Meningioma benign tumors possess significant levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) activity. Two different 17β-HSDs have been cloned and characterized. The cytosolic 17β-HSD I which exclusively catalyzes the interconversion of 17β-estradiol (E2) and estrone (E1) preferentially uses NADP+ and NADPH as cofactors. In contrast, the mitochondrial-microsomal 17β-HSD II catalyzes both the estrogenic as well as the androgenic substrates of the 17β-HSD and uses NAD+ and NADH as cofactors. We demonstrated here that the 17β-HSD activity in meningioma tissue homogenate is both estrogenic and androgenic with Km values of 2.4, 0.4, 14.7, and 2.0 µM for E2, E1, testosterone (T), and Δ4-androstenedione (Δ4), respectively. NAD+-NADH is almost exclusively used as cofactor in this tissue. Moreover, fractionation of meningioma tissue revealed that most of the 17β-HSD activity is present in the mitochondrial-microsomal fraction. Although Northern blot analysis on meningiomas with a specific probe for human 17β-HSD I showed no band, the specific cDNA probe of human 17β-HSD II hybridized at the expected size of 1.5 kb, which was also present in placenta. On four different meningioma tumors, we were able to correlate 17β-HSD II mRNA expression to high levels of 17β-HSD activity. Taken together, the present data suggest that the meningioma 17β-HSD could be the 17β-HSD II.
The signal transducer and activator of transcription 5 (Stat5) has been shown to cooperate with some nuclear receptors. However, an interaction has never been demonstrated with the androgen receptor (AR). Given that the PRL-inducible protein/gross cystic disease fluid-15 (PIP/GCDFP-15) is both a PRL-controlled and an androgen-controlled protein, we used its promoter region to investigate the potential interaction between Stat5 and androgen receptor. Dihydrotestosterone or PRL alone slightly modulated or did not modulate the luciferase activity of all reporter gene constructs. In contrast, a maximal increase was observed using the -1477+42 reporter gene construct after exposure to both dihydrotestosterone and PRL. The requirement of half-site androgen-responsive elements and two consensus Stat5-binding elements, Stat5#1 and Stat5#2, was determined by site-directed mutagenesis. Activated Stat5B binds with a higher affinity to Stat5#2 than to Stat5#1. Stat5ADelta749 and Stat5BDelta754 mutants demonstrated that the Stat5 trans-activation domain is involved in the hormonal cooperation. The cooperation depends on the PRL-induced phosphorylation on Tyr(694) in Stat5A and Tyr(699) in Stat5B, as demonstrated using the Stat5AY694F and Stat5BY699F proteins. The use of AR Q798E, C619Y, and C784Y mutants showed that trans-activation, DNA-binding, and ligand-binding domains of AR are essential. Our study thus suggests a functional cooperation between AR and Stat5.
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