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  • Title: Characterization of cyclooxygenase-2 acetylation and prostanoid inhibition by aspirin in cellular systems.
    Author: Tacconelli S, Contursi A, Falcone L, Mucci M, D'Agostino I, Fullone R, Sacco A, Zucchelli M, Bruno A, Ballerini P, Dovizio M, Patrignani P.
    Journal: Biochem Pharmacol; 2020 Aug; 178():114094. PubMed ID: 32535107.
    Abstract:
    The most recognized mechanism of aspirin (acetylsalicylic acid, ASA) action, at therapeutic dosing, is the inhibition of prostanoid biosynthesis through the acetylation of cyclooxygenase (COX)-isozymes (COX-1 at serine-529 and COX-2 at serine-516). Whether aspirin, also when given at the low-doses recommended for cardiovascular prevention, reduces the risk of colorectal cancer by affecting COX-2 activity in colorectal adenomatous lesions is still debated. We aimed to develop a direct biomarker of aspirin action on COX-2 by assessing the extent of acetylation of COX-2 at serine-516 using the AQUA strategy, enabling absolute protein quantitation by liquid chromatography-mass spectrometry. We compared the extent of acetylation and the inhibition of prostanoid biosynthesis by ASA using human recombinant COX-2 (hu-COX-2), the human colon cancer cell line HCA-7, isolated human monocytes stimulated with LPS (lipopolysaccharide) or human intestinal epithelial cells stimulated with interleukin (IL)-1β. Hu-COX-2 exposed in vitro to an excess of ASA was acetylated by approximately 40-50% associated with the inhibition of COX-2 activity by 80-90%. In the three cell-types expressing COX-2, the extent of COX-2 acetylation and reduction of prostaglandin (PG) E2 biosynthesis by ASA was concentration-dependent with comparable EC50 values (in the low μM range). The maximal % acetylation of COX-2 averaged 80%, at ASA 1000 μM, and was associated with a virtually complete reduction of PGE2 biosynthesis (97%). In conclusion, we have developed a proteomic assay to evaluate the extent of acetylation of COX-2 at serine-516 by aspirin; its use in clinical studies will allow clarifying the mechanism of action of aspirin as anticancer agent.
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