IDENTIFICATION, EXPRESSION, AND REGULATION OF THE TRANSCRIPTIONAL FACTOR POLYOMAVIRUS ENHANCER ACTIVATOR-3, AND ITS PUTATIVE ROLE IN REGULATING THE EXPRESSION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE MESSENGER-RNA-IV IN THE RAT EPIDIDYMIS

Gamma-glutamyl transpeptidase (GGT) mRNA-IV is highly expressed in the initial segment of the rat epididymis and is regulated by testicular factors. The promoter region for GGT mRNA-IV contains five conserved p olyomavirus enhancer activator 3 (PEA3)-binding motifs (5'-AGGAAG-3'). We hypothesize that PEAS is present in the rat epididymis and is regu lated by one or more testicular factors. Western blot analyses showed that a 62-kDa protein was detected in the nuclear extract from the rat initial segment at higher levels than in the distal epididymal region s. Electrophoretic mobility shift assays (EMSAs) showed that the nucle ar extract specifically bound to the PEAS motif, forming a DNA-protein complex. This complex contained the 62-kDa PEAS protein as demonstrat ed by EMSAs and South-western analyses. Northern blot analyses and RNa se protection analyses showed that PEAS mRNA was predominantly express ed in the initial segment as compared to the distal epididymal regions and was under the regulation of testicular factors. These results sug gest that PEAS could be involved in the regulation of expression of th e rat GGT mRNA-IV gene in response to testicular factors in the initia l segment.