Distribution and characterization of specific cellular binding proteins for bone morphogenetic protein-2

Cellular Response of Anodized Titanium Surface by Poly(Lactide-co-Glycolide)/Bone Morphogenic Protein-2

Background

The purpose of this study is to examine physical characteristics of and initial biological properties to anodized titanium treated with poly(d,l-lactide-co-glycolide) (PLG) mixed with recombinant human bone morphogenic protein-2 (rhBMP-2).

Methods

Titanium specimens were prepared in groups of four as follows: group NC was anodized under 300 V as control; group PC was anodized then dropped and dried with solution 0.02 ml PLG; group D was anodized then dropped and dried with solution 0.02 ml PLG/rhBMP-2 (3.75 μg per disc); and group E was anodized then coated with 0.02 ml PLG/rhBMP-2 (3.75 μg per disc) by electrospray. Human osteoblastic-like sarcoma cells were cultured. Cell proliferation and alkaline phosphatase (ALP) activity test were carried out. Runx-2 gene was investigated by the reverse transcription-polymerase chain reaction. Immunofluorescence outcome of osteogenic proteins was observed.

Results

After 3 days, there were significantly higher proliferations compared rhBMP-2 loaded titanium discs with rhBMP-2 unloaded discs. The ALPase activity on rhBMP-2 loaded titanium discs was significantly higher than in rhBMP-2 unloaded discs. The expression level of Runx2 mRNA presented the highest on the PLG/rhBMP-2-coated surface.

Conclusion

PLG polymers mixed with rhBMP-2 might improve proliferation, differentiation and osteogenic protein formation of cells on the anodized titanium.

Combined defects in oxidative phosphorylation and fatty acid β-oxidation in mitochondrial disease

Mitochondria provide the main source of energy to eukaryotic cells, oxidizing fats and sugars to generate ATP. Mitochondrial fatty acid β-oxidation (FAO) and oxidative phosphorylation (OXPHOS) are two metabolic pathways which are central to this process. Defects in these pathways can result in diseases of the brain, skeletal muscle, heart and liver, affecting approximately 1 in 5000 live births. There are no effective therapies for these disorders, with quality of life severely reduced for most patients. The pathology underlying many aspects of these diseases is not well understood; for example, it is not clear why some patients with primary FAO deficiencies exhibit secondary OXPHOS defects. However, recent findings suggest that physical interactions exist between FAO and OXPHOS proteins, and that these interactions are critical for both FAO and OXPHOS function. Here, we review our current understanding of the interactions between FAO and OXPHOS proteins and how defects in these two metabolic pathways contribute to mitochondrial disease pathogenesis.

Robust and precise morphogen-mediated patterning: trade-offs, constraints and mechanisms

The patterning of many developing tissues is organized by morphogens. Genetic and environmental perturbations of gene expression, protein synthesis and ligand binding are among the sources of unreliability that limit the accuracy and precision of morphogen-mediated patterning. While it has been found that the robustness of morphogen gradients to the perturbation of morphogen synthesis can be enhanced by particular mechanisms, how such mechanisms affect robustness to other perturbations, such as to receptor synthesis for the same morphogen, has been little explored. Here, we investigate the interplay between the robustness of patterning to the changes in receptor synthesis and morphogen synthesis and to the effects of cell-to-cell variability. Our analysis elucidates the trade-offs and constraints that arise as a result of achieving these three performance objectives simultaneously in the context of simple, steady-state morphogen gradients formed by diffusion and receptor-mediated uptake. Analysis of the interdependence between length scales of patterning and these performance objectives reveals several potential mechanisms for mitigating such trade-offs and constraints. One involves downregulation of receptor synthesis in the morphogen source, while another involves the presence of non-signalling cell-surface morphogen-binding molecules. Both of these mechanisms occur in Drosophila wing discs during their patterning. We computationally elucidate how these mechanisms improve the robustness and precision of morphogen-mediated patterning.

Influence of p-cresol on the proteome of the autotrophic nitrifying bacterium Nitrosomonas eutropha C91

In this study, the effect of the organic micropollutant and known inhibitor of nitrification, p-cresol, was investigated on the metabolism of the ammonia oxidizing bacteria (AOB) Nitrosomonas eutropha C91 using MS-based quantitative proteomics. Several studies have demonstrated that AOB are capable of biotransforming a wide variety of aromatic compounds making them suitable candidates for bioremediation, yet the underlying molecular mechanisms are poorly described. The effect of two different concentrations of the aromatic micropollutant p-cresol (1 and 10 mg L(-1)) on the metabolism of N. eutropha C91, relative to a p-cresol absent control, was investigated. Though the rate of nitrification in N. eutropha C91 appeared essentially unaffected at both concentrations of p-cresol relative to the control, the expressional pattern of the proteins of N. eutropha C91 changed significantly. The presence of p-cresol resulted in the repressed expression of several key proteins related to N-metabolism, seemingly impairing energy production in N. eutropha C91, contradicting the observed unaltered rates of nitrification. However, the expression of proteins of the TCA cycle and proteins related to xenobiotic degradation, including a p-cresol dehydrogenase, was found to be stimulated by the presence of p-cresol. This indicates that N. eutropha C91 is capable of degrading p-cresol and that it assimilates degradation intermediates into the TCA cycle. The results reveal a pathway for p-cresol degradation and subsequent entry point in the TCA cycle in N. eutropha C91. The obtained data indicate that mixotrophy, rather than cometabolism, is the major mechanism behind p-cresol degradation in N. eutropha C91.

Respiratory supercomplexes: structure, function and assembly

The mitochondrial respiratory chain consists of 5 enzyme complexes that are responsible for ATP generation. The paradigm of the electron transport chain as discrete enzymes diffused in the inner mitochondrial membrane has been replaced by the solid state supercomplex model wherein the respiratory complexes associate with each other to form supramolecular complexes. Defects in these supercomplexes, which have been shown to be functionally active and required for forming stable respiratory complexes, have been associated with many genetic and neurodegenerative disorders demonstrating their biomedical significance. In this review, we will summarize the functional and structural significance of supercomplexes and provide a comprehensive review of their assembly and the assembly factors currently known to play a role in this process.

Coding polymorphisms of bone morphogenetic protein 2 contribute to the development of childhood IgA nephropathy

Bone morphogenetic proteins (BMPs) are multi-functional growth factors belonging to the transforming growth factor β (TGFB) superfamily and are important in both preservation of kidney function and resistance to injury. BMP2 is highly regulated in the kidney, and high affinity binding sites for BMP2 have been identified in kidney epithelial cells. BMP2 has been demonstrated to play various roles in the pathogenesis of renal diseases. However, the role of the BMP2 gene in glomerulonephritis has not been previously investigated. We aimed to evaluate the association of BMP2 gene polymorphisms with immunoglobulin A nephropathy (IgAN) in children. We evaluated 187 pediatric patients with biopsy-confimed IgAN and 262 healthy controls. Two coding single nucleotide polymorphisms (cSNPs) in the BMP2 gene [rs235768 (missense, Arg190Ser) and rs1049007 (synonymous, Ser87Ser)] were selected and genotyped by direct sequencing. Genotypes of rs1049007 were associated with childhood IgAN in the codominant model II (GG vs. AA) [p=0.02; OR (95% CI), 0.16 (0.04-0.70)] and in the recessive model [p=0.0023; OR (95% CI), 0.16 (0.04-0.69)]. We also found an association between rs235768 and IgAN in the codominant model II (TT vs. AA) [p=0.01; OR (95% CI), 0.08 (0.01-0.57)] and in the recessive model [p=0.0002; OR (95% CI), 0.07 (0.01-0.55)]. After Bonferroni correction, these associations of rs235768 and rs1049007 with IgAN risk remained significant. In the haplotype analysis, the TG haplotype [p=0.01; OR (95% CI), 6.76 (1.55-29.50) in the dominant model] and AA haplotype [p=0.01; OR (95% CI), 0.08 (0.01-0.59) in the recessive model] showed associations with IgAN. The BMP2 gene may contribute to susceptibility to IgAN in Korean children.

Heparan sulfate acts as a bone morphogenetic protein coreceptor by facilitating ligand-induced receptor hetero-oligomerization

Cell surface heparan sulfate (HS) not only binds several major classes of growth factors but also sometimes potentiates their activities--an effect usually termed "coreception." A view that coreception is due to the stabilization of growth factor-receptor interactions has emerged primarily from studies of the fibroblast growth factors (FGFs). Recent in vivo studies have strongly suggested that HS also plays an important role in regulating signaling by the bone morphogenetic proteins (BMPs). Here, we provide evidence that the mechanism of coreception for BMPs is markedly different from that established for FGFs. First, we demonstrate a direct, stimulatory role for cell surface HS in the immediate signaling activities of BMP2 and BMP4, and we provide evidence that HS-BMP interactions are required for this effect. Next, using several independent assays of ligand binding and receptor assembly, including coimmunoprecipitation, cross-linking, and fluorescence fluctuation microscopy, we show that HS does not affect BMP binding to type I receptor subunits but instead enhances the subsequent recruitment of type II receptor subunits to BMP-type I receptor complexes. This suggests a view of HS as a catalyst of the formation of signaling complexes, rather than as a stabilizer of growth factor binding.

Structure and organization of mitochondrial respiratory complexes: a new understanding of an old subject

The enzymatic complexes of the mitochondrial respiratory chain have been extensively investigated in their structural and functional properties. A clear distinction is possible today between three complexes in which the difference in redox potential allows proton translocation (complexes I, III, and IV) and those having the mere function to convey electrons to the respiratory chain. We also have a clearer understanding of the structure and function of most respiratory complexes, of their biogenesis and regulation, and of their capacity to generate reactive oxygen species. Past investigations led to the conclusion that the complexes are randomly dispersed and functionally connected by diffusion of smaller redox components, coenzyme Q and cytochrome c. More-recent investigations by native gel electrophoresis and single-particle image processing showed the existence of supramolecular associations. Flux-control analysis demonstrated that complexes I and III in mammals and I, III, and IV in plants kinetically behave as single units, suggesting the existence of substrate channeling. This review discusses conditions affecting the formation of supercomplexes that, besides kinetic advantage, have a role in the stability and assembly of the individual complexes and in preventing excess oxygen radical formation. Disruption of supercomplex organization may lead to functional derangements responsible for pathologic changes.

Receptor oligomerization and beyond: a case study in bone morphogenetic proteins

Background

Transforming growth factor (TGF)β superfamily members transduce signals by oligomerizing two classes of serine/threonine kinase receptors, termed type I and type II. In contrast to the large number of ligands only seven type I and five type II receptors have been identified in mammals, implicating a prominent promiscuity in ligand-receptor interaction. Since a given ligand can usually interact with more than one receptor of either subtype, differences in binding affinities and specificities are likely important for the generation of distinct ligand-receptor complexes with different signaling properties.

Results

In vitro interaction analyses showed two different prototypes of binding kinetics, 'slow on/slow off' and 'fast on/fast off'. Surprisingly, the binding specificity of ligands to the receptors of one subtype is only moderate. As suggested from the dimeric nature of the ligands, binding to immobilized receptors shows avidity due to cooperative binding caused by bivalent ligand-receptor interactions. To compare these in vitro observations to the situation in vivo, binding studies on whole cells employing homodimeric as well as heterodimeric bone morphogenetic protein 2 (BMP2) mutants were performed. Interestingly, low and high affinity binding sites were identified, as defined by the presence of either one or two BMP receptor (BMPR)-IA receptor chains, respectively. Both sites contribute to different cellular responses in that the high affinity sites allow a rapid transient response at low ligand concentrations whereas the low affinity sites facilitate sustained signaling but higher ligand concentrations are required.

Conclusion

Binding of a ligand to a single high affinity receptor chain functioning as anchoring molecule and providing sufficient complex stability allows the subsequent formation of signaling competent complexes. Another receptor of the same subtype, and up to two receptors of the other subtype, can then be recruited. Thus, the resulting receptor arrangement can principally consist of four different receptors, which is consistent with our interaction analysis showing low ligand-receptor specificity within one subtype class. For BMP2, further complexity is added by the fact that heterooligomeric signaling complexes containing only one type I receptor chain can also be found. This indicates that despite prominent ligand receptor promiscuity a manifold of diverse signals might be generated in this receptor limited system.

Action, localization and structure-function relationship of growth factors and their receptors in the prostate

Whereas the direct action of sex steroids, namely of androgens, on prostate cell division was questioned as early as in the 1970s, and remains so, the interest in prostatic growth factors (GFs) is rather recent but has expanded tremendously in the last five years. This lag period can be partly explained by the fact that, at the time, androgen receptors had just been discovered, and newly developed hormonal regimens or strategies to treat patients with prostate carcinoma (PCa) or epithelioma had generated great enthusiasm and hopes in the medical and scientific community. Another point to consider was the difficulty in maintaining prostate tissues in organ cultures and the relative novelty of culturing prostate epithelial cells in monolayers. Failures of sex steroids to elicit a direct positive response on prostate cell divisionin vitro, as seenin vivo, were interpreted as resulting from inappropriate models or culture conditions. However, the increasing number of reports confirming the lack of mitogenic activity of sex steroidsin vitro, coupled with the powerful mitogenic activity of GFs displayed in other systems, the discovery of GF receptors (GF-Rs), and the elucidation of their signalling pathways showing sex steroid receptors as potential substrates of GF-activated protein kinases gradually led to an increased interest in the putative role of GFs in prostate physiopathology. Of utmost importance was the recognition that hormone refractiveness was responsible for PCa progression, and for the poor outcome of patients with advanced disease under endocrine therapies. This problem remains a major issue and it raises several key questions that need to be solved at the fundamental and clinical levels.

Bone morphogenetic protein-2 antagonizes renal interstitial fibrosis by promoting catabolism of type I transforming growth factor-beta receptors

TGF-beta is a therapeutic target for renal fibrosis. Scientists have long sought ways to antagonize TGF-beta to ameliorate diabetic nephropathy. Bone morphogenetic protein (BMP-2) is a member of the TGF-beta superfamily and is highly regulated in the kidney. Thus, the role of BMP-2 was investigated in NRK-49F cells (rat fibroblasts). We showed that TGF-beta1 induces an increase in fibronectin. Treatment with exogenous BMP-2 or pCMV-BMP-2 significantly reversed the TGF-beta1-induced increase in fibronectin concomitant with a significant decrease in type I TGF-beta receptors (TGF-beta RI). Moreover, BMP-2 significantly shortened the half-life of TGF-beta RI. These results are related to proteosomal activation because MG132, a proteasome inhibitor, abolished BMP-2-mediated degradation of TGF-beta RI. This was confirmed because BMP-2 time course dependently enhanced the ubiquitination level of TGF-beta RI. In addition, Smads would seem to be involved in the interaction of BMP-2 and TGF-beta. We demonstrated that BMP-2 significantly reversed the TGF-beta1-induced increase in pSmad2/3 and reversed the TGF-beta1-induced decrease in inhibitory Smad7. Most importantly, Smad7 small interfering RNA abolished the BMP-2-induced decrease in TGF-beta RI. We evaluated the clinical efficacy of BMP-2 using unilateral ureteral obstruction rats. BMP-2 was administered ip for 7 d. In the unilateral ureteral obstruction kidneys, interstitial fibrosis was prominent. However, treatment with BMP-2 dramatically reduced Masson's trichrome staining (collagen) in the interstitial and tubular areas of the kidneys concomitantly with a reduction in TGF-beta RI. These results suggest that BMP-2 acts as a novel fibrosis antagonizing cytokine partly by down-regulating TGF-beta RI and Smads.

Biodegradable gelatin microparticles as delivery systems for the controlled release of bone morphogenetic protein-2

This work evaluated gelatin microparticles and biodegradable composite scaffolds for the controlled release of bone morphogenetic protein-2 (BMP-2) in vitro and in vivo. Gelatin crosslinking (10 and 40mM glutaraldehyde), BMP-2 dose (6 and 60ng BMP-2 per mg dry microparticles), buffer type (phosphate buffered saline (PBS) and collagenase-containing PBS), and gelatin type (acidic and basic) were investigated for their effects on BMP-2 release. Release profiles were also observed using poly(lactic-co-glycolic acid) (PLGA) microparticles with varying molecular weights (8300 and 57,500). In vitro and in vivo studies were conducted using radiolabeled BMP-2; the chloramine-T method was preferred over Bolton-Hunter reagent for radioiodination with this system. BMP-2 release from PLGA microparticles resulted in a moderate burst release followed by minimal cumulative release, while BMP-2 release from gelatin microparticles exhibited minimal burst release followed by linear release kinetics in vitro. Growth factor dose had a small effect on its normalized release kinetics probably because of an equilibrium between gelatin-bound and unbound BMP-2. Differences in release from acidic and basic gelatin microparticles may result from the different pretreatment conditions used for gelatin synthesis. The in vitro release kinetics for both gelatin microparticles alone and within composite scaffolds were dependent largely on the extent of gelatin crosslinking; varying buffer type served to confirm that controlled release relies on enzymatic degradation of the gelatin for controlled release. Finally, in vivo studies with composite scaffolds exhibited minimal burst and linear release up to 28 days. In summary, dose effects on BMP-2 release were found to be minimal while varying gelatin type and release medium can alter release kinetics. These results demonstrate that a systematic control of BMP-2 delivery from gelatin microparticles can be achieved by altering the extent of basic gelatin crosslinking.

Bone morphogenetic protein-2 is a negative regulator of hepatocyte proliferation downregulated in the regenerating liver

AIM: To characterize the expression and dynamic changes of bone morphogenetic protein (BMP)-2 in hepatocytes in the regenerating liver in rats after partial hepatectomy (PH), and examine the effects of BMP-2 on proliferation of human Huh7 hepatoma cells.

METHODS: Fifty-four adult male Wistar rats were randomly divided into three groups: A normal control (NC) group, a partial hepatectomized (PH) group and a sham operated (SO) group. To study the effect of liver regeneration on BMP-2 expression, rats were sacrificed before and at different time points after PH or the sham intervention (6, 12, 24 and 48 h). For each time point, six rats were used in parallel. Expression and distribution of BMP-2 protein were determined in regenerating liver tissue by Western blot analysis and immunohistochemistry. Effects of BMP-2 on cell proliferation of human Huh7 hepatoma cell line were assessed using an MTT assay.

RESULTS: In the normal liver strong BMP-2 expression was observed around the central and portal veins. The expression of BMP-2 decreased rapidly as measured by both immunohistochemistry and Western blot analysis. This decrease was at a maximum of 3.22 fold after 12 h and returned to normal levels at 48 h after PH. No significant changes in BMP-2 immunoreactivity were observed in the SO group. BMP-2 inhibited serum induced Huh7 cell proliferation.

CONCLUSION: BMP-2 is expressed in normal adult rat liver and negatively regulates hepatocyte proliferation. The observed down regulation of BMP-2 following partial hepatectomy suggests that such down regulation may be necessary for hepatocyte proliferation.

Mullerian Inhibiting Substance Regulates Androgen-Induced Gene Expression and Growth in Prostate Cancer Cells through a Nuclear Factor-κB-Dependent Smad-Independent Mechanism

Mullerian inhibiting substance (MIS), a member of the TGFβ superfamily, causes regression of the Mullerian duct in male embryos. The presence of MIS type II and type I receptors in tissues and cell lines derived from the prostate suggests that prostate is a likely target for MIS. In this report, we demonstrate that MIS inhibits androgen-stimulated growth of LNCaP cells and decreases their survival in androgen-deprived medium by preventing cell cycle progression and inducing apoptosis. Expression of dominant-negative Smad1 reversed the ability of MIS to decrease LNCaP cell survival in androgen-deprived medium but not androgen-stimulated growth, whereas abrogation of nuclear factor-κB (NFκB) activation ablated the suppressive effects of MIS on both androgen-stimulated growth and androgen-independent survival. The effect of MIS on androgen-induced growth was not due to changes in androgen receptor expression. However, MIS suppressed androgen-stimulated transcription of prostate-specific antigen; ablation of NFκB activation reversed MIS-mediated suppression of prostate-specific antigen. These observations suggest that MIS regulates androgen-induced gene expression and growth in prostate cancer cells through a NFκB-dependent but Smad1-independent mechanism. Thus, MIS, in addition to potentially regulating prostate growth indirectly by suppressing testicular testosterone synthesis, may also be a direct regulator of androgen-induced gene expression and growth in the prostate at the cellular level.

SOST/sclerostin, an osteocyte-derived negative regulator of bone formation

Sclerosteosis and Van Buchem disease are two closely related bone disorders characterized by progressive bone thickening due to increased bone formation. Sclerosteosis is associated with mutations in the SOST gene and Van Buchem disease with a 52 kb deletion downstream of the SOST gene that probably affects transcription of the gene. Expression of the gene product sclerostin in bone is restricted to osteocytes and it is a negative regulator of bone formation. It inhibits BMP-stimulated bone formation, but cannot antagonize all BMP responses. The exclusive bone phenotype of good quality of patients with sclerosteosis and Van Buchem disease and the specific localization of sclerostin make it an attractive target for the development of bone forming therapeutics.

The potential of endothelin antagonism as a therapeutic approach

Endothelin (ET) is a pivotal physiological regulator of blood pressure through its effects on blood vessels, heart, lung and kidneys, and the ET system can be overactive in disorders such as pulmonary hypertension, heart failure and renal disease. Such observations stimulated interest among scientists and pharmaceutical companies that have set up high-throughput screens to search for antagonists of ET receptors. The emerging compounds have been tested in animals with exciting results, leading to great hope that such inhibitors could be translated into human drugs with desirable therapeutic activities and few side effects. This review will describe the most relevant results obtained in experimental animals in a wide variety of disease conditions and focus on the data of selected compounds that have been employed in clinical trials.

Bone morphogenetic protein 2 is expressed by, and acts upon, mature epithelial cells in the colon

BACKGROUND AND AIMS

The recent findings of bone morphogenetic protein (BMP) receptor Ia mutations in juvenile polyposis and frequent Smad4 mutations in colon cancer suggest a role for BMPs in the colonic epithelium and colon cancer. We investigated the role of BMP2 in the colon.

METHODS

We assessed BMP receptor expression in cell lines using the reverse-transcribed polymerase chain reaction and immunoblotting. We investigated the effect of BMP2 on cell lines using the MTT assay and by immunoblotting for markers of differentiation, proliferation, and apoptosis. We assessed the expression of BMP2, its receptors, and signal transduction elements in mouse and human colon tissue using immunohistochemistry. We also investigated the effect of the BMP antagonist noggin in vivo in mice by assessing colon tissue with immunohistochemistry and immunoblotting. Finally, we investigated the expression of BMP2 in microadenomas from familial adenomatous polyposis patients.

RESULTS

BMP receptors (BMPR) Ia, BMPR Ib, and BMPR II are all expressed in colonic epithelial cell lines. BMP2 inhibits colonic epithelial cell growth in vitro, promoting apoptosis and differentiation and inhibiting proliferation. BMP2, BMPRIa, BMPRIb, BMPRII, phosphorylated Smad1, and Smad4 are expressed predominantly in mature colonocytes at the epithelial surface in normal adult human and mouse colon. Noggin inhibits apoptosis and proliferation in mouse colonic epithelium in vivo. BMP2 expression is lost in the microadenomas of familial adenomatous polyposis patients.

CONCLUSIONS

These data suggest that BMP2 acts as a tumor suppressor promoting apoptosis in mature colonic epithelial cells.

Endocytic trafficking during Drosophila development

During the last decade, many of the factors and mechanisms controlling membrane and protein trafficking in general and endocytic trafficking in particular have been uncovered. We have a detailed understanding of the different endocytic trafficking steps: plasma membrane budding, endocytic vesicle motility and fusion with the endosome, recycling, transcytosis and lysosomal degradation. The kinetics and trafficking pathway of many signaling receptors and the relevance of endocytic trafficking during signaling in many mammalian cultured cells are also well understood. However, only in recent years has the role of endocytic trafficking during cell-to-cell communication during development, i.e. during patterning, induction and lateral inhibition, begun to be explored. The contribution of Drosophila developmental genetics and cell biology has been fundamental in elucidating the essential role of endocytosis during these processes. Reviewed here are some of the recent developments on the role of endocytic trafficking during long- and short-range signaling and during lateral inhibition.

Protein kinase C-independent activation of protein kinase D is involved in BMP-2-induced activation of stress mitogen-activated protein kinases JNK and p38 and osteoblastic cell differentiation

An important role for JNK* and p38 has recently been discovered in the differentiating effect of bone morphogenetic protein 2 (BMP-2) on osteoblastic cells. In this study, we investigated the molecular mechanism by which BMP-2 activates JNK and p38 in MC3T3-E1 osteoblastic cells. Activation of JNK and p38 induced by BMP-2 was blocked by the protein kinase C/protein kinase D (PKC/PKD) inhibitor Go6976 but not by the related compound, Go6983, a selective inhibitor of conventional PKCs. Associated with this inhibitory effect of Go6976, BMP-2 induced a selective and a dose-dependent Ser916 phosphorylation/activation of PKD, which was also blocked by Go6976. In contrast to the recently described PKC-dependent molecular mechanism involved in activation of PKD by G protein-coupled receptor agonists, BMP-2 did not induce a phosphorylation of PKD on Ser744/748. To further document an implication of PKD in activation of JNK and p38 induced by BMP-2, we constructed MC3T3-E1 cells stably expressing PKD antisense oligonucleotide (AS-PKD). In AS-PKD clones having low PKD levels, activation of JNK and p38 by BMP-2, but not of Smad1/5, was markedly impaired compared with empty vector transfected (V-PKD) cells. Analysis of osteoblastic cell differentiation in AS-PKD compared with V-PKD cells showed that mRNA and protein expressions of alkaline phosphatase and osteocalcin induced by BMP-2 were markedly reduced in AS-PKD. In conclusion, results presented in this study indicate that BMP-2 can induce activation of PKD in osteoblastic cells by a PKC-independent mechanism and that this kinase is involved in activation of JNK and p38 induced by BMP-2. Thus, this pathway, in addition to Smads, appears to be essential for the effect of BMP-2 on osteoblastic cell differentiation.

Release of recombinant human bone morphogenetic protein 2 from a newly developed carrier

After implantation of a polymer-coated gelatin sponge (PGS) containing either 0.4 or 1.0 mg of 125I-rhBMP-2 for each 1 cm(3) of PGS into the right ulnar of rabbits, changes in the level of radioactivity at the implant site and in the blood were measured for 21 days after implantation, and the cumulative excretion ratio of radioactivity in the urine and feces was calculated. For both doses, radioactivity at the implant site was eliminated biphasically. The concentration of trichloroacetic acid (TCA)-precipitable radioactivity in the blood reached a maximum 6 h after implantation, at which time it was equivalent to 1.41% of the administered dose (0.4 mg/cm(3)). The remaining radioactivity was eliminated rapidly thereafter, falling below the detection limit within 48 h. The t(1/2alpha) was about 0.1 days, the t(1/2beta) was about 3 days, and the mean resident time (MRT) value was about 4 days. By 17 days after implantation, 88.1% of the administered radioactivity had been excreted in the urine, and 1.7% had been excreted in the feces. TCA precipitation test results indicated that most of the radioactivity excreted in urine was a low-molecular weight decomposition product. At 21 days after implantation, the radioactivity of the PGS implant site had declined to 0.5% of the administered amount. Autoradiographs of the implant site taken 28 days after implantation revealed that, at both doses, the residual radioactivity was confined to the area of the implanted PGS. These results indicate that PGS retains an appropriate amount of recombinant human bone morphogenetic protein 2 (rhBMP-2) at the orthotopically implanted site for at least 21 days enough to induce bone regeneration. Thus, PGS shows great clinical potential as a carrier for rhBMP-2.

Respiratory chain supercomplexes of mitochondria and bacteria

Respiratory chain complexes are fragments of larger structural and functional units, the respiratory chain supercomplexes or "respirasomes", which exist in bacterial and mitochondrial membranes. Supercomplexes of mitochondria and bacteria contain complexes III, IV, and complex I, with the notable exception of Saccharomyces cerevisiae, which does not possess complex I. These supercomplexes often are stable to sonication but sensitive to most detergents except digitonin. In S. cerevisiae, a major component linking complexes III and IV together is cardiolipin.In Paracoccus denitrificans, complex I itself is rather detergent-sensitive and thus could not be obtained in detergent-solubilized form so far. However, it can be isolated as part of a supercomplex. Stabilization of complex I by binding to complex III was also found in human mitochondria. Further functional roles of the organization in a supercomplex are catalytic enhancement by reducing diffusion distances of substrates or, depending on the organism, channelling of the substrates quinone and cytochrome c. This makes redox reactions less dependent of midpoint potentials of substrates, and permits electron flow at low degree of substrate reduction.A dimeric state of ATP synthase seems to be specific for mitochondria. Exclusively, monomeric ATP synthase was found in Acetobacterium woodii, in P. denitrificans, and in spinach chloroplasts.

Do morphogen gradients arise by diffusion?

Many patterns of cell and tissue organization are specified during development by gradients of morphogens, substances that assign different cell fates at different concentrations. Gradients form by morphogen transport from a localized site, but whether this occurs by simple diffusion or by more elaborate mechanisms is unclear. We attempt to resolve this controversy by analyzing recent data in ways that appropriately capture the complexity of systems in which transport, receptor interaction, endo- and exocytosis, and degradation occur together. We find that diffusive mechanisms of morphogen transport are much more plausible-and nondiffusive mechanisms much less plausible-than has generally been argued. Moreover, we show that a class of experiments, endocytic blockade, thought to effectively distinguish between diffusive and nondiffusive transport models actually fails to draw useful distinctions.

Endothelin receptor antagonists in cardiology clinical trials

Endothelin-1 (ET-1) is enhanced and has been demonstrated to be a prognostic marker in patients with advanced stages of heart failure, acute ischaemic syndromes, myocardial infarction and pulmonary hypertension. Activation of the endothelin (ET) system is associated with adverse haemodynamic consequences in patients with congestive heart failure and results in coronary vasoconstriction in patients with coronary artery disease (CAD). Moreover, ET-1 raises blood pressure, induces vascular and myocardial hypertrophy and acts as the natural counterpart of nitric oxide (NO), which exerts vasodilating, antithrombotic and antiproliferative effects. This article reviews recently completed and ongoing clinical trials examining the effects of ET receptor antagonists in patients with heart failure, CAD, arterial hypertension and pulmonary hypertension.

Quinol:fumarate oxidoreductases and succinate:quinone oxidoreductases: phylogenetic relationships, metal centres and membrane attachment

A comprehensive phylogenetic analysis of the core subunits of succinate:quinone oxidoreductases and quinol:fumarate oxidoreductases is performed, showing that the classification of the enzymes as type A to E based on the type of the membrane anchor fully correlates with the specific characteristics of the two core subunits. A special emphasis is given to the type E enzymes, which have an atypical association to the membrane, possibly involving anchor subunits with amphipathic helices. Furthermore, the redox properties of the SQR/QFR proteins are also reviewed, stressing out the recent observation of redox-Bohr effect upon haem reduction, observed for the Desulfovibrio gigas and Rhodothermus marinus enzymes, which indicates a direct protonation event at the haems or at a nearby residue. Finally, the possible contribution of these enzymes to the formation/dissipation of a transmembrane proton gradient is discussed, considering recent experimental and structural data.

Archaeal complex II: 'classical' and 'non-classical' succinate:quinone reductases with unusual features

Reversible succinate dehydrogenase (SDH) activities have been ubiquitously detected in organisms from the three domains of life. They represent constituents either of respiratory complexes II in aerobes, or of fumarate dehydrogenase complexes in anaerobes. The present review gives a survey on archaeal succinate:quinone oxidoreductases (SQRs) analyzed so far. Though some of these could be studied in detail enzymologically and spectroscopically, the existence of others has been deduced only from published genome sequences. Interestingly, two groups of enzyme complexes can be distinguished in Archaea. One group resembles the properties of SDHs known from bacteria and mitochondria. The other represents a novel class with an unusual iron-sulfur cluster in subunit B and atypical sequence motifs in subunit C which may influence electron transport mechanisms and pathways. This novel class of SQRs is discussed in comparison to the so-called 'classical' complexes. A phylogenetic analysis is presented suggesting a co-evolution of the flavoprotein-binding subunit A and subunit B containing the three iron-sulfur clusters.

Mullerian-inhibiting substance regulates NF-kappa B signaling in the prostate in vitro and in vivo

Mullerian-inhibiting substance (MIS) is a member of the transforming growth factor beta superfamily, a class of molecules that regulates growth, differentiation, and apoptosis in many cells. MIS type II receptor in the Mullerian duct is temporally and spatially regulated during development and becomes restricted to the most caudal ends that fuse to form the prostatic utricle. In this article, we have demonstrated MIS type II receptor expression in the normal prostate, human prostate cancer cell lines, and tissue derived from patients with prostate adenocarcinomas. MIS induced NF-kappaB DNA binding activity and selectively up-regulated the immediate early gene IEX-1S in both androgen-dependent and independent human prostate cancer cells in vitro. Dominant negative IkappaBalpha expression ablated both MIS-induced increase of IEX-1S mRNA and inhibition of growth, indicating that activation of NF-kappaB signaling was required for these processes. Androgen also induced NF-kappaB DNA binding activity in prostate cancer cells but without induction of IEX-1S mRNA, suggesting that MIS-mediated increase in IEX-1S was independent of androgen-mediated signaling. Administration of MIS to male mice induced IEX-1S mRNA in the prostate in vivo, suggesting that MIS may function as an endogenous hormonal regulator of NF-kappaB signaling and growth in the prostate gland.

Therapeutic potential of bone morphogenetic proteins

Recently, there has been substantial progress in the area of bone morphogenetic protein (BMP) research. This review serves as an up-to-date summary of the history of BMPs, the mechanisms of BMP signalling and the role of BMPs in adipose, kidney, liver, bone and nervous system. The potential of BMPs as therapeutic agents will also be discussed.

Altered growth responses of pulmonary artery smooth muscle cells from patients with primary pulmonary hypertension to transforming growth factor-beta(1) and bone morphogenetic proteins

BACKGROUND

Mutations in the type II receptor for bone morphogenetic protein (BMPR-II), a receptor member of the transforming growth factor-beta (TGF-beta) superfamily, underlie many cases of familial and sporadic primary pulmonary hypertension (PPH). We postulated that pulmonary artery smooth muscle cells (PASMCs) from patients with PPH might demonstrate abnormal growth responses to TGF-beta superfamily members.

METHODS AND RESULTS

For studies of (3)H-thymidine incorporation or cell proliferation, PASMCs (passages 4 to 8) were derived from main pulmonary arteries. In control cells, 24-hour incubation with TGF-beta(1) (10 ng/mL) or bone morphogenetic protein (BMP)-2, -4, and -7 (100 ng/mL) inhibited basal and serum-stimulated (3)H-thymidine incorporation, and TGF-beta(1) and BMPs inhibited the proliferation of serum-stimulated PASMCs. In contrast, TGF-beta(1) stimulated (3)H-thymidine incorporation (200%; P<0.001) and cell proliferation in PASMCs from PPH but not from patients with secondary pulmonary hypertension. In addition, BMPs failed to suppress DNA synthesis and proliferation in PASMCs from PPH patients. Reverse transcription-polymerase chain reaction of PASMC mRNA detected transcripts for type I (TGF-betaRI, Alk-1, ActRI, and BMPRIB) and type II (TGF-betaRII, BMPR-II, ActRII, ActRIIB) receptors. Receptor binding and cross-linking studies with (125)I-TGF-beta(1) confirmed that the abnormal responses in PPH cells were not due to differences in TGF-beta receptor binding. Mutation analysis of PASMC DNA failed to detect mutations in TGF-betaRII and Alk-1 but confirmed the presence of a mutation in BMPR-II in 1 of 5 PPH isolates.

CONCLUSIONS

We conclude that PASMCs from patients with PPH exhibit abnormal growth responses to TGF-beta(1) and BMPs and that altered integration of TGF-beta superfamily growth signals may contribute to the pathogenesis of PPH.

Germline mutations of the gene encoding bone morphogenetic protein receptor 1A in juvenile polyposis

Juvenile polyposis (JP; OMIM 174900) is an autosomal dominant gastrointestinal hamartomatous polyposis syndrome in which patients are at risk for developing gastrointestinal cancers. Previous studies have demonstrated a locus for JP mapping to 18q21.1 (ref. 3) and germline mutations in the homolog of the gene for mothers against decapentaplegic, Drosophila, (MADH4, also known as SMAD4) in several JP families. However, mutations in MADH4 are only present in a subset of JP cases, and although mutations in the gene for phosphatase and tensin homolog (PTEN) have been described in a few families, undefined genetic heterogeneity remains. Using a genome-wide screen in four JP kindreds without germline mutations in MADH4 or PTEN, we identified linkage with markers from chromosome 10q22-23 (maximum lod score of 4.74, straight theta=0.00). We found no recombinants using markers developed from the vicinity of the gene for bone morphogenetic protein receptor 1A (BMPR1A), a serine-threonine kinase type I receptor involved in bone morphogenetic protein (BMP) signaling. Genomic sequencing of BMPR1A in each of these JP kindreds disclosed germline nonsense mutations in all affected kindred members but not in normal control individuals. These findings indicate involvement of an additional gene in the transforming growth factor-beta (TGF-beta) superfamily in the genesis of JP, and document an unanticipated function for BMP in colonic epithelial growth control.

Experimental anterior spine fusion using bovine bone morphogenetic protein: a study in rabbits

We developed an experimental model to study the merit of bovine bone morphogenic protein (bBMP) injection into the intervertebral disc to induce anterior interbody fusion. A total of 24 rabbits, divided into three groups of 8 animals each, were used. One hundred and fifty microg of partially purified bBMP was employed in the first group and 10 microg bBMP in the second group. In the control group, a sham operation was performed. The animals were followed radiographically at weekly intervals and animals were killed 3, 6, and 12 weeks postoperatively. After sacrifice, a mechanical and histologic evaluation of fusion was performed. Results of radiographic and histologic evaluation showed bone formation, which had resulted in the bridging of adjacent endplates, in the 150-microg group. In the 10-microg group, new bone formation was less extensive. In the control group, intradiscal bone formation was seen in only 1 animal. Range of motion measurements on flexion/extension films showed significantly decreased motion in segments that were fused with 150-microg of BMP. This study demonstrated the utility of an experimental model which allowed investigation of how anterior spine fusion may be further studied. Intradiscal injection of BMP could ultimately play a role in the development of minimally invasive techniques for anterior spinal fusion.

Comparative morphology of the marrow sac

Electron microscopic techniques have been used to profile the morphologies of marrow sacs in different laboratory species. These structures all comprise a condensed layer of overlapping fibroblast-like stromal cells and apparently confine the medullary and endosteal osteoblast/lining cells to separate histiotypic compartments. There were some variations in the morphology of the sac cells in the different species. In rats, cats, and sheep, scanning electron microscopy (SEM) showed a seamless arrangement of marrow sac cells which resembled a thin, flat simple squamous epithelium; they displayed few intercellular cytoplasmic processes. In the rabbit and pigeon, the sac comprised a more woven, multilayered fabric of broadly elongate flat fibroblast-like cells which displayed numerous intercellular processes. Transmission electron microscopy (TEM) showed that all marrow sac cells were attenuated with elongated nuclei, a few small round mitochondria, and a sparse rough endoplasmic reticulum. In the majority of animals, the sac was one to two cell layers thick. The rabbit and pigeon sacs were multilayered, and never less than three to four cells deep. The cell layers were not closely apposed. Tight or gap junctions were absent at the points of intercellular contact. These morphological results suggest that marrow sacs are common elements of the vertebrate skeleton with species specific morphologies.

Characterization of receptors for osteogenic protein-1/bone morphogenetic protein-7 (OP-1/BMP-7) in rat kidneys

BACKGROUND

Osteogenic protein-1/bone morphogenetic protein-7 (OP-1/BMP-7), a member of the transforming growth factor-beta superfamily, has been shown to prevent kidney damage from ischemia/reperfusion injury in rats. The molecular events involved in OP-1 action on kidney are not yet understood.

METHODS

In this study, we evaluated the biodistribution of (125)I-labeled OP-1 in rat kidneys. Adult rats received a single intravenous injection of 250 microg (125)I-labeled OP-1 per kg body wt, a dose that was effective in protecting kidneys from ischemic injury. Tissue localization, in situ hybridization, and immunostaining with a specific receptor antibody were performed to identify OP-1 cellular targets. Also, isolated plasma membranes from kidney cortex and medulla regions were analyzed to identify and characterize receptor structural components that recognize OP-1.

RESULTS

At 10 and 180 minutes following injection, the relative uptake of (125)I-labeled OP-1 was consistently higher in kidney cortex than in medulla region. Upon autoradiography, kidney tissue sections revealed that OP-1 bound to the convoluted tubule epithelium, glomeruli, and collecting ducts. Moreover, in situ hybridization and immunostaining methods have shown localization of mRNA transcripts and the protein for BMP receptor type II in the cortex and medulla in similar areas as (125)I-labeled OP-1. Bulk membranes (enriched with plasma membranes) isolated from the cortex and medulla regions of kidney each bound specifically to (125)I-OP-1, and the binding of (125)I-labeled OP-1 was inhibited by unlabeled OP-1 in a dose-dependent manner. However, platelet-derived growth factor, transforming growth factor-beta, insulin-like growth factor, fibroblast growth factors, and other members of BMP family such as BMP-2 and cartilage-derived morphogenetic protein-1/growth and differentiation factor-5 (CDMP-1/GDF-5) failed to inhibit the binding of (125)I-labeled OP-1 to receptors, suggesting a high degree of specificity with which OP-1 bound to kidney receptors. Scatchard analysis of quantitative binding data indicated that the OP-1 receptors of kidney contained a single class of high-affinity binding sites for OP-1 with an association constant (Ka) of 2.26 x 109 mol/L-1 and a binding capacity of 1.01 pmol of OP-1 per mg membrane protein. When analyzed by a ligand blot technique, plasma membranes isolated from kidney cortex and medulla each showed the presence of a prominent specific band with a relative molecular mass (Mr) of 100 kD. Further analysis by Western blotting indicated that an antibody raised against BMP type II receptor effectively recognized the 100 kD OP-1 binding component of kidney plasma membranes.

CONCLUSIONS

We demonstrated, to our knowledge for the first time, the presence of membrane-bound, specific, high-affinity OP-1 receptors in rat kidney tissues, which are likely to mediate OP-1 actions in the kidney. The major OP-1-binding component of the kidney appears to be a long form of BMP type II receptor with a Mr of 100 kD. In vivo and in vitro evidence suggests that the cellular targets for OP-1 are convoluted tubule epithelium, glomeruli, and collecting ducts. OP-1 does not share receptor binding properties with other growth factors, including BMP-2 and CDMP-1, suggesting that its mode of action in kidney appears to be specific.

Gene therapy approaches for modulating bone regeneration

Following injury, bone has the ability to regenerate itself to a form and function nearly indistinguishable from the pre-injury state. However, if the injury is beyond a critical limit, recovery will not occur without therapeutic interventions. Autografts and implants with banked bone continue as the treatments of choice, although each exhibits limitations and liabilities. Alternatives have included the utilization of bone-graft substitutes that may incorporate bone derivatives and soluble signaling molecules such as mitogens and morphogens. In addition, an evolving treatment modality, gene therapy, offers an exciting avenue for bone regeneration. This review presents some of the current concepts for developing a rational gene therapy approach in bone regeneration.

Bone morphogenetic protein-9. An autocrine/paracrine cytokine in the liver

Bone morphogenetic proteins (BMPs) occupy important roles during development serving to direct cells through specific differentiation programs. While several BMPs are essential for embryonic viability, their significance in mediating intercellular communication in the context of adult organ systems remains largely unknown. In the adult rat we characterized the tissue- and cell-specific transcription and translation of BMP-9. Utilizing a ribonuclease protection assay, we determined that in the adult animal, BMP-9 expression occurs predominantly in the liver. Furthermore, we determined that the non-parenchymal cells of the liver, i.e. endothelial, Kupffer, and stellate cells, are the major sources of this message. Western analyses corroborate the ribonuclease protection assay results, confirming that LEC and KC contain an abundance of immunoreactive BMP-9. Using [(125)I]BMP-9, a receptor with specific binding affinity for BMP-9 was characterized in primary cultures of hepatic endothelial cells and Kupffer cells. BMP-9 binding to these cell types was observed to be fully reversible and highly specific for this ligand. Additionally, we demonstrate that BMP-9 is specifically internalized upon binding to its receptor. This may represent a novel BMP receptor and is the first to be characterized in primary cultures of mature liver non-parenchymal cells. Our results depict BMP-9 as a potential autocrine/paracrine mediator in the hepatic reticuloendothelial system.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

Osteogenesis with coral is increased by BMP and BMC in a rat cranioplasty

Autologous bone marrow cells (BMC), bone morphogenetic protein (BMP) and natural coral exoskeleton (CC) were used to enhance the repair of large skull bone defects in a craniotomy model. Nine millimeter calvarial defects were created in adult rats and were either left empty (control defects) or implanted with CC alone, CC-BMC, CC-BMP, or CC-BMC-BMP. After 1 or 2 months, osteogenesis was insufficient to allow union when defects were left empty or filled with CC. Addition of BMC alone to CC had no positive influence on osteogenesis at any time and increased CC resorption at 2 months (0.1 +/- 0.1 mm2 versus 0.5 +/- 0.3 mm2). In contrast addition of BM P or BM P/BMC to CC led to a significant increase in osteogenesis and allowed bone union after 1 month. At 2 months, the combination of CC-BM P-BMC was the most potent activator of osteogenesis. Filling a defect with CC-BMP-BMC resulted in significantly increased bone surface area (11 +/- 2.7 mm2) in comparison to filling a defect with CC-BMP (7.0 +/- 1.4 mm2), CC-BMC (3.5 +/- 1.1 mm2) or CC (4.5 +/- 0.4 mm2). CC resorption was significantly decreased in the presence of BMP with or without BMC at both times. These data are in accordance with the presence of progenitor cells in bone marrow that are inducible by BMP to the osteogenic pathway in a cranial site. The increase in material resorption in defects filled with CC-BMC could suggest that cells from the granulocyte-macrophage lineage survived the grafting procedure and were still active after 2 months.

Specific activation of the p38 mitogen-activated protein kinase signaling pathway and induction of neurite outgrowth in PC12 cells by bone morphogenetic protein-2

Bone morphogenetic protein (BMP)-2 has the capacity to induce the neuronal differentiation of PC12 cells. Unlike nerve growth factor, however, BMP-2 failed to induce the activation of the 41-/43-kDa mitogen-activated protein (MAP) kinase pathway in these cells. In contrast, BMP-2 characteristically induced the sustained activation of the p38 MAP kinase pathway. Pretreatment of PC12 cells with SB203580 inhibited the BMP-2-induced neurite outgrowth formation in a dose-dependent manner; this inhibition coincided well with the ability of SB203580 to inihibit the BMP-2-induced activation of the p38 MAP kinase pathway. Overexpression in PC12 cells of wild-type MAP kinase kinase (MKK)-6 enhanced the BMP-2-induced activation of p38 MAP kinase, whose activation correlated well with the ability of these cells to induce neurite outgrowth in response to BMP-2. Transient expression of kinase-negative forms of MKK3/6 inhibited the formation of neurite outgrowth in response to BMP-2. Furthermore, expression of constitutively active forms of MKK3/6 induced neurite outgrowth without BMP-2 stimulation, and SB203580 inhibited this induction. These results clearly indicate that activation of the p38 MAP kinase pathway is necessary for BMP-2-induced neuronal differentiation of PC12 cells. Our results also suggest that activation of the p38 MAP kinase pathway alone can induce the neuronal differentiation of PC12 cells.

Characterization of rhBMP-2 pharmacokinetics implanted with biomaterial carriers in the rat ectopic model

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a member of the bone morphogenetic protein family involved in de novo bone induction. Successful use of rhBMP-2 requires implantation with a biomaterial which can act as a scaffold for cell invasion for osteoinduction and retains rhBMP-2 at a site of implantation. This study was carried out to characterize rhBMP-2 pharmacokinetics from a variety of biomaterial carriers in a rat ectopic model. Retention of rhBMP-2 within carriers after 3 h was variable among the carriers (range, 75-10%), with collagenous sponges retaining the highest fraction of implanted dose. A gradual loss of rhBMP-2 was subsequently observed, the kinetics of which was strongly dependent on the implanted carrier. Collagenous carriers were observed to lose rhBMP-2 gradually from the implant site, whereas some of the mineral-based carriers retained a fraction of implanted rhBMP-2 within the implants. These differences in protein pharmacokinetics among carriers, in addition to their physicochemical nature, are expected to affect the biological activity of implanted rhBMP-2.

Bone morphogenetic protein-2 promotes survival and differentiation of striatal GABAergic neurons in the absence of glial cell proliferation

We examined the potential neurotrophic effects of bone morphogenetic protein (BMP)-2 on the survival and differentiation of neurons cultured from the rat developing striatum at embryonic day 16, a period during which the mRNAs for BMP-2 and its receptor subunits (types IA, IB, and II) were detected. BMP-2 exerted potent activity to promote the survival of striatal neurons and increased the number of surviving microtubule-associated protein-2-positive cells by 2.4-fold as compared with the control cultures after 4 days in vitro. Although basic fibroblast growth factor (bFGF) also showed relatively high activity to promote the survival of striatal neurons, transforming growth factor-beta1, -beta2, and -beta3, glial cell line-derived neurotrophic factor, or brain-derived neurotrophic factor promoted their survival weakly. Striatal neurons cultured in the presence of BMP-2 or bFGF possessed extensive neurite outgrowths, the majority of which were GABA-immunoreactive. Inhibition of glial cell proliferation by 5-fluorodeoxyuridine did not affect the capacity of BMP-2 to promote the survival of striatal GABAergic neurons. In contrast, the ability of bFGF to promote the survival of striatal neurons was inhibited significantly by the treatment of cells with 5-fluorodeoxyuridine. All these results suggest that BMP-2 exerts potent neurotrophic effects on the striatal GABAergic neurons in a glial cell-independent manner.

Bone morphogenetic protein-2 inhibits MAPK-dependent Elk-1 transactivation and DNA synthesis induced by EGF in mesangial cells

Bone morphogenetic protein-2 (BMP-2) is a member of the TGFbeta superfamily of growth and differentiation factors. We investigated the effect of BMP-2 on epidermal growth factor (EGF)-induced mitogenic signaling in kidney glomerular mesangial cells. BMP-2 dose-dependently inhibits EGF-induced DNA synthesis. Maximum effect was obtained at a concentration of 100 ng/ml. BMP-2 had no inhibitory effect on the EGF receptor (EGFR)-associated tyrosine kinase activity indicating that inhibition of DNA synthesis is due to regulation of post-receptor signaling event(s). EGF stimulates MAPK activity in mesangial cells in a time-dependent manner. Inhibition of MAPK by the MEK inhibitor PD098059 blocks EGF-induced DNA synthesis indicating the requirement of this enzyme activity in EGF-mediated mitogenic signaling. Furthermore, we show that exposure of mesangial cells to BMP-2 blocks EGF-induced MAPK activity which leads to phosphorylattion of Elk-1 transcription factor. Using a GAL-4 DNA binding-domain-Elk-1 transactivation domain fusion protein-based reporter assay, we demonstrate that BMP-2 inhibits EGF-induced Elk-1-mediated transcription. These data provide the first evidence that BMP-2 signaling in mesangial cells initiates a negative regulatory cross-talk with MAPK-based transcription to inhibit EGF-induced DNA synthesis.

Bone morphogenetic protein 2 inhibits platelet-derived growth factor-induced c-fos gene transcription and DNA synthesis in mesangial cells. Involvement of mitogen-activated protein kinase

Bone morphogenetic proteins (BMPs) play an important role in nephrogenesis. The biologic effect and mechanism of action of these proteins in the adult kidney has not yet been studied. We investigated the effect of BMP2, a member of these growth and differentiation factors, on mitogenic signal transduction pathways induced by platelet-derived growth factor (PDGF) in glomerular mesangial cells. PDGF is a growth and survival factor for these cells in vitro and in vivo. Incubation of mesangial cells with increasing concentrations of BMP2 inhibited PDGF-induced DNA synthesis in a dose-dependent manner with maximum inhibition at 250 ng/ml. Immune complex tyrosine kinase assay of PDGF receptor beta immunoprecipitates from lysates of mesangial cells treated with PDGF showed no inhibitory effect of BMP2 on PDGF receptor tyrosine phosphorylation. This indicates that the inhibition of DNA synthesis is likely due to postreceptor events. However, BMP2 significantly inhibited PDGF-stimulated mitogen-activated protein kinase (MAPK) activity that phosphorylates the Elk-1 transcription factor, a component of the ternary complex factor. Using a fusion protein-based reporter assay, we also show that BMP2 blocks PDGF-induced Elk-1-mediated transcription. Furthermore, we demonstrate that BMP2 inhibits PDGF-induced transcription of c-fos gene, a natural target of Elk-1 that normally forms a ternary complex that activates the serum response element of the c-fos gene. These data provide the first evidence that in mesangial cells, BMP2 signaling cross-talks with MAPK-based transcriptional events to inhibit PDGF-induced DNA synthesis. One target for this inhibition is the early response gene c-fos.

Type IIA procollagen containing the cysteine-rich amino propeptide is deposited in the extracellular matrix of prechondrogenic tissue and binds to TGF-beta1 and BMP-2

Type II procollagen is expressed as two splice forms. One form, type IIB, is synthesized by chondrocytes and is the major extracellular matrix component of cartilage. The other form, type IIA, contains an additional 69 amino acid cysteine-rich domain in the NH2-propeptide and is synthesized by chondrogenic mesenchyme and perichondrium. We have hypothesized that the additional protein domain of type IIA procollagen plays a role in chondrogenesis. The present study was designed to determine the localization of the type IIA NH2-propeptide and its function during chondrogenesis. Immunofluorescence histochemistry using antibodies to three domains of the type IIA procollagen molecule was used to localize the NH2-propeptide, fibrillar domain, and COOH-propeptides of the type IIA procollagen molecule during chondrogenesis in a developing human long bone (stage XXI). Before chondrogenesis, type IIA procollagen was synthesized by chondroprogenitor cells and deposited in the extracellular matrix. Immunoelectron microscopy revealed type IIA procollagen fibrils labeled with antibodies to NH2-propeptide at approximately 70 nm interval suggesting that the NH2-propeptide remains attached to the collagen molecule in the extracellular matrix. As differentiation proceeds, the cells switch synthesis from type IIA to IIB procollagen, and the newly synthesized type IIB collagen displaces the type IIA procollagen into the interterritorial matrix. To initiate studies on the function of type IIA procollagen, binding was tested between recombinant NH2-propeptide and various growth factors known to be involved in chondrogenesis. A solid phase binding assay showed no reaction with bFGF or IGF-1, however, binding was observed with TGF-beta1 and BMP-2, both known to induce endochondral bone formation. BMP-2, but not IGF-1, coimmunoprecipitated with type IIA NH2-propeptide. Recombinant type IIA NH2-propeptide and type IIA procollagen from media coimmunoprecipitated with BMP-2 while recombinant type IIB NH2-propeptide and all other forms of type II procollagens and mature collagen did not react with BMP-2. Taken together, these results suggest that the NH2-propeptide of type IIA procollagen could function in the extracellular matrix distribution of bone morphogenetic proteins in chondrogenic tissue.

Constitutive activation of the 41-/43-kDa mitogen-activated protein kinase signaling pathway in human tumors

The 41-kDa and 43-kDa mitogen-activated protein (MAP) kinases play a pivotal role in the mitogenic signal transduction pathway and are essential components of the MAP kinase cascade, which includes MAP kinase kinase (MEK) and Raf-1. As aberrant activation of signal transducing molecules such as Ras and Raf-1 has been linked with cancer, we examined whether constitutive activation of the 41-/43-kDa MAP kinases is associated with the neoplastic phenotype of 138 tumor cell lines and 102 primary tumors derived from various human organs. Constitutive activation of the MAP kinases was observed in 50 tumor cell lines (36.2%) in a rather tissue-specific manner: cell lines derived from pancreas, colon, lung, ovary and kidney showed especially high frequencies with a high degree of MAP kinase activation, while those derived from brain, esophagus, stomach, liver and of hematopoietic origin showed low frequencies with a limited degree of MAP kinase activation. We also detected constitutive activation of the 41-/43-kDa MAP kinases in a relatively large number of primary human tumors derived from kidney, colon and lung tissues but not from liver tissue. Many tumor cells, in which point mutations of ras genes were detected, showed constitutive activation of MAP kinases, however, there were also many exceptions to this observation. In contrast, the activation of the 41-/43-kDa MAP kinases was accompanied by the activation of Raf-1 in the majority of tumor cells and was completely associated with the activation of MEK and p90rsk in all the tumor cells examined. These results suggest that the constitutive activation of 41-/43-kDa MAP kinases in tumor cells is not due to the disorder of MAP kinases themselves, but is due to the disorder of Raf-1, Ras, or some other signaling molecules upstream of Ras.