5alpha-reductase type 2 and Androgen receptor compose the androgen responsiveness of the Gonadotropin-releasing hormone (GnRH) GT1-1 neurons

Gonadal steroids are potent modulators of gonadotropin releasing hormone (GnRH) secretion, and androgen binding sites and 5α-reductase activity have been found in the immortalized GnRH secreting cell line GT1-1, suggesting the existence of a direct androgenic control of GnRH dynamics. Two isoforms of the 5α-reductase have been cloned with very different biochemical/functional properties: 5α-reductase type 1 (widely distributed in the body) and 5α-reductase type 2 (confined in androgen target structures). We have analysed whether, in GT1-1, androgen binding sites are linked to 'classical' androgen receptor, and which 5α-reductase isoform is active. Reverse transcriptase-polymerase chain reaction analysis showed that the mRNAs coding for androgen receptor and for the two 5α-reductase isoforms are all expressed in GT1-1 cells. However, the 5α-reductase enzymatic reaction showed a peak of activity at a narrow pH around 5.5, the optimum for the 5α-reductase type 2. The affinity for testosterone, of the enzyme present in GT1-1 cells, was very similar to that observed for the recombinant type 2 isozyme expressed in yeasts. The data indicate that GT1-1 cells (i) express a 'classical' androgen receptor and (ii) contain the 5α-reductase type 2 isoform, a specific marker of androgen-responsiveness.