Subcellular distribution of DNA-binding and non-DNA-binding 1,25-dihydroxyvitamin D receptors in chicken intestine

Clinical and biochemical findings in parents of children with vitamin D-dependent rickets Type II

Vitamin D-dependent rickets type II is a rare disease caused by a disorder of the receptor for 1, 25-dihydroxyvitamin D (1, 25(OH)2D). Several parameters of this receptor-effector system were investigated to obtain biochemical information on the presumed heterozygotes of vitamin D-dependent rickets type II in parents of five patients and in their age-matched controls. It was found that the serum concentrations of 1, 25-(OH)2D and 24,25-dihydroxy-vitamin D (24,25(OH)2D), and the ratio of 1,25-(OH)2D/24,25-(OH)2D differed significantly in the parents from those of the patients and the respective control groups. In the parents' cultured skin fibroblasts, the activity of 25-hydroxyvitamin D-24-hydroxylase induced by 10(-8) mol/L 1, 25-(OH)2D3 ranged from 50 to 82% of that of their controls (versus 1-13% of controls for the patients). The binding capacity of the parents' [3H]1, 25-(OH)2D3 to the nucleus was 38-54% of that of their control subjects (versus 7-27% of controls for the patients). The parents' values were thus in a range between those of the patients and the control groups. These findings suggest that, in the parents, a partial impairment of the receptor system for 1, 25-(OH)2D led to an imbalance of vitamin D metabolism, thus confirming that vitamin D-dependent rickets type II is an autosomal recessive inherited disease. Serum concentrations of 1, 25-(OH)2D and 24, 25-(OH)2D may provide useful parameters for detecting heterozygotes of this disease.

Immunocytology with microwave-fixed fibroblasts shows 1 alpha,25-dihydroxyvitamin D3-dependent rapid and estrogen-dependent slow reorganization of vitamin D receptors

Prior studies have given no evidence for regulation of vitamin D receptor (VDR) compartmentalization or subcellular organization. Microwave fixation (9-15 s) and an indirect immunodetection system of avidin-biotin enhancement and phycoerythrin fluorophore resulted in sufficient spatial and temporal resolution to allow analysis of these processes. We studied cultured fibroblasts from normals or from patients with four different types of hereditary defect compromising VDR function (mutant cells). Compartmentalization of VDRs in the absence of 1,25-dihydroxyvitamin D3 (calcitriol) was regulated by serum or estrogen. VDRs were mainly cytoplasmic in cells cultured without serum and phenol red, but VDRs were mainly intranuclear after addition of serum or an estrogen to cells for at least 18 h (slow regulation). Calcitriol initiated a rapid and multistep process (rapid regulation) of reorganization in a portion of VDRs: clumping within 15-45 s, alignment of clumps along fibrils within 30-45 s, perinuclear accumulation of clumps within 45-90 s, and intranuclear accumulation of clumps within 1-3 min. We found similar rapid effects of calcitriol on VDRs in various other types of cultured cells. These sequential VDR pattern changes showed calcitriol dose dependency and calcitriol analogue specificity characteristic for the VDR. In mutant fibroblasts VDR pattern changes after calcitriol were absent or severely disturbed at selected steps. Treatment of normal cells with wheat germ agglutinin, which blocks protein transport through nuclear pores, also blocked calcitriol-dependent translocation of VDRs. We conclude that immunocytology after microwave fixation provides evidence for regulation of VDR organization and localization.

Effect of 1,25-dihydroxyvitamin D3 on mouse mammary tumor (GR) cells: evidence for receptors, cellular uptake, inhibition of growth and alteration in morphology at physiologic concentrations of hormone

Mammary glands are target tissues for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). We have examined a mouse mammary tumor cell line (GR) for receptors of 1,25(OH)2D3 and have examined alterations in the growth and morphology of these cells in response to 1,25(OH)2D3. GR cells contain a high affinity (Kd approximately 10(-11)), low-capacity receptor with a high specificity for 1,25(OH)2D3. The 1,25(OH)2D3 receptor in GR cells has a sedimentation coefficient of 3.5 and elutes from DEAE cellulose columns with approximately 0.15 M KCl. These properties of the receptor are similar to those reported for other 1,25(OH)2D3 receptors. 1,25(OH)2D3 is internalized by GR cells in situ and specifically bound 1,25(OH)2D3 is found predominantly, if not entirely, in the nucleus as determined by cell fractionation and autoradiographic techniques. The incubation of GR cells in culture for 7 days with 1,25(OH)2D3 markedly alters cell growth. Cell growth is retarded in a dose-dependent manner; physiologic concentrations (10(-10) M) of 1,25(OH)2D3 retard cell growth by approximately 50%. In addition, GR cells incubated with 10(-9) to 10(-8) M 1,25(OH)2D3 undergo marked morphological changes. The incubation of GR cells with other vitamin D metabolites such as 25-hydroxyvitamin D3 (25(OH)D3) at a concentration of 10(-9) M does not significantly alter cell growth or morphology. The presence of high affinity receptors for 1,25(OH)2D3, the specific internalization of 1,25(OH)2D3 predominantly into the nuclei, and the significant effects of physiological concentrations of 1,25(OH)2D3 on cell growth suggest a direct, specific, nuclear effect of 1,25(OH)2D3 on GR cells. The mouse mammary tumor model might be useful in examining the effect of 1,25(OH)2D3 on tumor formation.

The relationship between the vitamin D system and cancer

The classic function of 1,25-dihydroxyvitamin D3, the hormonally active form of vitamin D, is the maintenance of normal levels of calcium and phosphorus in the blood. 1,25-Dihydroxyvitamin D3 binds to a specific receptor protein and exerts its biologic action by a mechanism analogous to that proposed for other steroid hormones, that is, the receptor-ligand complex acts on the chromatin to induce transcription of specific genes. Intracellular receptors that bind 1,25-dihydroxyvitamin D3 with high affinity have been found in a large number of tumor cell lines examined as melanoma, osteosarcoma, and human breast and colonic carcinoma cells. The 1,25-dihydroxyvitamin D3 receptor in these cells has characteristics similar to the receptor in bone and intestine, the known target tissues of the hormone. In fact, 1,25-dihydroxyvitamin D3 inhibits the proliferation of melanoma, osteosarcoma, and breast carcinoma cells. More recently, 1,25-dihydroxyvitamin D3 has been shown to suppress the growth and induce monocytic differentiation of murine and human myeloid leukemia cells in vitro. These results point to a previously unsuspected involvement of vitamin D in cell proliferation and differentiation and suggest that analogs of the vitamin D hormone may be of interest as possible therapeutic agents in the treatment of malignancy.