Targeted Cyclooxygenase Gene (Ptgs) Exchange Reveals Discriminant Isoform Functionality

Abstract

The prostaglandin G/H synthase enzymes, commonly termed COX-1 and COX-2, differ markedly in their responses to regulatory stimuli and their tissue expression patterns. COX-1 is the dominant source of "housekeeping" prostaglandins, whereas COX-2 synthesizes prostaglandins of relevance to pain, inflammation, and mitogenesis. Despite these distinctions, the two enzymes are remarkably conserved, and their subcellular distributions overlap considerably. To address the functional interchangeability of the two isozymes, mice in which COX-1 is expressed under COX-2 regulatory elements were created by a gene targeting "knock-in" strategy. In macrophages from these mice, COX-1 was shown to be lipopolysaccharide-inducible in a manner analogous to COX-2 in wild-type macrophages. However, COX-1 failed to substitute effectively for COX-2 in lipopolysaccharide-induced prostaglandin E 2 synthesis at low concentrations of substrate and in the metabolism of the endocannabinoid 2-arachidonylglycerol. The marked depression of the major urinary metabolite of prostacyclin in COX-2 null mice was only partially rescued by COX-1 knock-in, whereas the main urinary metabolite of prostaglandin E 2 was rescued totally. Replacement with COX-1 partially rescued the impact of COX-2 deletion on reproductive function. The renal pathology consequent to COX-2 deletion was delayed but not prevented, whereas the corresponding peritonitis was unaltered. Insertion of COX-1 under the regulatory sequences that drive COX-2 expression indicated that COX-1 can substitute for some COX-2 actions and rescue only some of the consequences of gene disruption. Manipulation of COX-2 also revealed a preference for coupling with distinct downstream prostaglandin synthases in vivo. These mice will provide a valuable reagent with which to elucidate the distinct roles of the COX enzymes in mammalian biology.

Histamine Directly and Synergistically with Lipopolysaccharide Stimulates Cyclooxygenase-2 Expression and Prostaglandin I2 and E2 Production in Human Coronary Artery Endothelial Cells

“…rpL7 mRNA expression was used for normalization. expression and TXA 2 production support the concept of a distinct coupling pattern of COX-2 with PGE 2 and PGI 2 synthases and that of COX-1 with TXA 2 synthase (25,26). It is intriguing that, despite the coexistence of both COX-1 and COX-2 in HCAEC, histamine is able to segregate its influence on COX-2/PGE 2 /PGI 2 pathway and not on COX-1/TXA 2 pathway.…”

Evaluation of the immunoexpression of COX-1, COX-2 and p53 in Crohn's disease

“…Cyclooxygenase (COX), an enzyme important for the synthesis of prostaglandins, is present in three isoforms. COX-1 shows low or constitutive expression in a variety of tissues (5,23,44) . COX-2 is highly inducible in response to cellular activation by hormones, proinflammatory cytokines, growth factors and tumor promoters (41,44) .…”

“…COX-1 shows low or constitutive expression in a variety of tissues (5,23,44) . COX-2 is highly inducible in response to cellular activation by hormones, proinflammatory cytokines, growth factors and tumor promoters (41,44) . COX-3, which is encoded by the same gene as the COX-1 isoform, has been demonstrated in vitro in macrophage lines (4,11,24) .…”

Two Pathways for Cyclooxygenase-2 Protein Degradation in Vivo

“…Each COX isoform subserves a distinct set of biologies (10 -12). Both the enzymatic properties and the patterns of expression of the isoforms contribute to their unique functions (12). In part because of the association of COX-2 expression with pathologies such as inflammation and colon cancer (13)(14)(15), many studies have been performed to elucidate the mechanisms of transcriptional regulation of COX-2 as reviewed recently (6,7).…”