Differentiation‐associated expression of prostaglandin G/H synthase in monocytic cells

Abstract

Significant progress in the investigation of the regulation of prostanoid formation has recently been made by cloning a second gene coding for prostaglandin G/H synthase (PGHS; EC 1.14.99.1). In this study we examined the expression of the two PGHS isoforms during phorbol ester induced monocytic differentiation of human myeloid leukemia cells (U937). Murine and ovine PGHS‐1 probes hybridized to 2.8‐ and 5.5‐kb mRNA species, whereas the murine PGHS‐2 probe hybridized to a 5.3‐kb species. Western blot analysis using antisera to mouse PGHS‐1 and to a synthetic peptide derived from a mouse PGHS‐2‐specific region revealed a band of 70 kDa for PGHS‐1 and a doublet of about 85 kDa for PGHS‐2. Unlike PGHS‐2, which was not expressed in U937 control cells, both PGHS‐1 protein and mRNA were detected in untreated U937 cells. TPA strongly induced PGHS‐2 protein and also increased the amount of PGHS‐1 protein. Correspondingly, a marked induction of PGHS‐2 mRNA was found, but virtually no change in the expression of the PGHS‐1 2.8‐kb mRNA occurred. The induction of both PGHS isoforms turned out to be dexamethasone‐sensitive. The suppression of PGHS‐2 induction was more pronounced. These results suggest that both PGHS‐1 and to a larger extent PGHS‐2 contribute to the upregulation of prostanoid synthesis during monocytic differentiation.