Parathyroid hormone (PTH) regulates serum calcium and phosphate levels, which, in turn, regulate PTH secretion and mRNA levels. PTH mRNA levels are markedly increased in rats fed low calcium diets and decreased after low phosphate diets, and this effect is posttranscriptional. Protein-PTH mRNA binding studies, with parathyroid cytosolic proteins, showed three protein-RNA bands. This binding was to the 3-untranslated region (UTR) of the PTH mRNA and was dependent upon the terminal 60 nucleotides. Parathyroid proteins from hypocalcemic rats showed increased binding, and proteins from hypophosphatemic rats decreased binding, correlating with PTH mRNA levels. There is no parathyroid cell line; however, a functional role was provided by an in vitro degradation assay. Parathyroid proteins from control rats incubated with a PTH mRNA probe led to an intact transcript for 40 min; the transcript was intact with hypocalcemic proteins for 180 min and with hypophosphatemic proteins only for 5 min. A PTH mRNA probe without the 3-UTR, or just the terminal 60 nucleotides, incubated with hypophosphatemic proteins, showed no degradation at all, indicating that the sequences in the 3-UTR determine PTH mRNA degradation. Hypocalcemia and hypophosphatemia regulate PTH gene expression post-transcriptionally. This correlates with binding of proteins to the PTH mRNA 3-UTR, which determines its stability. PTH1 is the major hormone that regulates calcium homeostasis and also has an important role in regulating bone strength. In turn, the synthesis and secretion of PTH is finely regulated by the serum calcium concentration, with hypocalcemia resulting in a marked increase in serum PTH, PTH mRNA levels, and parathyroid cell number (1, 2). Changes in extracellular calcium are sensed by the PT cell by a cell membrane sensor, which then leads to a change in intracellular calcium and inositol triphosphate concentrations (3). How these factors then determine the levels of PTH secretion, gene expression, and PT cell proliferation is not clear.A negative calcium regulatory element in the atrial natriuretic peptide gene, with a homologous sequence in the PTH gene (4) has been shown to bind a protein (ref1), which was known to activate several transcription factors (5). Because no parathyroid cell line is available, these studies were performed in nonparathyroid cell lines, so their relevance to physiologic PTH gene regulation remains to be established. A post-transcriptional effect of calcium on PTH gene expression in primary cultures of bovine parathyroid cells has been demonstrated (6), which correlated with binding of parathyroid proteins to the 5Ј-and 3Ј-untranslated regions (UTRs) of bovine PTH mRNA probes (7).PTH leads to a decrease in serum phosphate by increasing renal phosphate excretion, and in turn, serum phosphate has a direct effect to increase PTH secretion and PTH mRNA levels (8 -11). Dietary induced hypophosphatemia leads to a dramatic decrease in PTH gene expression, and this effect is posttranscriptional (8).We have now studied th...

Silver, Justin, Rachel Kilav, and Tally Naveh-Many. Mechanisms of secondary hyperparathyroidism. Am J Physiol Renal Physiol 283: F367-F376, 2002; 10.1152/ajprenal.00061.2002

No abstract

Calcium and phosphate regulate parathyroid hormone (PTH) gene expression post-transcriptionally by changes in protein-PTH mRNA 3 -untranslated region (UTR) interactions, which determine PTH mRNA stability. We have identified the protein binding sequence in the PTH mRNA 3 -UTR and determined its functionality. The protein-binding element was identified by binding, competition, and antisense oligonucleotide interference. The sequence was preserved among species suggesting its importance. To study its functionality in the context of another RNA, a 63-base pair cDNA PTH sequence was fused to the growth hormone (GH) gene. There is no parathyroid (PT) cell line and therefore an in vitro degradation assay was used to determine the stability of transcripts for PTH, GH, and a chimeric GH-PTH 63 nucleotides with PT cytosolic proteins. The fulllength PTH transcript was stabilized by PT proteins from rats fed a low calcium diet and destabilized by proteins from rats fed a low phosphate diet, correlating with PTH mRNA levels in vivo. These PT proteins did not affect the native GH transcript. However, the chimeric GH transcript was stabilized by low calcium PT proteins and destabilized by low phosphate PT proteins, similar to the PTH full-length transcript. Therefore, we have identified a PTH RNA-protein binding region and shown that it is sufficient to confer responsiveness to calcium and phosphate in a reporter gene. This defined element in the PTH mRNA 3 -UTR is necessary and sufficient for the regulation of PTH mRNA stability by calcium and phosphate.Parathyroid hormone (PTH) 1 acts to maintain serum calcium within a narrow physiological range (1). A 7-transmembranous calcium-sensing receptor on the parathyroid (PT) cell recognizes small changes in serum-ionized calcium and regulates PTH secretion (2). Low serum calcium increases PTH secretion, PTH mRNA levels (3), and if prolonged, PT cell proliferation (4). PTH then acts to correct serum calcium by mobilizing calcium from bone and increasing renal reabsorption of calcium. Phosphate also regulates the PT, with low serum phosphate decreasing serum PTH, PTH mRNA levels, and PT cell proliferation (4 -8).The effects of dietary calcium and phosphate on PTH gene expression are both post-transcriptional (5, 9). The PTH cDNA consists of three exons coding for the 5Ј-UTR (exon I), the prepro region of PTH (exon II), and the structural hormone together with the 3Ј-UTR (exon III) (10, 11). The rat 3Ј-UTR is 239 nt long out of the 712 nt of the full-length PTH RNA (11). The 3Ј-UTR is 42% conserved between human and rat, while the coding region is 78% conserved at the nt level (11).We have shown that cytosolic proteins from PTs bind to the 3Ј-UTR of the rat PTH mRNA (9). PT proteins from hypocalcemic rats show increased binding to the PTH mRNA 3Ј-UTR by mobility shift and UV cross-linking assays and this protein-RNA binding is decreased with hypophosphatemic PT proteins. Thus the level of protein-RNA binding directly correlates with PTH mRNA levels. Since there is no PT cell line, an...

Regulation of the parathyroid hormone gene by vitamin D,late the PTH gene and these will be considered in the calcium, and phosphate. Secondary hyperparathyroidism is a present review. frequent complication of chronic renal failure resulting in severe bone disease. Secondary hyperparathyroidism is composed of increased in parathyroid hormone (PTH) synthesis THE PTH GENEand secretion due to an increase in PTH gene expression andThe parathyroid cell is committed to the synthesis of parathyroid cell proliferation. PTH gene expression is regulated by calcium, phosphate and 1,25-dihydroxy vitamin D PTH, implying that there are specific trans-and cis-fac-(1,25(OH) 2 D). 1,25(OH) 2 D 3 injected to rats leads to a dramatic tors acting on the PTH gene that are specific to the cell decrease in PTH gene transcription without any increase in and gene. The gene itself is expressed once in the human serum calcium. Hypocalcemia leads to a large increase in PTH genome and is a relatively simple gene. It has been cloned mRNA levels which is post-transcriptional. Hypophosphatein a number of species and in all species it consists of mia leads to a marked decrease in PTH gene expression that is also post-transcriptional. The mechanisms of the post-tran-three exons and two introns. These exons code for the scriptional effects of calcium and phosphate on the PTH gene 5Ј-untranslated region and the presequence of the gene, have shown to be due to changes in protein-RNA interactions the pro-sequence and for the translated hormone and at the PTH mRNA 3Ј-UTR. Hypocalcemia leads to increased the 3Ј-untranslated region, respectively. The PTH gene binding of parathyroid cytosolic proteins to the PTH mRNA 1 C.Y. was on sabbatical leave from Erciyes University Medical School, cium [3]. There is a subsequent decrease in PTH secretion. Kayseri, Turkey.