulum(ER),areubiquitinatedtoagreaterextentthanthewild-type(wt)receptor,andinduceERstresswithincreasedlevelsofERchaperonesascomparedwithwt-MC4RandappearanceofCCAAT/enhancer-bindingproteinhomologousprotein.ExpressionoftheX-box-binding-protein-1withselectiveactivationofaprotectivebranchoftheunfolded protein response did not have any effect on the cell surface expression of MC4R-I316S. Conversely, the pharmacologicalchaperone4-phenylbutyricacid(PBA)increasedthecellsurfaceexpressionofwt-MC4R,MC4R-I316S,andI317Tbymorethan40%.PBAdecreased ubiquitination of MC4R-I316S and prevented ER stress induced by expression of the mutant, suggesting that the drugfunctionstopromoteMC4Rfolding.MC4R-I316Srescuedtothecellsurfaceisfunctional,witha52%increaseinagonist-inducedcAMPproduction,ascomparedwithuntreatedcells.Alsodirectinhibitionofwt-MC4RandMC4R-I316Subiquitinationbyaspecificinhibitoroftheubiquitin-activatingenzyme1increasedbyapproximately40%theexpressionofthereceptorsatthecellsurface,andtheeffectsofPBAandubiquitin-activatingenzyme1wereadditive.Thesedataofferacell-basedrationalethatdrugsthatimproveMC4Rfoldingor decrease ER-associated degradation of the receptor may function to treat some forms of hereditary obesity.