Isolation, characterization, and chromosome mapping of a human A-C1 Ha-Ras suppressor gene (HRASLS)

Recently, we cloned a cDNA encoding a novel mouse protein, named A-C1, by differential display between two mouse cell lines, embryonic fibroblast C3H10T1/2 and chondrogenic ATDC5. Mouse A-C1 has homology with a ras-responsive gene, rat Ha-rev107 (Hrasls), and modulates a Ha-ras-mediated signaling pathway. Here, we report a cDNA encoding a human homolog of mouse A-C1. The deduced amino acid sequence of human A-C1 consists of 168 amino acids, and shows 83% identity with that of mouse A-C1. Human A-C1 mRNA was expressed in skeletal muscle, testis, heart, brain, and thyroid in vivo. Moreover, expression of human A-C1 mRNA was detected at a high level in human osteosarcoma-derived U2OS cells in vitro. By FISH analysis the human A-C1 gene (HRASLS) was mapped to human chromosome 3q28--> q29.

Parathyroid hormone-related peptide inhibits the expression of bone morphogenetic protein-4 mRNA through a cyclic AMP/protein kinase A pathway in mouse clonal chondrogenic EC cells, ATDC5

The bone morphogenetic proteins (BMPs) play crucial roles in chondrogenic differentiation. Little is known, however, regarding the regulation of BMP gene expression. Here we examined the effect of parathyroid hormone-related peptide (PTHrP) (1-141), a full-length form of PTHrP molecules, on the expression of BMP-4 mRNA in clonal mouse chondrogenic EC cells, ATDC5. In differentiated ATDC5 cells, the expression of BMP-4 mRNA was inhibited by PTHrP (1-141), which stimulated cAMP accumulation and protein kinase A (PKA) activity in these cells. Dibutyryl cAMP, a permeable analog of cAMP, mimicked and H-89, a selective PKA inhibitor, blocked this effect of PTHrP (1-141). Moreover, actinomycin D attenuated the inhibition of BMP-4 mRNA expression by PTHrP (1-141). These results indicate that PTHrP (1-141) transcriptionally inhibits the expression of BMP-4 mRNA through a cAMP/PKA pathway in ATDC5 cells.

Tumour necrosis factor-alpha up-regulates the expression of BMP-4 mRNA but inhibits chondrogenesis in mouse clonal chondrogenic EC cells, ATDC5

Tumour necrosis factor (TNF)-alpha causes the degradation of articular cartilage in arthritis via direct actions on chondrocytes. However, it remains unknown whether TNF-alpha affects chondrogenesis in chondroprogenitors. In the present study, we assessed the effects of TNF-alpha in vitro on chondrogenesis using mouse clonal chondrogenic EC cells, ATDC5. TNF-alpha (10 ng/ml) stimulated [3H] thymidine incorporation in undifferentiated ATDC5 cells, and suppressed cartilaginous nodule formation and the accumulation of cartilage-specific proteoglycan. We recently showed that undifferentiated ATDC5 cells express BMP-4 and that exogenously administered BMP-4 promotes chondrogenesis in these cells. Interestingly, TNF-alpha up-regulated the expression of BMP-4 mRNA in undifferentiated ATDC5 cells in time- and dose-dependent manners. However, exogenously administered BMP-4 was not capable of reversing the inhibitory action of TNF-alpha on chondrogenesis in ATDC5 cells. These results indicate that TNF-alpha stimulates both cell proliferation and BMP-4 expression but inhibits chondrogenesis in chondroprogenitor-like ATDC5 cells.

Molecular cloning and biological activity of a novel Ha-Ras suppressor gene predominantly expressed in skeletal muscle, heart, brain, and bone marrow by differential display using clonal mouse EC cells, ATDC5

We cloned a cDNA encoding a novel mouse protein, named A-C1, by differential display between two mouse cell lines: embryonic fibroblast C3H10T1/2 and chondrogenic ATDC5. The deduced amino acid sequence of A-C1 consists of 167 amino acids and shows 46% identity with that of a ras-responsive gene, rat Ha-rev107. Northern blot analysis showed a distinct hybridization band of 3.2 kilobases. Expression of A-C1 mRNA was detected in undifferentiated ATDC5 cells and myoblastic C2C12 cells, while none of C3H10T1/2 cells, NIH3T3 fibroblasts, Balb/c 3T3 fibroblasts, osteoblastic MC3T3-E1 cells, and ST2 bone marrow stromal cells expressed A-C1 mRNA in vitro. Moreover, A-C1 mRNA was expressed in skeletal muscle, heart, brain, and bone marrow in adult mice. By in situ hybridization, A-C1 gene expression was localized in hippocampus as well as bone marrow cells. By immunocytochemistry, A-C1 protein was detected in the cytoplasm as well as perinuclear region of the cells. Transfection of A-C1 cDNA into Ha-ras-transformed NIH3T3 cell line caused increase in the number of flat colonies and inhibition of cell growth. Our data indicate that A-C1 is expressed in some specific tissues in vivo and modulates Ha-ras-mediated signaling pathway.

In vitro analysis of the stimulation of bone formation by highly bioactive apatite- and wollastonite-containing glass-ceramic: released calcium ions promote osteogenic differentiation in osteoblastic ROS17/2.8 cells

We analyzed the mechanisms of the efficient bone formation on the osteoconductive surface of apatite- and wollastonite-containing glass-ceramic (AW) by using an in vitro system. AW releases Ca ions and bonds to bone via a submicron-thick hydroxycarbonate apatite (HCA) layer. AW disks were conditioned with simulated body fluid (SBF) to grow HCA layers, and the amount of released Ca ion was regulated by modulating the conditioning time from 24 to 240 h. Surface-transformed AW disks increased alkaline phosphatase (AP) activity in osteoblastic ROS17/2.8 cells by 1.5- to threefold over unconditioned disks. AW disks conditioned for 24 h [AW(24)], which had a homogeneous, submicron-thick apatite layer and increased extracellular ionized Ca concentration ([Ca(2+)](e)) in the culture medium to the greatest extent, enhanced the AP activity the most. High [Ca(2+)](e) promoted osteogenic differentiation in ROS17/2.8 cells: It increased AP activity in a dose-dependent manner by up to 1.6-fold, and up-regulated the expression of AP, osteocalcin (OC), and transforming growth factor-beta1 mRNAs in dose- and time-dependent manners. AW(24) enhanced AP activity in ROS17/2.8 cells as much as AW disks conditioned with SBF containing serum to exhibit in vivo surface-structure changes. AW(24) increased AP activity in ROS17/2.8 cells by 1.6-fold and enhanced the expression of AP and OC mRNAs significantly, compared with sintered hydroxyapatite (HA). After implantation of AW and HA in the distal metaphyses of rabbit femurs, thin, newly formed bone lined with cuboidal, osteoblast-like cells was characteristically observed adjacent to the AW surface within 8 days. These results provide evidence for the hypothesis that AW stimulates bone formation on its surface by increasing [Ca(2+)](e) to promote the HCA layer formation and the differentiation of osteogenic cells.

Effects of transforming growth factor-beta signaling on chondrogenesis in mouse chondrogenic EC cells, ATDC5

Cellular condensation of chondroprogenitors is a distinct cellular event in chondrogenesis. During this process, N-cadherin mediates cell-cell interactions responsible for the initial stage of cellular condensation and subsequently fibronectin contributes to cell-matrix interactions mediating a progression of chondrogenesis. We previously showed that chondrogenesis in mouse chondrogenic EC cells, ATDC5, was induced, at a high incidence in the presence of insulin, through formation of cellular condensation. In this study, we took advantage of the sequential progression of chondrogenesis in ATDC5 cells and evaluated, in vitro in these cells, the role of endogenous transforming growth factor (TGF)-beta in chondrogenesis. ATDC5 cells expressed TGF-beta2 mRNA at a cellular condensation stage. The treatment of undifferentiated ATDC5 cells with anti-TGF-beta32 neutralizing antibody inhibited the accumulation of Alcian blue stainable proteoglycan in a dose-dependent manner. Transfection of a dominant-negative mutant of mouse TGF-beta type II receptor to undifferentiated ATDC5 cells completely inhibited cellular condensation. Moreover, exogenously administered TGF-beta2 upregulated the expression of fibronectin and type II collagen (a phenotypic marker gene of chondrogenesis) mRNAs and downregulated that of N-cadherin mRNA in time- and dose-dependent manners. These results indicate that TGF-beta stimulates chondrogenesis via initiation of cellular condensation by transition from an initial N-cadherin-contributing stage to a fibronectin-contributing stage during processes of chondrogenesis in ATDC5 cells.

Bone morphogenetic protein-6 and parathyroid hormone-related protein coordinately regulate the hypertrophic conversion in mouse clonal chondrogenic EC cells, ATDC5

We evaluated the roles of bone morphogenetic protein (BMP)-6, BMP-4 and parathyroid hormone-related protein (PTHrP) in the hypertrophic conversion using mouse chondrogenic EC cells, ATDC5. In ATDC5 cells, the expression of BMP-6 and PTHrP receptor mRNAs increased in parallel with the progression of chondrogenic differentiation of these cells, exhibiting a time course similar to that of type II collagen, a phenotypic marker of proliferating chondrocytes, while BMP-4 mRNA was continuously expressed throughout the differentiation processes. The expression of type X collagen mRNA, a phenotypic marker of hypertrophic chondrocytes, was upregulated by BMP-6 and BMP-4, and downregulated by PTHrP(1-141). The expression of BMP-6 mRNA was upregulated while that of BMP-4 mRNA was downregulated by both BMP-6 and BMP-4. Moreover, the expression of BMP-6 mRNA was downregulated by PTHrP(1-141). Furthermore, even in the presence of PTHrP(1-141), BMP-6 increased the transcript level of type X collagen in a dose-dependent manner. These results indicate that transiently expressed BMP-6 promotes the hypertrophic conversion in association with the augmentation of BMP-6 gene expression by BMP signals and that both BMP-6 and PTHrP coordinately regulate the rate of the hypertrophic conversion of ATDC5 cells.

Hedgehog signaling molecules in bone marrow cells at the initial stage of fracture repair

Ihh is a secreted protein expressed in chondrocytes in cartilaginous soft callus and thought to be involved in regulation of chondrogenic differentiation in fracture repair processes. However, gene expression and function of Ihh and its signaling molecules, Ptc and Smo, at the initial stage of fracture repair remain unknown. In the present study, we showed by RT-PCR of mouse rib fractures that the upregulation of Ihh mRNA occurred within hours after fracture, immediately followed by that of Ptc mRNA, and that both Ihh and Ptc mRNAs exhibited the time course similar to those of OP and OC mRNAs at the initial stage of fracture repair. The transcript level of Smo mRNA gradually increased within hours after fracture and was continuously maintained throughout the subsequent fracture repair processes. By in situ hybridization analysis, the transcripts of Ptc and Smo genes localized in bone marrow of unfractured ribs, and those of Ihh, Ptc, and Smo were expressed in the vicinity of the fracture site at 8 h after fracture. Furthermore, in adherent bone marrow cells in culture, mrIhh-N upregulated the gene expression of TGF-beta(1) as well as OPGL, a potent stimulator of osteoclastogenesis and osteoclast activity. These observations suggest that Ihh may play roles in the initial stage of fracture repair via TGF-beta(1) and OPGL.

TAK-778, a novel synthetic 3-benzothiepin derivative, promotes chondrogenesis in vitro and in vivo

TAK-778, a novel synthetic 3-benzothiepin derivative, stimulates the formation of cartilaginous nodules in mouse chondroprogenitor-like ATDC5 cells in vitro in association with upregulation of the gene expression of transforming growth factor-beta(2), but not bone morphogenetic protein-4 and insulin-like growth factor-I. One-shot injection of the TAK-778-containing sustained-release microcapsules accelerated the repair process of the full thickness defects of articular cartilage in rabbit knees. Our in vitro and in vivo results indicate that TAK-778 may be a therapeutically useful synthetic agent for articular cartilage repair.

Noggin and bone morphogenetic protein-4 coordinately regulate the progression of chondrogenic differentiation in mouse clonal EC cells, ATDC5

Here we report the gene expression and regulation and the function of noggin in clonal mouse chondrogenic EC cells, ATDC5. In ATDC5 cells, the expression of Noggin mRNA increased in parallel with the progression of chondrogenic differentiation. The treatment with conditioned medium of noggin-transfected COS-7 cells decreased the levels of type II and type X collagen gene transcripts of differentiated ATDC5 cells in a dose-dependent manner, and this inhibitory action was reversed by exogenously administered BMP-4 in a dose-dependent manner. The steady-state level of noggin gene transcripts was markedly upregulated by exogenously administered BMP-4 in time- and dose-dependent manners. Furthermore, this stimulatory effect of BMP-4 was attenuated by treatment with actinomycin D, but not with cycloheximide. These results indicate that noggin and BMP-4 coordinately regulate the progression of chondrogenic differentiation in ATDC5 cells.

Indian hedgehog in the late-phase differentiation in mouse chondrogenic EC cells, ATDC5: upregulation of type X collagen and osteoprotegerin ligand mRNAs

Endochondral bone formation includes a cascade of cellular events such as proliferation, maturation, hypertrophic conversion and calcification of chondrocytes and the cartilage replacement by bone. During these processes, hypertrophic conversion and calcification of chondrocytes (the late-phase differentiation) is a crucial process of chondrogenic differentiation. Indian hedgehog (Ihh), a secreted protein expressed in early hypertrophic chondrocytes, is thought to be involved in regulation of hypertrophic conversion via a feedback loop through the perichondrium. In the present study, we showed by Northern analysis and in situ hybridization that Smoothened (Smo), a key component in hedgehog signal transduction, was expressed in chondrocytes in both adult mice and mouse embryos at 16 days post-coitum in vivo, suggesting that Ihh directly acts on chondrocytes. We previously reported that Ihh, Patched and Smo were all expressed in differentiated ATDC5 cells. Exogenously administered mouse recombinant N-terminal protein of Ihh (mrIhh-N) upregulated the gene expression of type X collagen, a phenotypic marker of hypertrophic chondrocytes, as well as osteoprotegerin ligand (OPGL), a potent stimulator of osteoclastogenesis and osteoclast activity, while it did not modulate the expression of Ihh itself, bone morphogenetic protein (BMP)-4, BMP-6, transforming growth factor (TGF)-beta1 and TGF-beta2 in differentiated ATDC5 cells. Moreover, when added to the osteoclast cultures, mrIhh-N markedly stimulated the formation of resorption pits on dentine slices. Our data support the hypothesis that Ihh stimulated the late-phase chondrogenic differentiation in differentiated ATDC5 cells and upregulated the gene expression of OPGL in these cells.

Cloning of a novel gene specifically expressed in clonal mouse chondroprogenitor-like EC cells, ATDC5

We cloned a full-length cDNA encoding a novel mouse protein, A-C2, by differential display method using mouse embryonic fibroblast C3H10T1/2 cells and mouse chondroprogenitor-like EC cells, ATDC5. The deduced amino acid sequence of A-C2 consisted of 106 amino acids with no significant homology to the sequences previously reported. Northern blot analysis showed two major bands of 2.1 and 1.8 kb sizes. Expression of A-C2 mRNA was exclusive to ATDC5 cells at their undifferentiated stage. None of ATDC5 cells at their differentiated stage and adult mice tissues examined expressed A-C2 gene.

Three phase 99Tcm (V)DMSA scintigraphy in Paget's disease: an indicator of pamidronate effect

The use of three phase 99Tcm (V)DMSA scintigraphy is reported in a patient with Paget's disease of bone before and after intravenous pamidronate therapy. It was a useful modality for estimating the activity of Pagetoid lesions and the therapeutic effect of pamidronate, from a different aspect to bone scintigraphy. Three phase 99Tcm (V)DMSA scintigraphy evaluates both the blood flow and the metabolic activity of Pagetoid bone.

Preoperative imaging for parathyroid localization in primary hyperparathyroidism

BACKGROUND

We retrospectively studied the results of diagnostic imaging using 3 different modalities to determine their usefulness for preoperative localization of the parathyroid, and whether accurate preoperative localization information could be used to modify the surgical approach for parathyroidectomy in patients with primary hyperparathyroidism.

METHODS

Images of 37 parathyroid adenomas or hyperplasias in 35 patients with primary hyperparathyroidism were obtained using ultrasonography, computed tomography, and subtraction scintigraphy (using thallium 201 [thallous chloride] and either iodine 123 or technetium 99m pertechnetate [99mTcO4-]).

RESULTS

Approximately three fourths of the adenomas or hyperplasias were successfully identified by ultrasound (76.7%) and computed tomography (76.4%), even when the weight of the tumor was less than 500 mg. However, subtraction scintigraphy was of limited use (61.3% successfully identified). A combination of these modalities gave excellent results for detecting adenomas and hyperplasias, leading to an accurate prediction rate of 96.0%.

CONCLUSION

We conclude that using the combination of these 3 imaging modalities is very useful for the detection of parathyroid adenomas and hyperplasias, and that with such accurate localization information, the unilateral approach alone, or even simple excision of the parathyroid tumors might be feasible, enabling less invasive surgical treatment.

Cloning of a mouse smoothened cDNA and expression patterns of hedgehog signalling molecules during chondrogenesis and cartilage differentiation in clonal mouse EC cells, ATDC5

Hedgehog (hh) family proteins appear to use the conserved targets in their signalling pathway including Patched (Ptc), Smoothened (Smo), and Gli. Although Indian hedgehog (Ihh) plays an important role in endochondral bone formation, the involvement of hh signalling molecules in skeletogenesis is unknown. We cloned a mouse (m) Smo cDNA and studied the expression patterns of Ihh, Ptc, Smo, and Gli mRNAs in mouse chondrogenic EC cells, ATDC5. The deduced amino acid sequence of mSmo consisted of 793 amino acids and was 98 and 93% homologous to the rat (r) Smo and human (h) Smo, respectively. In ATDC5 cells, the expression of Ihh mRNA paralleled that of type X collagen mRNA. Smo, Ptc, and Gli mRNAs were constitutively expressed throughout chondrogenesis and the subsequent cartilage differentiation processes except for the transient decrease in Ptc mRNA at the cellular condensation stage. Our data suggest that hh signalling molecules may be involved in chondrogenesis and cartilage differentiation in ATDC5 cells.

Synovial fluids from patients with osteoarthritis and rheumatoid arthritis contain high levels of parathyroid hormone-related peptide

High levels of immunoreactive and biologically active parathyroid hormone-related peptide (PTHrP) were detected in synovial fluids from patients with osteoarthritis (OA) and rheumatoid arthritis (RA). The levels of PTHrP immunoreactivity in synovial fluids, measured by a two-site immunoradiometric assay (IRMA) which detects hPTHrP(1-72) or longer peptides and a radioimmunoassay (RIA) specific to the carboxy-terminal portion of hPTHrP, were 3.2 +/- 0.3 pmol of hPTHrP(1-86)/l and 61 +/- 7.0 pmol of hPTHrP(109-141)/l in OA patients (mean +/- SE, n = 23), and 4.8 +/- 0.8 pmol of hPTHrP(1-86)/l and 164 +/- 30 pmol of hPTHrP(109-141)/l in RA patients (n = 26). Synovial fluid PTHrP levels distributed above the normal plasma reference ranges in each assay (0.7-2.6 pmol of hPTHrP(1-86)/l; 16-60.6 pmol of hPTHrP(109-141)/l). After concentration using sequential cation-exchange and reverse-phase chromatography, synovial fluid exhibited the activity that stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblastic ROS 17/2.8 cells expressing PTH/PTHrP receptors. The cAMP accumulation activity in synovial fluid was sensitive to coincubation with excess hPTHrP(3-40), a PTH/PTHrP receptor antagonist, and was completely neutralized by preincubation with a monoclonal antibody specific to hPTHrP but not PTH. Immunohistochemical analysis of RA synovium revealed that PTHrP was localized in fibroblast-like cells in the synovial pannus invading articular cartilage. Our data show that PTHrP is produced locally by the diseased synovial tissue and released into synovial fluid at high concentrations, allowing us to hypothesize that PTHrP plays a novel role as a paracrine/autocrine factor in the pathology of OA and RA.

Acute hepatic failure following transcatheter arterial embolization for the treatment of hepatocellular carcinoma

We conducted a retrospective analysis to evaluate the risk factors associated with the occurrence of acute hepatic failure following transcatheter arterial embolization (TAE) for hepatocellular carcinoma. From 1984 to 1993 we performed a total of 623 embolization procedures in 369 patients with both hepatocellular carcinoma and chronic liver disease. Within 2 weeks after TAE, 13 patients (2.1%) experienced hepatic failure as characterized by a rapid increase in serum bilirubin levels and the development of hepatic encephalopathy of grade 2 or higher. These results indicated that the following are risk factors for acute hepatic failure after TAE: poor hepatic functional reserve; high-dose infusion of chemotherapeutic agents, and a history of multiple embolization procedures.

Bone demineralization following urinary intestinal diversion assessed by urinary pyridinium cross-links and dual energy x-ray absorptiometry

PURPOSE

We investigated the acid-base balance and bone mineral status in patients with 3 types of urinary intestinal diversion.

MATERIALS AND METHODS

Of 46 men with urinary intestinal diversions 20 had a Kock pouch, 15 had an Indiana pouch and 11 had an ileal conduit. Acid-base balance was assessed by arterial blood gas analysis. Bone mineral status was measured by urinary pyridinium cross-links and dual energy x-ray absorptiometry. In addition, urinary deoxypyridinoline was measured in 79 patients.

RESULTS

Of the 46 patients 7 (15%) with the Kock pouch (1), Indiana pouch (5) and ileal conduit (1) had metabolic acidosis associated with significantly lower bone mineral densities (p < 0.05) and higher urinary pyridinium cross-links (p < 0.005) than did those with normal acid-base status. No difference was found in metabolic acidosis and bone demineralization among the 3 groups. Additionally, in 79 patients urinary deoxypyridinoline reached the highest level immediately postoperatively and then gradually decreased to the stable level within 1 or 2 years.

CONCLUSIONS

Metabolic acidosis following urinary intestinal diversion results in bone demineralization. The types of diversion did not cause differences in metabolic acidosis and bone resorption. Bone has a major role in buffering acid overload in the early postoperative period.

Oxyphil parathyroid adenoma associated with primary hyperparathyroidism and marked post-operative hungry bone syndrome

A rare case of functioning oxyphil parathyroid adenoma associated with primary hyperparathyroidism and marked hungry bone syndrome was revealed in a 29-year-old man with hypercalcemia and elevated circulating parathyroid hormone (PTH) level. A large parathyroid tumor weighing 8.4 g was resected and proved to be an oxyphil adenoma. Hypocalcemia was sustained after the operation, despite intensive calcium supplementation. During the postoperative 8 months, bone mineral density at the lumbar spine increased dramatically from 0.892 g/cm2 to 1.244 g/cm2, and whole body bone mineral content increased from 1,913.4 g to 2,419.2 g. This case gives insight to the reversibility of bone loss in this disorder.

Prostaglandin E receptor subtypes in mouse osteoblastic cell line

PGE2 is one of the key molecules in the osteoblast. It is the major prostanoid in the bone, and its production is under the control of both systemic and local factors. PGE2 has been reported to have multiple actions in the osteoblast, such as growth promotion and cell differentiation. To better understand the action of PGE2 in the osteoblast, we determined the PGE receptor subtypes in MC3T3-E1, an osteoblastic cell line derived from the normal mouse calvaria. Northern blot analysis revealed that EP1 and EP4 subtypes are expressed in MC3T3-E1. In contrast, EP3 subtype was not detected by either Northern blot analysis or RT-PCR. The contribution of each subtype was evaluated by studying the effects of subtype-specific analogs on osteoblastic function at confluency and 5 days after confluency. An EP1 agonist, 17-phenyl-omega-trinor PGE2, increased DNA synthesis and decreased alkaline phosphatase activity. 11-Deoxy-PGE1, and EP2 and EP4 agonist, decreased DNA synthesis and increased alkaline phosphatase activity at both stages. Butaprost, an EP2-selective agonist, showed effects similar to those of 11-deoxy-PGE1 only at confluency. Another and more differentiated osteoblastic marker, osteocalcin production, was detectable and was stimulated by 11-deoxy-PGE1 only 5 days after confluency. The exposure of these cells to EP1 agonist changed the cell shape to a more fibroblastic appearance. These results indicate that EP1, EP4, and probably EP2 are present in MC3T3-E1 cells; EP1 promotes cell growth, and EP2 and EP4 mediate differentiation of the osteoblast. Furthermore, the decreased response to EP2-specific agonist 5 days after confluency suggests that the expression of PGE receptor subtype is dependent on the stage of osteoblastic differentiation. This is the first report to determine PGE receptor subtypes in the bone.

Chondrogenic differentiation of clonal mouse embryonic cell line ATDC5 in vitro: differentiation-dependent gene expression of parathyroid hormone (PTH)/PTH-related peptide receptor

The regulatory role of parathyroid hormone (PTH)/PTH-related peptide (PTHrP) signaling has been implicated in embryonic skeletal development. Here, we studied chondrogenic differentiation of the mouse embryonal carcinoma-derived clonal cell line ATDC5 as a model of chondrogenesis in the early stages of endochondral bone development. ATDC5 cells retain the properties of chondroprogenitor cells, and rapidly proliferate in the presence of 5% FBS. Insulin (10 micrograms/ml) induced chondrogenic differentiation of the cells in a postconfluent phase through a cellular condensation process, resulting in the formation of cartilage nodules, as evidenced by expression of type II collagen and aggrecan genes. We found that differentiated cultures of ATDC5 cells abundantly expressed the high affinity receptor for PTH (Mr approximately 80 kD; Kd = 3.9 nM; 3.2 x 10(5) sites/cell). The receptors on differentiated cells were functionally active, as evidenced by a PTH-dependent activation of adenylate cyclase. Specific binding of PTH to cells markedly increased with the formation of cartilage nodules, while undifferentiated cells failed to show specific binding of PTH. Northern blot analysis indicated that expression of the PTH/PTHrP receptor gene became detectable at the early stage of chondrogenesis of ATDC5 cells, preceding induction of aggrecan gene expression. Expression of the PTH/PTHrP receptor gene was undetectable in undifferentiated cells. The level of PTH/PTHrP receptor mRNA was markedly elevated parallel to that of type II collagen mRNA. These lines of evidence suggest that the expression of functional PTH/PTHrP receptor is associated with the onset of chondrogenesis. In addition, activation of the receptor by exogenous PTH or PTHrP significantly interfered with cellular condensation and the subsequent formation of cartilage nodules, suggesting a novel site of PTHrP action.

1 alpha,25-dihydroxyvitamin D3 inhibits cell growth and chondrogenesis of a clonal mouse EC cell line, ATDC5

Here we report the effects of 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] in vitro on the growth and chondrogenesis of a chondroprogenitor-like clonal mouse EC cell line, 10(-10) to 10(-7) M ATDC5. 1,25(OH)2D3 inhibited [3H]thymidine incorporation in undifferentiated chondroprogenitor-like ATDC5 cells in time- and dose-dependent manners. 1,25(OH)2D3 suppressed cartilage-nodule formation and the accumulation of cartilage-specific proteoglycan in ATDC5 cells in a dose-dependent manner. The 1,25(OH)2D3-induced inhibition of cartilage-nodule formation was reversible and direct, unrelated to the antiproliferative action of the hormone on the undifferentiated ATDC5 cells. ATDC5 cells even in the precartilaginous stage expressed 4.4 kb vitamin D receptor (VDR) mRNA as assessed by northern blot analysis. The equilibrium saturation binding experiment revealed the presence of a single class of saturable and high-affinity binding sites for 1,25(OH)2D3 in the cytosols. These results provide evidence for the hypothesis that both recruitment and chondrogenesis of chondroprogenitors are negatively regulated by 1,25(OH)2D3 via a VDR-mediated process in vivo.

[Clinical studies using measurement of N-telopeptides of type 1 collagen (NTx) in patients with bone metastasis--comparison with bone scintigraphy and other metabolic bone markers]

Urinary metabolites of N-telopeptide of type 1 collagen cross-links (NTx) are known as a bone resorption marker. We performed a multi-center trial of NTx measurement in evaluation of bone metastasis. In total, 251 patients with or without bone metastasis from various malignancies were studied. Comparing with other bone markers such as urinary total deoxypyridinoline, osteocalcin, and bone specific alkaline phosphatase, NTx was the most sensitive one to detect bone metastasis and its levels correlated well with the extensiveness of bone metastasis. Measurement of NTx will be useful to determine to order bone scan in patients with malignancy and to monitor the clinical course in patients with bone metastasis.

Intraosseous hemangiomatosis: technetium-99m(V)dimercaptosuccinic acid and technetium-99m-hydroxymethylene diphosphonate imaging

We report a case of histologically proven intraosseous hemangiomatosis in which marked accumulation of pentavalent technetium-99m-dimercaptosuccinic acid (99mTc(V)DMSA) and technetium-99m-hydroxymethylene diphosphonate (99mTc-HMDP) was observed in the osteolytic hemangiomatous lesions.

Ovariectomy decreases the mRNA levels of transforming growth factor-beta 1 and increases the mRNA levels of osteocalcin in rat bone in vivo

Estrogen depletion causes postmenopausal osteoporosis. Here we report that steady state mRNA levels of transforming growth factor-beta 1 (TGF-beta 1) and osteocalcin in bone persistently decreased and increased, respectively, in vivo in estrogen-depleted rats after ovariectomy (OVX). 21 female Wistar rats (7-month-old) were randomized and underwent OVX or sham-operation, total RNA was extracted from tibiae and assessed by Northern blot analysis. OVX induced 70-80% decrease in TGF-beta 1 mRNA levels and 2- to 3-fold increase in mRNA levels of osteocalcin compared with controls three weeks after surgery. These changes persisted up to twelve weeks post-operation. OVX caused 15% reduction in femoral bone mineral density and 2-fold elevation in serum osteocalcin levels as early as two weeks post-operation. Moreover, estrogen depletion resulted in marked decrease and increase, respectively, in steady state mRNA levels of TGF-beta 1 and osteocalcin in vitro in osteoblastic rat osteosarcoma cells, ROS 17/2.8. Our results provide the first in vivo evidence that expression of TGF-beta and osteocalcin in bone is reciprocally regulated at the transcriptional level in estrogen deficient OVX rats and suggests that TGF-beta 1 may play a role in estrogen-dependent maintenance of normal bone density.

Bone morphogenetic proteins (BMP-2 and BMP-3) induce the late phase expression of the proto-oncogene c-fos in murine osteoblastic MC3T3-E1 cells

Here we report that bone morphogenetic proteins 2 and 3 (BMP-2 and BMP-3) induced marked expression of c-fos mRNA in a biphasic manner, i.e. the late phase (48 to 60 h) as well as the immediate-early phase (0.5 h), in murine osteoblastic MC3T3-E1 cells in vitro. The BMP-induced late phase c-fos gene expression was temporally associated with the onset of marked expression of the genes for osteocalcin and alkaline phosphatase, differentiation markers of mature osteoblasts. In contrast, none of TGF-beta 1, 10% FBS, IGF-I and IGF-II, which induced only the immediate-early c-fos mRNA expression, stimulated the expression of osteocalcin and alkaline phosphatase genes. These data suggest that in osteoblasts BMP-2 and BMP-3 induce the late phase expression of c-fos, which may play a role in transcriptional activation of the genes involved in differentiation of osteoblasts.

The effect of active vitamin D3 analogs and dexamethasone on the expression of osteocalcin gene in rat tibiae in vivo

We tested the effects of 1 alpha,25-dihydroxyvitamin D3 (1,25-(OH)2D3), 2 beta-(3-hydroxypropoxy)-1 alpha,25-dihydroxyvitamin D3 (ED-71) and dexamethasone on osteocalcin mRNA levels in rat tibiae in vivo. Northern blot analysis showed that both 1,25-(OH)2D3 and ED-71 caused an increase in osteocalcin mRNA levels in bone: 1,25-(OH)2D3 induced a transient increase in the mRNA levels followed by a decrease in the control level by 12 h post administration. In contrast, ED-71 caused a persistent increase in osteocalcin mRNA level for seven days post administration. Serum osteocalcin levels paralleled the osteocalcin mRNA level in bone in both groups. Dexamethasone caused a marked reduction in both osteocalcin mRNA and serum osteocalcin levels. Suppressive effect of dexamethasone on osteocalcin expression was persistent for seven days at higher dose. Our results represent the first demonstration of the effect of active vitamin D and corticosteroid on the expression of osteocalcin mRNA in bone in vivo.

Human parathyroid hormone-related peptide-(107-111) does not inhibit bone resorption in neonatal mouse calvariae

Recent analysis of the structure-function relationship of human PTH-related peptide (hPTHrP) has led to the discovery that its direct inhibitory activity on osteoclastic bone resorption resides fully in the 107-111 sequence of the peptide, as assessed by a bone resorption assay using isolated rat osteoclasts. Here we report that hPTHrP-(107-111) is inactive in neonatal mouse calvariae in culture. hPTHrP-(107-111), at doses of 10(-12)-10(-6) M and incubation periods up to 96 h, did not affect either basal or agonist-stimulated 45Ca release from prelabeled neonatal mouse calvariae, while salmon calcitonin was a potent and powerful inhibitor of both basal and stimulated 45Ca release from bone. Moreover, salmon calcitonin, but not hPTHrP-(107-111), inhibited the increase in osteoclast number in hPTHrP-(1-34)-treated bones. Furthermore, hPTHrP-(107-139) also failed to inhibit 45Ca release and the hPTHrP-(1-34)-induced increase in osteoclast number in this organ culture model when tested under conditions identical to those for hPTHrP-(107-111). The addition of indomethacin to hPTHrP-(107-111)- or hPTHrP-(107-139)-treated bones was without effect, excluding the possibility that the direct inhibitory activity of these peptides on osteoclasts is ablated by a prostaglandin-mediated mechanism. Although the mechanism underlying the apparent inability of the carboxyl-terminal PTHrP fragments to inhibit osteoclastic bone resorption in neonatal mouse calvariae is unknown, it may involve the complex microenvironment of osteoclasts in intact bone, which contains a large variety of cell types other than osteoclasts.

Metabolic bone disease following gastrectomy: assessment by dual energy X-ray absorptiometry

Although disorders in bone metabolism have long been recognized as typical sequelae of gastrectomy, there has until now been no reliable method of providing precise assessment of bone mass, resulting in a variation of reported incidence. In this study, metabolic bone disease was evaluated in a well characterized population: 34 men 2-5 years after gastrectomy; 11 men 6-10 years after gastrectomy; eight men 2-5 years after colonic resection; and 115 healthy men. The age range was 50-69 years. An innovative reliable method of dual energy X-ray absorptiometry was used which allows quantitative assessment of bone mineral content. Measurement of lumbar spine bone mineral density revealed that the mean(s.e.m.) bone mineral density in patients who had had a gastrectomy (2-5 years 0.84(0.03) g/cm2, 6-10 years 0.85(0.05) g/cm2) was significantly lower than that of patients who had undergone colonic resection (0.96(0.04) g/cm2) or healthy men (0.96(0.03) g/cm2). This study demonstrates that a high incidence of bone atrophy is induced at the relatively early period of 2-5 years after gastrectomy.

Bone morphogenetic proteins (BMP-2 and BMP-3) promote growth and expression of the differentiated phenotype of rabbit chondrocytes and osteoblastic MC3T3-E1 cells in vitro

We studied the effects of highly purified bone morphogenetic protein 2 and 3 (BMP-2 and -3) on growth plate chondrocytes and osteoblastic cells in vitro and compared to TGF-beta. A mixture of BMP-2 and 3 (BMPs) strongly stimulated DNA synthesis of chondrocytes in the presence of fibroblast growth factor (FGF). BMPs induced rapid maturation of chondrocytes at a growing stage: BMPs transformed the cells into rounded cells and induced marked accumulation of cartilage matrix; TGF-beta slightly reduced matrix accumulation and changed cell morphology into spindle-like in the presence of FGF. Moreover, exposure of chondrocytes to BMPs resulted in a dramatic increase of the putative approximately 80 kD PTH receptors expressed on the cell surface. In multilayered chondrocytes at the calcifying stage, BMPs stimulated alkaline phosphatase (ALPase) activity but TGF-beta inhibited it. In osteoblastic MC3T3-E1 cells, BMPs were found to be the most potent stimulator of ALPase activity thus far described: ALPase in the cells treated with approximately 100 ng/ml of BMPs reached 5- to 20-fold over the basal, whereas TGF-beta inhibited expression of ALPase activity in these cells. The stimulatory action of BMPs overrode the inhibition of ALPase activity by TGF-beta when the cells were incubated with TGF-beta and BMPs. BMPs also upregulated expression of the approximately 80 kD PTH receptor on the cells. These results suggest that BMPs have unique biologic activities in vitro that lead to growth and phenotypic expression of cells playing a critical role in endochondral bone formation.

Cholecystokinin receptor occupation and cholecystokinin-induced calcium mobilization in the early phase in rat pancreatic acini

We examined receptor occupation, calcium mobilization and amylase release for cholecystokinin octapeptide (CCK-8) within a 3-min incubation period at 37 degrees C using dispersed acini from rat pancreas. Analysis of competitive binding inhibition data obtained after a 3-min incubation revealed the presence of only a single class of CCK receptors, while two classes of CCK receptor, i.e., high-affinity and low-affinity CCK receptors, were detected when binding reached a steady-state after a 60-min incubation. The IC50 of CCK receptors calculated from the 3-min binding data was 19.0 +/- 0.5 nM (mean +/- S.D.), close to the Kd of the low-affinity CCK receptors determined by equilibrium binding studies. Exposure of fura-2-loaded acini to 10-1000 pM CCK-8 caused an immediate and dose-dependent increase in [Ca2+]i followed by a gradual decrease in [Ca2+]i. The CCK-stimulated amylase release after 3 min of incubation was biphasic; amylase release increased over the dose range of 3-300 pM CCK-8, peaked at 300 pM CCK-8 and decreased with supramaximal concentrations of CCK-8. Our data suggest that occupation of the low-affinity, but not the high-affinity, CCK receptors is more directly associated with calcium mobilization and subsequent stimulation of amylase release in rat pancreatic acini.

On the transforming growth factor beta-like activity of synthetic polypeptides comprising the amino-terminal sequence of human parathyroid hormone-related peptide

Purified native forms of human parathyroid hormone-related peptide (PTHrp) have recently been reported to display biological activities characteristic of transforming growth factor beta (TGF-beta). The TGF-beta-like property of PTHrp may reside within the amino N-terminal PTH-receptor binding region of the polypeptide, since a synthetic analog corresponding to amino acids 1-36 of human PTHrp is as active as purified native PTHrp in bioassays specific to TGF-beta. Complete lack of structural similarity between PTHrp and TGF-beta prompted us to address the question whether copresence of the TGF-beta-like and PTH-like biological activities in the N-terminal sequence of the PTHrp molecule is a general phenomenon observable with different N-terminal PTHrp peptides of varying amino acid chain length in a variety of target cells that respond in defined ways to TGF-beta in vitro. Two forms of synthetic N-terminal human PTHrp, PTHrp-(1-34) and [Tyr40]PTHrp-(1-40), which are fully active in conventional assays for PTH/PTHrp, were tested for effects in three in vitro bioassay systems for TGF-beta: 1) stimulation, and 2) inhibition, respectively, of epidermal growth factor-dependent soft-agar colony formation of either normal rat kidney-derived fibroblasts (NRK 49F) or human lung carcinoma cells (A549); and 3) biosynthesis of metabolically labeled fibronectin in both NRK 49F cells and clonal osteoblastic rat osteosarcoma cells (ROS 17/2.8). Human TGF-beta over the dose range of 2.5-80 pM significantly stimulated or inhibited soft-agar colony formation of either NRK 49F or A549 cells, respectively, and caused a severalfold increase in biosynthetically labeled [35S]fibronectin in NRK 49F and ROS 17/2.8 cells. In contrast, none of PTHrp-(1-34), [Tyr40]PTHrp-(1-40), and synthetic human PTH-(1-34), each tested at 0.1-10 nM, displayed detectable biological activity in any of the three assay systems. In addition, covalent cross-linking of intact NRK 49F and ROS 17/2.8 cells with either [125I]TGF-beta or 125I-[Tyr40] PTHrp-(1-40) revealed the presence of several distinct affinity-labeled receptor species for TGF-beta in both cell types and the 80K PTH/PTHrp receptors in ROS 17/2.8 cells. The affinity-labeled TGF-beta receptor species were insensitive to excess PTHrp and PTH peptides, and the 80K PTH/PTHrp receptors were insensitive to excess TGF-beta, indicating that PTHrp and TGF-beta do not cross-react with respect to receptor binding for interaction with these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Epidermal growth factor stimulates the anchorage-independent growth of human squamous cell carcinomas overexpressing its receptors

We examined the effects of epidermal growth factor (EGF) on the anchorage-dependent and -independent growth of four human squamous carcinoma cell lines that overexpress EGF receptors. While EGF inhibited anchorage-dependent growth, it stimulated anchorage-independent growth of all four cell lines tested. The results suggest that the proliferative responses to EGF are characterized by a preference for anchorage-independent, rather than -dependent growth, in cells overexpressing EGF receptors. Moreover, as EGF has been shown to stimulate the in vivo growth of squamous carcinoma cells overexpressing EGF receptors, it is also suggested that the in vitro EGF responsiveness of these cells in soft agar, but not in monolayer, better correlates with the in vivo EGF responsiveness.

[Rapid measurement of human parathyroid hormone-(1-84) by immunoradiometric assay for use in intraoperative determination of hyperfunctioning parathyroid glands]

Rapid measurement of serum intact parathyroid hormone concentration was achieved by modification of an immunoradiometric assay for the hormone. Incubation of serum samples for 15 min at 37 degrees C under shaking gave optimal results in terms of assay variance and reproducibility: intra-assay CVs were less than 10% over the hormone concentrations of 11-1,600 pg/ml; intra- and inter-assay CVs for two control sera at different hormone levels were less than 12%. The minimal detectable hormone concentration was found at 27.8 pg/ml. The serum hormone levels of 43 subjects (31 health subjects, 9 patients with primary hyperparathyroidism, and 3 patients with secondary hyperparathyroidism) determined by either rapid or regular assay well correlated with each other (r2 = 0.979, p less than 0.001). In two patients with parathyroid adenoma serum intact PTH levels fell rapidly to 12.1% of the preoperative values 20 min after ligation of the vascular pedicle to the hyperfunctioning glands. We conclude that the modified assay protocol allows rapid, accurate, and simple estimation of intact PTH concentrations, and can be used as an intraoperative measure to aid both diagnosis and surgical cure of hyperparathyroidism.

Episodic fluctuation in serum intact parathyroid hormone concentration in men

To evaluate the temporal features of physiological fluctuation in serum PTH concentration, we sampled peripheral blood at 4-min intervals for 24 h from five normal men (32.8 yr; range, 26-40 yr) and measured serum PTH levels using a two-site immunoradiometric assay with the exquisite sensitivity and specificity for human PTH-(1-84) (intact PTH). The resultant 24-h time series of serum intact PTH levels were assessed by contemporary techniques in chronophysiology for rhythmic and episodic peak detection. Cosinor analysis disclosed a significant circadian rhythm in serum intact PTH concentrations in all five men, with the mean circadian amplitude and acrophase of 7.2 +/- 4.4 ng/L and 2305 +/- 401 h, respectively (mean +/- SD; n = 5). No apparent fixed ultradian periodicity was found by autocorrelation and spectral analyses. Evaluation of episodic intact PTH pulsatility by Cluster analysis revealed 23.0 +/- 4.4 discrete PTH pulses/24 h (P less than 0.01 vs. signal-free noise), which occurred at an interpulse interval of 61.6 +/- 11.1 min. The average duration of a serum intact PTH peak was 42.8 +/- 7.3 min, and its mean incremental amplitude was 12.6 +/- 1.3 ng/L, which corresponded to a 31.8 +/- 5.2% increase above the preceding nadir. Discrete PTH peaks were separated by nonpulsatile valleys which lasted for 17.9 +/- 4.4 min. Cross-correlation between the time series of serum intact PTH and whole blood ionized calcium (Ca2+) was at its maximum (-0.5) at concurrent time points in three subjects, while significant positive correlation between serum intact PTH and simultaneous serum inorganic phosphorus concentrations was observed in four of five subjects. There was no apparent correlation between the levels of serum intact PTH and serum magnesium. Our data show that serum levels of intact PTH, the only biologically active form of PTH in the blood, is characterized by a significant circadian periodicity, spontaneous episodic pulsatility with distinct peak properties, and a significant temporal coupling with Ca2+ and inorganic phosphorus concentrations. We conclude that PTH secretion, as judged by the temporal pattern of serum intact PTH levels, is pulsatile in normal men.

Production of interleukin 1 beta, a potent bone resorbing cytokine, by cultured human myeloma cells

Supernatants of freshly isolated human myeloma cell cultures were examined both for bone-resorbing activity (BRA) in vitro using newborn mouse calvaria, and for identification of the causal substances of the BRA. Eight of 14 culture supernatants of myeloma cells had BRA. All of these BRA-positive supernatants were from patients with marked destructive bone lesions of multiple myeloma. The presence of interleukin 1 (IL-1), especially IL-1 beta, was demonstrated in seven of these BRA-positive supernatants but not in BRA-negative supernatants. The concentrations of IL-1 beta were high enough to induce bone resorption in the newborn mouse calvaria assay and the BRA was totally abolished by pretreatment of the supernatants with anti-IL-1 beta antibody but not with either anti-IL-1 alpha antibody or normal serum. Other bone resorbing cytokines such as tumor necrosis factor or lymphotoxin were not present in high enough concentrations to stimulate bone resorption and their levels did not correlate with the BRA. IL-1 beta mRNA was also identified in BRA-positive myeloma cells. These results demonstrate that IL-1 beta is the principal agent of BRA present in supernatants of myeloma cell cultures, and also identify a possible role of IL-1 beta in destructive bone lesions in patients with multiple myeloma.

Preparation of a photoreactive analog of parathyroid hormone [Nle8, Lys(N-epsilon-4-azido-2-nitrophenyl)13,Nle18,Tyr34]bovine parathyroid hormone-(1-34)NH2, a selective, high-affinity ligand for characterization of parathyroid hormone receptors

Photoaffinity radiolabeling techniques have been widely used to characterize the properties of peptide hormone receptors. However, the identity of authentic receptors is often uncertain because many macromolecules are labeled. These ambiguities are due, in part, to the use of a heterogeneous mixture of photoreactive photoligands, many of which have no or low affinity for the relevant hormone receptor. In this report, we describe the synthesis, purification, and structural analysis of the photoreactive parathyroid hormone analog, [Nle8,Lys(N-epsilon-4-azido-2-nitrophenyl)13,Nle18,Tyr34]-bovine parathyroid hormone-(1-34)NH2. The sulfur-free, oxidation-resistant, synthetic analog of bovine parathyroid hormone (PTH), [Nle8,Nle18,Tyr34]bovine PTH-(1-34)NH2 (NlePTH), was reacted with 4-fluoro-3-nitrophenylazide under nonaqueous conditions to yield several derivatives which were separated by reverse-phase high-performance liquid chromatography and analyzed by amino acid compositional analysis, thin-layer chromatography, and ultraviolet and visible absorption spectroscopy. Among the NlePTH derivatives generated, one of the least hydrophobic was shown to retain the highest potency as assessed in the canine renal cortical membrane radioreceptor assay. Sequence analysis of this peptide, after it had been derivatized with 4-fluoro-3-nitro-[2,6-3H]phenylazide and purified to homogeneity, permitted us to determine that the structure of this analog is [Nle8,Lys(N-epsilon-4-azide-2-nitrophenyl)13,Nle18,Tyr34]bovine PTH-(1-34)NH2. We emphasize the importance of using photoreactive ligands which are purified and subjected to detailed chemical and biological analyses for characterizing the properties of parathyroid hormone receptors and receptors for other peptide hormones.

Parathyroid hormone down-regulates the epidermal growth factor receptors in clonal osteoblastic mouse calvarial cells, MC3T3-E1: possible mediation by adenosine 3'5'-cyclic monophosphate

The effects of PTH on the binding and mitogenic activity of epidermal growth factor (EGF) were studied in clonal, PTH- and EGF-responsive mouse osteoblastic cell line, MC3T3-E1. Treatment of cells with synthetic rat PTH-(1-34) at 10(-10)-10(-8) M resulted in a dose-related decrease (maximally 30% relative to the control value) in the specific binding of a biologically active, 125I-iodolabeled derivative of recombinant human EGF ([125I]iodo-EGF). The PTH-induced decrease in EGF binding was time dependent, requiring at least 4 h of PTH treatment at 37 C for a maximal effect, completely reversible after cessation of PTH exposure and specific only to biologically active PTH. Scatchard analysis of saturation binding data revealed that the PTH-induced reduction of EGF binding was accounted for by a proportional decrease in the available EGF-binding sites without an alteration in binding affinity (Kd = 0.7-0.8 nM). PTH treatment resulted ina concomitant decrease in mitotic responsiveness to EGF (maximally 40-50% of control). Both of these down-regulatory effects of PTH were closely mimicked by forskolin, cholera toxin, or (Bu)2cAMP. Addition of either colchicine or cytochalasin-B during PTH treatment completely abolished the PTH-induced reduction of EGF binding. These data indicate that PTH down-regulates EGF receptors and reduces the mitotic responsiveness to EGF, probably via a cAMP-dependent cytoskeleton-mediated mechanism(s) in osteoblastic MC3T3-E1 cells.

Interaction of human parathyroid hormone-related peptide with parathyroid hormone receptors in clonal rat osteosarcoma cells

Synthetic peptides corresponding to the amino-terminal region of the human parathyroid hormone-related peptide (hPTHrp) were used to characterize the interaction of hPTHrp with parathyroid hormone (PTH) receptors in clonal rat osteosarcoma cells (ROS 17/2.8). Both hPTHrp-(1-34) and [Tyr40]hPTHrp-(1-40) showed full agonist activity in stimulating cyclic AMP accumulation in ROS cells; human PTHrp-(1-34) was approximately 2.5-fold as potent as hPTH-(1-34). Both [Tyr-40]hPTHrp-(3-40) and hPTH-(3-34) inhibited the cyclic AMP increase induced by either hPTHrp or PTH with parallel dose-inhibition curves. Binding to intact ROS cells of a 125I-labeled [Tyr40]hPTHrp-(1-40) (125I-[Tyr40]hPTHrp-(1-40)) which retains full biological activity was time- and temperature-dependent and reversible. Binding of 125I-[Tyr40]hPTHrp-(1-40) and 125I-labeled [Nle8, Nle18, Tyr34]bovine PTH-(1-34)NH2 to ROS cells was competed for, to the same extent and with the comparable potency, by either unlabeled hPTHrp or PTH peptides. The binding capacity and affinity of receptors in ROS cells were strikingly similar for hPTHrp and PTH. Affinity cross-linking with either radioligand resulted in high affinity, specific labeling of an apparently identical macromolecule centering at Mr = 80,000, which was detected in sodium dodecyl sulfate-polyacrylamide gel electrophoresis in both reducing and nonreducing conditions. The data indicate that hPTHrp and PTH, their amino-terminal fragments at least, interact with the identical receptors with regard to affinity, capacity, specificity, and physicochemical characteristics in osteoblastic ROS 17/2.8 cells.

Osteoclast-mediated osteolysis in bone metastasis from renal cell carcinoma

Osteolytic characteristics of bone metastasis from renal cell carcinoma were morphologically and biochemically investigated. First, undecalcified ground sections of bone metastases were made from four patients with renal cell carcinoma. Second, renal cell carcinoma cell line (RCC-K1) was established from one of the four patients, and its effect on bone resorption in vitro was examined. Marked proliferation and activation of osteoclasts around the tumor cells was histologically demonstrated. Conditioned medium from the RCC-K1 cells contained potent bone-resorbing activity in vitro. The activity was reduced to basal level by calcitonin, but was not blocked by indomethacin. The activity was lost after dialysis (MW cutoff 3500), while it was retained after 2 weeks of storage. Levels of prostaglandin E2 and 1,25-dihydroxyvitamin D of the RCC-K1-conditioned medium were insufficient to cause bone resorption in vitro. The conditioned medium did not stimulate cAMP accumulation in rat osteoblastic cells. These results suggest that renal cell carcinoma causes bone destruction through the stimulation of osteoclasts by locally secreting an unknown humoral factor or factors.

Characterization and agonist-induced down-regulation of parathyroid hormone receptors in clonal rat osteosarcoma cells

PTH receptors on two stable clonal rat osteosarcoma cell lines, ROS 17/2 and ROS 17/2.8, were characterized using an HPLC-purified, synthetic, sulfur-free, radioiodinated analog of bovine PTH, [Nle8,Nle18,Tyr,34]bovine PTH-(1-34)amide. PTH binding is specific for PTH agonists and antagonists and is dependent on the time and temperature of incubation. There is an excellent correlation between binding affinities of PTH agonists and antagonists in these intact cell systems with those in canine renal membranes. Peptides unrelated to PTH do not bind. Both ROS 17/2 and 17/2.8 have a single class of saturable, high affinity PTH binding sites that, by kinetic analysis and Scatchard analysis of saturation and competition studies, has a dissociation constant (Kd) of 0.8-1.4 nM. Bmax is approximately 36,000 and 72,000 sites per cell in ROS 17/2 and 17/2.8, respectively. A close correlation was found between the binding of PTH agonists to their receptors in ROS 17/2 cells with their relative biological potencies as measured by stimulation of adenylate cyclase in plasma membranes prepared from these cells. Prolonged treatment of ROS 17/2 and 17/2.8 cells with PTH agonists results in a dose- and time-dependent decrease of available cell-surface binding sites, without alterations in Kd. PTH antagonists do not regulate PTH receptors. Regulation of PTH receptors by PTH agonists is dependent on the dose and time of exposure to ligand over a dose range of 10(-8) to 10(-11) M. Cells exposed to agonists (greater than or equal to 10(-8) M) for 48 h show maximally decreased receptor number; continued exposure to agonists (greater than or equal to 10(-8) M) does not further decrease PTH receptor number, which remains constant at about 15% of control values. Agonist-induced down-regulation occurs with less than 10(-11) M agonists, a concentration less than 10% of the minimal dose detected by direct ligand competition. Treatment of ROS 17/2 cells with PTH agonists results in a dose- and time-dependent decrease of PTH-stimulated adenylate cyclase. This agonist-induced desensitization correlates closely with the decreased availability of PTH receptors: it is maximal in cells exposed to agonists (greater than 10(-8) M) for 48 h and also does not decrease further with continued exposure of the cells to agonist. Future studies with these stable ROS cell lines should permit detailed analysis of the biochemical mechanisms underlying homologous and heterologous regulation of PTH receptors and desensitization and sensitization of the adenylate cyclase response.

Parathyroid hormone receptors are plasma membrane glycoproteins with asparagine-linked oligosaccharides

In the preceding article, we described physicochemical and kinetic properties of parathyroid hormone (PTH) receptors in clonal rat osteosarcoma cells (ROS 17/2.8) using photoaffinity ligand labeling and showed that the physiologically relevant receptor-ligand complex has an apparent Mr = 80,000. In this study, the photoaffinity labeled Mr = 80,000 receptor was localized exclusively on the cell surface plasma membrane and its glycoprotein nature was demonstrated through the use of lectin affinity-chromatography and specific exo- and endoglycosidases. Rinsing ROS cells, preincubated in the dark with 125I-labeled [Nle8, N-epsilon-(4-azido-2-nitrophenyl)Lys13,Nle18,Tyr34]bovine PTH-(1-34)-NH2 (NAP-NlePTH) (4 h, 15 degrees C, equilibrium conditions) with acidic phosphate-buffered saline (pH 2.5, 30 s, 4 degrees C) before photolysis resulted in selective and nearly total disappearance of the labeled Mr = 80,000 receptor. PTH receptor integrity to acid rinsing and photolysis was shown by relabeling the Mr = 80,000 receptor after a second incubation of these cells with 125I-labeled NAP-NlePTH, followed by photolysis. Adsorption of Triton X-100-solubilized, 125I-labeled NAP-NlePTH receptors to wheat germ agglutinin-agarose is nearly complete and highly selective, and elution with N-acetylglucosamine resulted in virtually total recovery of the labeled receptors from the column. The wheat germ agglutinin-retarded PTH receptors show increased electrophoretic mobility upon treatment with neuraminidase which was inhibited by simultaneous addition of 2,3-dehydro-3-desoxy-N-acetylneuraminic acid, a specific neuraminidase inhibitor. Endoglycosidase F treatment of the Mr = 80,000 receptors generated a single, labeled polypeptide with a Mr = 59,000 which migrated as a narrow band. PTH receptors on ROS 17/2.8 cells appear to be monomeric plasma membrane glycoproteins with an apparent Mr of 80,000 which contain a Mr = 59,000 polypeptide backbone and a polymeric arrangement of N-acetylglucosamine with N-acetylneuraminic acid as major terminal sugar residues.

Photoaffinity labeling of parathyroid hormone receptors in clonal rat osteosarcoma cells

A photoreactive derivative of a sulfur-free bovine parathyroid hormone (PTH) analogue, [Nle8,N-epsilon-(4-azido-2-nitrophenyl)Lys13,Nle18,Tyr34]bovine PTH-(1-34)-NH2 (NAP-NlePTH), was purified from the products of the reaction of [Nle8,Nle18,Tyr34]bovine PTH-(1-34)-NH2 (NlePTH) with 4-fluoro-3-nitro-phenylazide and was used to identify binding components of the PTH receptor in clonal rat osteosarcoma cells (ROS 17/2.8). The purified analogue, NAP-NlePTH, is a fully active agonist in three different ROS 17/2.8 cell bioassays: 1) specific binding to saturable PTH receptors; 2) stimulation of cyclic AMP accumulation; and 3) inhibition of cellular alkaline phosphatase activity; this analogue gave dose response curves parallel to and 25-33% as potent as its parent molecule, NlePTH. Radioiodinated NAP-NlePTH (125I-labeled NAP-NlePTH) retained maximal receptor-binding potency. Radioligand saturation studies in intact cells showed that the Kd of PTH receptors for the photoligand was slightly less than that for 125I-labeled NlePTH (2.8 and 0.8 nM, respectively), but that the Bmax was essentially identical for both radioligands (8 fmol/10(5) cells). Photoaffinity labeling of ROS 17/2.8 cells revealed several 125I-labeled macromolecular components by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. One predominant 125I-labeled band, having an apparent Mr of 80,000 daltons (including Mr = 4,347 ligand; hereafter referred to as the Mr = 80,000 protein), was consistently demonstrated in both reducing and nonreducing conditions. Its labeling was completely inhibited by coincubation with NlePTH (10 nM) at 26-fold molar excess to the photoligand, but not by biologically inactive PTH fragments or unrelated hormone. Labeling of several other macromolecular components persisted in the presence of NlePTH (1 microM). Only the labeling of the Mr = 80,000 protein showed saturation kinetics for photoaffinity labeling; the dose of 125I-labeled NAP-NlePTH (0.8 nM) to half-saturate labeling of the Mr = 80,000 protein was close to the Kd (2.8 nM) of specific binding of the photoligand to receptors in intact ROS 17/2.8 cells. Pretreatment of the cells with NlePTH and dexamethasone led to the predicted proportional decrease or increase, respectively, in labeling of the Mr = 80,000 protein. Our data, using a highly purified photoactive derivative of PTH, having carefully defined chemical and biological properties, show a plasma membrane component of Mr = 80,000 in ROS 17/2.8 cells that possesses the affinity, binding capacity, and physiological characteristics of the PTH receptor.

Co-purification of bone resorbing activity and adenylate cyclase stimulating activity from human tumours associated with the humoral hypercalcaemia of malignancy

We have partially purified a tumour factor capable of stimulating both bone resorption in vitro and cAMP accumulation in osteoblastic ROS 17/2 cells from three human tumours associated with humoral hypercalcaemia of malignancy. Purification of tumour factor by sequential acid urea extraction, gel filtration and cation-exchange chromatography, reverse-phase high performance liquid chromatography followed by analytical isoelectric focussing provided a basic protein (pI greater than 9.3) with a molecular weight of approximately 13,000 as a major component of the final preparation which retained both the two bioactivities. Bone resorbing activity and cAMP-increasing activity in purified factor correlated with each other. cAMP-increasing activity of the factor was heat- and acid-stable, but sensitive to alkaline ambient pH. Treatment with trypsin destroyed cAMP-increasing activity of the factor. Synthetic parathyroid hormone (PTH) antagonist, human PTH-(3-34) completely inhibited the cAMP-increasing activity of the factor. The results suggest that this protein factor, having its effects on both osteoclastic and osteoblastic functions, may be involved in development of enhanced bone resorption in some patients with humoral hypercalcaemia of malignancy.