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Human tumor cells inoculated into the arterial circulation of immunocompromised mice can reliably cause bone metastases, reproducing many of the clinical features seen in patients. Animal models permit the identification of tumor-produced factors, which act on bone cells, and of bone-derived factors. Local interactions stimulated by these factors drive a vicious cycle between tumor and bone that perpetuates skeletal metastases. Bone metastases can be osteolytic, osteoblastic, or mixed. Parathyroid hormone-related protein, PTHrP, is a common osteolytic factor, while vascular endothelial growth factor and interleukins 8 and 11 also contribute. Osteoblastic metastases can be caused by tumor-secreted endothelin-1, ET-1. Other potential osteoblastic factors include bone morphogenetic proteins, platelet-derived growth factor, connective tissue growth factor, stanniocalcin, N-terminal fragments of PTHrP, and adrenomedullin. Osteoblasts are the main regulators of osteoclasts, and stimulation of osteoblast proliferation can increase osteoclast formation and activity. Thus, combined expression of osteoblastic and osteolytic factors can lead to mixed metastases or to increased osteolysis. Prostate-specific antigen is a protease, which can cleave PTHrP and thus change the balance of osteolytic versus osteoblastic responses to metastatic tumor cells. Bone itself stimulates tumor by releasing insulin-like growth factors and transforming growth factor-beta. Secreted factors transmit the interactions between tumor and bone. They provide novel targets for therapeutic interactions to break the vicious cycle of bone metastases. Clinically approved bisphosphonate anti-resorptive drugs reduce the release of active factors stored in bone, and PTHrP-neutralizing antibody, inhibitors of the RANK ligand pathway, and ET-1 receptor antagonist are in clinical trials. These adjuvant therapies act on bone cells, rather than the tumor cells. Recent gene array experiments identify additional factors, which may in the future prove to be clinically important targets.

In patients with advanced disease, several cancer types frequently metastasize to the skeleton, where they cause bone destruction. Osteolytic metastases are incurable and cause pain, hypercalcemia, fracture, and nerve compression syndromes. It was proposed over a century ago that certain cancers, such as that of the breast, preferentially metastasize to the favorable microenvironment provided by bone. Bone matrix is a rich store of immobilized growth factors that are released during bone resorption. Histological analysis of osteolytic bone metastases indicates that the bone destruction is mediated by the osteoclast rather than directly by the tumor cells. These observations suggest a vicious cycle driving the formation of osteolytic metastases: tumor cells secrete factors stimulating osteoclasts through adjacent bone marrow stromal cells; osteoclastic resorption in turn releases growth factors from the bone matrix; finally, locally released growth factors activate the tumor cells. This vicious cycle model has now been confirmed at the molecular level. In particular, transforming growth factor beta (TGF3beta) is abundant in bone matrix and released as a consequence of osteoclastic bone resorption. Bone-derived TGFbeta plays an integral role in promoting the development and progression of osteolytic bone metastases by inducing tumor production of parathyroid hormone-related protein (PTHrP), a known stimulator of osteoclastic bone resorption. In breast cancer cells TGFbeta appears to stimulate PTHrP secretion by a posttranscriptional mechanism through both Smad and p38 mitogen activated protein (MAP) kinase signaling pathways. Osteolytic metastases can be suppressed in vivo by inhibition of bone resorption, blockade of TGFbeta signaling in tumor cells, and by neutralization of PTHrP. Other factors released from bone matrix may also act on tumor cells in bone, which in turn may produce other factors that stimulate bone resorption, following the vicious cycle paradigm established for TGFbeta and PTHrP. An understanding at the molecular level of the mechanisms of osteolytic metastasis will result in more effective therapies for this devastating complication of cancer.

Corynebacterium matruchotii is a microbial inhabitant of the oral cavity associated with dental calculus formation. It produces membrane-associated proteolipid capable of inducing hydroxyapatite formation in vitro. This proteolipid was purified from chloroform:methanol extracts by chromatography on Sephadex LH-20 and migrated on SDS-polyacrylamide gel electrophoresis at 6-9 kDa. Removal of covalently attached acyl moieties by methanolic KOH decreased its molecular mass to approximately 5.5 kDa. The amino acid sequence of the apoproteolipid indicated a peptide of 50 amino acids, a calculated molecular weight of 5354 Da, and an isoelectric point of 4.28. Sequence analysis revealed an 8 amino acid sequence with homology to human phosphoprotein phosphatase 2A as well as several potential acylation sites and one phosphorylation site. The purified proteolipid induced calcium precipitation in vitro. Deacylation of the proteolipid by hydroxylamine treatment resulted in >50% loss of calcium-precipitating activity, suggesting that covalently attached lipids are required. Degenerate oligonucleotide primers, based on the amino acid sequence, were used to amplify the gene for the 5.5 kDa proteolipid from total chromosomal DNA of C. matruchotii by PCR. A 166 bp cDNA was isolated and sequenced, confirming the amino acid sequence of the proteolipid. Thus, we have sequenced a unique bacterial proteolipid that is involved in the formation of dental calculus by precipitating Ca2+ and possibly in transport of inorganic phosphate, necessary for hydroxyapatite formation.

Autocrine products of osteoclasts such as interleukin-6 may play an important role in normal osteoclast formation and activity. To identify novel stimulatory factors for osteoclasts, we have prepared a mammalian cDNA expression library generated from highly purified human osteoclast-like multinucleated cells (MNC) formed in long term bone marrow cultures and screened this library for autocrine factors that enhance MNC formation. A candidate clone which stimulated MNC formation was isolated. Sequence analysis showed that this cDNA encoded annexin II (AXII). Purified recombinant AXII significantly increased MNC formation in human bone marrow cultures in the absence of 1,25-(OH)2 vitamin D3 and enhanced MNC formation in mouse bone marrow cultures treated with 10(-9) M 1,25-(OH)2 vitamin D3. The enhanced MNC formation in murine marrow cultures resulted in increased bone resorption. Treatment of fetal rat long bones with AXII and 1,25-(OH)2 vitamin D3 significantly increased bone resorption compared to 1,25-(OH)2 vitamin D3 alone. Reverse transcriptase polymerase chain reaction analysis demonstrated that AXII mRNA was expressed at high levels in RNA isolated from highly purified giant cells from osteoclastomas, human osteoclast-like MNC, and pagetic bone. Western blot analysis of conditioned media collected from human marrow cultures showed that AXII was present in the media. Furthermore, approximately 50% of total AXII produced by cells transfected with AXII cDNA was present in the conditioned media. These data suggest that the AXII is an autocrine factor that enhances osteoclast formation and bone resorption and demonstrate a previous unknown function for AXII.

Rhodanese is a small (33 kDa) monomeric sulfurtransferase which is synthesized on cytoplasmic ribosomes and imported into the mitochondrial matrix without cleavage of its amino terminus. When we transfected mammalian cell lines with rhodanese cDNA under the control of an efficient viral promoter, up to 40% of the overexpressed protein was secreted into the medium. This secretion was not the result of cell lysis, did not occur via the endoplasmic reticulum, and did not require the amino-terminal mitochondrial import signal. Addition of a carboxyl-terminal peptide extension did not block secretion, nor did a number of inhibitors of cellular sorting processes. Rhodanese polypeptide is known to associate with chaperonin proteins. In the absence of available mitochondrial import sites, such a complex in the cytoplasm of transfected cells could deliver unfolded rhodanese to export pores on the inner surface of the plasma membrane. This mechanism could contribute to the nonclassical secretion of cytoplasmically synthesized interleukins, growth factors, and lectins.

Mutants of rhodanese (EC 2.8.1.1) which substitute serine residues for each of the 4 cysteine residues have been studied to determine the roles of cysteines in the structure and function of the enzyme. The proteins compared in these studies were: the wild-type, C63S, C247S, C254S, C263S, C254S/C263S, and C63S/C254S/C263S. These current studies show that cysteine 247 is the only cysteine required for the activity of the enzyme. Although the other sulfhydryl groups do not participate in sulfur transfer, mutations of the noncatalytic cysteines result in the destabilization of the native structure of the enzyme. All the active proteins had similar kinetic parameters. Mutants substituting cysteine 254, compared with the other species, were: (a) more resistant than wild-type to inactivation by dithiothreitol, (b) more readily reactivated following oxidative inactivation, and (c) found to adopt conformations that show increased exposure of hydrophobic surfaces following removal of the transferable sulfur. On the other hand, cysteine to serine substitutions had very little effect on: (a) the rates of oxidative inactivation, (b) the increased fluorescence following the removal of transferable sulfur, or (c) the effectiveness of spontaneous refolding after urea denaturation. Forms of rhodanese that were formerly considered to be irreversibly oxidized can be reactivated if the protein is denatured in urea before reductants are used. It is proposed that these forms differ from reversibly oxidized states due to the inaccessibility of intramolecular disulfides to reductants and not to the formation of higher oxidation states of the protein.

Parathyroid hormone-related protein (PTH-rP) has been implicated as a causative factor in the humoral hypercalcemia of malignancy. Animal models of hypercalcemia of malignancy that have traditionally utilized human or animal tumors or injections or infusions of hypercalcemic factors have limitations that may prevent exact delineation of the biologic effects of tumor-produced PTH-rP.To assess the effects of tumor-produced PTH-rP in vivo, we have transfected Chinese hamster ovarian (CHO) cells with cDNA encoding human preproPTH-rP-(1-141) which then stably express only PTH-rP. We inoculated these tumor cells into nude mice, and compared tumor-bearing nude mice with similar tumor-bearing nude mice inoculated with non-transfected CHO cells using standard parameters of calcium homeostasis.The nude mice carrying tumors expressing PTH-rP became hypercalcemic over 12 to 18 days. Blood ionized calcium values correlated positively with plasma PTH-rP concentration and tumor volume. Plasma PTH-rP concentrations in hypercalcemic mice were similar to those reported in humans with hypercalcemia of malignancy. Bone histology and histomorphometry from hypercalcemic nude mice demonstrated increased bone resorption when compared with mice bearing nontransfected CHO tumors.We have produced an animal model of tumor-produced PTH-rP by transfecting CHO cells with the cDNA for PTH-rP and inoculating these tumor cells into nude mice. Hypercalcemia in this model is mediated in part by the effects of PTH-rP to increase osteoclastic bone resorption. The model is advantageous because PTH-rP alone is secreted in a prolonged, constitutive fashion with pharmacokinetics similar to naturally occurring tumors. It should prove to be a useful model to study the effects of tumor-produced PTH-rP in vivo.

A cDNA for the enzyme rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) has been cloned from a bovine adrenal library. An initiator methionine codon precedes the amino-terminal amino acid found in the isolated protein. Rhodanese is synthesized in the cytoplasm and transferred to the mitochondrial matrix. Thus, any amino-terminal sequence required for organelle import is retained in the mature protein. Furthermore, the DNA sequence shows that there are three additional amino acids, Gly-Lys-Ala, at the carboxyl terminus that are not found by protein sequencing. Additionally, comparison of the published amino acid sequence with that encoded by the open reading frame revealed three differences in the amino acid sequence. Comparison of the bovine and chicken liver sequences shows an overall level of 70% sequence homology, but there is complete identity of all residues that have been implicated in the function of the enzyme. When two mammalian cells, cos-7 and 293 cells, were transiently transfected with a plasmid containing the rhodanese coding region, rhodanese activity in lysates increased approximately 20-fold. Fluorograms of denaturing polyacrylamide gels detected a large increase in a polypeptide that co-migrated with the native protein and reacted with anti-rhodanese antibodies. Nondenaturing gels showed two active species that co-migrated with the two major electrophoretic forms purified by current procedures. Escherichia coli, transformed with a plasmid containing the rhodanese coding region, showed a 15-fold increase in rhodanese activity over baseline values. When the E. coli recombinant protein was analyzed on a nondenaturing gel, only one species was observed that co-electrophoresed with the more electropositive variant seen in purified bovine liver rhodanese. This single variant could be converted by carboxypeptidase B digestion to a form of the enzyme that co-migrated with the more electronegative species isolated from bovine liver. Thus, two major, enzymatically active electrophoretic variants, commonly observed in mammalian cells, can be accounted for by carboxyl-terminal processing without recourse to other post-translational modifications.

Synthetic oligonucleotides were used to screen a rat striatal cDNA library for sequences corresponding to the tachykinin peptides substance P and neurokinin A. The cDNA library was constructed from RNA isolated from the rostral portion of the rat corpus striatum, the site of striatonigral cell bodies. Two types of cDNAs were isolated and defined by restriction enzyme analysis and DNA sequencing to encode both substance P and neurokinin A. The two predicted preprotachykinin protein precursors (130 and 115 amino acids in length) differ from each other by a pentadecapeptide sequence between the two tachykinin sequences, and both precursors possess appropriate processing signals for substance P and neurokinin A production. The presence of a third preprotachykinin mRNA of minor abundance in rat striatum was established by S1 nuclease protection experiments. This mRNA encodes a preprotachykinin of 112 amino acids containing substance P but not neurokinin A. These three mRNAs are derived from one rat gene as a result of differential RNA processing; thus, this RNA processing pattern further increases the diversity of products that can be generated from the preprotachykinin gene.

A stable analogue has been prepared of the enediolate anion believed to occur transiently in the reaction of phosphoglucose isomerase. This compound, 5-phosphoarabinonate, is the strongest known competitive inhibitor of the enzyme (Ki = 3 times 10(-7) M below pH 7). A distinctive pH dependence of binding, also found for two other aldonic acid omega-phosphates, 6-phosphogluconate and 4-phosphoerythronate, involves pertubation of a pKa from 7.0 in the free enzyme to 9.0 in the enzyme-inhibitor complex. This perturbation may reflect a catalytically advantageous increase in basicity which occurs around the transition state of the normal enzymatic reaction.

Isolated rat pancreatic islets were incubated in high (28 mM) or low (2.8 mM) glucose for 0, 1 or 4 hr and insulin biosynthesis and messenger RNA quantified. During the 4 hr course of the experiments the fraction of protein synthesised specifically into proinsulin increased in the presence of high vs low glucose (14.3 +/- 3.7 vs 0.8 +/- 0.5%, p less than 0.01). The relative amount of proinsulin mRNA was found to be about 5-fold higher in islets incubated in high glucose at 4 hr as determined by RNA blot hybridization. Total translatable islet mRNA was unaffected by glucose in the medium. These data extend observations of changes in proinsulin mRNA in rats in vivo during fasting and glucose injection, and suggest a direct effect of glucose on islets. These data further demonstrate that glucose modulates selectively the level of proinsulin mRNA during incubation of isolated pancreatic islets and that changes in the level of proinsulin mRNA play an important role in regulation of insulin biosynthesis.

Previous studies by Southern blot analysis of human × mouse somatic cell hybrids localized the renin gene to region p21→qter of human chromosome 1. Using a DNA insert encoding exons 2–5, the renin gene was mapped to human chromosome bands 1q25→q32 by in situ hybridization. The sublocalization of the renin gene will facilitate subsequent detailed linkage analysis of human chromosome 1.

In contrast to the strongly pH-dependent inhibition of phosphoglucose isomerase by substrate analogues with a free carboxyl group, inhibition of this enzyme by neutral sugar phosphates is essentially invariant between pH 7 and 9. Competitive inhibition constants for glucitol 6-phosphate (40 muM), arabinose 5-phosphate (50 muM), and erythritol 4-phosphate (100 muM) were found to be of the same order of magnitude as that reported previously for substrate binding constants (50 to 240 muM). The unique exception is erythrose 4-phosphate whose Ki (0.7 muM, independent of pH) reflects a tightness of binding similar to that found at pH values near or below neutrality for the transition state analogue 5-phosphorarabinonate. The pH independence of inhibition by erythrose 4-phosphate and other neutral sugar phosphates may reflect a mode and locus of binding to phosphoglucose isomerase different from that of the aldonate inhibitors.