Relationship between TGF alpha-induced DNA synthesis and prostaglandin synthesis in human HaCaT keratinocytes

The relationship between transforming growth factor alpha (TGF alpha)-induced cell proliferation and prostaglandin synthesis was investigated using growth-arrested human keratinocytes of the HaCaT line. Depending on the TGF alpha concentration, the stimulation of DNA synthesis (5-fold) was found to be either insensitive (at < 10 ng/ml TGF alpha) or sensitive (at > or = 20 ng/ml TGF alpha) to inhibition by both indomethacin, an inhibitor of prostaglandin synthases (PGHS) 1 and 2 and the PGHS 2-specific inhibitor NS-398. Indomethacin-effected inhibition did not correlate with cytotoxicity and was restricted to a narrow time window after growth factor administration. The indomethacin- and NS-398-sensitive mitogenic effect of TGF alpha correlated with an early increase of arachidonic acid release and prostaglandin (PGE2, PGF2alpha) synthesis, whereas the PGHS inhibitor-insensitive TGF alpha effect did not. TGF alpha-induced prostaglandin synthesis was due to a growth factor-induced PGHS-2 activity as indicated by its suppression by NS-398. However, attempts to overcome the PGHS inhibitor-dependent suppression of TGF alpha-induced DNA synthesis by adding prostaglandins (E1, E2, F2alpha, G2) to the cultures proved to be unsuccessful. Thus, TGF alpha-induced synthesis of prostaglandins seems not to be involved in the mediation of the mitogenic effect of the growth factor on human keratinocytes in culture.