TESTOSTERONE REGULATES TISSUE-SPECIFIC CHANGES IN THE BINDING OF A 47-KILODALTON PROTEIN TO A HIGHLY CONSERVED SEQUENCE IN THE 3'-UNTRANSLATED REGION OF EPIDERMAL GROWTH-FACTOR MESSENGER-RIBONUCLEIC-ACID

Epidermal growth factor (EGF) transcripts that use the terminal polyad enylation signal display a dramatic sex difference in the pattern of p olyadenylation in the murine submaxillary gland (SMG), whereas those i n the kidney do not. It takes 3 days before testosterone treatment beg ins to change the polyadenylation pattern in female SMG to resemble th e male pattern, a finding that supports previous suggestions that post transcriptional mechanisms are involved in regulating EGF expression. The conservation of a unique 23-b sequence centered on the terminal po lyadenylation signal in all published mammalian EGF sequences suggeste d that trans-acting factors involved in EGF messenger RNA (mRNA) metab olism might bind to this sequence. To investigate this, we prepared P- 32-RNA containing the 3' terminal EGF 23-b sequence plus a short poly- A tail, and incubated it with SMG cytosol. Cytosol retarded the electr ophoretic mobility of this RNA as a single prominent band on 8% PAGE, and by W-cross-linking, a single prominent 47-kDa protein was detected on 10% SDS-PAGE. Trypsin abolished both the gel-retarding and cross-l inking activities. Cytosol from female SMGs contained approx imately 8 times more of both the RNA binding activities than male cytosol. Inje cting testosterone (200 mu g QOD) into female mice altered both the RN A binding activities in a biphasic fashion, initially increasing them by about 40% at 2 days, then decreasing them by about 65% greater than or equal to 5 days, reaching male levels. Kidney cytosol contained bo th RNA binding activities but displayed neither sexual dimorphism nor testosterone-responsiveness. The tissue-specific testosterone dependen t changes observed in the 47-kDa protein occur before the increase in EGF mRNA levels and before the change in EGF mRNA polyadenylation, so this cytosolic protein could be a trans-acting factor involved in EGF polyadenylation.