Functional characterization of cyclooxygenase-2 polymorphisms

Cyclooxygenases (COX)-1 and -2 are the key enzymes in the conversion of ara chidonic acid to prostaglandins. COX-2 appears to play an emerging role in inflammation and carcinogenesis. Nonsteroidal anti-inflammatory drugs (NSAI Ds) are used for the treatment of numerous diseases and reduce the risk of developing colorectal cancer. Polymorphisms in the COX-2 gene could alter e nzyme expression, function, and/or the response to NSAIDs. Therefore, they could modify individual risks for developing cancer and other diseases or t he occurrence of side effects or sensitivity toward selective or nonselecti ve COX inhibitors. We sequenced the COX-2 gene of 72 individuals and identi fied rare polymorphisms in the promoter and the coding region. A COX-2 mole cular model was used to locate the coding region polymorphisms relative to functional sites in the protein, and the COX-2 V511A polymorphism was very near to the active site. This variant protein was expressed, and function w as evaluated, but no difference was detected in metabolism of the COX-2 sub strates, arachidonic acid, linoleic acid, and 2-arachidonyl glycerol, compa red with the wild type. The K-m values for arachidonic acid showed no diffe rences between the COX-2 wild type and V511A mutant. Inhibition with select ive or nonselective COX inhibitors was essentially the same for the two enz ymes. The absence of functionally important polymorphisms in the COX-2 gene may suggest that there has been selective pressure against those single nu cleotide polymorphisms because of the critical role of this enzyme in maint enance of homeostasis.