Prostaglandin Synthase 2 Expression in Epidermal Growth Factor-Dependent Proliferation of Mouse Keratinocytes

BALB/c mouse keratinocytes (BALB/MK) are nontumorigenic epithelial cells which are dependent on mouse epidermal growth factor (EGF) for maintaining proliferation in culture. In BALB/MK the oxygenation of both arachidonic acid and linoleic acid was dependent on EGF. EGF stimulated the formation of prostaglandin E2and prostaglandin F2αfrom arachidonic acid and 9- and 13-hydroxyoctadecadienoic acid (HODE) from linoleic acid. Analysis of the linoleic acid metabolites determined the ratio of 9-HODE to 13-HODE was approximately 6 to 4, and the 9-HODE was the (R) enantiomer, consistent with metabolism by prostaglandin G/H synthase (PGHS). The formation of these linoleic acid metabolites was sensitive to indomethacin, a PGHS inhibitor. EGF induced the expression of PGHS-2 mRNA after 30 min, which peaked after 1 h, and remained expressed for at least 24 h after the addition of EGF. A less significant increase in the expression of PGHS-1 mRNA occurred 4 h after EGF stimulation. Immunoblot analysis did not detect expression of PGHS-1 protein. However, PGHS-2 protein expression was increased 2 h after EGF exposure and was dependent on EGF. PGHS-2 protein was not transiently expressed as reported with other cell types, but was continually expressed in proliferating cells maintained with EGF at a subconfluent density. Indomethacin significantly attenuated EGF-dependent mitogenesis and cell proliferation. These results suggest that PGHS-2 activity contributes to the proliferative response of BALB/MK to EGF.