The cytosolic 47-kilodalton protein that binds to the 3' untranslated region of epidermal growth factor transcripts responds to orchiectomy in a tissue-specific fashion.

The submaxillary gland (SMG) of the male mouse is known to contain more epidermal growth factor (EGF) messenger RNA (mRNA) than that of the female. In contrast, the SMG of female mice contains more of a cytosolic 47-kDa RNA binding protein that binds to a unique 23-b sequence at the end of the 3' untranslated region (3' UTR) of EGF, which includes the canonical polyadenylation signal in an AU-rich region containing a potential mRNA destabilizing sequence. Testosterone treatment can change the activity of this 47-kDa protein within 1 day, which precedes the change produced in the level and in the polyadenylation of EGF mRNA in female mice. In the kidney, however, neither the 47-kDa protein nor the polyadenylation pattern changed after testosterone. We now report that 2 weeks following orchiectomy of Balb/c mice, mature EGF peptide immunoreactivity levels fall by 96% (P < 0.0002), and mRNA levels fall by 76% (P < 0.0001). Orchiectomy also enhances the RNA binding activities of the 47-kDa protein in SMG cytosol but not in the kidney: UV cross-linking to 3' UTR RNA is increased by 67% (P < 0.01) and shifting of the gel mobility of the RNA is increased by 47% (P < 0.05). The polyadenylation pattern of EGF transcripts also changes in SMG but not in kidney cytosol. After orchiectomy, the population of EGF transcripts in the SMG with short, heterogenous poly-A tails (<50 A's) decreases by 31% (P < 0.03), whereas transcripts with long poly-A tails of approximately 50, 70, 100, and 200 A's all increase and become more distinct, resembling the pattern found in the normal female. Thus, 2 weeks after orchiectomy, the responses in EGF expression, EGF mRNA polyadenylation, and the activities of the 47-kDa 3' UTR binding protein are the reciprocal of the responses produced by injecting female mice with testosterone for 5 days, providing further evidence that circulating androgens regulate EGF expression posttranscriptionally in a sexually dimorphic, tissue-specific fashion.