Cytoplasmic and nuclear binding components for 1alpha25-dihydroxyvitamin D3 in chick parathyroid glands.

Abstract

Specific binding of la,25-dihydroxyvitamin D3 [la,25(OH) (1) they sediment at 6 S in 0.3 M KCI-sucrose gradients, (2) they are observed in all tissues examined, (3) they have a higher affinity for 25-(OH)D3 than la,25-(0H)2D3, and (4) they are not found in the nucleus of the parathyroid glands, in vitro. The discovery of unique la,25.OH)2D3-binding components in the parathyroid glands is consistent with the sterol hormone's action at this endocrine site and possible involvement in the regulation of parathyroid hormone synthesis and secretion. Vitamin D3 action to mobilize calcium and phosphate at intestine and bone is thought to be mediated by the metabolite la,25-dihydroxyvitamin D3 [la,25-(OH)2D3] (1-4). Its production from 25-hydroxyvitamin D3 [25-(OH)D3] by the renal la-hydroxylase appears to be regulated by calcium (5), phosphate (6, 7), parathyroid hormone (PTH) (7,8), and the vitamin D status of the animal (9). Evidence suggests that hypocalcemia stimulates PTH secretion which in turn enhances the production of la,25-(OH)2D3 at the kidney (7, 8). Thus PTH, rather than calcium, may be the dominant modulator of the renal la-hydroxylase (10) and the finding of abnormal circulating 1a,25-(OH)2D3 in humans with parathyroid disease is consistent with this concept (11,12). DeLuca has proposed that PTH and phosphate deficiency may be functioning through a common intracellular mechanism to enhance the la-hydroxylase by lowering the phosphate level in the renal cell (10). Moreover, MacIntyre and associates (13) have suggested that la,25-(OH)2D3 might control its own biosynthesis directly at the kidney by a negative feedback mechanism involving the de novo synthesis of the la-hydroxylase enzyme. Clearly, the fashion in which la,25-(OH)2D3, PTH, and phosphate deficiency interact to control the formation of 1a,25-(OH)2D3 at its kidney endocrine site must be completely understood before the exact role of 1a,25-(OH)2D3 in the homeostatic regulation of calcium and phosphate can be elucidated.Henry and Norman (14) Homogenates were centrifuged at 1200 X g for 10 min. Nuclear pellets were removed, and the resulting supernatant was centrifuged at 100,000 X g for 1 hr at 0°to yield a final supernatant fraction (cytosol). The cytosol (0.2-1.0 ml) was incubated with sterol (in 20,l ethanol) for 1 hr at 00 and then analyzed for sterol binding components.Purified nuclear extracts (chromatin) were prepared from nuclear pellets by a modification (7) of the method of Haussler et al. (1) and were resuspended in 0.01 M Tris-HCl, pH 7.5, and centrifuged for 20. min at 48,000 X g. The pellet from 300 mg of tissue was reconstituted with cytosol (2.5 ml)Abbreviations: 25-(OH)D3, 25-hydroxyvitamin D3; la-(OH)D3, la-hydroxyvitamin D3; la,25-(OH)2D3, la,25-dihydroxyvitamin D3; PTH, parathyroid hormone. 4871

Serum Parathyroid Hormone Suppression by Intravenous 1,25-Dihydroxy vitamin D3 in Patients on Maintenance Haemodialysis

“…The parathyroid gland possesses specific receptors for calcitriol [5,6] and this metabolite decreases PTH secretion independent of ambient calcium levels [7,8]. The administration of 1,25-dihydroxyvitamin D3 [l,25(OH)2D3] leads to a marked decrease of prepro-PTH mRNA gene transcription.…”

Inhibition of Parathyroid Hormone Secretion by 25-Hydroxycholecalciferol and 24,25-Dihydroxycholecalciferol in the Dog

“…The biologic funicetionis of 24,25-(OH)2D3 remain to be elucidated. (OH)2D3 in parathyroid glands has been reported (11,12), and (c) simultaneous administration of 1,25-(OH)2D3 and 24,25-(OH)2D3, but not their separate administration, mediate a reduction of parathyroid gland weight and DNA content in rachitic chicks independent of any effects on serum calcium (13). In addition, calcium binding protein, similar to the one which is D-dependent and found in intestinal mucosa, has been reported to be present in porcine parathyroid glands (14).…”

22-Oxacalcitriol Upregulates p21<i>^WAF1/Cip1</i> in Human Parathyroid Glands

“…2d) may occur from the process of its upregulation [6]. Furthermore, several studies confirm its cytosolic localization [20,21]. The quantitative analysis of the expression of VDR by Western blotting could not be performed, because its molecular weight on SDS-PAGE may be changed by ligand-induced stabilization [21] or post-transcriptional processing.…”