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At least 19 recordsLinked to original sources
PubMed2004

Overexpression of Smurf1 negatively regulates mouse embryonic lung branching morphogenesis by specifically reducing Smad1 and Smad5 proteins.

Early embryonic lung branching morphogenesis is regulated by many growth factor-mediated pathways. Bone morphogenetic protein 4 (BMP4) is one of the morphogens that stimulate epithelial branching in mouse embryonic lung explant culture. To further understand the molecular mechanisms of BMP4-regulated lung development, we studied the biological role of Smad-ubiquitin regulatory factor 1 (Smurf1), an ubiquitin ligase specific for BMP receptor-regulated Smads, during mouse lung development. The temporo-spatial expression pattern of Smurf1 in mouse embryonic lung was first determined by quantitative real-time PCR and immunohistochemistry. Overexpression of Smurf1 in airway epithelial cells by intratracheal introduction of recombinant adenoviral vector dramatically inhibited embryonic day (E) 11.5 lung explant growth in vitro. This inhibition of lung epithelial branching was restored by coexpression of Smad1 or by addition of soluble BMP4 ligand into the culture medium. Studies at the cellular level show that overexpression of Smurf1 reduced epithelial cell proliferation and differentiation, as documented by reduced PCNA-positive cell index and by reduced mRNA levels for surfactant protein C and Clara cell protein 10 expression. Further studies found that overexpression of Smurf1 reduced BMP-specific Smad1 and Smad5, but not Smad8, protein levels. Thus overexpression of Smurf1 specifically promotes Smad1 and Smad5 ubiquitination and degradation in embryonic lung epithelium, thereby modulating the effects of BMP4 on embryonic lung growth.

Animals↗
PubMed2006

Jun activation domain-binding protein 1 binds Smad5 and inhibits bone morphogenetic protein signaling.

OBJECTIVE: Bone morphogenetic proteins (BMPs) play an important role in the development and the homeostasis and pathology of cartilage tissue, particularly in the differentiation and anabolic activity of chondrocytes. The present study was undertaken to identify binding partners of the Smad proteins, the intracellular mediators of BMP activity, which might actively modify BMP signaling in chondrocytes. METHODS: Yeast 2-hybrid technology was used to screen a complementary DNA library, constructed from human adult articular cartilage, for molecular binding partners of Smad5, a major intracellular mediator of BMP signaling. Primary interaction partners were verified by coimmunoprecipitation, and the relevance of the interactions to BMP signaling was evaluated by transcriptional reporter assay. Additionally, messenger RNA expression analysis (conventional and quantitative polymerase chain reaction) and immunostaining were performed in adult normal and osteoarthritic articular cartilage. RESULTS: We identified a novel Smad5 interactor, Jun activation domain-binding protein 1 (Jab1), expressed in adult cartilage. The interaction was confirmed in coimmunoprecipitation experiments. Overexpression of Jab1 resulted in an attenuation of BMP-dependent transcriptional responses, suggesting that Jab1 acts as an inhibitor of BMP signaling. CONCLUSION: Jab1 is a newly identified intracellular (negative) modulator of BMP signaling in chondrocytes and other cells. Jab1 represents an interesting molecule for understanding anabolic signaling in chondrocytes, as well as a potential therapeutic target for anabolic activation. Most interestingly, Jab1 appears to crosslink the BMP and interleukin-1 pathways.

Aged↗
PubMed2004

Cartilage-derived morphogenetic proteins enhance the osteogenic protein-1-induced osteoblastic cell differentiation of C2C12 cells.

Previous studies have shown that osteogenic protein-1 (OP-1; also known as BMP-7) induces differentiation of the pluripotent mesenchymal cell line C2C12 into osteoblastic cells. OP-1 also alters the steady-state levels of messenger RNA (mRNA) encoding for the cartilage-derived morphogenetic proteins (CDMPs) in C2C12 cells. In the present study, the effects of exogenous CDMPs on bone cell differentiation induced by OP-1 in C2C12 cells were examined. Exogenous CDMP-1, -2, and -3 synergistically and dose-dependently enhanced OP-1 action in stimulating alkaline phosphatase (AP) activity and osteocalcin (OC) mRNA expression. AP staining studies revealed that the combination of OP-1 and CDMP enhanced OP-1 action by stimulating those cells that had responded to OP-1 and not by activating additional cells. The combination did not change the mRNA expression of the BMPs and their receptors. CDMP-1 enhanced the suppression of the OP-1-induced expression of the myogeneic differentiation regulator MyoD. CDMP-1 and OP-1 alone stimulated Smad5 protein expression, but the combination of OP-1 and CDMP-1 stimulated synergistically Smad5 protein expression. Thus, one mechanism of the observed synergy involved enhancement of the induced Smad5 protein expression. At the same protein concentration, CDMP-1 is most potent in enhancing OP-1 activity in inducing osteoblastic cell differentiation of C2C12 cells. CDMP-3 is about 80% as potent as CDMP-1, and CDMP-2 is the least potent (about 50% of CDMP-1).

Alkaline Phosphatase↗
PubMed1998

Intracellular signaling of osteogenic protein-1 through Smad5 activation.

Smad proteins play pivotal roles in the intracellular signaling of the multifunctional transforming growth factor-beta (TGF-beta) family members downstream of serine/threonine kinase type I and type II receptors. Smad2 and Smad3 are specific mediators of TGF-beta and activin, while Smadl and Smad5 are involved in bone morphogenetic protein-2 (BMP-2) and BMP-4 signaling. Here we report that osteogenic protein-1 (OP-1), also termed BMP-7, binds predominantly to BMPR-IB in the rat osteoprogenitor-like cell line, ROB-C26. Smad1, Smad5, and Smad8, but not Smad2 and Smad3, were found to stably interact with the kinase-deficient BMPR-IB after it was phosphorylated by the BMPR-II kinase. In ROB-C26 cells, which express Smad2, Smad3, Smad4, and Smad5, OP-1 was found to stimulate the phosphorylation of Smad5. Whereas transfection of wild-type Smad5 enhanced the OP-1-induced response, transfection of wild-type Smad2 had no effect on OP-1 signaling. A Smad5-2SA mutant, in which the two most carboxy-terminal serine residues were mutated to alanine residues, was found to act as a dominant negative inhibitor of OP-1-induced responses upon its transfection into various cell types, including ROB-C26 cells, in contrast to ectopic expression of a Smad2-2SA mutant which was without effect. Smad5, therefore, is a key component in the intracellular signaling of OP-1.

Amino Acid Sequence↗
PubMed2004

Smad5: signaling roles in hematopoiesis and osteogenesis.

Smad5 belongs to the receptor-activated Smad that function as intracellular signal transducers for transforming growth factor-beta superfamily. Smad5 protein is composed of N-terminal domain responsible for DNA-binding, C-terminal domain primarily required for protein-protein interaction, and the linker region containing motif essential for ubiquitinized degradation. Recent investigation reveals Smad5 as a negative regulator of embryonic hematopoiesis in a haploinsufficiency fashion, helping to elucidate the cytogenetic mechanism, by which Smad5 acts as leukemia suppressor. To date, osteogenesis governed by Smad5-mediated signals is delicately orchestrated by its comprehensive interactions with global osteogenesis regulator Runx2, transcriptional repressor Rob and Smad-interacting protein 1. Further delineation of its roles in hematopoiesis and osteogenesis will undoubtedly provide valuable insights into leukemia therapy and tissue engineering.

Bone Morphogenetic Protein Receptors↗
PubMed2003

Retinoic acid stimulates chondrocyte differentiation and enhances bone morphogenetic protein effects through induction of Smad1 and Smad5.

Whereas bone morphogenetic protein (BMP)-signaling events induce maturational characteristics in vitro, recent evidence suggests that the effects of other regulators might be mediated through BMP-signaling events. The present study examines the mechanism through which retinoic acid (RA) stimulates differentiation in chicken embryonic caudal sternal chondrocyte cultures. Both RA and BMP-2 induced expression of the chondrocyte maturational marker, colX, in chondrocyte cultures by 8 d. Though the RA effect was small, it synergistically enhanced the effect of BMP-2 on colX and phosphatase activity. Inhibition of either RA or BMP signaling, with selective inhibitors, interfered with the inductive effects of these agents but also inhibited the complementary pathway, demonstrating a codependence of RA and BMP signaling during chondrocyte maturation. BMP-2 did not enhance the effects of RA on an RA-responsive reporter construct, but RA enhanced basal activity and synergistically enhanced BMP-2 stimulation of the BMP-responsive chicken type X collagen reporter. A similar synergistic interaction between RA and BMP-2 was observed on colX expression. RA did not increase the expression of the type IA BMP receptor but did markedly up-regulate the expression of Smad1 and Smad5 proteins, important participants in the BMP pathway. Inhibition of RA signaling, with the selective inhibitor AGN 193109, blocked RA-mediated induction of the Smad proteins and chondrocyte differentiation. These findings demonstrate that RA induces the expression of BMP-signaling molecules and enhances BMP effects in chondrocytes.

Alkaline Phosphatase↗
PubMed2000

Differential expression of cSmad1 and cSmad5 in the primitive streak during chick embryo gastrulation.

Whole mount in situ hybridization was performed to determine the expression patterns of cSmad1 and cSmad5 during gastrulation stages (Hamburger-Hamilton 2-6) of chicken embryogenesis. It was revealed that cSmads 1 and 5 mRNAs are prominently expressed in the developing primitive streak. As determined from cross-sectional analysis of stage 4 embryos, most transcripts were associated with the ingressing mesoderm. However, whereas cSmad5 was expressed throughout the streak at all stages examined, the strongest expression of cSmad1 was confined to the posterior half of the streak.

Animals↗
PubMed2005

Bone morphogenetic protein signaling pathway plays multiple roles during gastrointestinal tract development.

The bone morphogenetic protein (BMP) signaling pathway plays an essential role during gastrointestinal (GI) tract development in vertebrates. In the present study, we use an antibody that recognizes the phosphorylated and activated form of Smad1, 5, and 8 to examine (by immunohistochemistry) the endogenous patterns of BMP signaling pathway activation in the developing GI tract. We show that the endogenous BMP signaling pathway is activated in the mesoderm, the endoderm, and the enteric nervous system (ENS) of the developing chick GI tract and is more widespread than BMP ligand expression patterns. Using an avian-specific retroviral misexpression technique to activate or inhibit BMP signaling pathway activity in the mesoderm of the gut, we show that BMP activity is required for the pattern, the development, and the differentiation of all three tissue types of the gut: mesoderm (that forms the visceral smooth muscle), endoderm (that forms the epithelium), and ectoderm (that forms the ENS). These results demonstrate that BMP signaling is activated in all the tissue layers of the GI tract during the development and plays a role during interactions and reciprocal communications of these tissue layers.

Animals↗
PubMed2001

The role of BMP signaling in outgrowth and patterning of the Xenopus tail bud.

Tail bud formation in Xenopus depends on interaction between a dorsal domain (dorsal roof) expressing lunatic fringe and Notch, and a ventral domain (posterior wall) expressing the Notch ligand Delta. Ectopic expression of an activated form of Notch, Notch ICD, by means of an animal cap graft into the posterior neural plate, results in the formation of an ectopic tail-like structure containing a neural tube and fin. However, somites are never formed in these tails. Here, we show that BMP signaling is activated in the posterior wall of the tail bud and is involved in the formation of tail somites from this region. Grafts into the posterior neural plate, in which BMP signaling is activated, will form tail-like outgrowths. Unlike the Notch ICD tails, the BMP tails contain well-organized somites as well as neural tube and fin, with the graft contributing to both somites and neural tube. Through a variety of epistasis-type experiments, we show that the most likely model involves a requirement for BMP signaling upstream of Notch activation, resulting in formation of the secondary neural tube, as well as a Notch-independent pathway leading to the formation of tail somites from the posterior wall.

Animals↗
PubMed2002

BMP pathways are involved in otic capsule formation and epithelial-mesenchymal signaling in the developing chicken inner ear.

The vertebrate inner ear consists of a complex labyrinth of epithelial cells that is surrounded by a bony capsule. The molecular mechanisms coordinating the development of the membranous and bony labyrinths are largely unknown. Previously, using avian retrovirus encoding Noggin (RCAS-Noggin) or beads soaked with Noggin protein, we have shown that bone morphogenetic proteins (BMPs) are important for the development of the otic epithelium in the chicken inner ear. Here, using two additional recombinant avian retroviruses, dominant negative and constitutively active forms of BMP receptors IB (BMPRIB), we show that BMPs, possibly acting through BMPRIB, are important for otic capsule formation. We also show that Bmp2 is strongly expressed in the prospective semicircular canals starting from the canal outpouch stage, suggesting that BMP2 plays an important role in canal formation. In addition, by correlating expression patterns of Bmps, their receptors, and localization of phosphorylated R-Smad (phospho R-Smad) immunoreactivity, an indicator of BMP activation, we show that BMPs emanating from the otic epithelium influence chondrogenesis of the otic capsule including the cartilage surrounding the semicircular canals.

Animals↗
PubMed2003

Expression of Smad4 and Smad7 in human thyroid follicular carcinoma cell lines.

Smad proteins have been shown tomediate the signal transduction pathway downstream of the transforming growth factor beta (TGFbeta). TGFbeta induces the phosphorylation of Smad2 and Smad3 which associate with Smad4 and translocate to the nucleus where they regulate gene transcription; besides these stimulatory Smads, the inhibitory Smads, Smad6 and Smad7, oppose signaling by blocking receptors and interrupting the phosphorylation of Smads2/3. The loss of TGFbeta-sensitivity, caused by inactivation of components of TGFbeta signaling, as Smad4, underlies a wide variety of human disorders, including cancer. In addition, the overexpression of the inhibitory Smad7, which prevents the phosphorylation of Smad2/3 and consequently inhibits TGFbeta signaling pathways, was observed in some diseases. In the present study we investigated the expression of Smad4 and Smad7 in thyroid cell lines (NPA papillary carcinoma, WRO follicular carcinoma and ARO anaplastic carcinoma) by RT-PCR and immunocytochemistry. Our results show that Smad4 was expressed in all thyroid cell lines and controls analyzed, differently from other classes of tumors where Smad4 expression was deleted. On the other hand, Smad7 was overexpressed in ARO anaplastic cell line, the most malignant follicular thyroid carcinoma. Our data suggest that the abrogation of the TGFbeta response by Smad7 overexpression may be a mechanism for the tumor aggressiveness observed in undifferentiated thyroid tumors.

Adenocarcinoma, Follicular↗
PubMed2006

Shedding of a soluble form of BMP receptor-IB controls bone cell responses to BMP.

Bone morphogenetic proteins (BMP) are members of the transforming growth factor beta (TGF-beta) superfamily and are involved in a wide variety of biological processes, including osteoblast differentiation and bone healing. The activities of the BMP are mediated by signal transduction via three BMP receptors (BMPR-IA, -IB and -II), which are thus essential for the biological actions of the BMP. Although the precise mechanisms which control the BMPR are not yet known, it is possible that post-translational regulation of these cell surface antigens by shedding could modulate their expression and thereby at least partly determine the response of the cells to the BMP. To test this possibility, the present study has examined whether soluble forms of the BMPR are produced by shedding from primary human bone cells in vitro. The results showed that human bone cells expressed both mRNA transcripts and antigens corresponding to BMPR-IA, -IB and -II. Incubation of the cells with phorbol 12-myristate 13-acetate (PMA), a potent inducer of proteolytic shedding, resulted in a pronounced decrease in cell surface expression of all three BMPR and, concurrently, the presence of "soluble" forms of these antigens in culture supernatants. Moreover, PMA treatment significantly reduced the level of BMP-2-induced Smad1/5 phosphorylation, a major early activation step in signal transduction initiated by BMP/BMPR interaction. It is notable that, while treatment of bone cells with interleukin-1beta (IL-1beta) also reduced the level of surface BMPR-IB, this inflammatory cytokine had no effect on BMPR-IA or -II levels, hence only the soluble form of BMPR-IB was detected. Furthermore, in addition to down-regulating BMP-2-induced Smad1/5 phosphorylation, IL-1beta also caused a reduction in the level of BMP-2-induced alkaline phosphatase activity and osteocalcin expression, both closely associated with bone cell differentiation. In conclusion, our study has provided evidence, for the first time, that BMPR can be modulated at the cell surface by the shedding of a soluble form of the antigen, resulting in a markedly diminished response to BMP-2 in vitro.

Blotting, Western↗
PubMed2006

BMP-6 inhibits human bone marrow B lymphopoiesis--upregulation of Id1 and Id3.

OBJECTIVE: In mammals, factors produced by bone marrow (BM) stromal cells are instrumental in orchestrating the developmental process of B lymphocytes. Bone morphogenetic proteins (BMPs) are multifunctional cytokines previously found to regulate hematopoietic stem cells. In the present study, we have explored the role of BMP-6 in human B progenitor cells. MATERIALS AND METHODS: In vitro B lymphopoiesis of CD10(+) B progenitor cells from human BM was evaluated in the presence or absence of BMP-6 in short- or long-term coculture on MS-5 stromal cells, by tracking CFSE-labeled CD10(+) B progenitor cells or by quantification of CD19(+) cells. DNA synthesis in the pre-B cell line Nalm-6 was measured by (3)H-thymidine incorporation. BMP-6-induced phosphorylation of Smad1/5/8 was determined by Western blot analysis, whereas elevation of Id1-Id4 mRNA levels and basal BMP-6 mRNA levels were measured by real-time and conventional RT-PCR, respectively. RESULTS: By in vitro coculture of CD10(+) B progenitor cells or monoculture of Nalm-6 cells, we found that BMP-6 inhibited B lymphopoiesis by impeding cell proliferation. Furthermore, in CD10(+) B progenitors as well as in Nalm-6 cells, BMP-6 rapidly induced phosphorylation of Smad1/5/8, followed by an upregulation of Id1 and Id3 mRNA levels. Finally, we demonstrated that human bone marrow stromal cells express BMP-6 mRNA whereas B progenitor cells did not. CONCLUSIONS: We suggest that BMP-6, produced by the BM, may participate to fine-tune the balance between proliferation, apoptosis, and differentiation in human B progenitor cells during BM B lymphopoiesis.

B-Lymphocytes↗
PubMed2003

AMH signaling: from receptor to target gene.

Anti-Müllerian hormone (AMH), also known as Müllerian inhibiting substance (MIS), is a member of the transforming growth factor beta (TGFbeta) superfamily and plays a crucial role during male sexual differentiation. Although the AMH type II receptor has been identified, the identity of the other signaling components has remained unknown. This review describes the identification of candidate AMH type I receptors and an AMH-target gene involved in Müllerian duct regression.

Activin Receptors, Type I↗
PubMed2003

Controlling cell fate by bone morphogenetic protein receptors.

Bone morphogenetic proteins (BMPs) are multifunctional proteins that regulate the fate of different cell types, including mesenchymal and endothelial cells. BMPs inhibit myogenic differentiation, but promote the differentiation of mesenchymal cells into osteoblasts. Furthermore, endothelial migration and tube formation are stimulated by BMPs. Like other members of the transforming growth factor-beta (TGF-beta) superfamily, BMPs elicit their cellular effects via specific types I and II serine/threonine receptors. The activated BMP type I receptor phosphorylates specific receptor-regulated (R)-Smad proteins, which assemble into heteromeric complexes with common partner (Co)-Smad4. Heteromeric Smad complexes efficiently translocate into the nucleus, where they regulate the transcription of target genes. Inhibitors of differentiation (Id) are genes that are specifically induced by BMPs in tissues of different origin. Promoter analysis of Id1 indicates three distinct sequence elements that are sufficient and essential for efficient BMP-induced activation. Furthermore, recent studies reveal an important effector function for Id1 in various BMP-induced biological responses.

Activin Receptors, Type I↗
PubMed2004

New insights into TGF-beta-Smad signalling.

Transforming growth factor beta (TGF-beta) initiates its diverse cellular responses by binding to and activating specific cell surface receptors that have intrinsic serine/threonine kinase activity. These activated TGF-beta receptors stimulate the phosphorylation of receptor-regulated Smad proteins, which in turn form complexes with Smad4 that accumulate in the nucleus and regulate the transcription of target genes. TGF-beta responses can be cell-type specific and are dependent on both the concentration of TGF-beta signalling components and the activity of other signal transduction pathways, which can either synergize with or antagonize the TGF-beta pathway. Recent research has provided insights into the specificity determinants of TGF-beta-Smad signalling, including combinatorial ligand-receptor associations, selective interactions between the Smads and other pathway components that are mediated through defined binding motifs, and the differential regulation of duration and intensity of signalling.

Active Transport, Cell Nucleus↗
PubMed2003

Bone morphogenetic protein signaling in articular chondrocyte differentiation.

Articular chondrocytes progressively undergo dedifferentiation into a spindle-shaped mesenchymal cellular phenotype in monolayers. Chondrocyte dedifferentiation is stimulated by retinoic acid. On the other hand, bone morphogenic proteins (BMPs) stimulate differentiation of chondrocytes. We examined the mechanism of effects of BMP in chondrocyte differentiation with use of a recombinant adenovirus vector system. Constitutively active forms of BMP type I receptors (BMPR-IA and BMPR-IB) and those of activin receptor-like kinase (ALK)-1 and ALK-2 maintained differentiation of chondrocytes in the presence of retinoic acid. The BMP receptor-regulated signaling substrates, Smad1/5, weakly induced chondrocyte differentiation; the effects of Smad1/5 were enhanced by BMP-7 treatment. Inhibitory Smad, Smad6, blocked increase of expression of chondrocyte markers by BMP-7 in a dose-dependent manner. SB202190, a p38 mitogen-activated protein kinase inhibitor, inhibited this effect of BMP-7; however, since SB202190 suppressed phosphorylation of Smad1/5, this may be due to blockade of BMP receptor activation. These results together strongly suggest that induction of chondrocyte differentiation by BMP-7 is regulated by Smad pathways.

Activin Receptors, Type I↗
PubMed2000

Negative regulation of BMP/Smad signaling by Tob in osteoblasts.

Bone morphogenetic protein (BMP) controls osteoblast proliferation and differentiation through Smad proteins. Here we show that Tob, a member of the emerging family of antiproliferative proteins, is a negative regulator of BMP/Smad signaling in osteoblasts. Mice carrying a targeted deletion of the tob gene have a greater bone mass resulting from increased numbers of osteoblasts. Orthotopic bone formation in response to BMP2 is elevated in tob-deficient mice. Overproduction of Tob represses BMP2-induced, Smad-mediated transcriptional activation. Finally, Tob associates with receptor-regulated Smads (Smad1, 5, and 8) and colocalizes with these Smads in the nuclear bodies upon BMP2 stimulation. The results indicate that Tob negatively regulates osteoblast proliferation and differentiation by suppressing the activity of the receptor-regulated Smad proteins.

Alleles↗