DIFFERENT INTRACELLULAR LOCATIONS FOR PROSTAGLANDIN ENDOPEROXIDE-H SYNTHASE-1 AND SYNTHASE-2

The subcellular locations of prostaglandin endoperoxide synthase-1 and -2 (PGHS-1 and -2) were determined by quantitative confocal fluoresce nce imaging microscopy in murine 3T3 cells and human and bovine endoth elial cells using immunocytofluorescence with isozyme-specific antibod ies, In all of the cell types examined, PGHS-1 immunoreactivity was fo und equally distributed in the endoplasmic reticulum (ER) and nuclear envelope (NE), PGHS-2 immunoreactivity was also present in the ER and NE. However, PGHS-2 staining was twice as concentrated in the NE as in the ER, A histofluorescence staining method was developed to localize cyclooxygenase/peroxidase activity. In quiescent 3T3 cells, which exp ress only PGHS-1, histofluorescent staining was most concentrated in t he perinuclear cytoplasmic region. In contrast, histochemical staining for PGHS-2 activity was about equally intense in the nucleus and in t he cytoplasm, a pattern of activity staining distinct from that observ ed with PGHS-1, Our results indicate that there are significant differ ences in the subcellular locations of PGHS-1 and PGHS-2, It appears th at PGHS-1 functions predominantly in the ER whereas PGHS-S may functio n in the ER and the NE, We speculate that PGHS-1 and PGHS-2 acting in the ER and PGHS-2 functioning in the NE represent independent prostano id biosynthetic systems.