Identification of AUF1 as a parathyroid hormone mRNA 3 '-untranslated region-binding protein that determines parathyroid hormone mRNA stability

Parathyroid hormone (PTH) mRNA levels are posttranscriptionally increased b y hypocalcemia and decreased by hypophosphatemia, and this is mediated by c ytosolic proteins binding to the PTH mRNA 3'-untranslated region (UTR). The same proteins are also present in other tissues, such as brain, but only i n the parathyroid is their binding regulated by calcium and phosphate. The function of the PTH mRNA 3'-UTR-binding proteins was studied using an in vi tro degradation assay. Competition for the parathyroid-binding proteins by excess unlabeled 3'-UTR destabilized the full-length PTR transcript in this assay, indicating that these proteins protect the RNA from RNase activity. The PTH RNA 3'-UTR-binding proteins were purified by RNA affinity chromato graphy of rat brain S-100 extracts. The eluate from the column was enriched in PTH RNA 3'-UTR binding activity. Addition of eluate to the In vitro deg radation assay with parathyroid protein extracts stabilized the PTH transcr ipt. A major band from the eluate at 50 kDa was sequenced and was identical to AU-rich binding protein (AUF1). Recombinant AUF1 bound the full-length PTH mRNA and the 3'-UTR. Added recombinant AUF1 also stabilized the PTH tra nscript in the in vitro degradation assay. Our results show that AUF1 is a protein that binds to the PTH mRNA 3'-UTR and stabilizes the PTH transcript .