title: Modulation of D-serine levels via ubiquitin-dependent proteasomal degradation of serine racemase.
abstract: Mammalian serine racemase is a brain-enriched enzyme that converts L- into D-serine in the nervous system. D-Serine is an endogenous co-agonist at the "glycine site" of N-methyl D-aspartate (NMDA) receptors that is required for the receptor/channel opening. Factors regulating the synthesis of D-serine have implications for the NMDA receptor transmission, but little is known on the signals and events affecting serine racemase levels. We found that serine racemase interacts with the Golgin subfamily A member 3 (Golga3) protein in yeast two-hybrid screening. The interaction was confirmed in vitro with the recombinant proteins in co-transfected HEK293 cells and in vivo by co-immunoprecipitation studies from brain homogenates. Golga3 and serine racemase co-localized at the cytosol, perinuclear Golgi region, and neuronal and glial cell processes in primary cultures. Golga3 significantly increased serine racemase steady-state levels in co-transfected HEK293 cells and primary astrocyte cultures. This observation led us to investigate mechanisms regulating serine racemase levels. We found that serine racemase is degraded through the ubiquitin-proteasomal system in a Golga3-modulated manner. Golga3 decreased the ubiquitylation of serine racemase both in vitro and in vivo and significantly increased the protein half-life in pulse-chase experiments. Our results suggest that the ubiquitin system is a main regulator of serine racemase and D-serine levels. Modulation of serine racemase degradation, such as that promoted by Golga3, provides a new mechanism for regulating brain d-serine levels and NMDA receptor activity.
authors.affiliation: Department of Biochemistry, The Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel.
authors.forename: Elena
authors.initials: E
authors.lastname: Dumin
authors.forename: Inna
authors.initials: I
authors.lastname: Bendikov
authors.forename: Veronika N
authors.initials: VN
authors.lastname: Foltyn
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Misumi
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ikehara
authors.forename: Elena
authors.initials: E
authors.lastname: Kartvelishvily
authors.forename: Herman
authors.initials: H
authors.lastname: Wolosker
mesh_terms: D000818:Animals; D001324:Autoantigens; D002458:Cell Fractionation; D002460:Cell Line; D002478:Cells, Cultured; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007536:Isomerism; D007668:Kidney; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008565:Membrane Proteins; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D019998:Racemases and Epimerases / Q000235:genetics / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism*; D000099300:Serine Racemase
chemical_list: D001324:Autoantigens; D005998:Glycine; D007770:L-Lactate Dehydrogenase; D008565:Membrane Proteins; D046988:Proteasome Endopeptidase Complex; D011506:Proteins; D019998:Racemases and Epimerases; D016194:Receptors, N-Methyl-D-Aspartate; D011994:Recombinant Proteins; D012694:Serine; D025801:Ubiquitin; D000099300:Serine Racemase; C512726:Golga3 protein, mouse; C512727:MEA1 protein, human; C512728:Mea1 protein, mouse