Nuclear entry of nonviral vectors

Nonviral gene delivery is limited to a large extent by multiple extracellular and intracellular barriers. One of the major barriers, especially in nondividing cells, is the nuclear envelope. Once in the cytoplasm, plasmids must make their way into the nucleus in order to be expressed. Numerous studies have demonstrated that transfections work best in dividing populations of cells in which the nuclear envelope disassembles during mitosis, thus largely eliminating the barrier. However, since many of the cells that are targets for gene therapy do not actively undergo cell division during the gene transfer process, the mechanisms of nuclear transport of plasmids in nondividing cells are of critical importance. In this review, we summarize recent studies designed to elucidate the mechanisms of plasmid nuclear import in nondividing cells and discuss approaches to either exploit or circumvent these processes to increase the efficiency of gene transfer and therapy.

Construction of a BAC contig for a 3 cM biologically significant region of mouse chromosome 1

One QTL and genes and phenotypes have been localized in the region between 92 cM and 95cM of mouse chromosome 1. The QTL locus contributes to approximately 40% of the variation of the peak bone density between C57BL/6J (B6) and CAST/EiJ (CAST) strains. Other loci located in this chromosomal region include a neural tube defect mutant loop-tail (Lp), a lymphocyte-stimulating determinant (Lsd), and the Transgelin 2 (Tagln 2). The human chromosome region homologous to this region is 1q21-23, which also contains a QTL locus for high bone mineral density (BMD). Furthermore, it has been reported that this region may have duplicated several times in the mouse genome. Therefore, genomic sequencing of this region will provide important information for mouse genome structure, for positional cloning of mouse genes, and for the study of human homologous genes. In order to provide a suitable template for genomic sequencing by the NIH-sponsored genomic centers, we have constructed a BAC contig of this region using the RPCI-23 library. We have also identified the currently available mouse genomic sequences localized in our BAC contig. Further analysis of these sequences and BAC clones indicated a high frequency of repetitive sequences within this chromosomal area. This region also contains L1 retrotransposon sequences, providing a potential mechanism for the repetitive sequences described in the literature.

Inhibition of human osteoblast marker gene expression by retinoids is mediated in part by insulin-like growth factor binding protein-6

All-trans -retinoic acid (atRA) inhibits osteoblast marker gene expression and markedly increases expression of insulin-like growth factor binding protein-6 (IGFBP-6) in human osteoblasts. The possibility that IGFBP-6 inhibits the osteoblast phenotype and also mediates the inhibitory effect of atRA on osteoblast marker gene expression was explored using an antisense approach. Stable human osteoblast-like osteosarcoma SaOS-2 cells were prepared that expressed antisense IGFBP-6 RNA under basal and atRA-stimulated conditions. The functional expression of IGFBP-6 antisense RNA was confirmed by measuring IGFBP-6 mRNA by Northern analysis or by measuring IGFBP-6 protein in the conditioned media (CM) by radioimmunoassay. Antisense clones produced less mRNA and had less IGFBP-6 protein in the CM than controls. IGFBP-6 protein levels in the CM were inversely correlated with alkaline phosphatase (ALP) activity, whereas IGFBP-3 and IGFBP-4 protein levels were not. We reasoned that atRA would have little or no effect on ALP activity in IGFBP-6 antisense clones if atRA mediated its inhibitory effects by recruiting IGFBP-6. In the majority of IGFBP-6 antisense clones with the lowest IGFBP-6 mRNA and CM protein levels and only modest changes in other IGF system components, atRA did not significantly decrease ALP activity. These findings provide evidence that atRA recruits IGFBP-6 to inhibit the human osteoblast phenotype.

Structure and characterization of the human insulin-like growth factor binding protein (IGFBP)-6 promoter: identification of a functional retinoid response element

The 1.7 kb human insulin-like growth factor binding protein (IGFBP)-6 gene 5'-flanking region was sequenced and found to have promoter activity in human osteoblasts. The sequence contains four clustered transcription start sites and three retinoic acid response elements (RAREs) with widely spaced half-sites. Only the proximal DR15 RARE was functional. Retinoids increased IGFBP-6 promoter activity up to 3-fold.

TWIST, a basic helix-loop-helix transcription factor, can regulate the human osteogenic lineage

Basic helix-loop-helix (bHLH) transcription factors have been shown to play an important role in controlling cell type determination and differentiation. TWIST, a member of the bHLH transcription factor family, is involved in the development of mesodermally derived tissue, including the skeleton. We examined the role of human TWIST in osteoblast metabolism using stable expression of sense and antisense TWIST in human osteoblast HSaOS-2 cells. Changes in morphology and osteogenic phenotype characterized these stable clones. Cells that overexpressed TWIST exhibited a spindle shaped morphology, reduced levels of alkaline phosphatase, a reduced proliferation rate, and failed to respond to basic fibroblast growth factor (bFGF). In contrast, those that underexpressed TWIST demonstrated a cuboidal epithelial-like morphology characteristic of differentiated osteoblasts. TWIST antisense cells exhibited increased levels of alkaline phosphatase and type I collagen mRNA, initiated osteopontin mRNA expression, and had a reduced proliferation rate. These results indicate that TWIST overexpressing cells may de-differentiate and remain in an osteoprogenitor-like state, and antisense TWIST cells progress to a more differentiated mature osteoblast-like state. Therefore, the level of TWIST can influence osteogenic gene expression and may act as a master switch in initiating bone cell differentiation by regulating the osteogenic cell lineage.

Studies on the role of human insulin-like growth factor-II (IGF-II)-dependent IGF binding protein (hIGFBP)-4 protease in human osteoblasts using protease-resistant IGFBP-4 analogs

To characterize the insulin-like growth factor binding protein-4 (IGFBP-4) protease produced by human osteoblasts (hOBs), we localized and determined the role of the proteolytic domains in human IGFBP-4 (hIGFBP-4) in modulating IGF-II actions. N-terminal amino acid sequence and mass spectrometric analyses of the 6xHis-tagged IGFBP-4 proteolytic fragments revealed that Met135-Lys136 was the only cleavage site recognized by the IGF-II-dependent IGFBP-4 protease produced by hOBs. This cleavage site was confirmed by the finding that deletion of His121 to Pro141 blocked proteolysis. However, unexpectedly, deletion of Pro94 to Gln119 containing no cleavage site had no effect on IGF-II binding activity but blocked proteolysis. Addition of the synthetic peptide corresponding to this region at concentrations of 250 or 1000 molar excess failed to block IGFBP-4 proteolysis. These data suggest that residues 94-119 may be involved in maintaining the IGFBP-4 conformation required to expose the cleavage site rather than being involved in direct protease-substrate binding. To determine the physiological significance of the IGF-II-dependent IGFBP-4 protease, we compared the effect of the wild-type IGFBP-4 and the protease-resistant IGFBP-4 analogs in blocking IGF-II-induced cell proliferation in normal hOBs, which produce IGFBP-4 protease, and MG63 cells, which do not produce IGFBP-4 protease. It was found that protease-resistant IGFBP-4 analogs were more potent than the wild-type protein in inhibiting IGF-II-induced cell proliferation in hOBs but not in MG63 cells. These data suggest that IGFBP-4 proteolytic fragments are not biologically active and that IGFBP-4 protease plays an important role in regulating IGFBP-4 bioavailability and consequently the mitogenic activity of IGFs in hOBs.

Progesterone stimulation of human insulin-like growth factor-binding protein-5 gene transcription in human osteoblasts is mediated by a CACCC sequence in the proximal promoter

Insulin-like growth factor-binding protein-5 (IGFBP-5) is produced by osteoblasts and potentiates insulin-like growth factor mitogenic stimulation in osteoblast cell cultures. Progesterone (PG) increased IGFBP-5 expression in normal human osteoblasts and increased IGFBP-5 transcription in U2 human osteosarcoma cells. We developed a chloramphenicol acetyltransferase reporter construct containing the human IGFBP-5 proximal promoter sequence, which includes TATA and CAAT boxes, and five putative PG response element half-sites. 10(-8) M PG increased promoter activity of this construct in U2 cells co-transfected with a PG receptor isoform A (PR(A)) expression vector. Analysis of 5' deletion constructs indicates that PG transactivation of IGFBP-5 promoter activity does not require the PG response element half-sites but does require the region -162 to -124 containing two tandem CACCC box sequences. Mutation of the proximal CACCC box at -139 eliminated PG transactivation. Gel shift assays using a -162 to -124 DNA fragment, U2 cell nuclear extracts, and purified PR(A) protein indicate that nuclear factors bind to a CACCC sequence at -139 and that PR(A) alters the pattern of transcription factor interaction with the CACCC sequence. Using a luciferase reporter construct containing base pairs -252 to +24 of the IGFBP-5 promoter, we found that both PR(A) and PR(B) isoforms mediated PG stimulation of promoter activity. These results suggest that PG may stimulate IGFBP-5 gene transcription via a novel mechanism involving PR and CACCC-binding factors.

The diagnosis and treatment of osteoporosis: future prospects

Osteoporosis is a common disease that affects millions of patients throughout the world. We anticipate that both the diagnosis and the treatment of this disease will be revolutionized by the integration of genomics and informatics. It is predicted that a genetic algorithm will be developed to identify at-risk patients before they develop osteoporosis, so that preventive measures can be instituted. The sequencing of the human genome will lead to revolutionary advances in at least three areas of osteoporosis therapy: small molecule therapy, protein therapy and gene therapy. One area of focus for future therapeutics in osteoporosis will be on osteogenic agents, which should have a high likelihood of success because the skeleton has the innate capacity to regenerate itself.

Structure-function analysis of the human insulin-like growth factor binding protein-4

To identify the molecular mechanism by which insulin-like growth factor binding protein-4 (IGFBP-4) exerts its inhibitory effects on insulin-like growth factor (IGF) actions, we localized and determined the role of the IGF binding domain in modulating IGF actions in human osteoblasts. Deletion analysis using IGFBP-4 expressed in bacteria revealed that the N-terminal sequence Leu72-Ser91 was essential for IGF binding. The C-terminal fragments (His121-Glu237 or Arg142-Glu237) did not bind to IGF but loss of these regions decreased IGF binding activity. Detailed deletion analysis identified the residues Cys205-Val214 as the motif to facilitate IGF binding. Mitogenic studies revealed that an IGFBP-4 mutant (His74 replaced by Pro74) and an N-terminal peptide (N terminus to Thr71) with little IGF binding activity failed to inhibit IGF-II-induced human osteoblast proliferation. An N-terminal peptide (N terminus to Asn182) with reduced IGF binding activity inhibited IGF action but with lower potency. In contrast, an IGFBP-4 mutant (His74 replaced with Ala74) exhibited similar IGF binding activity and potency in inhibiting the activity of IGF-II compared with the wild type. Therefore, the N-terminal sequence (Leu72-Ser91) and the C-terminal sequence (Cys205-Val214) are necessary to form the high affinity IGF binding domain, which is the major structural determinant of the IGFBP-4 function.

Osteogenic protein-1 stimulates production of insulin-like growth factor binding protein-3 nuclear transcripts in human osteosarcoma cells

To begin delineating molecular mechanisms by which osteogenic protein-1 (OP-1) modulates its effect on the insulin-like growth factor (IGF) system in human skeletal cells, we evaluated time-course effects of OP-1 on the expression of IGFBP-3 messenger RNA (mRNA) in human SaOS-2 osteosarcoma cells and found that 100 ng/ml of OP-1 increased (maximum 10.7-fold at 24 h; P < 0.01) the level of IGFBP-3 mRNA in a time-dependent manner (from 3-36 h; treatment x time interaction, P < 0.001). The stimulatory effect of OP-1 on IGFBP-3 mRNA was not promoted by transcript stabilization; actually, OP-1 treatment selectively increased the decay of mRNA for IGFBP-3 (T1/2 = 5 h vs. 24 h for OP-1 and controls), but not for IGFBP-4 or beta-actin. Conversely, OP-1 acutely increased IGFBP-3 nuclear transcript abundance in total RNA samples ranging between 1-24 h of treatment. After 6 h of treatment, OP-1 produced an average 4-fold increase (P < 0.02; n = 4 experiments) in the level of IGFBP-3 nuclear transcripts vs. a 3-fold increase (P < 0.01; n = 2 experiments) in mRNA abundance. The OP-1 stimulated induction of IGFBP-3 nuclear transcript and mRNA expression was dependent on de novo protein synthesis. Transient transfection experiments were undertaken to isolate putative OP-1 stimulatory cis-elements within 1.8-kb of the IGFBP-3 5'-flanking region in SaOS-2 and TE-85 osteosarcoma cells. In these experiments, OP-1 did not stimulate IGFBP-3 proximal promoter activity in either cell line, thus suggesting that OP-1 reactive domains may be located either beyond the currently established 5'-flanking region, or within internal exon/intron regions of the IGFBP-3 gene. In conclusion, OP-1 treatment stimulates IGFBP-3 expression in human osteoblastic cells by a mechanism that largely promotes the production of IGFBP-3 nuclear transcripts, a process that requires de novo protein synthesis, and overrides an OP-1-induced targeted degradation of IGFBP-3 steady-state mRNA.

Osteogenic protein-1 stimulates mRNA levels of BMP-6 and decreases mRNA levels of BMP-2 and -4 in human osteosarcoma cells

Bone morphogenetic proteins (BMPs) are novel growth and differentiation factors that act on mesenchymal stem cells to initiate new bone formation in vivo and promote the growth and differentiation of cells in the osteoblastic lineage. In the present study, we examined the effects of recombinant human osteogenic protein-1 (also known as BMP-7) on the expression of related members of the BMP family using SaOS-2 and U2-OS, two human osteosarcoma cell strains. Evaluation of BMP-2, -4, and -6 mRNA expression indicates that OP-1 stimulated the mRNA levels of BMP-6 in both SaOS-2 cells (threefold) and U2-OS cells (fivefold) after 24 hours of treatment, while decreasing the mRNA levels of BMP-4 in SaOS-2 cells (80%) and BMP-2 and BMP-4 in U2-OS cells by 50% and 72%, respectively. BMP-2 mRNA expression, as examined by Northern blot analysis, was below detectable limits in SaOS-2 cultures. These results demonstrate that OP-1 modulates the mRNA expression of related members of the BMP family, suggesting a possible mode of action of OP-1 on the growth and differentiation of cells in the osteoblastic lineage in vitro.

Structural and functional analysis of the 5'-flanking region of the human insulin-like growth factor binding protein (IGFBP)-4 gene

More than 3 kb of the human (h)IGFBP-4 gene 5'-flanking region was sequenced and assessed for promoter activity. The hIGFBP-4 promoter resides within a CpG island and demonstrates strong basal activity in human osteoblast-like osteosarcoma and COS-7 monkey kidney cells. Transient transfection of cells with hIGFBP-4 promoter-linked deletion constructs demonstrated that multiple cooperating cis-acting elements within 836 bp of the 5'-flanking region contributed to overall promoter strength.

Evidence for a role for insulin-like growth factor binding proteins in glucocorticoid inhibition of normal human osteoblast-like cell proliferation

Glucocorticoids (GCs) inhibit bone formation in vivo and inhibit osteoblast proliferation and collagen synthesis in vitro. These effects may be mediated by alterations in the insulin-like growth factor (IGF) system. In the present study of normal human osteoblast-like (HOB) cells, we tested the hypothesis that dexamethasone (Dex) inhibits IGF anabolic activity in bone by altering expression of IGF binding proteins (IGFBPs), particularly by decreasing expression of IGFBP-5 and IGFBP-3 (which enhance IGF activity) and increasing expression of IGFBP-4 (which inhibits IGF actions). Dexamethasone treatment caused a dose-dependent inhibition of HOB cell proliferation (69 +/- 4% of control at 10(-8) mol/l Dex) in seven separate experiments. Dexamethasone decreased IGFBP-5 mRNA levels to 20-30% of control (10(-8) and 10(-7) mol/l for 24 h). In six of six HOB preparations, 10(-8) mol/l Dex decreased IGFBP-5 mRNA levels (35 +/- 7% of control) and this effect was time dependent. Dexamethasone also decreased IGFBP-3 mRNA levels (74 +/- 9% of control in three HOB preparations). Dexamethasone decreased secretion of 29-31-kD IGFBP-5 and 38-42-kD IGFBP-3 proteins, determined by Western ligand blot and IGFBP-5 immunoblot, and induced a dose-dependent decrease in IGFBP-3 and IGFBP-5 secretion determined by specific radioimmunoassays. The effects of Dex on IGFBP-4 mRNA and on secretion of 25-kD IGFBP-4 levels were inconsistent between different cell preparations. Results suggest that GC inhibition of IGFBP-5 and IGFBP-3 production could decrease IGF activities and contribute to GC inhibition of bone formation.

Recombinant synthesis of insulin-like growth factor-binding protein-4 (IGFBP-4): Development, validation, and application of a radioimmunoassay for IGFBP-4 in human serum and other biological fluids

Insulin-like growth factor-binding protein-4 (IGFBP-4), like the five other IGFBPs present in human serum, acts as a transport protein for insulin-like growth factor I (IGF-I) and IGF-II and modulates their biological effects. To investigate the role of IGFBP-4 in the physiology of the IGF system, we developed a sensitive RIA for IGFBP-4 employing, as antigen, tracer, and standard, recombinant human IGFBP-4 (rhIGFBP-4) expressed in Escherichia coli as a fusion protein with glutathione S-transferase and affinity purified with glutathione-derivatized resin. Antibody against the rhIGFBP-4 fusion protein was raised in guinea pigs; tracer and standard were provided by the rhIGFBP-4 moiety that had been cleaved from the rhIGFBP-4 fusion protein and repurified by reverse phase high pressure liquid chromatography. We report that both IGFBP-4 purified from PC3 human prostate cell-conditioned medium and rhIGFBP-4 bound IGF and migrated in electrophoresis gels in an identical manner; that in gel permeation chromatography, rhIGFBP-4 coeluted with the IGFBP-4 present in human serum; and that both are equally immunoreactive with the IGFBP-4 antiserum. Employing this IGFBP-4 RIA, we determined that no IGFBP other than IGFBP-4 reacted with the IGFBP-4 antiserum, and that recovery of IGFBP-4 from serum samples exceeded 90% when exogenous IGFBP-4 was added and was unaffected by the addition of IGFs or by repeated freezing and thawing of the sample. We employed this IGFBP-4 RIA to demonstrate an increase in IGFBP-4 in TE85 human osteosarcoma cell-conditioned medium after treatment with dibutyryl cAMP, PTH, and 1,25-dihydroxyvitamin D3, agents known to increase the IGFBP-4 messenger ribonucleic acid level. Application of this RIA to the measurement of IGFBP-4 in human serum revealed that the circulating level of IGFBP-4 in 41 individuals in the 61-87 yr age group (546 +/- 135 microgram/L) was 35% higher than that in 24 individuals in the 23-40 yr age group (404 +/- 156 microgram/L). The mean circulating level of PTH was also 20% higher in the 61-87 yr group compared to that in the 23-40 yr group (P < 0.01). In addition, serum IGFBP-4 amounts showed a significant positive correlation with age (r = 0.54; P < 0.001) and serum PTH (r = 0.26; P < 0.01). These data validate this IGFBP-4 RIA and illustrate its utility in illuminating the physiological mechanisms that regulate IGFBP-4 in vivo and influence its effects on the IGFs in both normal and abnormal pathology and in aging.

Retinoic acid regulates insulin-like growth factor-binding protein expression in human osteoblast cells

Retinoic acid (RA) regulates the growth and differentiation of numerous cells types and plays a key role in skeletal development. Previous studies have demonstrated that insulin-like growth factors (IGFs) are important local regulators of bone cell proliferation and differentiation and that IGF-binding proteins (IGFBPs) modulate their activities. In an attempt to test the hypothesis that RA mediates its effects on bone cells in part by regulating IGFBP expression, we first examined the effect of RA on IGFBP expression in human osteoblast model systems and then compared these responses to the effects of RA on IGFBP expression in human skin fibroblasts. The most dramatic effect of RA on IGFBPs++ in all cell types tested was to increase IGFBP-6 messenger RNA (mRNA) abundance more than 1000% of the control value. Significant effects on IGFBP-5 mRNA abundance were also found, with maximal reductions to 35% of control within 24 h of treatment. In addition, RNA maximally increased IGFBP-3 and -4 mRNA to 580% and 390% of the control value, respectively, in SaOS-2 cells, but had variable effects on IGFBP-3 and -4 mRNA levels in human bone cells, U2-OS, and human skin fibroblasts. The levels of the 24-, 29- to 32-, and 38- to 42 kDa IGFBPs in the conditioned medium of RA-treated cultures increased, as determined by ligand blot analysis, whereas the amount of IGFBP-5 was reduced, as determined by RIA. Cycloheximide abolished the RA-stimulated increase in IGFBP-6 mRNA and reduced baseline IGFBP-5 mRNA levels, but did not affect RA-modulated mRNA levels of the other IGFBPs. RA modestly increased the stabilities of all four IGFBP mRNAs, which could contribute to the observed increases in IGFBP-3 and IGFBP-4 mRNA levels; however, the 217% increase in the IGFBP-5 mRNA half- life in the presence of RA could not contribute to the reduction in mRNA levels. In addition, the small increase in the IGFBP-6 mRNA half-life could not account for the 1900% increase in the mRNA level. These data suggest that RA stimulated changes in IGFBP-5 and -6 mRNA levels may in part be mediated by alterations in transcription or other early posttranscription regulatory mechanisms. In conclusion, RA significantly regulates IGFBP expression in human osteoblast cells.

Regulation of insulin-like growth factor system components by osteogenic protein-1 in human bone cells

Bone morphogenetic proteins (BMPs) have the unique ability to convert mesenchymal cells into matrix-producing osteoblasts. To understand the mechanism(s) by which a BMP produces a multitude of effects on bone cells, we examined the effects of recombinant human osteogenic protein (OP)-1 (referred to as BMP-7) on the insulin-like growth factor (IGF) regulatory system, an important growth factor system in bone. After 48 h of treatment, OP-1 increased the level of IGF-II (3- and 2-fold, respectively, at 100 ng/ml) in the conditioned medium (CM) of SaOS-2 and TE85 human osteosarcoma cells with osteoblastic characteristics, whereas IGF-I levels were low to undetectable in the CM of either cell type. OP-1 treatment had no significant effect on the messenger RNA (mRNA) level for type 1 and type 2 IGF receptors. In TE85 and SaOS-2 cells, 100 ng/ml OP-1 increased the level of IGF binding protein (BP)-3 more than 10-fold, decreased the IGFBP-4 level by 50%, and increased the level of the 29-32.5 kDa IGFBP-5 3-fold in the CM as determined by analysis with Western ligand blot, Western immunoblot, and RIA. The effect of OP-1 on IGFBP production was time and dose dependent. The OP-1 induced changes in the levels of IGFBPs were associated with decreased IGFBP-3 and -5 protease activity (29% and 71%, respectively) and proportional changes in IGFBP mRNA levels. OP-1 increased the level of IGFBP-3 mRNA (2- and 10-fold, respectively, after 4 and 24 h of treatment at 100 ng/ml) and of IGFBP-5 mRNA (more than 5-fold after 24 h of treatment) but decreased the level of IGFBP-4 mRNA (> 50% after 24 h at 100 ng/ml). OP-1 treatment had no effect on IGFBP-4 protease activity. These results collectively demonstrate that OP-1 can act locally by modulating the IGF regulatory system, suggesting that the mitogenic/differentiative effect of OP-1 on human bone cells may in part be mediated via IGF-II by increasing its secretion, and by regulating the balance between the stimulatory (e.g. IGFBP-5) and inhibitory (e.g. IGFBP-4) classes of IGFBPs both at the level of production (mRNA) and at the level of degradation but not by up-regulating the IGF receptor.

Paradoxical effects of phosphate to directly regulate the level of skeletal alkaline phosphatase activity in human osteosarcoma (SaOS-2) cells and inversely regulate the level of skeletal alkaline phosphatase mRNA

Recent studies indicate that the amount of alkaline phosphatase (ALP) activity in human osteoblast-line cells is proportional to the concentration of phosphate in the culture medium. The current studies were intended to extend those observations and to determine whether the effects of phosphate (and phosphate esters and analogs) to alter the cellular level of ALP activity, in human osteosarcoma SaOS-2 cells, reflected regulation at the level of transcription. Consistent with previous findings, we found direct, time- and dose-dependent correlations between the concentration of phosphate and the amount of ALP activity/mg cell protein (P < 0.05). Surprisingly, we also found a negative correlation between the phosphate concentration in the medium and the level of skeletal ALP mRNA (e.g., r = -0.98, P < 0.01 at 24 hours). As the highest cellular levels of skeletal ALP activity were associated with the lowest levels of ALP mRNA, these data indicated that the phosphate-dependent increase in ALP activity was not mediated by an increase in transcription and, conversely, that the effect of phosphate withdrawal to decrease ALP activity was not mediated by a decrease in transcription.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence comparison and predicted structure for the four exon-encoded regions of human insulin-like growth factor binding protein 4

The IGFBPs bind to and modulate the function of the IGFs in various ways. Human IGFBP-4 inhibits IGF mediated cell proliferation. The IGFBP exon-encoded regions were aligned and secondary structure predictions for hIGFBP-4 were developed yielding predicted 3D co-ordinates for each such region of hIGFBP-4. The exon 1 encoded region is the most conserved among the IGFBPs. That of hIGFBP-4 is predicted as an array of beta-strands that include the glycine and cysteine rich IGFBP consensus pattern and that terminate with a helix. The exon 2 encoded region is the most variable among the IGFBPs. That of hIGFBP-4 is predicted as mostly an amphipathic helix. The remaining regions are also conserved among the IGFBPs. Those of hIGFBP-4 are also predicted to contain helices. The predicted structure of hIGFBP-4 comprises amino terminal beta-strands with four helices in the carboxy terminal two thirds of the molecule.

The effects of the insulin-like growth factors and transforming growth factor beta on the Jun proto-oncogene family in MC3T3-E1 cells

Previous studies have demonstrated that when cells of the mouse osteoblastic cell line MC3T3-E1 are exposed to IGF-I and IGF-II they exhibit rapid and transient induction of the transcript from the proto-oncogene c-fos [8]. To clarify the relationship between induction of cell proliferation and proto-oncogene expression in MC3T3-E1 cells, the acute affects of IGF-I and IGF-II, growth factors that stimulate cell proliferation, and of TGF-beta 1, which inhibits cell proliferation, northern analyses with cDNA-derived probes for the proto-oncogenes c-jun, jun-B, and jun-D were undertaken. Concurrent northern analyses with a probe for c-fos extended our previous results to include the effect of TGF-beta 1 on c-fos. IGF-I does not induce the c-jun, jun-B, or jun-D transcripts, the former and latter being produced at detectable levels constitutively. After 1 hour of exposure to IGF-II the c-jun transcript response ranges from onefold to 13-fold and the jun-D transcript response ranges around two-fold. After 1 hour of exposure to TGF-beta 1, the jun-B transcript response ranges from eightfold to 24-fold, the c-fos transcript response ranges between sixfold and sevenfold. The differences observed in the magnitude and kinetics of the induction provoked by these growth factors is consistent with the presence of a regulatory circuit acting through the Jun family members which may act to stimulate transcription differentially when bound to DNA either as homodimers or, with Fos family proteins, as heterodimers.

Effect of tumor necrosis factor-alpha on the expression of insulin-like growth factor I and insulin-like growth factor binding protein 4 in mouse osteoblasts

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine produced by immune cells, which has multiple effects on bone cells and is therefore thought to mediate changes in bone metabolism occurring during inflammation. In the present study we have investigated the effect of TNF-alpha on the secretion of insulin-like growth factor I (IGF-I) and IGF binding protein 4 (IGFBP-4) by clonal mouse osteoblasts (MC3T3-E1 cells) using subconfluent in vitro cultures and serum-free conditions. The IGF-I was determined by radioimmunoassay under conditions eliminating the interference of IGFBPs. Treatment of MC3T3-E1 cultures with TNF-alpha for 24 h resulted in a dose-dependent decrease in IGF-I secretion (maximally to 34 +/- 9.7% of control with 60 pmol/l TNF-alpha; mean +/- SD). The TNF-alpha treatment also resulted in decreased messenger ribonucleic acid (mRNA) levels of IGF-I at 4 and 24 h, as detected by Northern analysis. Because basal secretion of IGFBPs is very low in MC3T3-E1 cells, effects of TNF-alpha on IGFBP secretion were studied in cultures in which IGFBP-4 expression was increased by calcitriol (1,25(OH)2D3) treatment. The presence of TNF-alpha (600 pmol/l) inhibited this calcitriol-induced stimulation of IGFBP-4 mRNA levels from 4 h onwards, with complete inhibition of the calcitriol effect occurring at 24 h. We also observed a dose-dependent inhibition of calcitriol-stimulated IGFBP-4 secretion into the culture medium (as detected by Western ligand blot), with the maximal inhibition occurring with 600 pmol/l TFN-alpha to 25 +/- 7% of control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

1,25-Dihydroxyvitamin D3 increases secretion of insulin-like growth factor binding protein-4 (IGFBP-4) by human osteoblast-like cells in vitro and elevates IGFBP-4 serum levels in vivo

Insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) are thought to play an important role in the regulation of bone metabolism. In the present study, we investigated the effect of 1,25-dihydroxyvitamin D(3) [1,25-(OH)2D3] on the expression and secretion of IGFBPs in human osteoblast-like osteosarcoma cells (MG63) and untransformed human bone-derived cells in vitro. Northern blot analysis revealed that 1,25-(OH)2D3 (10(-8) mol/L) increased IGFBP-4 messenger RNA maximally 11-fold over control level in MG63 cells (after 24 h treatment) and 2.8-fold in human bone-derived cells (at 10(-10) mol/L). 1,25-(OH)2D3 increased secretion of IGFBP-4 2- and 3-fold, respectively, in MG63 cells and in human bone-derived cells. In normal human bone-derived cells, 1,25-(OH)2D3 also stimulated messenger RNA expression (3.9-fold) and the secretion of IGFBP-3 (2.2-fold). 1,25-(OH)2D3 also increased IGFBP-4 expression in skin fibroblasts but not in hepatocellular carcinoma cells. Consistent with these in vitro findings, treatment of human subjects with high doses of oral 1,25-(OH)2D3 (2-3 micrograms/day) for psoriasis resulted in a significant increase in serum IGFBP-4 concentration compared with pretreatment levels. Our observations present direct evidence that 1,25-(OH)2D3 plays an important role in the regulation of IGFBP secretion in vitro and in vivo.

Dibutyryl cyclic adenosine monophosphate differentially regulates cell proliferation in low and high alkaline phosphatase SaOS-2 human osteosarcoma cells: evidence for mediation by the insulin-like growth factor-II system

In the present study, we have sought to determine whether a given signal transduction pathway can have diverse effects on subpopulations of cells of a lineage depending upon the stage of differentiation. To test this hypothesis, we selected the cyclic adenosine monophosphate (cAMP) signal transduction pathway because of its recognized importance in mediating the actions of many hormones, e.g., parathyroid hormone which acts on the bone-forming cells, the osteoblasts. Subpopulations of human osteosarcoma SaOS-2 cells with low (LSaOS) and high (HSaOS) alkaline phosphatase (ALP) content were chosen as model systems for preosteoblasts (pre-OB) and osteoblasts (OB), respectively. Dibutyryl cyclic AMP (DBcAMP) treatment of serum free cultures produced a differential effect on the proliferation of LSaOS cells (40 +/- 5% of control at 1 mM DBcAMP, P < 0.001) compared with HSaOS cells (no statistically significant effect). The finding supports the hypothesis. Next, we sought evidence for mediation, at least in part, by the insulin-like growth factor (IGF)-II regulatory system. We report that the basal expression of IGF-II, IGF binding protein (IGFBP)-3, and IGFBP-4 was higher in LSaOS cells than in HSaOS cells with the opposite true for type I IGF receptor. DBcAMP treatment of LSaOS cells decreased IGF-II and IGFBP-3 but increased IGFBP-4 and type I IGF receptor; no effect was observed for the type II IGF receptors. DBcAMP treatment of HSaOS cells had no detectable effect on IGF-II; IGFBP-3, or type I and type II IGF receptor expression; only IGFBP-4 expression increased with DBcAMP. These observations suggest that the differential regulation of cell proliferation by the cAMP signal transduction pathway may be mediated, at least in part, by the IGF-II regulatory system.

Mechanism of mitogenic action of aluminum ion on human bone cells: potential involvement of the insulin-like growth factor regulatory system

Aluminum ion at micromolar concentrations significantly stimulated the [3H]thymidine incorporation into human TE85 osteosarcoma cell DNA. Cells treated with mitogenic concentrations of aluminum ion for 48 h showed biphasic stimulation in secretion of IGFs (insulin-like growth factors) into the conditioned medium. Treatment of the human osteosarcoma TE85 cells with mitogenic doses of aluminum ion for 24 h also markedly and reproducibly increased the steady-state level of IGF-II mRNA in a dose-dependent, biphasic manner. The effect of aluminum ion on the steady-state level of IGF-I mRNA could not be determined since the IGF-I mRNA in these cells was not detectable with our oligodeoxynucleotide probes. To test whether the mitogenic effects of aluminum ion could be mediated through IGFs, the stimulation of [3H]thymidine incorporation of TE85 cells was evaluated in the presence and the absence of an inhibitory IGF binding protein (i.e., IGFBP-4). The presence of IGFBP-4 significantly reduced the stimulation in thymidine incorporation by a mitogenic concentration of aluminum ion. Western ligand blot analysis revealed that mitogenic concentrations of aluminum ion also inhibited the secretion of IGF-binding proteins, particularly the inhibitory IGFBP-4, which could lead to the potentiation of the overall activity of IGFs. In conclusion, these findings are consistent with the premise that the mitogenic action of aluminum ion on human bone cells is, in part, mediated by an increased local bone cell production and activity of IGFs.

Fibroblast growth factor enhances the transcription and stability of human chorionic gonadotropin beta-subunit messenger ribonucleic acid in Jar choriocarcinoma cells

In previous studies, we found that basic fibroblast growth factor (bFGF) significantly stimulated the secretion of hCG beta in the Jar choriocarcinoma cell line. In the present study, the effect of bFGF on the steady state hCG beta mRNA level in this cell line was determined. Application of Northern analyses with total RNA isolated from bFGF-stimulated Jar cells revealed that, in a time-dependent manner, the steady state hCG beta mRNA level increased progressively, reaching 4-fold of the control value within 4 h after exposure to bFGF. The observed accumulation was due in part to increased transcription (2.4-fold relative to that in control cultures), as determined by nuclear transcription studies. In addition, bFGF increased the stability of the hCG beta message; the message half-life was increased from approximately 3 h (in control cultures) to greater than 6 h (in bFGF-treated cultures). These data demonstrate that bFGF stimulates hCG beta mRNA accumulation in a complex manner regulated through both transcriptional and posttranscriptional mechanisms.

Ovariectomy selectively reduces the concentration of transforming growth factor beta in rat bone: implications for estrogen deficiency-associated bone loss

Previous work showed that production of transforming growth factor beta (TGF-beta) by osteoblast-like rat UMR 106 cells was increased by 17 beta-estradiol at physiological concentrations. To determine whether ovariectomy alters the concentration of TGF-beta in rat long bones, female Sprague-Dawley rats were either sham-operated (n = 19) or ovariectomized (n = 19), pair-fed a semisynthetic diet for 6 weeks, and sacrificed. Tibial and femoral diaphyses were removed and extracted by demineralization. Ovariectomy lowered serum estrogen; did not alter body weight, serum magnesium, or serum 1,25-dihydroxyvitamin D; and produced only modest differences in serum calcium and phosphate concentrations. Hydroxyproline was higher and extractable protein was lower in bones from ovariectomized rats than in bones from sham-operated rats; calcium content did not differ between the two groups of animals. Ovariectomy lowered the concentration of TGF-beta in bone but did not change the concentration of insulin-like growth factors I or II compared with values in bone from control animals. The reduction of bone TGF-beta was evident 6 weeks after surgery but not at 3 weeks. Treatment of ovariectomized rats with estrogen eliminated the TGF-beta deficit. To determine whether 17 beta-estradiol increased TGF-beta production by normal bone cells, mouse osteoblasts were treated for 2 days with 17 beta-estradiol. The production of TGF-beta was increased almost 2-fold by 1 nM 17 beta-estradiol, and short-term treatment stimulated the intracellular accumulation of TGF-beta 1 mRNA. We conclude that ovariectomy reduces deposition of TGF-beta in rat bone and that diminished skeletal TGF-beta could play a role in the pathogenesis of bone loss, fractures, and microfractures that occur in estrogen-deficient states. Our results support the possibility that estrogen and bone TGF-beta may be necessary for normal maintenance of the skeleton in female rats.

Studies on regulation of insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-4 production in human bone cells

Previous studies have shown that the actions of IGF-II in bone are determined not only by its concentration, but also by the concentration of IGFBP-4 as well as other IGFBPs. In this study, we sought to determine by Western ligand blotting the effects of growth hormone, IGF-I and IGF-II on the production of IGFBP-3 and IGFBP-4 in TE89 human osteosarcoma cells and in untransformed normal human bone cells derived from rib. Human growth hormone at 10 micrograms/l decreased the amount of IGFBP-4 but had no effect on the IGFBP-3 level in the conditioned medium of low density cultures of TE89 cells and human bone cells derived from rib. Human growth hormone had no effect on IGFBP-3 or IGFBP-4 levels in the conditioned medium of high density human bone cell cultures. IGF-I and IGF-II, which increased human bone cell proliferation, decreased the level of IGFBP-4 (30% of control at 100 micrograms/l IGF-I and IGF-II) but increased the level of IGFBP-3 (3-10 fold at 100 micrograms/l IGF-I and IGF-II) after 48 h of treatment in the conditioned medium of both low and high density TE89 cell cultures. Similar changes in IGFBP-3 and IGFBP-4 levels were also seen in the conditioned medium of human bone cells derived from rib after treatment with IGF-I and IGF-II. Studies to determine the underlying molecular mechanisms by which IGF-II decreased the amount of IGFBP-4 in the conditioned medium revealed that IGF-II decreased the IGFBP-4 mRNA abundance and increased the IGFBP-3 mRNA abundance in human bone cells. Based on the above findings, we conclude that the production of both IGFBP-3 and IGFBP-4 is regulated in bone cells and that local and systemic agents may modulate the responsiveness of bone cells to IGFs by regulated secretion of IGFBP-3 and IGFBP-4.

Transforming growth factor-beta 1 mRNA in neonatal ovine molars visualized by in situ hybridization: potential role for the stratum intermedium

Human dentine contains relatively large amounts of transforming growth factor-beta (TGF-beta), which might originate from odontoblasts. The expression of the TGF-beta 1 message in developing teeth was examined by in situ hybridization. The analysis was made on 5-microns serial sections of mandibular third molars of neonatal sheep cut from tissues that had been fixed in glutaraldehyde and paraffin-embedded. A 35S-labelled cRNA probe, complementary to TGF-beta 1 mRNA, was constructed from human TGF-beta 1 cDNA. Northern analysis of total RNA from sheep placenta and neonatal third molars demonstrated hybridization to a single 2.4 kb TGF-beta 1 transcript from both tissues, indicating cross-reactivity of the human probe in the sheep. In the neonatal molars, in situ hybridization was observed in cells of the inner enamel epithelium, mature ameloblasts and mature odontoblasts, but not within preodontoblasts before dentine matrix formation. TGF-beta 1 mRNA expression was also evident in the cells of the dental papilla but scarcely so in the stellate reticulum. The most striking feature was the appearance of hybridization signal in the cells of the stratum intermedium before hybridization was evident in the inner enamel epithelium. Control sections incubated with RNAase before incubation with probe did not show evidence of hybridization. These findings suggest that TGF-beta 1 may have an important regulatory role in the differentiation of ameloblasts and odontoblasts, perhaps by modulating matrix formation during amelogenesis or odontogenesis. They also suggest a potential novel regulatory role for the cells of the stratum intermedium.

Progesterone and promegestone stimulate human bone cell proliferation and insulin-like growth factor-2 production

Recent clinical studies suggest that progesterone may be involved in the regulation of bone turnover and could promote bone formation. This study was undertaken to evaluate whether progesterone and promegestone (a 19 nor-PG derivative) may have a direct effect on human bone cells and, if so, whether growth factor production could be involved in promoting this effect. The osteosarcoma cell line TE85 and untransformed normal human osteoblastic cells derived from iliac crest were used as in vitro model systems. Progesterone and promegestone were found to significantly increase [3H]thymidine incorporation in TE85 cells in a dose-dependent manner at concentrations ranging from 10(-12) to 10(-8) mol/l after four days of cultivation (p less than 0.01, ANOVA). Consistent with this response in the TE85 cells, progesterone and promegestone increased cell number in human osteoblastic cells after six days of treatment (p less than 0.05, ANOVA). To determine whether this effect on cell proliferation was mediated by the insulin-like growth factor (IGF) regulatory system, the levels of IGF-1, IGF-2 and IGF binding protein (IGFBP) were measured in the conditioned media of both TE85 and human osteoblast cells. While no significant changes in IGF-1 levels were found in the conditioned media of progesterone and promegestone treated cultures, progesterone and promegestone at the concentration of 5 nmol/l significantly increased IGF-2 levels 2.4 and 1.5-fold respectively, at 48 h in the conditioned medium of TE85 cells as compared to control. Similarly, a 4.1 and 1.9-fold increase in IGF-2 levels was found upon treatment with progesterone and promegestone in human osteoblastic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation of normal human bone cells by transforming growth factor-beta and 1,25(OH)2 vitamin D3

To investigate the role of transforming growth factor-beta 1 (TGF beta) in bone metabolism, the effects of this agent on the differentiation characteristics of human bone cells were studied in vitro. Human bone cells were isolated from femoral head samples by collagenase digestion. Differentiation characteristics included alkaline phosphatase activity, osteocalcin production, and mRNA levels for alkaline phosphatase, type I alpha 2-procollagen, and osteocalcin. The effect of TGF beta on alkaline phosphatase was not constant, but varied with the incubation conditions. At high cell density and in the presence of serum, TGF beta decreased alkaline phosphatase activity. However, at low cell density and under serum-free conditions, TGF beta stimulated alkaline phosphatase activity. The addition of 1,25(OH)2 vitamin D3 also stimulated alkaline phosphatase. The combination of the two agents gave a greater increase in activity than the sum of the activities when the two agents were given alone. The percentage of cells that stain positively for alkaline phosphatase changed in parallel with the change in specific activity. The percentage of positive cells increased from 17% to 64%, while the specific activity increased from 22 to 169 mU/mg protein. To investigate the mechanism of this stimulation, mRNA levels were measured at 24 hours. Individually, TGF beta and 1,25(OH)2D3 increased message levels for alkaline phosphatase and type I procollagen, but the greatest effect was produced by the combination of the two factors. 1,25(OH)2D3 increased osteocalcin mRNA levels, but TGF beta markedly inhibited this stimulation. TGF beta also inhibited production of osteocalcin by the human bone cells. TGF beta appears to modulate differentiation of human bone cells in combination with 1,25(OH)2D3 and other factors.

Low-amplitude, low-frequency electric field-stimulated bone cell proliferation may in part be mediated by increased IGF-II release

We have developed an in vitro model incorporating a low-amplitude (10(-7) V/cm), low frequency (f less than 100 Hz), capacitively coupled electric field in order to study the mechanism through which an electric field may increase bone cell proliferation. Utilizing this model we have previously shown that electric field-stimulated bone cell proliferation was dependent on release of mitogen activity into the culture medium from exposed cells. The current studies were intended to characterize this mitogen activity. In these studies we found that electric field-stimulated human bone cell proliferation was associated with increased IGF-II mRNA accumulation and IGF-II secretion suggesting that IGF-II may in part mediate the increase in bone cell proliferation following electric field exposure.

1,25-Dihydroxyvitamin D3 stimulates both alkaline phosphatase gene transcription and mRNA stability in human bone cells

We have previously reported that 1,25(OH)2D3 stimulated the cellular alkaline phosphatase (ALP) activity and increased the steady-state level of ALP mRNA in a human osteosarcoma cell line (TE-85), under serum-free conditions. To define the molecular mechanism by which 1,25(OH)2D3 acts to stimulate ALP activity, the time courses of the increases in ALP activity and in the steady-state ALP mRNA level in response to 1,25(OH)2D3 were evaluated. 1,25(OH)2D3 progressively increased the steady-state level of ALP mRNA from 5 to 24 h of treatment, at which time a plateau was observed. In contrast, no significant increase in ALP-specific activity was detected until after 10 h of treatment, at which time the activity increased linearly with time up to 72 h. These time courses are consistent with the premise that the increased ALP activity was the result of increased gene expression. Nuclear runoff analysis indicated that the transcription rate of the ALP gene was more than five-fold higher in the 1,25(OH)2D3-treated cells than in the control cells. In addition, it was found that 1,25(OH)2D3 treatment increased ALP mRNA stability. The 1,25(OH)2D3-induced increase in ALP mRNA stability was not due to an interaction of the 1,25(OH)2D3-receptor complex with the ALP mRNA, since the removal of 1,25(OH)2D3 did not abolish its stabilizing effect. In the presence of cycloheximide, the stabilizing effect of 1,25(OH)2D3 was abolished, suggesting that a 1,25(OH)2D3-inducible protein factor was involved. Based on these findings, we have proposed a model in which 1,25(OH)2D3 stimulated ALP activity in human bone cells through mechanisms involving both (1) increased transcription of the ALP gene and (2) increased stability of ALP mRNA, an effect which requires the de novo synthesis of a protein, a putative ALP mRNA "stabilizing factor."

1,25-Dihydroxyvitamin D3 differentially regulates the production of insulin-like growth factor I (IGF-I) and IGF-binding protein-4 in mouse osteoblasts

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] induces differentiation and inhibits proliferation in many cell types including bone cells. These effects may be mediated by the modulation of the insulin-like growth factor (IGF) regulatory system. Therefore we investigated the effects of 1,25-(OH)2D3 on transcript and protein levels of both IGF-I and IGF binding proteins (IGFBPs) in clonal mouse osteoblasts. Subconfluent cultures were treated in serum-free medium with 1,25-(OH)2D3. Secreted IGF-I was measured using a RIA under conditions eliminating the interference of IGFBPs. 1,25-(OH)2D3 (10(-11)-10(-8) M) inhibited IGF-I release in a dose dependent manner at 24 h (maximally to 30 +/- 5% of control, mean +/- SEM of seven independent experiments). In a time course study IGF-I increased in the media of control cultures over a 48-h period, while IGF-I secretion was completely prevented from 6 h onward in 1,25-(OH)2D3 treated cultures. Northern blot analysis revealed four IGF-I transcripts of 0.9, 1.8, 4.4, and 7.5 kilobases (kb). 1,25-(OH)2D3 decreased levels of the 7.5 kb IGF-I transcript from 4-48 h, with maximal inhibition occurring at 24 h (25% of control). Western ligand blots of the culture medium demonstrated secretion of a 25-kilodalton IGFBP, which comprised greater than or equal to 90% of the secreted IGFBPs. The 25-kilodalton IGFBP had previously been shown to have sequence similarity with IGFBP-4, a binding protein which inhibits the action of IGFs on bone cells. 1,25-(OH)2D3 treatment increased secretion of IGFBP-4 up to 14-fold over 24 h. 1,25-(OH)2D3 also increased IGFBP-4 (2.2 kb) transcript levels within 30 min, with the maximal stimulation of 8-fold occurring after 8 h. [3H]Thymidine incorporation into cells was inhibited by 1,25-(OH)2D3 both under basal and serum-stimulated conditions. Our results are consistent with the hypothesis that the effects of 1,25-(OH)2D3 on osteoblast proliferation may be mediated in part by decreased levels of IGF-I and increased concentrations of inhibitory IGFBP-4. It is proposed that this alteration in the IGF system may be an important functional autocrine or paracrine switch in the transition of osteoblasts from states of proliferation to differentiation.

Interleukin-6 messenger RNA expression and interleukin-6 protein secretion in cells isolated from normal human bone: regulation by interleukin-1

Recent evidence suggests that cytokines, in addition to regulating hematopoiesis and immune functions, may be important paracrine regulators of bone turnover. Interleukin-1 (IL-1) and IL-6 are cytokines that are produced by and affect both hematopoietic and nonhematopoietic cell types. IL-1 stimulates bone resorption and inhibits osteoblast proliferation and collagen production. Previous reports that IL-6 was secreted in murine osteoblast and bone organ cultures in response to IL-1 and PTH suggested that IL-6 has paracrine effects on bone resorption or formation. To determine whether IL-6 has a paracrine function in human bone, IL-6 expression in cells isolated from normal human bone was investigated. IL-6 mRNA levels in untreated cultures were low and variable, and IL-6 secretion was undetectable. PTH had no effect on IL-6 mRNA levels or IL-6 secretion. IL-1 beta increased IL-6 mRNA levels, maximally 40-fold at 12 h. IL-1 beta increased IL-6 secretion to 0.13 nM, more than 80-fold that of untreated controls at 12 h. IL-1 beta also increased IL-1 beta mRNA levels, maximally 9-fold at 12 h, but did not increase cellular levels or secretion of IL-1 beta protein. Recombinant human IL-6 at 0.5-5 nM stimulated resorption in neonatal mouse calvarial organ cultures but had no effect on human bone-derived cell DNA synthesis or type I procollagen mRNA levels. The results suggest that IL-6 production by human osteoblasts may function to enhance osteolytic activity of IL-1 but does not affect proliferative and matrix biosynthetic aspects of bone formation that were tested. Because osteoblasts and bone marrow cells are in close proximity, IL-6 produced by osteoblasts may also function to amplify IL-1 stimulation of immune responses and hematopoiesis in bone marrow.

Insulin-like growth factor II and transforming growth factor beta 1 regulate insulin-like growth factor I secretion in mouse bone cells

Bone cells in culture produce and respond to growth factors, suggesting that local as well as systemic factors regulate bone volume. Previous studies have shown that IGF-I is the major mitogen produced by mouse bone cells and that its production is regulated by systemic agents such as PTH and estrogen. Because IGF-II and transforming growth factor beta 1 have been shown, respectively, to increase and decrease MC3T3-E1 cell proliferation, we tested the hypothesis that these two growth factors modulate the production of IGF-I in this cell line. In order to eliminate artifacts owing to IGF binding proteins, conditioned media samples were pretreated with IGF-II before measurement of IGF-I by RIA. After 24 h treatment at a density of 2.5 x 10(4) cells/cm2, IGF-II (10 micrograms/l) induced a 2.2-fold increase compared with untreated control (9.5 +/- 1.5 vs 4.2 +/- 0.44 pg/micrograms protein, p less than 0.001), whereas transforming growth factor beta 1 (1 microgram/l) caused a 66% decrease in IGF-I production (1.5 +/- 0.3 vs 4.2 +/- 0.44 pg/micrograms protein, p less than 0.001). Both IGF-II and transforming growth factor beta 1 regulated IGF-I production in a dose-, time- and cell density-dependent manner. The lowest effective doses for IGF-II and transforming growth factor beta 1 were 1 and 0.01 microgram/l, respectively. These results support a role for IGF-II and transforming growth factor beta 1 as potent modulators of IGF-I secretion in mouse bone cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulinlike growth factor II and transforming growth factor beta regulate collagen expression in human osteoblastlike cells in vitro

Insulinlike growth factor II (IGF-II) and transforming growth factor beta (TGF-beta) are the most abundant polypeptide growth factors found in human bone matrix and are produced by human bone cells in vitro. IGF-II and TGF-beta 1 increased total protein synthesis, collagenous protein synthesis, and the steady-state level of type I procollagen mRNA in a time-dependent manner in osteoblastlike cells isolated from human bone. Type III procollagen mRNA expression was low in untreated cultures and was not affected by IGF-II or TGF-beta. TGF-beta 1 elevated type I procollagen mRNA rapidly, with the maximal observed change at 10 h. In contrast, procollagen mRNA levels increased more slowly in response to IGF-II and reached a lower maximal level than with TGF-beta, but the response was sustained through 24 h. Collagenous protein synthesis in IGF-II- and TGF-beta-treated cells increased in parallel with increases in procollagen mRNA levels and was higher at 21 h for TGF-beta 1 and at 36 h for IGF-II. The difference in the time course and magnitude of change in type I procollagen mRNA levels in response to IGF-II and TGF-beta 1 suggests that these two growth factors work through distinct mechanisms that provide both a rapid transient response and a later sustained response in bone matrix biosynthetic activity.

Inhibitory insulin-like growth factor-binding protein: cloning, complete sequence, and physiological regulation

In this study we report the preparation of a human osteosarcoma cell cDNA library and describe the isolation and sequence determination of a clone encoding the complete sequence of a novel human insulin-like growth factor (IGF)-binding protein (hIGFBP-4). Previous work indicated that hIGFBP-4 is the predominant IGFBP expressed by human osteoblast-like cells, and that IGFBP-4 binds and inhibits the mitogenic activities of IGF-I and IGF-II. Sequence determination revealed that hIGFBP-4 is a unique gene product with significant amino- and carboxy-terminal sequence similarity to three other known IGFBPs. Identical alignment of 18 cysteines in IGFBP-4 and the three other IGFBPs is a key structural feature of this protein family. In vitro studies of human osteoblast-like cells suggest that PTH regulates the expression of hIGFBP-4 and that the PTH effect is mediated through a cAMP mechanism. hIGFBP-4 mRNA was also expressed in skin fibroblasts, and thus, this inhibitory IGFBP could be an important physiological regulator of IGF actions in bone cells and other cell types as well.

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.

Stimulation of cellular alkaline phosphatase activity and its messenger RNA level in a human osteosarcoma cell line by 1,25-dihydroxyvitamin D3

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) significantly stimulated cellular alkaline phosphatase activity in a human osteoblastic osteosarcoma cell line (TE-85 cells) in serum-free medium with 0.1% bovine serum albumin as the hormone carrier in a dose- and a time-dependent manner. The extent of the maximal stimulation was greater and the minimal dose that was required for stimulation was lower than those previously reported for TE-85 cells in the presence of serum. The magnitude of the stimulation of alkaline phosphatase activity by 1,25(OH)2D3 varied with the cell density. Daily changes of conditioned medium, as compared with no medium changes, significantly reduced the magnitude of the stimulation, suggesting that endogenous factors secreted into culture medium could play an enhancing role. Finally, application of Northern blot analysis using an oligodeoxynucleotide probe corresponding to a unique sequence of the human bone/liver/kidney alkaline phosphatase cDNA coding region revealed that 1,25(OH)2D3 increased the alkaline phosphatase mRNA level, suggesting that the increase in alkaline phosphatase activity was a result of either an increase in the rate of transcription or an increase in message stability.

Alkaline phosphatase activity from human osteosarcoma cell line SaOS-2: an isoenzyme standard for quantifying skeletal alkaline phosphatase activity in serum

Earlier we described a kinetic assay for quantifying skeletal alkaline phosphatase (ALP) isoenzyme activity in serum. The precision of the assay depends on including ALP standards for the skeletal, hepatic, intestinal, and placental isoenzymes. We wondered whether human osteosarcoma cells could provide an efficient alternative to human bone or Pagetic serum as a source of the skeletal ALP standard. ALP activities prepared from five human osteosarcoma cell lines were compared with a bone-derived ALP standard with respect to heat stability and sensitivity to chemical effectors. Two of the cell lines (SaOS-2 and TE-85) contained ALP activities that resembled the bone-derived standard. We selected SaOS-2 cells for additional evaluation (as a potential source of isoenzyme standard), because they contained 40-50 times more ALP activity than did the TE-85 cells. To include the SaOS-2 cell-derived ALP activity in the quantitative isoenzyme assay, we diluted the enzyme in a solution containing heat-inactivated (i.e., ALP-negative) human serum. Surprisingly, this dilution caused a 60-125% increase in maximum enzyme activity. In the quantitative assay of ALP isoenzyme in serum, the SaOS-2 derived ALP was indistinguishable from the serum skeletal ALP standard, with respect to the above criteria and assay variations. Evidently ALP from SaOS-2 cells is suited as a standard for measuring skeletal ALP activity in this assay.

Alkaline phosphatase activity from human osteosarcoma cell line SaOS-2: an isoenzyme standard for quantifying skeletal alkaline phosphatase activity in serum

Earlier we described a kinetic assay for quantifying skeletal alkaline phosphatase (ALP) isoenzyme activity in serum. The precision of the assay depends on including ALP standards for the skeletal, hepatic, intestinal, and placental isoenzymes. We wondered whether human osteosarcoma cells could provide an efficient alternative to human bone or Pagetic serum as a source of the skeletal ALP standard. ALP activities prepared from five human osteosarcoma cell lines were compared with a bone-derived ALP standard with respect to heat stability and sensitivity to chemical effectors. Two of the cell lines (SaOS-2 and TE-85) contained ALP activities that resembled the bone-derived standard. We selected SaOS-2 cells for additional evaluation (as a potential source of isoenzyme standard), because they contained 40-50 times more ALP activity than did the TE-85 cells. To include the SaOS-2 cell-derived ALP activity in the quantitative isoenzyme assay, we diluted the enzyme in a solution containing heat-inactivated (i.e., ALP-negative) human serum. Surprisingly, this dilution caused a 60-125% increase in maximum enzyme activity. In the quantitative assay of ALP isoenzyme in serum, the SaOS-2 derived ALP was indistinguishable from the serum skeletal ALP standard, with respect to the above criteria and assay variations. Evidently ALP from SaOS-2 cells is suited as a standard for measuring skeletal ALP activity in this assay.

Meningioma in the parotid region

Meningiomas occurring ectopically in the neck are exceptional. We report two patients who presented as parotid and parapharyngeal masses and analyze them along with 27 previously reported cases. Typical patients present with parotid or parapharyngeal masses and cranial nerve palsies. Meningioma is not considered in differential diagnosis. The tumor is an extension of an unsuspected intracranial mass, occasionally with associated multiple meningiomas or other neurogenic tumors. Ectopic meningiomas should be considered in patients with parotid and parapharyngeal masses, particularly those with cranial nerve deficits; jugular foramen syndrome is most characteristic. Associated occult intracranial and temporal bone tumors and the cranial form of neurofibromatosis should be suspected. Treatment of cervical meningiomas is excision. The most important aspect of intracranial-extracranial lesions is recognition and treatment of the intracranial portion.

Complementary DNA sequence of lamprey fibrinogen beta chain

The cDNA sequence of the beta chain of lamprey fibrinogen has been determined. To that end, an oligonucleotide probe was synthesized that corresponded to an amino acid sequence from the carboxy-terminal region of the lamprey fibrinogen beta chain. The insert actually began with residue 3 of the fibrin beta chain; it ran through to a terminator codon following the carboxy-terminal residue at position 443 and then continued for an additional 606 nucleotides of noncoding sequence to its 3' end. The inferred amino acid sequence was verified by comparison with assorted cyanogen bromide fragments isolated from the beta-chain protein, including two carbohydrate-containing peptides that corresponded to segments containing the carbohydrate-attachment consensus sequence. Overall, the lamprey chain is 49% identical with the beta chain from human fibrinogen. This is the same degree of resemblance as was found for the lamprey and human gamma chains. Moreover, the principal regions of conservation are the same in both the beta and gamma chains. Differences and similarities in the physiological behavior of the two fibrinogens are assessed in terms of the observed amino acid replacements.

Lamprey fibrinogen gamma chain: cloning, cDNA sequencing, and general characterization

A cDNA library from lamprey liver was constructed in pBR322 and screened with a synthetic mixed oligonucleotide probe, the sequence of which was based on a partial amino acid sequence of the lamprey fibrinogen gamma chain determined by conventional procedures. Among the positive clones was one containing a 600-base insert that covered the carboxy-terminal third of the chain and another with a 1950-base insert that stretched more than full length. The two inserts were sequenced by the Maxam-Gilbert procedure. The DNA sequencing was corroborated by reference to the amino acid sequences of five cyanogen bromide peptides that compose the carboxy-terminal 130 amino acids, as well as to a number of tryptic peptides from elsewhere in the molecule. The clone with the smaller insert (6G) contained 594 nucleotides (not counting G and C tails), 435 of which are coding and correspond to residues 264-408 of the gamma chain. The remaining 159 nucleotides included the terminator codon followed by a noncoding segment. The larger clone (2E) coded for 408 amino acids that could be readily aligned with the 411-residue human gamma chain. A 24-residue signal peptide adjacent to the proposed amino terminal was also inferred. The amino acid sequence of the fibrinogen gamma chain has been differentially conserved during evolution, the lamprey and human sequences being more than 70% identical in certain key regions but dropping to less than 25% in other sections, including the segment thought to be a part of the "coiled coils". Overall, the resemblance amounts to 50% identity. Of the 10 cysteines found in mammalian chains, 9 are at identical positions, but the tenth, which in mammalian fibrinogens is a part of the interdimeric bridging, is absent in the lamprey.

Identification of the polypeptides encoded in the ATPase 6 gene and in the unassigned reading frames 1 and 3 of human mtDNA

Antibodies prepared against chemically synthesized peptides predicted from the DNA sequence have been used to identify the polypeptides encoded in the ATPase 6 gene and in unidentified reading frames (URFs) 1 and 3 of human mtDNA. In particular, antibodies directed against the COOH-terminal nonapeptide of the putative polypeptide encoded in the ATPase 6 reading frame immunoprecipitated specifically component 17 of the HeLa cell mitochondrial translation products, the reaction being inhibited by the specific peptide. Similarly, antibodies directed against the COOH-terminal undecapeptide of the putative URF1 product or against the COOH-terminal heptapeptide of the presumptive URF3 product were effective in immunoprecipitating specifically component 12 or, respectively, component 24 of the mitochondrial translation products. The sizes of proteins 17, 12, and 24, as estimated from their electrophoretic mobilities, are compatible with their being the products of the ATPase 6 gene, URF1, and URF3, respectively.

Antibodies against synthetic peptides reveal that the unidentified reading frame A6L, overlapping the ATPase 6 gene, is expressed in human mitochondria

Antibodies prepared against chemically synthesized peptides predicted from the DNA sequence have been used to detect human mitochondrial gene products. In particular, antibodies directed against either the NH2-terminal decapeptide or the COOH-terminal undecapeptide of cytochrome c oxidase subunit II (COII) were both very effective in immunoprecipitating the previously identified COII polypeptide from an SDS lysate of mitochondria from HeLa cells. Similarly, antibodies directed against the COOH-terminal nonapeptide of the putative polypeptide encoded in the unidentified reading frame A6L, which overlaps the ATPase 6 gene, immunoprecipitated specifically a component (#25) of the HeLa cell mitochondrial translation products; antibodies directed against the NH2-terminal octapeptide also precipitated protein 25, although less efficiently. The size of protein 25, as estimated from its electrophoretic mobility, is compatible with its being the unidentified reading frame A6L product. Furthermore, a fingerprinting analysis of this protein after trypsin digestion has given results consistent with this identification.

gamma and alpha chains of human fibrinogen possess sites reactive with human platelet receptors

Fibrinogen, a clottable plasma protein, agglutinates both prokaryotic cells (e.g., staphylococci) and eukaryotic cell fragments (e.g., platelets) through interaction with specific receptors. To identify the region of the fibrinogen molecule responsible for its interaction with human platelets, we prepared polypeptide chain subunits (alpha, beta, and gamma) of human fibrinogen by reduction and carboxymethylation. A mixture of the chains induced aggregation (clumping) of human platelets separated from plasma proteins and treated with ADP. When individual chains of fibrinogen were tested, gamma-chain multimers caused platelet aggregation at a molar concentration comparable with that of intact human fibrinogen. The beta chain remained inactive, and the alpha chain was 1/4th to 1/5th as reactive as the gamma chain. Monospecific antibody fragments against the gamma chain inhibited binding of 125I-labeled fibrinogen to the human platelet receptor and blocked aggregation of platelets induced by ADP in the presence of fibrinogen or gamma-chain multimers. These results indicate that the gamma chain of human fibrinogen bears the main site for interaction with the platelet receptor.

Shadow-cast electron microscopy of fibrinogen with antibody fragments bound to specific regions

Specimens of human fibrinogen mixed with Fab fragments of antibodies that were specific for various portions of the fibrinogen molecule were tungsten shadow-cast and examined by electron microscopy. Typical trinodular fibrinogen molecules were observed when Fab fragments were omitted or when fragments from nonimmune sera were used. In the experimental fibrinogen-Fab preparations, a significant number of molecules were found with an extra nodule. In the case of Fab fragments from antibodies directed to fragment E, the additional nodule was attached to the central sphere of the fibrinogen molecule. Similarly, anti-fragment D preparations yielded molecules that were derivatized on the terminal spheres. Fragments from antibodies raised against a cyanogen bromide fragment of fibrinogen alpha chains (residues 241-476) also led to exclusive derivatization of the terminal domains, although in these cases the additional material was often separated discretely from the terminal sphere by a gap. These experiments confirm longstanding notions that the central domain of a trinodular fibrinogen molecule corresponds to the plasmin-derived fragment E and that the terminal spheres correspond to fragments D. Moreover, the carboxy-terminal two-thirds of alpha chains protrude from the extremities of the molecule, as had been inferred on the basis of indirect biochemical data.

Identification and characterization of a brain-specific antigen enriched in neonatal brain. II. Antigenic stability, species cross-reactivity and tumor cell association

NABSA is a brain-specific antigen enriched in neonatal brain. Microcomplement fixation was used to determine the extent of serological stability of NABSA towards heat denaturation and freeze-thaw denaturation. NABSA antigenic activity was progressively lost from neonatal and adult brain solutions incubated at temperatures above 40 degrees C. All activity was lost above 65 degrees C. Dilute solutions of NABSA were stable at 8 degrees C for at least two weeks and could be frozen and thawed in Tris.phosphate buffer at concentrations above 2 mg/ml with little loss of activity. NABSA was found in every vertebrate species tested. An unusually close structural similarity (a frequent characteristic of both brain-specific antigens and fetal antigens) was demonstrated by serological methods among the mammalian and avian NABSAs. NABSA was detected by microcomplement fixation analysis in 4 out of 16 rat and murine neural clonal tumor cell lines. There was no clear limitation of NABSA to a particular class of neural cell (as defined by the phenotypes of these tumor cell classes) or to rapidly dividing or stationary phase cells. NABSA may be a brain-specific oncofetal antigen (OFA-associated), since it is present in tumor cells of the nervous system and high levels are found in immature brain.