Expression and subcellular location of COX‐2 in human gastric cancer cells

OBJECTIVE: To detect the expression of cyclooxygenase (COX) in human gastric cancer cell lines and determine the subcellular location of its isoforms. METHODS: Immunohistochemistry, reverse transcription–polymerase chain reaction (RT‐PCR), and laser scanning confocal microscopy (LSCM) were used to investigate the expression and distribution of COX. RESULTS: Positive staining for COX‐2 and COX‐1 protein was seen in human gastric cancer cell lines MKN45, SGC7901 and AGS. However, COX‐2 staining was absent and COX‐1 staining was weak in the MGC803 cell line, although COX‐2 mRNA was present in all four cell lines. When compared with COX‐1, COX‐2 was more strongly expressed at both protein and mRNA levels in the gastric cancer cell lines, which was confirmed by double labeling and LSCM. A quantitative analysis of fluorescein intensity indicated that the pixel intensity peak of COX‐2 had a gray scale value of 50–70, while COX‐1 was only 10. The LSCM technique also revealed the presence of COX‐2 in the cytoplasm and nuclear envelope and COX‐1 in the cytoplasm only. CONCLUSIONS: In human gastric cancer cells, COX‐2 is expressed at higher levels than COX‐1 and the different distributions of the two isoforms suggest that their roles in cell function are distinct.