DISCUSSION(8)

Since multiple РЕАЗ-binding motifs (5′-AGGAAG-3′) are present in promoter IV of the rat GGT gene , and PEA3 can bind to promoter IV of the rat GGT gene, it is proposed that PEA3 is involved in the transactivation of expression of GGT mRNA-IV in the rat initial segment. The DNA-binding and transactivation activity of PEA3 has been shown to be under the regulation of TPA, a tumor promoter, and growth factors including bFGF via a ras-raf-MAPK (mitogen-activated protein kinase) signal transductional pathway. In the present study, TPA and bFGF were found to regulate GGT catalytic activity and GGT protein level in the initial segment following EDL (Figs. 5-8). Since a-ra/and c-ra/-l have also been shown to be present in the initial segment, we hypothesize that a signal transduction pathway (bFGF—> bFGFR—>raf—>MAPK—»PEA3—>GGT mRNA-IV) is involved in regulation of the expression of GGT mRNA-IV, GGT catalytic activity, and GGT protein level in the rat initial segment. Further studies are underway to test this hypothesis. buy prednisone

It should be noted that PE A3-binding motifs are also present in numerous epididymal genes such as CRISP-1, AEG, 5a-reductase; D.W. Russell, unpublished communication), GPX, proenkephalin, HE5, and ESP I genes. Like the GGT gene, all these genes are expressed in the epididymis in a region-specific manner, and the expression of these genes is under the regulation of androgen and/or testicular factors. The discovery of bFGF-like proteins in luminal fluid of rat rete testis and through the epididymal regions in this study leads us to believe that like androgens and ABP, growth factors such as bFGF in the rRTF are also required for normal epididymal function.