Prostaglandin H synthase (PGHS) is the rate-limiting enzyme responsible for the formation of the prostaglandins from arachidonic acid. Prostaglandins (and other metabolites) elicit signals for inflammation, which is thought to be required for tumor promotion in the mouse skin carcinogenesis model. This study was designed to examine the effect of protein kinase C (PKC)-activating tumor promoters (4 beta-12-O-tetradecanoylphorbol-13-acetate (TPA)), non-PKC-type promoters (anthralin, benzoyl peroxide, okadaic acid), and mitogens (epidermal growth factor (EGF)) on the levels of the constitutive (PGHS-1) and inducible (PGHS-2) forms of PGHS in murine keratinocytes. Northern analysis of mRNA isolated from cultures treated with TPA (1 microgram/mL) showed that a single treatment of TPA produced a sevenfold increase in PGHS-2 mRNA by 1 h that decreased by 6 h after treatment. PGHS-2 protein levels were elevated threefold by 3 h and remained elevated through 9 h. Downregulation of PKC with a second TPA treatment 15 h after the first resulted in diminished induction of PGHS-2 expression. Of the other promoters examined, anthralin (5 microM), benzoyl peroxide (10 microM), and okadaic acid (1 microM) induced PGHS-2 mRNA with different kinetics and to different extents. Additionally, the non-tumor-promoting phorbol ester analogue 4 alpha-12-O-tetradecanoylphorbol-13-acetate induced PGHS-2 mRNA significantly by 1 h, and this response remained elevated up to 6 h after treatment. Elevated PGHS-2 expression was also observed by 3 h in response to EGF (10 ng/mL) treatment. Collectively, these observations indicate that there are several different signaling pathways by which PGHS-2 can be upregulated in murine keratinocytes.