EFFECTS OF CYCLOPENTENONE PROSTAGLANDINS AND RELATED-COMPOUNDS ON INSULIN-LIKE GROWTH-FACTOR-I AND WAF1 GENE-EXPRESSION

The molecular pathways by which the cyclopentenone prostaglandins (PGA and PGJ series) inhibit cell growth and tumorigenicity are poorly und erstood. These cellular responses may be caused by specific regulation of growth-related and stress-induced genes. A variety of prostaglandi ns were tested for their ability to regulate insulin-like growth facto r-I (IGF-I) and Waf1 gene expression in C6 rat glioma cells. The prost aglandins (in order of potency) PGJ(2) > PGA(1) > PGA(2) approximate t o PGD(2) >> PGE(2) all significantly repressed IGF-I gene expression. With the exception of PGE(2), the same prostaglandins that repressed I GF-I also induced Waf1 gene expression. However, the order of potency for Waf1 induction was different than for IGF-I repression: PGA(2) > P GA(1) approximate to PGJ(2) > PGD(2). The different order of potency o f the prostaglandins in regulating IGF-I and Waf1 gene expression sugg ests that different intracellular signals may be involved in regulatin g the two genes. Augmentation of glutathione levels by pretreatment of cells with N-acetyl-L-cysteine attenuated the effect of PGA(2) on IGF -I and Waf1 gene expression. Conversely, depletion of the intracellula r glutathione pool by pretreatment with buthionine sulfoximine potenti ated the effect of PGA(2) on the expression of both genes. These resul ts suggest that conjugation with glutathione prevents the regulation o f gene expression by PGA(2). We also tested the effect of several simp ler compounds that contain a five-membered ring system on IGF-I and Wa f1 gene expression. 2-Cyclopenten-1-one, but not cyclopentanone or cyc lopentene, repressed IGF-I and induced Waf1 gene expression, demonstra ting the requirement for an alpha,beta-unsaturated carbonyl for regula tion of the two genes. The dione compound 3-cyclopentene-1,3-dione, wh ich has two potentially reactive carbons rather than one, was consider ably more potent than 2-cyclopenten-1-one in repressing IGF-I gene exp ression (IC50 = 30 mu M for 4-cyclopentene-1,3-dione as compared with 167 mu M for 2-cyclopenten-1-one). Additional results indicated that d iethyl maleate, which has two alpha,beta-unsaturated carbonyls in a no n-cyclic configuration, also repressed IGF-I gene expression (IC50 = 2 14 mu M) and induced Waf1 gene expression, indicating that the cyclic structure is not required for either effect. (C) 1998 Elsevier Science B.V.