Intron 1 retaining cyclooxygenase 1 splice variant is induced by osmotic stress in human intestinal epithelial cells

• Published in: Prostaglandins, leukotrienes and essential fatty acids Vol. 73; no. 5; pp. 343 - 350
• Main Authors: Nurmi, J.T., Puolakkainen, P.A., Rautonen, N.E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.11.2005; Elsevier
• Subjects: Alternative Splicing - genetics; Biological and medical sciences; Caco-2 Cells; Colorectal Neoplasms - enzymology; Cyclooxygenase 1 - genetics; Cyclooxygenase 2 - genetics; Epithelial Cells - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic; Genetic Variation; Humans; Introns; Osmotic Pressure; Prostaglandin-Endoperoxide Synthases - genetics; RNA, Messenger - genetics; Vertebrates: endocrinology; Human; Osmotic shock; Alternative splicing; Digestive system; Enzyme; Cyclooxygenase 1; Gut; Epithelial cell; Oxidoreductases
• ISSN: 0952-3278; 1532-2823
• DOI: 10.1016/j.plefa.2005.07.004

The biological roles of intron 1 retaining cyclooxygenase (Cox) 1 splice variants Cox-3 and PCox-1a (Cox-1ir) are not known. In humans, Cox-3 transcription has previously been shown to occur in the brain and in the aorta. However, conclusive evidence regarding the existence of a human Cox-3 protein is lacking. We studied the expression of intron 1 retaining cyclooxygenase 1 splice variants in the human colon cancer cell line Caco-2 and in human colonic tissue samples. In Caco-2 cells, their transcription was induced up to 47-fold by osmotic stress. The corresponding protein, however, could not be detected by Western blotting. In human colonic tissue samples derived from intact and inflamed areas, a low level of Cox-1ir mRNA (1500±1280 copies per 100 ng total RNA; mean±standard deviation; n = 20 ) was also found. In Caco-2 cells, induction of Cox-1ir under osmotic stress was reversed by addition of the organic osmolyte betaine. Under hypertonic but not under isotonic conditions, splice variant-specific degradation of Cox-1ir mRNA using RNA interference resulted in increased production of fully spliced Cox-1 and Cox-2 mRNA ( P = 0.002 ). In summary, our results indicate that the intron 1 retaining Cox-1 splice variant RNA molecules are expressed by human intestinal epithelial cells in a controlled manner, are most likely not translated and play a regulatory role in the cyclooxygenase mediated epithelial osmoregulation.