Human prostatic cancer cells, PC3, elaborate mitogenic activity which selectively stimulates human bone cells

Prostatic cancer typically produces osteoblastic metastases which are not attended by marrow fibrosis (i.e., osteoblast but not stromal fibroblast proliferation). In the present study we sought to test the hypothesis that prostatic cancer cells produce factor(s) which act selectively on human osteoblasts. Such a paracrine mechanism would explain the observed increase in osteoblasts, unaccompanied by an increase in marrow fibroblasts. To test this hypothesis we investigated the mitogenic activity released by the human prostatic tumor cell line, PC3. PC3 cells have been reported previously to produce mitogenic activity for cells that was relatively specific for rat osteoblasts compared to rat fibroblasts. However, the effects of this activity on human cells has not been examined previously. PC3-conditioned medium (CM) (5-50 micrograms CM protein/ml) stimulated human osteoblast proliferation by 200-950% yet did not stimulate human fibroblast proliferation [( 3H]thymidine incorporation). PC3 CM also increased cell numbers in human osteoblast but not fibroblast cell cultures. To determine whether the osteoblast-specific mitogenic activity could be attributed to known bone growth factors, specific assays for these growth factors were performed. PC3 CM contained 10 pg insulin-like growth factor (IGF) I, less than 2 pg IGF II, 54 pg basic fibroblast growth factor, and 16 pg transforming growth factor beta/microgram CM protein. None of these growth factors alone or in combination could account for the observed osteoblast-specific PC3 cell-derived mitogenic activity. Furthermore, when 5 micrograms/ml PC3 CM was tested in combination with maximally effective concentrations of either basic fibroblast growth factor, IGF I, IGF II, or transforming growth factor beta, it produced an additive effect suggesting that PC3 CM stimulates osteoblast proliferation by a mechanism independent of these bone mitogens. Biochemical characterization supported the hypothesis that the PC3 cell growth factor was unique from other growth factors. The PC3 growth factor did not bind to heparin and was resistant to acid as well as the reducing agent, dithiothreitol. Sephadex G-75 and fast protein liquid chromatography Mono S cation-exchange chromatography revealed the PC3-derived mitogen to be an Mr 26,000-30,000 basic protein. Therefore, we conclude that PC3 cells release a mitogen which exhibits higher specificity for human osteoblasts than human fibroblasts and is unique from other growth factors tested. Production of this mitogen by human prostatic carcinoma cells could play an etiological role in the intense osteoblast-specific stimulation that occurs at sites of bone metastases.

Studies of the mechanism by which androgens enhance mitogenesis and differentiation in bone cells

Recently, we reported a direct effect of androgens on murine and human bone cells to stimulate bone cell proliferation and differentiation. To test whether this effect of androgenic steroids might be mediated by growth factors, we measured relative concentrations of insulin-like growth factor-I and -II (IGF-I and IGF-II) and transforming growth factor-beta (TGF beta) in the conditioned medium from androgen-treated murine calvarial cell cultures. Only the concentration of TGF beta was increased. Consistent with the increased secretion of TGF beta in the mouse calvarial cell system, we observed an increased expression of TGF beta mRNA in a normal human osteoblastic cell system. We also determined whether androgens alter the response to growth factors. We found that dihydrotestosterone (DHT) treatment enhanced the mitogenic effects of fibroblast growth factor (FGF) and IGF-II but not those of IGF-I. The enhanced effect of FGF and IGF-II after DHT pretreatment was not affected by addition of TGF beta-blocking antibodies or by changing the culture medium. This indicated that in addition to increased release of TGF beta, another mechanism might be involved in the action of DHT on human and murine bone cells. Thus, we investigated the binding of human IGF-II to human osteoblastic cells and observed an increase in IGF-II binding after DHT treatment. Our results are consistent with a mechanism of action of androgens on bone cells that involves the induction of TGF beta and, in addition, may sensitize the cells to show an enhanced response to FGF and IGF-II, possibly by changing the receptor binding of mitogenic growth factors.

An inhibitory insulin-like growth factor binding protein (In-IGFBP) from human prostatic cell conditioned medium reveals N-terminal sequence identity with bone derived In-IGFBP

Insulin-like growth factor binding proteins (IGFBPs), are produced by several cell types, are present in biological fluids, and may function in modulating insulin-like growth factor (IGF) biological activities. Recently the presence of multiple IGFBPs was reported in seminal fluid, suggesting that IGFBPs are produced by prostatic epithelium. We have found that human prostatic tumor cells of the PC3 cell line produce an IGFBP. PC3-IGFBP was purified to homogeneity using sequential IGF I affinity and HPLC C4 reverse phase chromatographies. Chemical cross-linking of PC3-IGFBP to 125I-IGF I revealed a molecular weight of 25 kDa. Its N-terminal sequence and amino-acid composition were highly homologous to that of a recently described 25 kDa inhibitory IGFBP (In-IGFBP), produced by osteoblasts in vitro. PC3-IGFBP inhibited basal and IGF II-stimulated bone cell DNA synthesis. We conclude that the PC3-IGFBP is very similar, if not identical to the osteoblast-derived In-IGFBP. Expression of PC3-IGFBP by metastatic human prostate tumor cells thus might affect the osteoblast proliferation that is induced by metastatic prostatic carcinoma. The PC3-IGFBP may be similar to a 24 kDa IGFBP described in seminal fluid and thus may be important in the regulation of cell proliferation in the male reproductive tract.

Nucleotide sequence, organisation and structural analysis of the products of genes in the nirB-cysG region of the Escherichia coli K-12 chromosome

The DNA sequence and derived amino-acid sequence of a 5618-base region in the 74-min area of the Escherichia coli chromosome has been determined in order to locate the structural gene, nirB, for the NADH-dependent nitrite reductase and a gene, cysG, required for the synthesis of the sirohaem prosthetic group. Three additional open reading frames, nirD, nirE and nirC, were found between nirB and cysG. Potential binding sites on the NirB protein for NADH and FAD, as well as conserved central core and interface domains, were deduced by comparing the derived amino-acid sequence with those of database proteins. A directly repeated sequence, which includes the motif -Cys-Xaa-Xaa-Cys-, is suggested as the binding site for either one [4Fe-4S] or two [2Fe-2S] clusters. The nirD gene potentially encodes a soluble, cytoplasmic protein of unknown function. No significant similarities were found between the derived amino-acid sequence of NirD and either NirB or any other protein in the database. If the nirE open reading frame is translated, it would encode a 33-amino-acid peptide of unknown function which includes 8 phenylalanyl residues. The product of the nirC gene is a highly hydrophobic protein with regions of amino-acid sequence similar to cytochrome oxidase polypeptide 1.

Quantitation of growth factors IGF-I, SGF/IGF-II, and TGF-beta in human dentin

Human bone matrix is known to contain a battery of polypeptide growth factors. Since dentin is a mineralized tissue similar to bone in composition and perhaps in formation, human dentin was assayed for the presence of similar growth factors. Root dentin proteins were extracted by demineralization in 4 M guanidine hydrochloride (Gu) and 30 mM Tris (pH 7.4) containing 20% EDTA and proteinase inhibitors. Gu-EDTA extracts were desalted and used for the following assays: (1) bone cell proliferation in chick calvarial cell mitogenic assay using the incorporation of [3H]thymidine into TCA-insoluble material; (2) osteocalcin by radioimmunoassay (RIA); (3) insulin-like growth factor I (IGF-I) by RIA; (4) skeletal growth factor/insulinlike growth factor II (SGF/IGF-II) by radioreceptor assay; and (5) transforming growth factor beta (TGF-beta) by bioassay. Gu-EDTA extracts stimulated bone cell proliferation. At 10 micrograms/ml, dentin proteins increased the incorporation of [3H]thymidine by calvarial cells to 320% of that by BSA-treated control cells. Consistent with the presence of mitogenic activity, growth factors were found in dentin in the following concentrations (ng/micrograms Gu-EDTA protein): (1) IGF-I, 0.06; (2) SGF/IGF-II, 0.52; and (3) TGF-beta, 0.017. All three growth factors were present in concentrations lower than that found in human bone. Osteocalcin was detected at a concentration of 3.0 mg/g Gu-EDTA protein, also much lower than that in bone.

Transcriptional regulation of comC: evidence for a competence-specific transcription factor in Bacillus subtilis

comC specifies a protein product that is required for genetic competence in Bacillus subtilis. The probable transcriptional start site of comC has been localized by high-resolution primer extension analysis and shown to be preceded by an appropriately positioned sequence that resembles the consensus promoter for the sigma A form of RNA polymerase. Low-resolution S1 nuclease transcription mapping was used to identify the comC terminator, which is located near a palindromic element recognizable in the DNA sequence. Deletion analysis of the sequence upstream from the likely promoter identified a region required in cis for the expression of comC. An overlapping, and possibly identical, sequence was shown to inhibit the expression of competence and of several late competence genes, when present in multiple copies. This was interpreted as due to the titration of a positively acting competence transcription factor (CTF) by multiple copies of the promoter-bearing fragment. In crude lysates of B. subtilis grown to competence, a DNA-binding activity that appeared to be specific for the comC promoter fragment was detected by gel retardation assays. This activity, postulated to be due to CTF, was detected only following growth in competence medium, only in the stationary phase of growth, and was dependent on the expression of ComA, a known competence-regulatory factor. In the presence of the mecA42 mutation, the ComA requirement for CTF activity was bypassed, and CTF activity could be detected in lysates prepared from a strain grown in complex medium. This behavior suggested that either the expression or the activation of CTF was regulated in a competence-specific manner. Comparison of the putative CTF-binding site defined by deletion analysis with a similarly positioned sequence upstream from the start site of the late competence gene comG revealed that both sequences contained palindromes, with 5 of 6 identical base pairs in each arm. It is suggested that these palindromic sequences comprise recognition elements for CTF binding and that CTF binding must occur for the appropriate expression of late competence genes.

Development of valid methods to measure insulin-like growth factors-I and -II in bone cell-conditioned medium

A variety of human cells and biological fluids have been shown to produce or contain insulin-like growth factor (IGF)-specific binding proteins (BPs). The existence of these BPs in serum and conditioned medium of cell and organ cultures has complicated radioligand assays for measurement of IGFs. Various strategies have been proposed to avoid interference of BPs with these assays, including acid-ethanol precipitation of BPs and acid-gel filtration. Many of these procedures are time consuming, exhibit low recoveries, and do not completely eliminate BP artifacts. In this study we have investigated interference of inhibitory IGF-BP (In-IGF-BP) purified from bone cell-conditioned medium in an IGF-II RRA and IGF-I RIA and developed methods to neutralize In-IGF-BP artifacts in IGF assays. In the IGF-II RRA, purified In-IGF-BP competed for [125I]IGF-II binding to H-35 cells in a dose-dependent manner and, thus, increased the apparent value for IGF-II in the medium. Fifty percent inhibition of [125I]IGF-II binding to H-35 cells was seen at 12.2 and 5.7 ng/ml unlabeled IGF-II and IN-IGF-BP, respectively. In-IGF-BP also competed for [125I]IGF-I in the IGF-I RIA; however, the interference was much less in the IGF-I RIA compared to the IGF-II RRA. Fifty percent displacement of [125I]IGF-I binding was seen at 0.25 and 5 ng/ml unlabeled IGF-I and In-IGF-BP, respectively. Our approach to eliminate BP artifacts was as follows. We knew that In-IGF-BP showed comparatively equal binding affinities with both IGF-I and IGF-II, and binding of these ligands to cell receptors (IGF-II) and antibodies (IGF-I) was very specific (2% and 0.5% cross-reactivity for IGF-I and IGF-II, respectively). Therefore, in the IGF-I RIA we blocked the In-IGF-BP artifacts by adding an excess of IGF-II, and in the IGF-II RRA we blocked the In-IGF-BP artifacts by adding an excess of IGF-I. By incubating purified In-IGF-BP with different amounts of IGF-I, we found that 30-min preincubation of 5 ng In-IGF-BP with 10 ng IGF-I completely blocked BP artifacts in the IGF-II RRA. Similarly, preincubation of In-IGF-BP with IGF-II blocked BP artifacts in the IGF-I RIA.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and N-terminal amino acid sequence of the tartrate-resistant acid phosphatase from human osteoclastoma: evidence for a single structure

Tartrate-resistant acid phosphatase type-5 was purified to apparent homogeneity from human osteoclastomas by sequential chromatography on CM-Sepharose, Phenyl-Sepharose, concanavalin A-Sepharose, FPLC Superose-12, and FPLC Mono-S. The purification over the original tissue extract was 1167-fold, with a yield of 16%. An identity in the N-terminal amino acid sequence and Mr was found between this enzyme and two type-5 tartrate-resistant acid phosphatases isolated from hairy cell leukemia spleen. However, they appeared to be different as assessed by amino acid composition. In contrast to a previous report, no evidence was found for two subunits of the tartrate-resistant acid phosphatase.

Insulin-like growth factor-I and insulin-like growth factor-II induce c-fos in mouse osteoblastic cells

We investigated the expression of c-fos in mouse osteoblast-like cultures treated with insulin-like growth factor (IGF)-I and IGF-II. The IGFs are present in bone, are produced by osteoblast-like cells in culture, and stimulate osteoblast cell proliferation. Quiescent, subconfluent cultures of the clonal osteoblast-like mouse calvarial cell line, MC3T3-E1, were treated with 10 ng/ml of IGF-I or IGF-II. RNA was extracted at 0, 15, 30, 60, 120 and 240 minutes, and c-fos messenger RNA (mRNA) was analyzed on Northern blots. Both IGFs transiently increased c-fos mRNA levels 25-28 fold at 15-30 min. To determine if c-fos induction was unique to the MC3T3-E1 cell line, effects of IGF-1 and IGF-II (3 ng/ml) were also tested in quiescent, serum-free primary mouse calvarial cells. Levels of c-fos mRNA were increased at 15 and 30 minutes (40-fold with IGF-I and 5-fold with IGF-II). These results indicate that IGF-I and IGF-II caused a rapid and transient induction of c-fos mRNA in murine osteoblasts.

Heterogeneity of latent transforming growth factor-beta isolated from bone matrix proteins

Transforming growth factor-beta (TGF beta) is a family of 25-kDa peptides that appear to be important regulators of cell proliferation, differentiation, and differentiated function in many tissues. TGF beta is present in platelets and serum and is released by cultured cells as several distinct large mol wt complexes of TGF beta with other proteins. These complexes are biologically inactive and are generically called latent TGF beta (L-TGF beta). Large quantities of TGF beta are present in bone matrix. This study was undertaken to determine whether the TGF beta in bone matrix was present as a free 25-kDa peptide or a large mol wt L-TGF beta complex. TGF beta activity was determined by inhibition of [3H]methylthymidine incorporation in mink lung epithelial cells. The specificity of inhibition was determined by treating fractions with a polyclonal rabbit antiporcine TGF beta-blocking antibody before assay. Latency was examined by assaying untreated and acid-treated fractions for TGF beta activity. Acid treatment of EDTA extracts of the bovine bone matrix proteins increased TGF beta activity from a mean of 0.8 pg/microgram protein to 56 pg/micrograms. Under native conditions L-TGF beta eluted from S400 between the 600-400 kDa mol wt standards. No activity eluted in the fractions with authentic 25-kDa TGF beta. Eighty-five percent of the L-TGF beta bound to lentil lectin, and this separated into four discrete L-TGF beta peaks (I-IV) at 0.22, 0.25, 0.35, and 0.42 M NaCl with Mono-Q anion exchange chromatography. Mono-Q pools II and III were reseparated by molecular size on Superose-12 under native and dissociative conditions. Under native conditions TGF beta activity was latent and eluted in the large mol wt fractions. No 25-kDa TGF beta was present. With dissociating conditions (4 M GuHCl) all TGF beta activity eluted in the small mol wt fractions identical to the elution position of authentic 25-kDa TGF beta. The active fractions from the dissociative separation of Mono-Q pool III were separated by C4 reverse phase HPLC. There were three discrete peaks of TGF beta activity corresponding to TGF beta 1, TGF beta 2, and an unidentified form of TGF. Maximum activation of L-TGF beta in each Mono-Q peak occurred at pH 3-3.5. There was partial activation at pH 4.5, but no additional activation at pH 1.5.(ABSTRACT TRUNCATED AT 400 WORDS)

Multiple osteocalcin fragments in human urine and serum as detected by a midmolecule osteocalcin radioimmunoassay

Reliable markers of bone formation are essential to the investigation of metabolic bone disorders. In this regard, evidence indicates that circulating levels of human osteocalcin (OC) correlate with the skeletal isoenzyme of alkaline phosphatase and can be used as an index of bone formation. A disadvantage of using serum OC as a marker of formation is its diurnal variation. To address this problem we carried out our studies to determine the usefulness of urine in the assessment of bone turnover. Using a midmolecule specific human OC RIA, we were able to detect OC in urine of normal adults (42 mugeq/g creatinine), normal children (849 mu/geq/g creatinine), and Paget's disease patients (613 mugeq/g creatinine). Immunoreactive fragments of OC in human urine and human serum were separated by high pressure liquid chromatography. Multiple fragments were found in normal adult urine that were not detected in normal adult serum. Uremic and Paget's disease sera contain several immunoreactive forms of OC, other than the intact molecule, not found in normal adult serum. Additionally, both Paget's disease sera and urine contained a specific peak of immunoreactive material, eluting at 25% acetonitrile, that was not found in any other serum or urine tested. Urinary OC (uOC) correlated with both skeletal alkaline phosphatase (r = 0.91) and serum OC (r = 0.83), indices of skeletal formation. While uOC has a diurnal variation similar to that of serum OC, determinations of 24-h uOC give integrated values of daily bone turnover rates. Z-Score analysis indicates that uOC (z = 14.04) is better able to distinguish between normal children with high bone turnover and normal adults than either skeletal alkaline phosphatase (z = 8.87) or serum OC (z = 9.01).

Skeletal growth factor and other growth factors known to be present in bone matrix stimulate proliferation and protein synthesis in human bone cells

The purpose of the study was to investigate the effect of skeletal growth factor/insulinlike growth factor II and other growth factors known to be present in bone matrix on the proliferation and differentiation of human bone cells. Cells were isolated by collagenase digestion from femoral heads obtained during hip replacement operations. Cells were cultured in DMEM medium with 10% calf serum. Third to fifth passage cells were plated in multiwell plates and the medium changed to low serum (0.1%) for 2 days. The medium was changed to serum-free medium prior to addition of growth factors. Cell proliferation was measured by the incorporation of [3H]thymidine into DNA and by the percentage of cells that incorporate bromodeoxyuridine. Protein synthesis was measured by the incorporation of [3H]proline into trichloroacetic acid-precipitable material. Skeletal growth factor/insulinlike growth factor II and insulinlike growth factor I stimulated cell proliferation and protein synthesis in a dose-dependent manner. Alkaline phosphatase-specific activity was not increased by these factors. Transforming growth factor beta 1 did not affect cell proliferation but stimulated protein synthesis and increased the specific activity of alkaline phosphatase. Fibroblast growth factor did not affect any of the cell parameters. These studies suggest that skeletal growth factor/insulinlike growth factor II, insulinlike growth factor I, and transforming growth factor beta 1 may play a role in the local control of the proliferation and differentiation of human osteoblasts.

Insulin-like growth factors I and II are present in the skeletal tissues of ten vertebrates

Previous studies have shown that insulin-like growth factor I and insulin-like growth factor II (IGF I and IGF II) constitute an important family of skeletal growth-regulating peptides. We undertook this study to determine if, as in the case of sera in various animals, IGF I and IGF II are conserved in the skeletal tissues of various vertebrates. Skeletal tissues of ten animals representing five of the six vertebrate classes were studied: monkey, dog, sheep, adult mice, neonatal mice, chicken, lizard, frog, trout, and shark. The skeletal tissues were pulverized and demineralized with 10% ethylenediaminetetraacetic acid (pH 7.0) to extract the soluble matrix proteins. The tissue extracts were concentrated, dialized, and subjected to specific human IGF assays. IGF I and IGF II were measured with a radioimmunoassay and a radioreceptor assay, respectively. We found that 1) there are detectable human IGF I- and II-like substances in all extracts, 2) IGF values obtained in the skeletal extracts were not caused by binding protein artifacts, 3) in general there is more IGF II than IGF I, and 4) the skeletal tissue levels of the IGFs are comparable with their respective serum levels. We conclude that, in the skeletal tissues of vertebrates, the IGFs are conserved and may be important regulators of osteogenesis.

A simple and efficient scheme for the purification of insulin-like growth factor II from human bone matrix extract

Human insulin-like growth factor II (IGF-II) has been purified to homogeneity from bone which contained 10-15 times more IGF-II than insulin-like growth factor-I (IGF-I). After extraction of IGF-II by demineralization of human bone powder with 10% EDTA containing 4M guanidine HCl at pH 7.4, IGF-II was separated from IGF binding proteins by hydroxylapatite chromatography in the presence of 4M guanidine HCl. The hydroxylapatite unbound fraction containing IGF-II was purified by affinity chromatography using Sm 1.2. monoclonal antibodies, which bind both IGF-I and IGF-II. The final purification of IGF-II was achieved by FPLC mono S ion-exchange chromatography in which IGF-II was separated from IGF-I. Human IGF-II thus purified was shown to be pure by (1) HPLC reverse-phase chromatography, (2) SDS-PAGE, and (3) N-terminal amino acid sequence. From 300 g of bone, 0.18 mg IGF-II was obtained with an overall recovery of 42%. These studies demonstrate the usefulness of (1) bone as a source of IGF-II purification and (2) antibodies that cross-react with both IGF-I and IGF-II for affinity purification of IGFs.

Interactions of growth factors present in bone matrix with bone cells: effects on DNA synthesis and alkaline phosphatase

It has been shown that bone cells produce and secrete several growth factors (GFs) which are also found in the bone matrix. To investigate the role of these growth factors in bone cell metabolism, we compared the effects of different factors separately and in combination with respect to osteoblastic cell proliferation and differentiation. While basic fibroblast GF (FGF), transforming GF beta-1 (TGF beta), and platelet-derived GF (PDGF) enhance DNA synthesis, they had the opposite effect on alkaline phosphatase (ALP) activity in cell extracts: FGF, TGF beta, and PDGF inhibited cell ALP but strongly stimulated DNA synthesis. The IGFs had little effect on cell ALP but increased the release of ALP into the conditioned medium. In mitogenic tests of combinations of GFs, most had at least additive effects at low concentrations, and FGF, TGF beta, and IGF2 produced synergistic effects. Evidence is presented for (1) the modulation of the effects of one GF by the action of other GF, (2) synergistic interactions between FGF, TGF beta, and IGF2, and (3) a possible role for the observed interactions among GF for the mitogenic effect of human bone extract.

Purification and N-terminal sequence of two tartrate-resistant acid phosphatases type-5 from the hairy cell leukemia spleen

Tartrate-resistant acid phosphatases types 5a and 5b were purified from human hairy cell leukemia spleen by sequential chromatography on Phenyl-Sepharose, CM-Sepharose, concanavalin A-Sepharose, FPLC Superose-12 and FPLC Mono-S. The purification over the original tissue extract was 1150- and 3300-fold, with a yield of 2.1% and 2.5%, respectively. Gel filtration indicated an Mr of about 30000 for both forms. There was a N-terminal sequence identity between the two enzymes. However, they appeared to be different as assessed by cation exchange chromatography and amino acid composition.

Molecular cloning and characterization of comC, a late competence gene of Bacillus subtilis

comC is a Bacillus subtilis gene required for the development of genetic competence. We have cloned a fragment from the B. subtilis chromosome that carries comC and contains all the information required to complement a Tn917lac insertion in comC. Genetic tests further localized comC to a 2.0-kilobase HindIII fragment. Northern (RNA) blotting experiments revealed that an 800-base-pair comC-specific transcript appeared at the time of transition from exponential to stationary phase during growth through the competence regimen. The DNA sequence of the comC region revealed two open reading frames (ORFs), transcribed in the same direction. The upstream ORF encoded a protein with apparent sequence similarity to the folC gene of Escherichia coli. Insertion of a chloramphenicol resistance determinant into this ORF and integration of the disrupted construct into the bacterial chromosome by replacement did not result in competence deficiency. The downstream ORF, which contained the Tn917lac insertion that resulted in a lack of competence, is therefore the comC gene. The predicted protein product of comC consisted of 248 amino acid residues and was quite hydrophobic. The comC gene product was not required for the expression of any other com genes tested, and this fact, together with the marked hydrophobicity of ComC, suggests that it may be a component of the DNA-processing apparatus of competent cells.

Isolation of an inhibitory insulin-like growth factor (IGF) binding protein from bone cell-conditioned medium: a potential local regulator of IGF action

Inhibitory insulin-like growth factor binding protein (In-IGF-BP) has been purified to homogeneity from medium conditioned by TE89 human osteosarcoma cells by two different methods using Sephadex G-100 gel filtration, FPLC Mono Q ion-exchange, HPLC C4 reverse-phase, HPLC CN reverse-phase, and affinity chromatographies. In-IGF-BP thus purified appeared to be homogeneous and unique by the following criteria. (i) N-terminal sequence analysis yielded a unique sequence (Asp-Glu-Ala-Ile-His-Cys-Pro-Pro-Glu-Ser-Glu-Ala-Lys-Leu-Ala). (ii) Amino acid composition of In-IGF-BP revealed marked differences with the amino acid compositions of other known BPs. (iii) In-IGF-BP exhibited a single band with a molecular mass of 25 kDa under reducing conditions on sodium dodecyl sulfate/polyacrylamide gels. IGF-I and IGF-II but not insulin displaced the binding of 125I-labeled IGF-I or 125I-labeled IGF-II binding to In-IGF-BP. In-IGF-BP inhibited basal, IGF-stimulated bone cell proliferation and serum-stimulated bone cell proliferation. Forskolin increased synthesis of In-IGF-BP in TE85 human osteosarcoma cells in a dose-dependent manner. Based on these findings, we conclude that In-IGF-BP is a protein that has a unique sequence and significant biological actions on bone cells.

Parathyroid hormone stimulates release of insulin-like growth factor-I (IGF-I) and IGF-II from neonatal mouse calvaria in organ culture

Effects of increased bone resorption on release of insulin-like growth factor-I (IGF-I) and IGF-II into the osteoblast microenvironment were investigated using neonatal mouse calvaria organ cultures. Release of these growth factors from calvaria into serum-free medium was quantitated using a human IGF-I RIA and human IGF-II RRA. Untreated calvaria released several-fold more IGF-II than IGF-I. PTH (from 1-12 nM) stimulated a dose-dependent increase in the release of both growth factors that correlated with increased calcium release and was sustained for up to 6 days. IGF-I and IGF-II release were maximally stimulated 5- to 10-fold and 1.5- to 2-fold, respectively, compared to untreated control values. Calcitonin inhibited PTH-stimulated resorption, but had no effect on PTH stimulation of IGF-I and IGF-II release, suggesting that PTH effects on IGF-I and IGF-II release were not dependent on resorption. Furthermore, the amounts of IGF-I and IGF-II released from calvaria during 6 days of culture were 5-fold more than the amounts of IGF-I and IGF-II present in the calvaria (bone plus cells) at the beginning of culture, suggesting that much of the IGF-I and IGF-II released was newly produced by calvaria cells. The results suggest that PTH directly stimulated calvarial osteoblasts to release IGF-I and IGF-II. Since IGF-I and IGF-II stimulate osteoblastic cell proliferation, the effect of PTH on the release of these and other growth factors may mediate coupling of bone formation to bone resorption.

Characterization of the receptor for insulin-like growth factor II in bone cells

We have previously shown that insulin-like growth factor II (IGF-II) is produced by bone cells and that IGF-II stimulates cell proliferation and collagen synthesis in bone cells. We now extend these in vitro findings by demonstrating specific IGF-II binding to bone cells derived from newborn mouse calvaria and embryonic chick calvaria. The kinetics of [125I] IGF-II binding in embryonic chick calvaria cells showed time and temperature dependence. Scatchard analysis of [125I]IGF-II binding to chick calvaria cells showed an apparent Kd of 1.4 x 10(-10) M, with a calculated receptor site concentration of 40,000/cell. The specificity characteristics showed that IGF-II was significantly more potent than IGF-I or insulin in displacing IGF-II tracer. Competition for binding of [125I]IGF-II by unlabeled IGF-II showed a dose-dependent displacement between 0.5 and 25 ng/ml. Fifty percent displacement of [125I]IGF-II binding to chick and mouse calvarial cells was achieved at 1-2 ng/ml; 90% of specific binding of [125I]IGF-II was displaceable in the presence of 125 ng/ml of unlabeled IGF-II. IGF-I showed less than 5% cross reactivity for displacement of [125I]IGF-II binding to chick and mouse bone cells. Type II receptor inhibitory antibodies, R-II-PAB1 inhibited the binding of [125I]IGF-II to mouse bone cells and H-35 rat hepatoma cells (which contain type II but not type I receptors) in a dose-dependent manner. R-II-PAB1 also inhibited basal cell proliferation as well as IGF-II-, IGF-I-, and fibroblast growth factor (FGF)-induced cell proliferation in mouse bone cells. In chick calvaria bone cells and TE89 human osteosarcoma cells, R-II-PABI inhibited neither binding of [125I]IGF-II nor IGF-II-induced cell proliferation. These results together with our findings that IGF-II increased chick bone cell proliferation in the presence of maximal doses of IGF-I suggest that at least part of the mitogenic action of IGF-II is mediated through type II rather than type I receptors in bone cells.

Beta 2-microglobulin is not a bone cell mitogen

During the purification of skeletal growth factor/insulin-like growth factor-II and transforming growth factor-beta (TGF beta) from EDTA extracts of bovine bone matrix significant mitogenic activity for cultured osteoblast (Ob)-like cells eluted in fractions that contained a nearly homogeneous peptide with a mol wt of about 14,000. This peptide has been purified to apparent homogeneity and identified as bovine beta 2-microglobulin (beta 2M) by amino-terminal amino acid sequencing. During the final purification of beta 2M by CN reverse phase HPLC the mitogenic activity for bone cells separated from the beta 2M protein peak. In spite of this the apparently homogeneous beta 2M preparation retained some mitogenic activity. The ED50 of the bone-derived beta 2M (4,890 +/- 462 ng/ml) was several orders of magnitude (2 x 10(3) to 1.4 x 10(5) times) greater than the ED50 of simultaneously assayed purified growth factors and was no different from the ED50 of the crude EDTA matrix extract (3,350 +/- 890 ng/ml). The beta 2M accounted for less than 0.002% of the total mitogenic activity for Ob-like cells present in the extracted matrix proteins. The following lines of evidence suggest that the mitogenic activity of bone matrix-derived beta 2M (BMD-beta 2M) is due to contamination of the BMD-beta 2M with TGF beta rather than an intrinsic property of beta 2M: 1) the coelution of TGF beta through four successive purification procedures and purification of TGF beta from adjoining fractions from C4 reverse phase HPLC; 2) the abolition of biological activity of BMD-beta 2M and TGF beta with reducing agents; 3) the lack of additive stimulation of [3H] methylthymidine incorporation into bone cells when beta 2M was added to maximally active concentrations of purified TGF beta; 4) the reduction of mitogenic activity when the BMD-beta 2M was incubated with anti-TGF beta; and 5) the inhibition of mink lung epithelial proliferation by the beta 2M preparation. Based on these findings we conclude that although beta 2M is present in bovine bone matrix extracts, it is not a mitogen for Ob-like cells.

Estradiol stimulates in vitro the secretion of insulin-like growth factors by the clonal osteoblastic cell line, UMR106

UMR106 cells, a rat osteosarcoma derived clonal line, secreted insulin-like growth factors (IGF) in vitro. The IGF-II levels corrected for the cell numbers were 7-8 times higher than the IGF-I levels in the medium. Both growth factors were higher by 4-5 fold in medium conditioned by rapidly growing cells than in medium conditioned by confluent cells. The addition of 17-beta-estradiol (E) to the culture medium was associated with a statistically significant increase in the IGF concentrations. This increment was metabolite specific, not occurring with 17-alpha-E, the inactive epimer of E. 1,25(OH)2D3 also increased the IGF-I concentration but prior treatment with E blocked the response to 1,25(OH)2D3, demonstrating antagonistic actions of these two hormones on IGF secretion by osteoblast-like cells.

Copurification of osteolytic and transforming growth factor beta activities produced by human lung tumor cells associated with humoral hypercalcemia of malignancy

The SK-Luci-6 cell line, established from a large-cell anaplastic lung tumor of a patient with humoral hypercalcemia of malignancy (HHM), was investigated to identify osteolytic factors produced that might mediate HHM. Most HHM-associated tumors are thought to produce parathyroid hormone-related proteins or transforming growth factor (TGF) alpha. SK-Luci-6 cells formed s.c. tumors and induced hypercalcemia in athymic nude mice. Serum-free conditioned medium from SK-Luci-6 cultures induced bone resorption in neonatal mouse calvariae in vitro, and also contained TGF-beta activity and mitogenic activity. SK-Luci-6 cell conditioned medium did not displace [125I]epidermal growth factor binding to cell receptors or stimulate cyclic AMP formation in rat osteosarcoma cells, suggesting that the conditioned medium did not contain TGF-alpha or parathyroid hormone-related proteins. The osteolytic, TGF-beta, and mitogenic activities copurified in several chromatographic separations: gel filtration in acid and then in guanidine HCl; ion exchange; and reverse phase. The results suggest that in the HHM-associated SK-Luci-6 tumor, the causative osteolytic factor produced by the tumor cells is not a parathyroid hormone-related protein or TGF-alpha but, rather, may be a TGF-beta.