Receptors for 1,25(OH)2-vitamin D3 enriched in cloned osteoblast-like rat osteogenic sarcoma cells

Target cell metabolism of 1,25-dihydroxyvitamin D3 to calcitroic acid. Evidence for a pathway in kidney and bone involving 24-oxidation

1,25-dihydroxyvitamin D3 is converted to calcitroic acid before being excreted in the bile. Biosynthesis of calcitroic acid has been demonstrated in two target cells of vitamin D, in the kidney and the osteoblastic cell line UMR-106. Calcitroic acid was identified by combinations of h.p.l.c., u.v. spectroscopy and mass spectrometry. Evidence is presented that calcitroate is derived from the 24-oxidation pathway, possibly through the intermediate 24,25,26,27-tetranor-1,23-dihydroxyvitamin D3. The 24-oxidation pathway to calcitroic acid in bone cells is stimulated by 1,25-dihydroxyvitamin D3. The pathway in both bone cells and perfused kidney operates at physiological concentrations of substrate and appears to be capable of rapid clearance of the hormone.

Identification of a vitamin D-responsive protein on the surface of human osteosarcoma cells

Monoclonal antibodies were elicited to membrane constituents of the osteoblastic human osteosarcoma cell line Saos-2. Two types of antibody reactivities were characterized: one group of antibodies identified fibroblastic and osteoblastic cultured cells, whereas the other group was specific for the parent cell line, Saos-2. Primary endothelial cells and hepatoma cells were not recognized by either group of antibodies. Through indirect immunofluorescent microscopy, the Saos-2-specific antigen was demonstrated to reside on the surface of these osteosarcoma cells. Metabolic radiolabeling of cultured Saos-2 cells and subsequent immunoprecipitation, electrophoretic separation, and autoradiography revealed this protein to have a Mr of 80,000. Similar experiments in the presence of hormones showed that the expression of this cell surface protein was influenced in an opposing fashion by the bone-regulating hormones parathyroid hormone and vitamin D. Vitamin D stimulated expression by 300%, whereas parathyroid hormone depressed expression by 50%. Thus, Saos-2 human osteoblastic cells demonstrate hormonal regulation through an apparently specific membrane protein.

Glucose transport system in UMR-106-01 osteoblastic osteosarcoma cells: regulation by insulin

Insulin is a potent stimulator of collagen synthesis and other osteoblastic cell functions. In various insulin-sensitive tissues, stimulation of glucose transport and glycolytic metabolism are hallmarks of insulin action and may play a role in insulin regulation of cellular function. However, the effects of insulin on glucose metabolism in osteoblast-like cells have not been defined. We therefore characterized 2-deoxy-D-glucose (2-DG) transport in UMR-106-01 rat osteoblastic osteosarcoma cells and examined its regulation by insulin. 2-DG (0.1 mM) uptake was shown to be linear with time over 45 minutes, temperature-sensitive, and inhibited by phloridzin. Competitive inhibition studies against other hexoses demonstrated a transport system stereospecificity for 2-DG similar to that previously demonstrated in fat and muscle cells. Kinetic analysis of 15 minute 2-DG uptake at 25 degrees C demonstrated a saturable transport mechanism with a Km (1.9 mM) similar to that observed for 2-DG transport in other tissues. Insulin stimulated 2-DG transport in a dose-related manner, with significant stimulation observed at 0.5 nM and maximal effect observed at 50 nM insulin. The stimulatory effect of insulin was reversibly inhibited by cytochalasin B (50 microM). Insulin stimulation of 2-DG transport was associated with a 1.7-fold increase in Vmax, while Km remained constant. When insulin effects on glucose transport were inhibited by the addition of 5 mM phloridzin, stimulatory effects on DNA and collagen synthesis were diminished, suggesting that stimulation of glucose transport may play a role in insulin effects on replication and function in osteoblast-like cells.

Micromolar aluminum levels reduce 3H-thymidine incorporation by cell line UMR 106-01

Aluminum-induced osteomalacia is a frequent complication observed in patients on maintenance hemodialysis. However, it is not known whether there are direct effects of aluminum on osteoblasts, or alternatively, whether the observed changes are due to changes in PTH or other factors. We sought to determine the effect of micromolar levels of aluminum on osteoblasts using a well-defined cell line derived from a 32P induced osteosarcoma of rat, UMR 106-01, which is alkaline-phosphatase positive, responds to PTH, and synthesizes type I collagen. Aluminum exposure was controlled using tissue culture media with [Al ] less than 1 microgram/liter (40 nM), produced by precipitation of aluminum salts at pH 8.5. The effect of defined [Al ], from 20 to 800 micrograms/liter (0.7 to 30 microM), was then determined by adding back aluminum while measuring DNA and protein synthesis. We found that aluminum depressed DNA synthesis, as determined by 3H-thymidine incorporation, by 60%, with half maximal effect at 20 micrograms/liter (740 nM) in cells at a density of 20,000/cm2. Alternatively, protein synthesis, as determined by 3H-leucine incorporation, did not decline, and in some cases increased. However, qualitative analysis of matrix proteins produced with and without 800 micrograms/liter (30 mM) [Al ] showed no differences. Direct measurements of cell number and protein synthesis confirmed these findings. Al does not alter the PTH-induced cAMP response of these cells. Thus, aluminum has a direct effect on cell division, and probably on protein synthesis, in this osteoblast-like cell line. These effects occur at levels of aluminum below those commonly contaminating tissue culture media, and thus are seen reproducibly only in media of defined [Al ].(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of calcitonin gene-related peptide on cyclic AMP formation in chicken, rat, and mouse bone cells

Mixed bone cell cultures obtained by sequential collagenase-trypsin digestion of newborn chick, rat, and mouse calvaria responded to calcitonin gene-related peptide (CGRP) with a dose-dependent increase in cyclic AMP formation. The amplitude of response to CGRP in each species was less than that to parathyroid hormone (PTH). The CGRP effect was not the result of an action as a weak calcitonin agonist, since in most instances a calcitonin effect was not observed. Only in early digests of mouse calvarial cells were consistent stimulatory effects of calcitonin on cyclic AMP noted, and these were always considerably less in amplitude than those to CGRP. It is concluded that chick, rat, and mouse bones contain cells in osteoblast-rich populations that respond specifically to CGRP with a rise in cyclic AMP.

Thyroid hormone 5'-deiodinase activity, nuclear binding, and effects on mitogenesis in UMR-106 osteoblastic osteosarcoma cells

The hyperthyroid state in vivo is associated with an increase in osteoblast number and activity, suggesting that thyroid hormone may stimulate osteoblast replication and function. We therefore examined the effects of T3 (16-1170 pM) on replication rate as assessed by cell counts in UMR-106 osteoblastic osteosarcoma cells cultured for 5-10 days in medium supplemented with 10% hormone-stripped fetal calf serum (FCS). Despite the virtual absence of thyroid hormone in the control medium (total T3 concentration, 0.02 ng/ml), the addition of T3 in concentrations to 1000 pM did not increase the cell replication rate. At higher T3 concentrations, a slight decrease in growth rate was observed. No significant 5'-monodeiodinase activity was detected in UMR-106 cell homogenates. However, nuclear binding of T3 was demonstrated in intact cells. A high-affinity nuclear binding component was identified with a Ka of 2.6 x 10(10) M-1 and a maximum binding capacity of 7.7 pg T3 per mg DNA, equivalent to 51 binding sites per cell nucleus. A lower affinity nuclear T3 binding component with a Ka of 1.8 x 10(9) M-1 was also identified. Thus, despite the presence of nuclear T3 receptors, UMR-106 cells do not exhibit a mitogenic response to T3.

Characterization of insulin binding in the UMR-106 rat osteoblastic osteosarcoma cell

The correlation of insulin receptor occupancy with classic insulin effects, such as stimulation of glucose uptake, have not been examined in osteoblastlike cells. Accordingly, we characterized insulin binding and examined its relationship to stimulation of glucose analog transport in the UMR-106 rat osteoblastic osteosarcoma cell line. Insulin binding in UMR-106 cells was found to be pH sensitive, temperature dependent, saturable, and specific. Proinsulin was 100-fold less effective than insulin in displacing specific [125I]insulin binding in these cells, whereas IGF-I at concentrations between 0.1 and 10 nM produced no displacement of [125I]insulin but did produce significant displacement of insulin binding at 100 and 1000 nM. Insulin receptor downregulation was observed after exposure to 100 nM insulin for 6 h at 37 degrees C and was temperature dependent. Insulin binding was reversible after 24 h at 4 degrees C. Insulin binding correlated directly with stimulation of 2-deoxyglucose uptake at insulin concentrations between 0.1 and 100 nM, with a half-maximal concentration (ED50) of 0.9 nM for both [125I]insulin binding displacement and stimulation of 2-deoxyglucose uptake. Hence, there was no evidence for spare insulin receptors with regard to stimulation of glucose analog transport. Scatchard analysis of insulin binding kinetics yielded a curvilinear plot, suggesting negative cooperativity. Analysis of insulin binding kinetics using a two-site model yielded a KD of 0.9 nM for the apparent high-affinity binding site and an estimated 80,000 high-affinity binding sites per cell. These findings demonstrate that osteoblastlike cells exhibit a relationship between insulin binding and glucose transport stimulation that is similar to that in liver cells and other insulin-sensitive tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Murine osteoblasts release bone-resorbing factors of high and low molecular weights: stimulation by mechanical deformation

Murine calvarial osteoblasts in monolayer culture were found to constitutively produce bone-resorbing factors; mechanical deformation significantly increased the synthesis and/or release of these factors. In short-term cultures (2 h) the resorptive activity was largely dialysable, indicating a relative molecular mass (Mr) less than 2000. Intermittent mechanical deformation stimulated the synthesis of these low Mr factors irrespective of serum conditions. Continuous deformation, however, was without effect. When the culture period was extended to 24 h, bone resorptive activity was stimulated by both intermittent and continuous deformation in the presence of 10% serum. This activity was dialysable. Over this same period in cultures with 2% serum, intermittent deformation also produced a non-dialysable bone-resorbing factor. We also cultured osteoblasts for 72 h in serum-free conditions and deformed the cells intermittently. Fractionation of the medium by high pressure liquid chromatography (HPLC) resolved three peaks of bone resorptive activity: peak I (Mr 50-60,000); peak II (Mr 5-20,000); and peak III (Mr less than 1000). Only peaks II and III were stimulated by mechanical deformation. These bone-resorbing factors remain as yet poorly characterized, but none of the activity in the HPLC fractions was attributable to interleukin-1 or prostaglandin E2.

Calbindin-D9K immunolocalization and vitamin D-dependence in the bone of growing and adult rats

This report presents evidence for the presence of the vitamin D-dependent calcium-binding protein, calbindin-D9K, in bone cells and matrix. In undecalcified frozen sections of growing and adult rat bone, calbindin-D9K was immunohistochemically localized in trabecular bone of the epiphysis and metaphysis and in cortical bone of the diaphysis. It was found within the cytoplasm of osteocytes, of osteoblasts lining the osteoid, and osteoblasts inside the osteoid seams. It was also found in the osteoblast processes and the anastomosed reticulum of the processes connecting the osteocytes with each other. Extracellularly, calbindin-D9K immunoreactivity was present in compact cortical bone in the areas of the mineralized matrix surrounding the osteocyte lacunae, and in the pericanalicular walls containing the cell processes. Calbindin-D9K immunoreactivity was low or absent from the cytoplasm of osteocytes in trabecular bone from severely vitamin D-deficient rats and restored in vitamin D-deficient rats given a single dose of 1,25(OH)2-VitD3. Thus, the synthesis of immunoreactive calbindin-D9K by osteoblasts and osteocytes in trabecular bone is vitamin D-dependent. The presence of immunoreactive calbindin-D9K in the osteocytes and their cell processes suggests that this calcium-binding protein is involved in the calcium fluxes regulating bone calcium homeostasis. Its localization in osteoblasts involved in bone formation and in their cell processes suggests that it has a role in the calcium transport from these cells towards the sites of active bone mineralization.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone-related protein: isolation, molecular cloning, and mechanism of action

Many factors, such as interleukin 1, TGF alpha, tumor necrosis factor alpha and beta, and PGs, have been implicated in etiological roles in HHM (Martin and Mundy, 1987). Much interest in the past has also centered upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and were found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the NH2 terminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support of this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have a similar intron--exon organization as the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have enabled detailed structure-function studies that have identified NH 2-terminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in a subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP have added to our understanding of the mechanisms of hypercalcemia and may contribute to the understanding of other metabolic bone diseases, such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in normal cell physiology.

Effects of lectins and tunicamycin on cAMP response to parathyroid hormone

Carbohydrate moieties of cell surface glycoproteins with an external orientation play a role in hormone recognition and/or transmembrane signal transmission. We have examined the effect of various lectins, which interact with specific cell surface glycosyl residues, and of tunicamycin, an antibiotic that inhibits glycosylation of proteins, on the adenosine 3',5'-cyclic monophosphate (cAMP) response to parathyroid hormone (PTH) in confluent cultured osteoblast-like rat osteosarcoma cells (UMR-106) and opossum kidney cells (OK cells). Incubation of both cell lines with wheat germ lectin (WGL), but not with concanavalin A, succinylated wheat germ, ricin, or soybean lectins, markedly reduced the PTH-induced cAMP production, whereas the stimulation obtained with forskolin, a compound that acts directly on the adenylate cyclase enzyme, was not affected. In contrast, tunicamycin did not cause any decrease in the cAMP response to PTH. These results indicate that the masking of sialic acid residue by WGL considerably blunted PTH-stimulated cAMP production in cultured osteoblast-like and kidney cells. An 80% inhibition of glycosylation of cell surface proteins did not appear to affect the response to PTH. Thus the functional role of this carbohydrate moiety in the PTH receptor remains to be determined.

Bone-resorbing agents promote and interferon-gamma inhibits bone cell collagenase production

Parathyroid hormone, prostaglandin E2, 1 alpha,25-dihydroxyvitamin D3, interleukin-1, tumor necrosis factor alpha, and epidermal growth factor, all known stimulators of bone resorption, markedly enhanced collagenase secretion by rat fetus osteoblastlike cells in primary culture as judged by enzyme-linked immunosorbent assay. Untreated cells contained no immunostainable or extractable collagenase. Collagenase was detected in the treated cells and media only after 1-3 h of treatment, and there was no increment in collagenase activity when cells were treated in the presence of actinomycin D or cycloheximide. Cells secreted collagenase in a latent form and also elaborated collagenase inhibitor; chromatographic separation of collagenase from collagenase inhibitor and subsequent activation of the collagenase with trypsin yielded the active species in stimulated but not in unstimulated cells. The ability of individual prostanoids, among seven tested, to promote collagenase production correlated positively with their reported capacity to promote bone resorption. Interferon-gamma (IFN-gamma), a known resorption inhibitor, blocked the increment in collagenase production caused by all agents tested. These results indicate a close linkage between stimulation of bone resorption and collagenase production by osteoblastlike cells. Various resorption stimulators, including some not previously tested for effects on collagenase, augment the de novo synthesis and secretion of collagenase and act by an IFN-gamma-inhibitable mechanism.

Parathyroid hormone-related protein: a novel gene product

Many factors, such as interleukin 1, transforming growth factor alpha, tumour necrosis factor alpha and beta, and prostaglandins, have been implicated in the pathogenesis of the humoral hypercalcaemia of malignancy (Mundy and Martin, 1982; Martin and Mundy, 1987; Mundy et al, 1984). Much interest in the past has also centred upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and found to encode a pre-pro-peptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the aminoterminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support of this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have an intron-exon arrangement that is more complex than the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have allowed detailed structure-function studies that have identified aminoterminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in a subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcaemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP has added to our understanding of the mechanisms of hypercalcaemia and may contribute to the understanding of other metabolic bone diseases, such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in normal cell physiology.

Evidence that the self-induced metabolism of 1,25-dihydroxyvitamin D-3 limits the homologous up-regulation of its receptor in rat osteosarcoma cells

The osteoblast-like osteosarcoma cell line UMR-106 has been shown to possess high-affinity receptors for 1,25-dihydroxyvitamin D (1,25-(OH)2D3). Also, these cells metabolize 1,25-(OH)2D3 to more polar metabolites. As previously demonstrated (Pols, H.A.P., et al. (1987) Biochim. Biophys. Acta 931, 115-119) the time course of specific binding of 1,25-(OH)2D3 in intact UMR-106 cells was found to be characterised by (a) an ascending phase, representing association with receptor, (b) a maximum at 90-120 min and (c) a rapid descending phase, closely associated with a decrease of medium 1,25-(OH)2D3 due to the metabolism of the hormone. The purpose of the present study was to investigate further the self-induced metabolism of 1,25-(OH)2D3 in relation to the homologous up-regulation of its receptor in these cells. Inhibition of metabolism of 1,25-(OH)2D3 with ketoconazole resulted, after a lag-time of about 90 min, in a sharp increase of receptor accumulation. This increase in receptor level in the presence of ketoconazole was blocked by coincubation with cycloheximide and actinomycin D. Preincubation experiments with unlabeled 1,25-(OH)2D3 showed that the elevation of hormone binding was 1,25-(OH)2D3-concentration dependent (ED50 200-300 pM). Addition of ketoconazole during these preincubations resulted in an even more pronounced accumulation of receptors, whereby the ED50 (50-60 pM) was comparable with the dissociation constant of the 1,25-(OH)2D3 receptor (41.3 +/- 4.3 pM). In summary, these data support the concept that the self-induced metabolism of 1,25-(OH)2D3 has a dual effect: (1) directly, by the regulation of the cellular concentration of and, consequently, receptor occupancy by the active form of vitamin D and (2) indirectly by its ability to modulate the ligand-dependent regulation of the 1,25-(OH)2D3.

Does interleukin-1 affect intracellular calcium in osteoblast-like cells (UMR-106)?

Interleukin-1 (IL-1) enhances bone resorption and formation in vitro, presumably through a primary action on osteoblasts, but the mechanism by which IL-1 activates bone cells is unknown. We investigated the possibility that the effect of IL-1 on osteoblasts is mediated through an increase in intracellular calcium [Ca++]i by studying the effects of purified human monocyte-derived IL-1 (hIL-1) and recombinant human IL-1 alpha (rhIL alpha) and beta (rhIL-1 beta) on [Ca++]i in the rat osteogenic sarcoma cell line UMR 106 using indo-1, a new-generation fluorescent Ca++-sensitive probe. hIL-1 (1 U/ml) resulted in an 85.5% rise in [Ca++]i over baseline that reached a peak after 30 seconds and returned to basal levels within 60 seconds. A similar transient rise in calcium was obtained upon exposure of the UMR cells to both the hIL-1 suspension buffer and to the concentration of fetal bovine serum present in the hIL-1 buffer. This effect was not abolished either by heat inactivation of both hIL-1 and serum or by pretreatment of hIL-1 with specific rabbit antihuman-IL-1 antibody. Moreover, exposure of the UMR cells to either rhIL-1 alpha or rhIL-1 beta or to a mixture of both at concentrations of 1 to 100 U/ml was not followed by any change in [Ca++]i. Our data do not support the idea that IL-1 can stimulate osteoblasts through a calcium-mediated pathway.

Heterogeneity of bone resorbing factors produced by unstimulated murine osteoblasts in vitro and in response to stimulation by parathyroid hormone and mononuclear cell factors

The bone resorbing activity of factors released from monolayer cultures of osteoblasts (OB) was examined by measurement of calcium released by neonatal mouse calvaria in vitro. Unstimulated conditioned media (CM) were found to contain significant bone resorbing activity, which was partially inhibited by indomethacin, dexamethasone and nordihydroguaiaretic acid. Ultrafiltration of CM (molecular weight cut-off of 5000) revealed bone resorbing activity in the filtrate and retentate. Fractionation of the CM by high-performance liquid chromatography revealed four major peaks of bone resorbing activity. Stimulation of the OB by mononuclear cell factor and parathyroid hormone significantly increased the synthesis and/or release of these factors with a relatively greater increase of lipid-soluble, low molecular-weight activity. These results suggested an important role for relatively small non-popular mediators in hormonally stimulated bone resorption.

Calcification of osteoblastlike rat osteosarcoma cells in agarose suspension cultures

Ros 17/2 clonal rat osteosarcoma cells calcify when cultured in the presence of 10 micrograms/ml beta-glycerol phosphate in an agarose gel. Culture in 1% agarose inhibited cell division while allowing cells to remain metabolically active and viable for over 21 days. Serial photography of the same microscopic field shows a progressive deposition of calcium phosphate during the course of the experiment. The deposition of calcium around cells was confirmed by calcium-specific stains, and by energy dispersive X-ray analysis (EDX) during scanning electron microscopy. Cells with high calcium content analyzed by EDX had Ca:P ratios similar to hydroxyapatite. Total calcium progressively increased in beta-glycerol phosphate-treated cultures whereas the control plates maintained a constant calcium content over 16 days. Alkaline phosphatase activity increased with time in culture whereas cells with beta-glycerol phosphate maintained the alkaline phosphatase values achieved at the time of initial calcification. Alkaline phosphatase staining revealed no correlation between the presence of the enzyme activity and calcification. Radioimmunoassay for the bone-specific vitamin K-dependent protein bone Gla protein showed that beta-glycerol phosphate-treated cells accumulate over sixfold greater amounts of this protein. Our studies show that ROS cells can calcify and accumulate bone-specific matrix components when cultured in a 3-dimensional agarose matrix.

Degradation of type I collagen films by mouse osteoblasts is stimulated by 1,25 dihydroxyvitamin D3 and inhibited by human recombinant TIMP (tissue inhibitor of metalloproteinases)

Mouse calvarial osteoblasts grown on native type I collagen films degrade collagen in response to 1,25 (OH) 2vitD3. Collagen degradation is accompanied by increased latent collagenase and gelatinase secretion and by a reduction in free TIMP. Exogenous human recombinant TIMP abolished 1,25 (OH) 2vitD3 stimulated collagen degradation and inhibited background collagenolysis. No active metalloproteinases were detectable in the culture medium suggesting sequestration of active enzyme at the site of action or inhibition by residual TIMP. Chondrocytes could not mimic osteoblasts in this system.

High lateral mobility of endogenous and transfected alkaline phosphatase: a phosphatidylinositol-anchored membrane protein

The lateral mobility of alkaline phosphatase (AP) in the plasma membrane of osteoblastic and nonosteoblastic cells was estimated by fluorescence redistribution after photobleaching in embryonic and in tumor cells, in cells that express AP naturally, and in cells transfected with an expression vector containing AP cDNA. The diffusion coefficient (D) and the mobile fraction, estimated from the percent recovery (%R), were found to be cell-type dependent ranging from (0.58 +/- 0.16) X 10(-9) cm2s-1 and 73.3 +/- 10.5 in rat osteosarcoma cells ROS 17/2.8 to (1.77 +/- 0.51) X 10(-9) cm2s-1 and 82.8 +/- 2.5 in rat osteosarcoma cells UMR106. Similar values of D greater than or equal to 10(-9) cm2s-1 with approximately 80% recovery were also found in fetal rat calvaria cells, transfected skin fibroblasts, and transfected AP-negative osteosarcoma cells ROS 25/1. These values of D are many times greater than "typical" values for membrane proteins, coming close to those of membrane lipid in fetal rat calvaria and ROS 17/2.8 cells (D = [4(-5)] X 10(-9) cm2s-1 with 75-80% recovery), estimated with the hexadecanoyl aminofluorescein probe. In all cell types, phosphatidylinositol (PI)-specific phospholipase C released 60-90% of native and transfection-expressed AP, demonstrating that, as in other tissue types, AP in these cells is anchored in the membrane via a linkage to PI. These results indicate that the transfected cells used in this study possess the machinery for AP insertion into the membrane and its binding to PI. The fast AP mobility appears to be an intrinsic property of the way the protein is anchored in the membrane, a conclusion with general implications for the understanding of the slow diffusion of other membrane proteins.

Early manifestations of vitamin D effects in rat osteogenic sarcoma cells

We have recently demonstrated that 48 hour exposure of ROS 17/2 cells to low concentrations of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) (1.0 pg/ml) stimulated the cellular accumulation of 45Ca, and exposure to high concentrations (160 pg/ml) inhibited such accumulation. In the present study, short-term (15 min) effects of the sterol on 45Ca accumulation in ROS 17/2 cells were compared with the long-term (48 hours) effects in order to clarify mechanisms responsible for 1,25(OH)2D3 control of calcium metabolisms in ROS 17/2 cells. ROS 17/2 cells were grown for 48 hours in the presence and absence of 1,25(OH)2D3 and then incubated for an additional 15 min in the presence and absence of 1,25(OH)2D3 immediately before measuring 45Ca accumulation. Cellular 45Ca was measured after incubating the cells in the medium containing 0.5 microCi/ml of 45CaCl2 for 4 min at 25 degrees C. The effect of actinomycin D was determined by preincubating the cells in 0.1 microgram/ml of actinomycin D for 45 min at 25 degrees C. Exposure to low concentrations (1.0 pg/ml) of 1,25(OH)2D3 for either 48 hours or 15 min increased 45Ca in the cells by 10-20%. An additional 15 min exposure following 48 hour exposure yielded an increase in the cellular 45Ca similar to that after 48 hours or 15 min exposure. Exposure to high concentrations (160 pg/ml) for either 48 hour or 15 min decreased cell 45Ca by approximately 20%. An additional 15 min exposure to the high concentrations did not change the 48 hour effect. Actinomycin D reversed early inhibitory effects of high concentrations, but had no effect on the early stimulatory effects of low concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Separation of protein hormones

The purpose of this review is to highlight modern techniques in HPLC and electrophoresis used for protein hormone separations. The advent of biotechnological methods for production of synthetic polypeptides and recombinant proteins will have a significant future impact on the types of therapeutics and metabolites that need to be monitored in the clinical laboratory. The protein hormone examples given in this work were selected because of the comprehensive body of separation science literature and not necessarily for their future importance in medicine. The intention was to present an array of general methods and techniques which may be useful to the clinical investigator for analysis of any protein hormone.

Purification and partial amino acid sequencing of rat bone tumor (UMR106) alkaline phosphatase

Cultured rat osteosarcoma (UMR106) alkaline phosphatase was purified to apparent homogeneity by sequential application of polyclonal antibody affinity, DEAE-cellulose, and Sepharose CL-6B chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the enzyme preparation treated with sodium dodecyl sulfate and mercaptoethanol showed the presence of a dominant band (using silver staining) corresponding to a molecular weight of 80,000. The amino acid composition was similar to those of various alkaline phosphatases. The N-terminal amino acid sequence was determined as follows: Phe-Val-Pro-Glu-Lys-Glu-Lys- Asp-Pro-Ser-Tyr-Trp-Arg-Gln-Gln-Ala-Gln-Glu-Thr-Leu- Lys-Asn-Ala-Leu-Lys-?-Gln-Lys-?-Asn-Val-Asn-Ala-Lys.

Parathyroid hormone acutely elevates intracellular calcium in osteoblastlike cells

Changes in cytoplasmic calcium concentration ([Ca2+]i) activate numerous cellular processes thus mediating the effects of a number of hormones, but whether this mechanism is involved in the activation of osteoblasts by parathyroid hormone (PTH) remains uncertain. To examine this question, [Ca2+]i has been measured in suspensions of UMR 106 cells, a rodent osteosarcoma cell line with an osteoblastic phenotype. Basal [Ca2+]i was 137 +/- 3.7 nM (n = 60) and after the addition of rat PTH-(1-34) [rPTH-(1-34)] there was a rapid, dose-related increase with return to base line within 1 min. Half-maximal stimulation was produced by 5 X 10(-8) M rPTH-(1-34). Complexing of intracellular calcium by EGTA addition immediately before that of rPTH did not affect the calcium transient; neither did MnCl2 (10(-4) M) nor diltiazem (10(-4) M). Verapamil (10(-5) M) reduced the [Ca2+]i peak height after rPTH to 0.48 +/- 0.14 of control (n = 7). 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoic acid and dantrolene both reduced the [Ca2+]i response to rPTH (0.65 +/- 0.08 and 0.29 +/- 0.13 of control, respectively). Forskolin (10(-6) and 10(-5) M) produced a slight [Ca2+]i transient smaller in amplitude than seen with PTH. It is concluded that PTH mobilizes an intracellular calcium pool in these osteoblastlike cells, and the predominant mechanism for this is independent of cAMP.

cDNA cloning of alkaline phosphatase from rat osteosarcoma (ROS 17/2.8) cells

Two cDNA clones of rat alkaline phosphatase (AP) were isolated from a rat osteosarcoma lambda gt 11 cDNA library (ROS 17/2.8) utilizing a human bone-liver-kidney (BLK) type AP cDNA. These clones contain overlapping DNA sequences of 597 and 520 bp, respectively, corresponding to the 3' noncoding region of AP mRNA. The sequence homology with the human BLK AP cDNA is 61%. In Northern blot analysis the rat cDNA hybridizes to a single band of 2.5 kb mRNA from ROS 17/2.8 and rat liver, under highly stringent conditions. Steady state levels of AP mRNAs measured in several rat osteosarcoma cell lines (ROS 17/2.8, ROS 2/3, ROS 25/1, UMR 106) correlate with the level of AP enzymatic activity in these cells. Dexamethasone, which stimulates AP enzymatic activity in ROS 17/2.8 cells, increases the relative abundance of AP mRNA in a dose-dependent manner. This probe can be used to study AP expression in rat tissues and cells.

Hormonal influences on bone cells

The methods for establishing osteoblast-rich rat calvarial cell cultures have been described, together with methods for the use of clonal osteogenic sarcoma cells of osteoblast phenotype. The latter clonal lines are useful for several purposes, but all the precautions and quality control measures necessary in the study of clonal lines must be observed. Some of the techniques for studying biochemical responses to hormones in these cells have also been detailed, but clearly others are applicable, including studies of the synthesis of matrix constituents. Osteoclast-like cells have not been considered in this chapter, because osteoclast culture methods have not yet been developed to the degree of purity and reproducibility necessary for this type of biochemical approach.

Cyclic AMP-dependent and -independent effects on tissue-type plasminogen activator activity in osteogenic sarcoma cells; evidence from phosphodiesterase inhibition and parathyroid hormone antagonists

The plasminogen activator (PA) in clonal osteogenic sarcoma cells of rat origin (UMR 106-01 and UMR 106-06) and in osteoblast-rich rat calvarial cells has been characterized using specific antibodies to be tissue-type PA (tPA). An Mr value of 75,000 by SDS-polyacrylamide gel electrophoresis and fibrin autoradiography supports this characterization. There was also evidence for an Mr 105,000 component, which could be due to a proteinase-inhibitor complex. The mechanism of regulation of this tPA activity has been studied in the clonal osteogenic sarcoma cells. Parathyroid hormone (PTH) and prostaglandin E2, which increase cyclic AMP production in the sarcoma cells, also increased tPA activity. The sensitivity and magnitude of the tPA response to PTH and prostaglandin E2 were increased by simultaneous treatment with isobutylmethylxanthine (IBMX) at drug concentrations which had little effect themselves on tPA activity. In UMR 106-06 cells, which unlike UMR 106-01 cells show a cyclic AMP response to calcitonin, tPA activity was also increased in response to calcitonin, and the effect was enhanced by IBMX. 1,25-Dihydroxyvitamin D-3 also increased tPA activity in the cells, but this response was not modified by IBMX. Synthetic peptide antagonists of PTH-responsive adenylate cyclase, [34Tyr]-hPTH (3-34) amide and [34Tyr]-hPTH (5-34) amide, inhibited the PTH-induced increase in tPA activity over the same concentration range at which they inhibited cyclic AMP production, but the antagonist peptides had no effect on the tPA responses to prostaglandin E2, calcitonin or 1,25-dihydroxyvitamin D-3. These data indicate that cyclic AMP mediates the actions of PTH, prostaglandin E2 and calcitonin in increasing tPA activity in the clonal osteogenic sarcoma cells. 1,25-Dihydroxyvitamin D-3, on the other hand, increases tPA activity through a mechanism independent of cyclic AMP.

Effects of ascorbic acid on alkaline phosphatase activity and hormone responsiveness in the osteoblastic osteosarcoma cell line UMR-106

L-ascorbic acid at physiological concentrations (10 micrograms/ml) increased alkaline phosphatase activity in the osteoblastlike rat osteosarcoma cell line, UMR-106. The increase was dose-dependent and detectable at 6 hours after the addition of 100 micrograms/ml ascorbic acid to the medium. Treatment of the cells with 100 micrograms/ml ascorbic acid potentiated the response of cAMP to both PTH and PGE1, while cell growth was inhibited. Furthermore, the number of colonies formed by the cells grown in the soft agar was significantly reduced by increasing concentrations of ascorbic acid. These results indicate that ascorbic acid might play some role in the differentiation of osteoblasts.

Calcitonin gene-related peptide (CGRP) acts independently of calcitonin on cyclic AMP formation in clonal osteogenic sarcoma cells (UMR 106-01)

In several human cancer cell lines and in a subclone of rat osteogenic sarcoma cells (UMR 106-06) possessing calcitonin receptors and a calcitonin-responsive adenylate cyclase, calcitonin gene-related peptide (CGRP) behaved as a weak calcitonin agonist. In another subclone of the same osteogenic sarcoma (UMR 106-01) with no measurable calcitonin receptors or response, both rat and human CGRP were found to increase cyclic AMP formation in a dose-dependent manner. The data indicate that CGRP is capable of a weak calcitonin-like action in cells with calcitonin receptors, but also that in some cells CGRP activates adenylate cyclase itself, independently of calcitonin receptors.

Advances in understanding cell interactions in tissue resorption. Relevance to the pathogenesis of periodontal diseases and a new hypothesis

Much of the connective tissue degradation that takes place in periodontal diseases is mediated by proteolytic enzymes. Previous studies have focused on the action of proteinases released by invading polymorphonuclear neutrophils and macrophages, and bacterial enzymes. In view of recent work establishing that resident connective tissue cells can be induced by cytokines to bring about the destruction of their own matrix, we propose a new hypothesis. In this we envisage that a critical step is the interaction of bacterial antigens with inflammatory cells, resulting in the production of a cytokine, interleukin-1. Our interpretation of in vitro evidence is that the loss of connective tissue attachment and bone matrix resorption in periodontal diseases is mediated by metalloproteinases such as collagenase and stromelysin released by cells of the periodontium. Such proteolytic destruction can be induced by interleukin-1, whose production may not be dependent on a specific microbial flora but may be triggered by a number of organisms. It is now clear that interleukin-1 has multiple actions on both immune and non-immune cells; these include the induction of lymphocyte differentiation and proliferation and the stimulation of bone and cartilage resorption, and prostaglandin and metalloproteinase synthesis by connective tissues. It seems likely that further knowledge about the production and function of this cytokine will have an increasing impact in many diseases that involve resorption, particularly since interleukin-1-like molecules can be produced by cell types other than monocytes/macrophages, including keratinocytes and fibroblasts.

Molecular characterization of the EGF receptor and involvement of glycosyl moieties in the binding of EGF to its receptor on a clonal osteosarcoma cell line, UMR 106-06

The epidermal growth factor receptor in cells of the UMR 106-06 clonal osteoblast line has been shown to be structurally similar to that previously characterized in other cell lines. A specific receptor component of approximately 165,000-185,000 Mr has been identified by polyacrylamide gel electrophoresis using the chemical crosslinker disuccinimidyl suberate to crosslink 125I-EGF to its receptor. Tunicamycin treatment of cells resulted in a dose-dependent loss of binding suggesting involvement of glycosyl moieties in EGF binding to its receptor. Competitive binding studies carried out using wheat germ lectin (WGL), concanavalin A (CON.A.), soybean lectin (SBL), and lentil lectin (ILL) to compete for binding of 125I-EGF revealed that CON A, WGL, and to a lesser extent LL could inhibit EGF binding; SBL was without effect. Treatment of the cells with neuraminidase which cleaves terminal sialic acid residues resulted in total loss of binding while alpha-glucosidase, beta-N-acetylglucosaminidase and alpha-mannosidase were without effect. These data indicate a specific interaction of EGF with terminal sialic acid residues of the EGF receptor. However, it would seem that the mannose residues which appeared to modify EGF binding were not available for the action of the above enzymes due to the presence of sialic acid.

Selective osteoblast mitogens can be extracted from prostatic tissue

Extracts of human prostatic carcinoma and of human benign prostatic hyperplasia were found to exhibit mitogenic activity in freshly isolated rat osteoblasts, rat fibroblasts, and osteoblast-derived osteosarcoma cells. This activity was markedly reduced by tryptic digestion of extracts, indicating its protein nature. Results of bioassay studies suggested that the prostatic material was different from a number of known growth factors. Analysis by reversed-phase high performance liquid chromatography revealed that extracts contained mitogenic activity for osteoblasts that was distinct from fibroblast-stimulating activity. Such osteoblast growth factors could form the basis of the skeletal osteogenic response to metastatic prostatic adenocarcinoma.

Vitamin A effects on UMR 106 osteosarcoma cells are not mediated by specific cytosolic receptors

Retinol and retinoic acid at 20 microM altered cell morphology and inhibited cell proliferation of UMR 106 osteosarcoma cells in culture. No specific cytosolic binding proteins for retinol could be detected.

Regulation of creatine kinase activity in rat osteogenic sarcoma cell clones by parathyroid hormone, prostaglandin E2, and vitamin D metabolites

We have previously shown that both parathyroid hormone (PTH) and prostaglandin E2 (PGE2) stimulate the activity of creatine kinase BB (CKBB) in rat bone cells in culture. Therefore, morphologically distinct rat osteogenic sarcoma cells in culture were tested for stimulation of CKBB activity by hormones that regulate skeletal tissues. PTH stimulated CKBB in the osteoblast-like clone ROS 17/2; 1 alpha,25(OH)2D3 inhibited this activity while PGE2, CT and 24R,25(OH)2D3 had no significant effect. PGE2 stimulated CKBB activity in the fibroblast-like clone ROS 24/1, which was unresponsive to PTH, CT and Vitamin D metabolites. 24R,25(OH)2D3 as well as PGE2 (but not PTH, CT or 1 alpha 25(OH)2D3) stimulated CKBB in clone ROS 25/1, suggesting that this fibroblast-like clone has some chondroblast-like character. Both PTH and PGE2 stimulated the brain type isoenzyme of CK (CKBB), although the osteogenic sarcoma cell clones contain a significant proportion of the muscle type of CK (CKMM). Thus, increased CKBB activity can serve as an additional characteristic marker for the action of steroid and polypeptide hormones and for prostaglandins.

Comparison of renal and osseous binding of parathyroid hormone and hormonal fragments

We compared receptor binding and adenylate cyclase stimulation of intact bovine parathyroid hormone (bPTH)-(1-84) and the synthetic amino-terminal fragments, bPTH-(1-34) and rat PTH (rPTH)-(1-34). Radioligands for binding studies were prepared by the lactoperoxidase technique and purified by high-pressure liquid chromatography. In both canine renal membranes and cloned rat osteosarcoma cells the amino-terminal fragments bound to a single order of sites; the affinity of rPTH-(1-34) exceeded that of bPTH-(1-34), correlating with its higher potency in stimulating adenylate cyclase. In studies with oxidized bPTH-(1--84), the middle and carboxyl regions of intact PTH were found to bind to both tissues but with higher affinity to osteosarcoma cells than to renal membranes. Our results demonstrate that rPTH-(1--34) is the most favorable probe of amino-terminal PTH binding and the most potent of the PTH peptides in stimulating renal and osseous adenylate cyclase. The results also show that midregion and carboxyl determinants within intact PTH contribute to hormone binding, which does not correlate with adenylate cyclase activation and appears more significant for skeletal than for renal binding.

Inhibitory effects of parathyroid hormone on growth of osteogenic sarcoma cells

The effects of the bone resorbing hormone, parathyroid hormone (PTH), on the growth of malignant osteoblastic cells have been examined. The malignant osteoblastic cells were a clonal line (UMR 106) derived from a transplantable rat osteogenic sarcoma. The predominant effect of PTH at doses above 10(-10) M was an inhibition of replication and DNA synthesis. Replication was decreased by PTH in both the presence or absence of serum and at various cell seeding densities. Both bovine PTH (1-84) and the synthetic hormone, human PTH (1-34), inhibited replication, but with bovine hormone being an order of magnitude more potent. The effects could be observed in as short a time as 6 hours with DNA synthesis and 24 hours with replication.

Regulation of prostaglandin production by osteoblast-rich calvarial cells

The effect of various factors upon prostaglandin (PG) production by the osteoblast was examined using osteoblast-rich populations of cells prepared from newborn rat calvaria. Bradykinin and serum, and to a lesser extent, thrombin, were all shown to stimulate PGE2 and 6-keto-PGF1 alpha (the hydration product of PGI2) secretion by the osteoblastic cells. Several inhibitors of prostanoid synthesis, dexamethasone, indomethacin, dazoxiben and nafazatrom, were tested for their effects on the calvarial cells. All inhibited PGE2 and PGI2 (the major arachidonic acid metabolites of these cells) production with half-maximal inhibition by all four substances occurring at approximately 10(-7) M. For dazoxiben and nafazatrom, this was in contrast to published results from experiments in vivo which have indicated that the compounds stimulated PGI2 production. Finally, since the osteoblast is responsive to bone-resorbing hormones, these were tested. Only epidermal growth factor (EGF) was shown to modify PG production. At early times EGF stimulated PGE2 release, however, the predominant effect of the growth factor was an inhibition of both PGE2 and PGI2 production by the osteoblastic cells. The present results suggest that the bone-resorbing hormones do not act to cause an increase in PG by the osteoblast and that any increase in PG production by these cells may be in response to vascular agents.

Estimation of 1,25 dihydroxyvitamin D by cytoreceptor and competitive protein binding assays without high pressure liquid chromatography

Using two different cultured rat osteosarcoma cell lines (UMR 106 and ROS 17/2.8) we have investigated the recently described cytoreceptor assay for 1,25-dihydroxyvitamin D (1,25-(OH)2D). The assay method is relatively simple and sensitive to 2.4 fmole per tube. Using either cell line, assay of serum samples, whose only preparation consisted of extraction and purification on a disposable diatomaceous earth column, produced variable values for serum 1,25-(OH)2D. Additional purification, using a disposable silicic acid minicolumn to remove other vitamin D metabolites resulted in consistent values and additional HPLC resulted in no further decrease in the values obtained. Our results show that a single two stage non-HPLC column can purify serum samples for assay in the cytoreceptor assay. The method is also applicable to the competitive protein binding assay employing calf thymus cytosol and the correlation between values obtained by both methods is highly significant. It is a sensitive, simple, and accurate method with technical advantages which allow greater sample throughput than other 1,25-(OH)2D assays.

1 alpha,25-dihydroxyvitamin D3 receptors and their action in embryonic chick chondrocytes

The role of vitamin D in the maturation of epiphyseal chondrocytes was investigated in the developing chick embryo. Cartilage tissues were divided into two parts: resting cartilage and growth cartilage. A cytosol component to which 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) is specifically bound first appeared in the growth cartilage on day 15, rapidly increased, and attained a maximum on day 19. The calcium content of the growth cartilage also began to increase on day 15 and continued to increase in parallel with the 1 alpha,25(OH)2D3 receptor levels. Glycosaminoglycan (GAG) synthesis by the growth cartilage cells increased from day 11-17 and rapidly declined thereafter reciprocally with the increase in calcium and receptor levels. In the resting cartilage, no cytosol receptor for 1 alpha,25(OH)2D3 was detected up to hatching time. The calcium content and GAG synthesis in the resting cartilage were very low and did not change appreciably throughout development. No receptor-like macromolecule for 24R,25-dihydroxyvitamin D3 (24R,25(OH)2D3) was recognized in either the resting or growth cartilage. 1 alpha,25(OH)2D3 added to the culture of chondrocytes from the epiphyseal growth cartilage inhibited GAG synthesis and stimulated its release from the cell layer into the medium in a dose-dependent manner. These in vitro effects of 1 alpha,25(OH)2D3 were not observed in chondrocytes obtained from 13-day-old growth cartilage and 19-day-old resting cartilage. 25-Hydroxyvitamin D3 and 24R,25(OH)2D3 had no effect on chondrocytes in any of the preparations. These results suggest that 1 alpha, 25 (OH)2D3 is directly involved in the maturation of chondrocytes and possibly in the calcification of growth cartilage.

Characterization of an osteoblast-like clonal cell line which responds to both parathyroid hormone and calcitonin

The clonal cell line UMR 106, which was originally derived from a rat transplantable osteogenic sarcoma with an osteoblastic phenotype, was subcloned after the emergence of a calcitonin-responsive adenylate cyclase was noted in late passages. Detailed studies on the stimulation of adenylate cyclase and activation profile of the cyclic AMP-dependent protein kinase isoenzymes in response to parathyroid hormone (PTH) and salmon calcitonin (SCT) were conducted on two subclones (UMR 106-01 and UMR 106-06). Both subclones responded in an identical manner to PTH, which stimulated adenylate cyclase and activated both isoenzyme I and isoenzyme II of cyclic AMP-dependent protein kinase. In contrast, only UMR 106-06 cells responded to calcitonin. At 3 X 10(-8)M SCT, there was a sevenfold stimulation of adenylate cyclase, 84% activation of isoenzyme I, and 44% activation of isoenzyme II. The activation profiles of the isoenzymes to PTH and SCT in UMR 106-06 were similar. Furthermore, their response to SCT correlates with the presence of specific, saturable binding of 125I-labeled SCT. Binding parameters indicate apparent Kd = 0.8 nM and 6,000 receptors/cell. These data point to a significant phenotypic change having taken place in this clonal cell line with prolonged maintenance in culture, with the emergence of a calcitonin receptor linked to adenylate cyclase and protein kinase activation.

Stimulation of plasminogen activator in osteoblast-like cells by bone-resorbing hormones

Hormonal control of plasminogen activator (PA) was studied in clonal rat osteogenic sarcoma cells which are phenotypically osteoblast, and in osteoblast-rich rat bone cell cultures. The bone-resorbing hormones (parathyroid hormone, prostaglandin E2, epidermal growth factor and 1,25-dihydroxyvitamin D3) stimulated PA activity in both cell types. The relative efficacies of vitamin D metabolites and of prostanoids reflect their relative potencies as stimulators of bone resorption.

1 alpha,25-dihydroxyvitamin D3 induces maturation of the human monocyte cell line U937, and, in association with a factor from human T lymphocytes, augments production of the monokine, mononuclear cell factor

The monocyte factor, interleukin 1, or other factors homologous with interleukin 1, modulates functions of a variety of cells, including T and B lymphocytes, synovial cells, and chondrocytes. We have reported that a human monocyte cell line, U937, produces interleukin 1 when incubated with a soluble factor from lectin-stimulated T lymphocytes. We have also shown that U937 cells have a specific cytosolic receptor for 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25[OH]2D3). We now report that 1 alpha,25(OH)2D3(10(-11)-10(-10) M) induces maturational changes in the U937 cells similar to those produced by conditioned medium from lectin-stimulated T lymphocytes (increase in Fc receptors and OKM1 binding and decrease in proliferation), but does not induce monokine production as measured by mononuclear cell factor activity. 1 alpha,25(OH)2D3 is 200-300-fold more effective than 25-hydroxyvitamin D3, which is consistent with the known biological potency of these vitamin D3 metabolites. 1 alpha,25(OH)2D3 and the lymphokine together markedly augment maturational effects and, in addition, augment monokine production. The specificity of the interaction is further demonstrated by the lack of augmentation of monokine production with 1 beta,25-dihydroxyvitamin D3 in the presence of lymphokine. These interactions of a classical hormone and the hormonelike product(s) of the immune system with U937 cells serve as a model for human monocyte/macrophage differentiation and suggest a role for these interactions in some aspects of inflammation.