Estradiol Up-regulates AUF1p45 Binding to Stabilizing Regions within the 3′-Untranslated Region of Estrogen Receptor α mRNA

Abstract Estradiol up-regulates expression of the estrogen receptor α gene in the uterus by stabilizing estrogen receptor α mRNA. Previously, we defined two discrete minimal estradiol-modulated stability sequences (MEMSS) within the extensive 3′-untranslated region of estrogen receptor α mRNA with an in vitro stability assay using cytosolic extracts from sheep uterus. We report here that excess MEMSS RNA inhibited the enhanced stability of estrogen receptor α mRNA in extracts from estradiol-treated ewes compared with those from control ewes. Several estradiol-induced MEMSS-binding proteins were characterized by UV cross-linking in uterine extracts from ewes in a time course study (0, 8, 16, and 24 h after estradiol injection). The pattern of binding proteins changed at 16 h post-injection, concurrent with enhanced estrogen receptor α mRNA stability and the highest rate of accumulation of estrogen receptor α mRNA. The predominant MEMSS-binding protein induced by estradiol treatment was identified as AUF1 (A + U-rich RNA-binding factor 1) protein isoform p45 (a product of the heterogeneous nuclear ribonucleoprotein D gene). Immunoblot analysis indicated that only two of four AUF1 protein isoforms were present in the uterine cytosolic extracts and that estradiol treatment strongly increased the ratio of AUF1 isoforms p45 to p37. Nonphosphorylated recombinant AUF1p45 protected estrogen receptor α mRNA in vitro in a dose-dependent manner. These studies describe estrogenic induction of AUF1p45 binding to the estrogen receptor α mRNA as a molecular mechanism for post-transcriptional up-regulation of gene expression.