title: Cyclooxygenase-2 knockdown by RNA interference in colon cancer.
abstract: Overexpression of cyclooxygenase-2 (COX-2) is observed early in colon cancer. Treatments with COX-2-specific NSAIDs have been shown to reduce polyp size and polyp number in FAP patients with a predisposition to colorectal adenoma and cancer. However, the use of COX-2-specific NSAIDs in colon cancer patients has recently revealed increased cardiovascular risks. These harmful side effects may be the result of COX-dependent and/or COX-independent mechanisms. RNA interference (RNAi) is a method of post-transcriptional gene silencing intrinsic to cells. This study employed RNAi to specifically knockdown endogenous COX-2 expression in the HT-29 colon cancer cell line, and to observe the apoptotic response as well as 15-hydroxyprostaglandin dehydrogenase (15-PGDH) expression levels. Following treatment with a COX-2 siRNA, we demonstrated a significant knockdown at the protein level of 57% as compared to a non-silencing siRNA control. Protein results were corroborated by concurrent decrease in COX-2 mRNA levels following the same treatment regimen. Despite previous studies using NSAID treatment to implicate COX-2 involvement in apoptosis, we did not observe any alteration in Bcl-2 expression and Caspase-3 activation following COX-2 knockdown in these cells. 15-PGDH, a physiological antagonist of COX-2 in its catabolism of PGE2, showed a modest but significant induction in response to COX-2 knockdown. The precise role of COX-2 in apoptosis and PGE2 regulation remains unclear; however, having shown that down-regulation of endogenous levels of COX-2 can be achieved in colon cancer by RNAi, this strategy should prove to be a valuable tool in revealing the specific function of COX-2 in tumourigenesis.
authors.affiliation: Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: George S
authors.initials: GS
authors.lastname: Charames
authors.forename: Bharati
authors.initials: B
authors.lastname: Bapat
mesh_terms: D003110:Colonic Neoplasms; D051546:Cyclooxygenase 2 / Q000235:genetics* / Q000378:metabolism; D020868:Gene Silencing; D019073:HT29 Cells; D006801:Humans; D006911:Hydroxyprostaglandin Dehydrogenases / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D014162:Transfection
chemical_list: D012333:RNA, Messenger; D034741:RNA, Small Interfering; D006911:Hydroxyprostaglandin Dehydrogenases; C035859:15-hydroxyprostaglandin dehydrogenase; D051546:Cyclooxygenase 2