title: A cyclooxygenase-2-dependent prostaglandin E2 biosynthetic system in the Golgi apparatus.
abstract: Cyclooxygenases (COXs) catalyze the committed step in prostaglandin (PG) biosynthesis. COX-1 is constitutively expressed and stable, whereas COX-2 is inducible and short lived. COX-2 is degraded via endoplasmic reticulum (ER)-associated degradation (ERAD) following post-translational glycosylation of Asn-594. COX-1 and COX-2 are found in abundance on the luminal surfaces of the ER and inner membrane of the nuclear envelope. Using confocal immunocytofluorescence, we detected both COX-2 and microsomal PGE synthase-1 (mPGES-1) but not COX-1 in the Golgi apparatus. Inhibition of trafficking between the ER and Golgi retarded COX-2 ERAD. COX-2 has a C-terminal STEL sequence, which is an inefficient ER retention signal. Substituting this sequence with KDEL, a robust ER retention signal, concentrated COX-2 in the ER where it was stable and slowly glycosylated on Asn-594. Native COX-2 and a recombinant COX-2 having a Golgi targeting signal but not native COX-1 exhibited efficient catalytic coupling to mPGES-1. We conclude that N-glycosylation of Asn-594 of COX-2 occurs in the ER, leading to anterograde movement of COX-2 to the Golgi where the Asn-594-linked glycan is trimmed prior to retrograde COX-2 transport to the ER for ERAD. Having an inefficient ER retention signal leads to sluggish Golgi to ER transit of COX-2. This permits significant Golgi residence time during which COX-2 can function catalytically. Cytosolic phospholipase A2α, which mobilizes arachidonic acid for PG synthesis, preferentially translocates to the Golgi in response to physiologic Ca(2+) mobilization. We propose that cytosolic phospholipase A2α, COX-2, and mPGES-1 in the Golgi comprise a dedicated system for COX-2-dependent PGE2 biosynthesis.
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Chong
authors.initials: C
authors.lastname: Yuan
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 smithww@med.umich.edu.
authors.forename: William L
authors.initials: WL
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000235:genetics / Q000378:metabolism; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D060746:Endoplasmic Reticulum-Associated Degradation / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D054513:Group IV Phospholipases A2 / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D019746:Intramolecular Oxidoreductases / Q000235:genetics / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D018613:Microscopy, Confocal; D009154:Mutation; D041681:NIH 3T3 Cells; D000071876:Prostaglandin-E Synthases; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007546:Isoquinolines; D007976:Leupeptins; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D001216:Asparagine; D051546:Cyclooxygenase 2; D054513:Group IV Phospholipases A2; D019746:Intramolecular Oxidoreductases; C000605862:PTGES protein, human; D000071876:Prostaglandin-E Synthases; C000605865:Ptges protein, mouse; D015232:Dinoprostone; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
keywords: Arachidonic Acid (AA) (ARA); Aspirin; COPII; Coxib; Cyclooxygenase (COX); Degron; Endoplasmic Reticulum-associated Protein Degradation (ERAD); Glycoprotein; NSAID; Prostaglandin