The COG and COPI Complexes Interact to Control the Abundance of GEARs, a Subset of Golgi Integral Membrane Proteins

Abstract

The conserved oligomeric Golgi (COG) complex is a soluble hetero-octamer associated with the cytoplasmic surface of the Golgi. Mammalian somatic cell mutants lacking the Cog1 (ldlB) or Cog2 (ldlC) subunits exhibit pleiotropic defects in Golgi-associated glycoprotein and glycolipid processing that suggest COG is involved in the localization, transport, and/or function of multiple Golgi processing proteins. We have identified a set of COG-sensitive, integral membrane Golgi proteins called GEARs (mannosidase II, GOS-28, GS15, GPP130, CASP, giantin, and golgin-84) whose abundances were reduced in the mutant cells and, in some cases, increased in COG-overexpressing cells. In the mutants, some GEARs were abnormally localized in the endoplasmic reticulum and were degraded by proteasomes. The distributions of the GEARs were altered by small interfering RNA depletion of ⑀-COP in wild-type cells under conditions in which COG-insensitive proteins were unaffected. Furthermore, synthetic phenotypes arose in mutants deficient in both ⑀-COP and either Cog1 or Cog2. COG and COPI may work in concert to ensure the proper retention or retrieval of a subset of proteins in the Golgi, and COG helps prevent the endoplasmic reticulum accumulation and degradation of some GEARs. INTRODUCTIONSeveral multisubunit peripheral membrane protein complexes are thought to play key roles in controlling Golgiassociated membrane trafficking and glycoconjugate processing (Waters et al., 1991;Barlowe et al., 2002;Schekman and Orci, 1996;Sacher et al., 1998;Siniossoglou and Pelham, 2001;Conibear et al., 2003;Storrie and Nilsson 2002;Roth, 2002). One of these is the conserved oligomeric Golgi (COG) complex (Krieger et al., 1981;Kingsley et al., 1986;Podos et al., 1994;Wuestehube et al., 1996;VanRheenen et al., 1998VanRheenen et al., , 1999Walter et al., 1998;Chatterton et al., 1999;Kim et al., 1999Kim et al., , 2001Spelbrink and Nothwehr, 1999;Whyte and Munro, 2001;Loh and Hong, 2002;Ram et al., 2002;Suvorova et al., 2002;Ungar et al., 2002;Farkas et al., 2003). Mutations in COG subunits (Cog1-8) have been shown to affect the structure and function of the Golgi in yeast, Drosophila melanogaster sperm, and mammalian somatic cells. Compromising COG function can cause defects in glycoconjugate synthesis, intracellular protein sorting, protein secretion and, in some cases, cell growth. For example, in mammalian recessive, null, Chinese hamster ovary (CHO) cell mutants called ldlB (Cog1-negative) and ldlC (Cog2-negative), multiple cisternae are dilated (Ungar et al., 2002), and there are pleiotropic defects in a number of medial-and trans-Golgi-associated reactions affecting virtually all N-linked, O-linked, and lipid-linked glycoconjugates (Kingsley et al., 1986). These glycoconjugate defects are somewhat reminiscent of those in brefeldin A-treated cells, in which the Golgi disintegrates and early Golgi processing enzymes are relocated to the endoplasmic reticulum (ER) (Doms et al., 1989;Perkel et al., 1989;van Echten et al., 1990;Sampath et al., 1992). The...

Molecular and clinical characterization of a Moroccan Cog7 deficient patient

“…Sequence analysis of Cog7 and Peanut lectin binding was performed as previously described by Wu et al [3] Western Blotting has been performed as previously described by Oka et al [10] Brefeldin A retrograde trafficking was carried out as previously described by Steet et al [11] …”

“…Cog7 deficient fibroblasts, treated with Brefeldin A, have been shown to have a delay in retrograde transport into the ER [10]. We compared these patient cells against control cells for impaired retrograde transport kinetics by incubating cells with 0.25ug/ml of BFA for different times.…”

Mutations inCog7affect Golgi structure, meiotic cytokinesis and sperm development duringDrosophilaspermatogenesis

“…Mutations in the genes encoding human COG1, COG4-COG8 have been associated with congenital disorders of glycosylation (CDG) (Foulquier et al, 2006Foulquier et al, 2007Kranz et al, 2007;Lübbehusen et al, 2010;Ng et al, 2007;Paesold-Burda et al, 2009;Reynders et al, 2009;Spaapen et al, 2005;Steet and Kornfeld, 2006;Wu et al, 2004) indicating a role for COG in the transport and/or stability of Golgi glycosylation enzymes. Indeed studies in both yeast and mammalian cells have suggested that COG complex might function as a vesicle-tethering factor in intra-Golgi retrograde COPI transport (Ungar et al, 2002), thus regulating the distribution and the stability of Golgi resident proteins (Oka et al, 2004;Shestakova et al, 2006;Suvorova et al, 2001;Suvorova et al, 2002;Walter et al, 1998). A set of Golgi proteins called GEARs including giantin matrix proteins and glycosyltransferases/ glycosidases were shown to mislocalize and to be abnormally degraded in Chinese hamster ovary (CHO) cells mutant for either Cog1 or Cog2 subunits (Oka et al, 2004).…”

“…Indeed studies in both yeast and mammalian cells have suggested that COG complex might function as a vesicle-tethering factor in intra-Golgi retrograde COPI transport (Ungar et al, 2002), thus regulating the distribution and the stability of Golgi resident proteins (Oka et al, 2004;Shestakova et al, 2006;Suvorova et al, 2001;Suvorova et al, 2002;Walter et al, 1998). A set of Golgi proteins called GEARs including giantin matrix proteins and glycosyltransferases/ glycosidases were shown to mislocalize and to be abnormally degraded in Chinese hamster ovary (CHO) cells mutant for either Cog1 or Cog2 subunits (Oka et al, 2004). Depletion of Cog3 in HeLa cells resulted in the accumulation of COG complexdependent (CCD) vesicles carrying Golgi v-SNARE proteins but no anterograde cargo molecules (Zolov and Lupashin, 2005).…”

Congenital disorders of glycosylation: a concise chart of glycocalyx dysfunction

“…The Conserved Oligomeric Golgi (COG) complex orchestrates the recycling of medial-and cis-Golgi resident proteins by acting as a tether to connect COPI vesicles with cis-Golgi membranes [49]. COG defects lead to abnormal glycosylation [50] because of missorting of 6 glycosylation enzymes and sugar transporters [51]. Whereas multiple classes of glycosylation are impaired, COG-related disorders are usually identified by detection of underglycosylated serum transferrin just like defects of N-glycosylation.…”