Comparison of Absolute Expression and Turnover Number of COX-1 and COX-2 in Human and Rodent Cells and Tissues

Abstract

Li Li,1 Rongjin Sun,1 Joseph Zenga,2 Heather Himburg,3 Lu Wang,1 Shengnan Duan,1 Jingwen Liu,1 Dinh Bui,1 Zuoxu Xie,1 Ting Du,4 Lijun Xie,1 Taijun Yin,1 Stu Wong,2 Song Gao,4 Ming Hu1 1Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX, USA; 2Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee, WI, USA; 3Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, USA; 4Department of Pharmaceutical Science, College of Pharmacy and Health Sciences, Texas Southern University, Houston, TX, USACorrespondence: Ming Hu, Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX, USA, Email [email protected] Song Gao, Department of Pharmaceutical Science, College of Pharmacy and Health Sciences, Texas Southern University, Houston, TX, USA, Email [email protected]: We aim to quantify the absolute protein expression of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) in various cells and tissues to determine the relative contribution of COX-1 and COX-2 to PGE2 production.Methods: An LC-MS method was developed and validated, then used for quantifying the absolute amounts of COX-1 and COX-2 in recombinant human COX-1 and COX-2, lysates from different cells, tissue microsomes of rodents and humans, Pirc rat colonic polyps, and biopsy specimens from squamous cell carcinoma (SCC) patients. The COX-1 and COX-2 turnover numbers were subsequently calculated based on apparent formation rates of PGE2.Results: A robust LC-MS method for quantification of COX-1 and COX-2 was developed and validated and then used to calculate their apparent turnover numbers. The results showed that COX-1 expression levels were much higher than that of COX-2 in all the tested tissues including the colonic epithelium of F344 (28-fold) and Pirc rats (20-fold), colonic polyps of Pirc rats (8-fold), and biopsy specimens of SCC patients (11– 17-fold). In addition, both COX-1 and COX-2 were higher in polyps when compared to adjacent mucosa of Pirc rats. The turnover number of recombinant human COX-2 was 14-fold higher than that of recombinant human COX-1. LPS stimulation increased COX-2 protein expression in three cell lines (Raw 264.7, SCC9 and EOMA) as expected but unexpectedly increased COX-1 protein expression (13.8-fold) in EOMA cells.Conclusion: In human oral cancer tissues and cells as well as Pirc rat colon, COX-1 plays an unexpectedly but more important role than COX-2 in abnormal PGE2 production since COX-1 expression is much higher than COX-2. In addition, COX-1 expression levels are inducible in cells, and higher in polyps than surrounding mucosa in Pirc rat colon. These results indicate that targeted suppression of local COX-1 should be considered to reduce colon-specific PGE2-mediated inflammation.Graphical Abstract: Keywords: cyclooxygenase-1, cyclooxygenase-2, turnover number, inflammation, absolute quantification, liquid chromatography with tandem mass spectrometry

Keywords

• cyclooxygenase-1
• cyclooxygenase-2
• turnover number
• inflammation
• absolute quantification
• liquid chromatography with tandem mass spectrometry