Smad1 interacts with homeobox DNA-binding proteins in bone morphogenetic protein signaling

Affinity-tagged SMAD1 and SMAD5 mouse lines reveal transcriptional reprogramming mechanisms during early pregnancy

Endometrial decidualization, a prerequisite for successful pregnancies, relies on transcriptional reprogramming driven by progesterone receptor (PR) and bone morphogenetic protein (BMP)-SMAD1/SMAD5 signaling pathways. Despite their critical roles in early pregnancy, how these pathways intersect in reprogramming the endometrium into a receptive state remains unclear. To define how SMAD1 and/or SMAD5 integrate BMP signaling in the uterus during early pregnancy, we generated two novel transgenic mouse lines with affinity tags inserted into the endogenous SMAD1 and SMAD5 loci (Smad1HA/HA and Smad5PA/PA). By profiling the genome-wide distribution of SMAD1, SMAD5, and PR in the mouse uterus, we demonstrated the unique and shared roles of SMAD1 and SMAD5 during the window of implantation. We also showed the presence of a conserved SMAD1, SMAD5, and PR genomic binding signature in the uterus during early pregnancy. To functionally characterize the translational aspects of our findings, we demonstrated that SMAD1/5 knockdown in human endometrial stromal cells suppressed expressions of canonical decidual markers (IGFBP1, PRL, FOXO1) and PR-responsive genes (RORB, KLF15). Here, our studies provide novel tools to study BMP signaling pathways and highlight the fundamental roles of SMAD1/5 in mediating both BMP signaling pathways and the transcriptional response to progesterone (P4) during early pregnancy.

Affinity-tagged SMAD1 and SMAD5 mouse lines reveal transcriptional reprogramming mechanisms during early pregnancy

Endometrial decidualization, a prerequisite for successful pregnancies, relies on transcriptional reprogramming driven by progesterone receptor (PR) and bone morphogenetic protein (BMP)-SMAD1/SMAD5 signaling pathways. Despite their critical roles in early pregnancy, how these pathways intersect in reprogramming the endometrium into a receptive state remains unclear. To define how SMAD1 and/or SMAD5 integrate BMP signaling in the uterus during early pregnancy, we generated two novel transgenic mouse lines with affinity tags inserted into the endogenous SMAD1 and SMAD5 loci (Smad1HA/HA and Smad5PA/PA). By profiling the genome-wide distribution of SMAD1, SMAD5, and PR in the mouse uterus, we demonstrated the unique and shared roles of SMAD1 and SMAD5 during the window of implantation. We also showed the presence of a conserved SMAD1, SMAD5, and PR genomic binding signature in the uterus during early pregnancy. To functionally characterize the translational aspects of our findings, we demonstrated that SMAD1/5 knockdown in human endometrial stromal cells suppressed expressions of canonical decidual markers (IGFBP1, PRL, FOXO1) and PR-responsive genes (RORB, KLF15). Here, our studies provide novel tools to study BMP signaling pathways and highlight the fundamental roles of SMAD1/5 in mediating both BMP signaling pathways and the transcriptional response to progesterone (P4) during early pregnancy.

Critical roles of microRNA-196 in normal physiology and non-malignant diseases: Diagnostic and therapeutic implications

MicroRNAs (miRNAs) have emerged as a critical component of regulatory networks that modulate and fine-tune gene expression in a post-transcriptional manner. The microRNA-196 family is encoded by three loci in the human genome, namely hsa-mir-196a-1, hsa-mir-196a-2, and hsa-mir-196b. Increasing evidence supports the roles of different components of this miRNA family in regulating key cellular processes during differentiation and development, ranging from inflammation and differentiation of stem cells to limb development and remodeling and structure of adipose tissue. This review first discusses about the genomic context and regulation of this miRNA family and then take a bird's eye view on the updated list of its target genes and their biological processes to obtain insights about various functions played by members of the microRNA-196 family. We then describe evidence supporting the involvement of the human microRNA-196 family in regulating critical cellular processes both in physiological and non-malignant inflammatory conditions, highlighting recent seminal findings that carry implications for developing novel therapeutic or diagnostic strategies.

PfSMAD1/5 Can Interact with PfSMAD4 to Inhibit PfMSX to Regulate Shell Biomineralization in Pinctada fucata martensii

The BMP2 signal transduced by SMAD1/5 plays an important role in osteoblast differentiation and bone formation. Shell formation of Pinctada fucata martensii is a typical biomineralization process that is similar to that of teeth/bone formation. However, whether the Pinctada fucata BMP2 (PfBMP2) signal transduced by PfSMAD1/5 occurs in P. f. martensii, how the PfBMP2 signal is transduced by PfSMAD1/5, and how PfSMAD1/5 regulates the biomineralization process in this species and other shellfish are poorly understood. Therefore, injection experiments of recombinant PfBMP2 and inhibitor dorsomorphin revealed that PfSMAD1/5 can transduce PfBMP2 signals. Subcellular localization and bimolecular fluorescence complementation assays indicated that PfSMAD1/5 phosphorylated by PfBMPR1b interacts with PfSMAD4 in the cytoplasm to form a complex, which translocates to the nucleus to transduce PfBMP2 signals. Co-immunoprecipitation and luciferase assays revealed that PfSMAD1/5 may interact with PfMSX to dislodge it from its binding element, resulting in initiation of mantle gene transcription. The in vivo functional assay showed that knockdown of PfMSAD1/5 decreased expression of shell matrix genes and disordered the nacreous layer, and the correlation assay of shell regeneration showed the concomitant expression pattern of PfSMAD1/5 and shell matrix genes. Together, these data showed that PfSMAD1/5 can transduce PfBMP2 signals to regulate shell biomineralization in P. f. martensii, which illustrated conservation of the BMP2-SMAD signal pathway among invertebrates. Particularly, the results suggest that there is only one PfMSX gene, which functions like the Hox gene in vertebrates, that interacts with PfSMAD1/5 in a protein-protein action form and plays the role of transcription repressor.

High Expression of MicroRNA-196a is Associated with Progression of Hepatocellular Carcinoma in Younger Patients

MicroRNAs are small RNAs involved in various biological processes and cancer metastasis. miR-196a was associated with aggressive behaviors in several cancers. The role of miR-196a in hepatocellular carcinoma (HCC) metastasis remains unknown. This study aimed to examine the role of miR-196a in HCC progression. Expression of miR-196a was measured in 83 human HCC samples. The HCC patients with high miR-196a expression had younger ages, lower albumin levels, higher frequency with alpha-fetoprotein (AFP) levels ≥20 ng/mL, more macrovascular invasion, and non-early stages. Kaplan-Meier analysis showed that high miR-196a expression was associated with lower recurrence-free survival. Knockdown of miR-196a decreased transwell invasiveness, sphere formation, transendothelial invasion, and Slug, Twist, Oct4, and Sox2 expression, suppressed angiogenesis, and reduced sizes of xenotransplants and number of pulmonary metastasis. Down-regulation of miR-196a decreased Runx2 and osteopontin (OPN) levels. Knockdown of Runx2 in vitro resulted in comparable phenotypes with miR-196a down-regulation. Restoration of Runx2 in miR-196a-knockdown HCC reverted tumor phenotypes. This study showed that high expression of miR-196a is associated with HCC progression in a subset of younger patients. miR-196a mediates HCC progression via upregulation of Runx2, OPN, epithelial-mesenchymal transition (EMT) regulators, and stemness genes. We proposed that miR-196a can be used as a prognostic marker and a potential therapeutic target.

The Application of microRNAs in Biomaterial Scaffold-Based Therapies for Bone Tissue Engineering

In recent years, the application of microRNAs (miRNAs) or anti-microRNAs (anti-miRNAs) that can induce expression of the runt-related transcription factor 2 (RUNX2), a master regulator of osteogenesis, has been investigated as a promising alternative bone tissue engineering strategy. In this review, biomaterial scaffold-based applications that have been used to deliver cells expressing miRNAs or anti-miRNAs that induce expression of RUNX2 for bone tissue engineering are discussed. An overview of the components of the scaffold-based therapies including the miRNAs/anti-miRNAs, cell types, gene delivery vectors, and scaffolds that have been applied are provided. To date, there have been nine miRNAs/anti-miRNAs (i.e., miRNA-26a, anti-miRNA-31, anti-miRNA-34a, miRNA-135, anti-miRNA-138, anti-miRNA-146a, miRNA-148b, anti-miRNA-221, and anti-miRNA-335) that have been incorporated into scaffold-based bone tissue engineering applications and investigated in an in vivo bone critical-sized defect model. For all of the biomaterial scaffold-based miRNA therapies that have been developed thus far, cells that are transfected or transduced with the miRNA/anti-miRNA are loaded into the scaffolds and implanted at the site of interest instead of locally delivering the miRNA/anti-miRNAs directly from the scaffolds. Thus, future work may focus on developing biomaterial scaffolds to deliver miRNAs or anti-miRNAs into cells in vivo.

Homeobox C8 is a transcriptional repressor of E-cadherin gene expression in non-small cell lung cancer

Loss of E-cadherin expression is a hallmark of epithelial-mesenchymal transition (EMT) in tumor progression. Because previous findings suggested that homeobox C8 (HOXC8) promotes EMT in non-small-cell lung cancer (NSCLC), we investigated whether E-cadherin is a target of HOXC8 protein. In this study, we report that HOXC8 binds to the E-cadherin promoter and acts as a transcriptional repressor to regulate E-cadherin transcription in NSCLC. We further show that loss of E-cadherin leads to an increase in anchorage-independent growth and migration of NSCLC cells, and the inhibitory effects mediated by HOXC8 knockdown can be largely rescued by reduction of E-cadherin expression, suggesting that the HOXC8-E-cadherin pathway is involved in lung cancer progression. Moreover, analysis of E-cadherin and HOXC8 expression indicates that expression of HOXC8 is strongly correlated with loss of E-cadherin expression, and high HOXC8 / low E-cadherin expression is significantly correlated with poor survival for lung cancer patients. Taken together, these data indicate that E-cadherin is a target gene of HOXC8 and that the loss of E-cadherin promotes the growth and migration of NSCLC.

Microcalcification and BMP-2 in breast cancer: correlation with clinicopathological features and outcomes

Background

Microcalcification is a very important diagnostic information in breast cancer. The purpose of this study was to determine the relationship of clinicopathological features and prognosis of breast cancer with microcalcification and to detect biomarkers related to the possible mechanisms of microcalcifications.

Patients and methods

All 529 subjects with microcalcifications were selected from patients who had been examined using breast mammography. The control group did not have detectable microcalcifications, and was matched in a ratio of 1:3. The clinicopathological factors, progression-free survival (PFS), and overall survival were evaluated by SPSS.

Results

There was a significant difference in tumor size between the two groups, with larger tumors in the calcification group than the control group, and the proportion of patients in the calcification group with tumors of >5 cm was 20.4% vs 17.2% in the control group (P=0.041). The proportion of patients with lymph node metastasis in the calcification group was higher than that of the control group (35% vs 27.9%, P=0.027). The recurrence rate in ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) patients with microcalcification was higher than that in the control group (P=0.035 and 0.044). BMP-2 expression was higher in breast cancer tissues, especially in breast cancer tissues with microcalcifications. The recurrence rate in the BMP-2(+) group was higher than that in the BMP-2(-) group both in DCIS and IDC (P=0.044 and 0.049). Microcalcifications and the positive expression of BMP-2 were independent factors affecting the PFS of the breast cancer patients.

Conclusion

Through the analysis of this study, it was found that the prognosis of the patients with microcalcification was relatively poor. BMP-2 was highly expressed in the breast cancer with microcalcification and was associated with poor prognosis.

Alteration of the exDNA profile in blood serum of LLC-bearing mice under the decrease of tumour invasion potential by bovine pancreatic DNase I treatment

Taking into account recently obtained data indicating the participation of circulating extracellular DNA (exDNA) in tumorigenesis, enzymes with deoxyribonucleic activity have again been considered as potential antitumour and antimetastatic drugs. Previously, using murine Lewis lung carcinoma and hepatocellular carcinoma A1 tumour models, we have shown the antimetastatic activity of bovine DNase I, which correlates with an increase of DNase activity and a decrease of exDNA concentration in the blood serum of tumour-bearing mice. In this work, using next-generation sequencing on the ABS SOLiD^™ 5.500 platform, we performed a search for molecular targets of DNase I by comparing the exDNA profiles of healthy animals, untreated animals with Lewis lung carcinoma (LLC) and those with LLC treated with DNase I. We found that upon DNase I treatment of LLC-bearing mice, together with inhibition of metastasis, a number of strong alterations in the patterns of exDNA were observed. The major differences in exDNA profiles between groups were: i) the level of GC-poor sequences increased during tumour development was reduced to that of healthy mice; ii) levels of sequences corresponding to tumour-associated genes Hmga2, Myc and Jun were reduced in the DNase I-treated group in comparison with non-treated mice; iii) 224 types of tandem repeat over-presented in untreated LLC-bearing mice were significantly reduced after DNase I treatment. The most important result obtained in the work is that DNase I decreased the level of B-subfamily repeats having homology to human ALU repeats, known as markers of carcinogenesis, to the level of healthy animals. Thus, the obtained data lead us to suppose that circulating exDNA plays a role in tumour dissemination, and alteration of multiple molecular targets in the bloodstream by DNase I reduces the invasive potential of tumours.

Embigin, regulated by HOXC8, plays a suppressive role in breast tumorigenesis

The transmembrane glycoprotein embigin (EMB) belongs to the immunoglobulin superfamily (IgSF) and a number of IgSF members have been identified as biomarkers for cancer progression. In this study, we show that embigin is transcriptionally regulated by Homeobox C8 (HOXC8) in breast cancer cells and embigin expression suppresses breast tumorigenesis. With aid of Western blot, luciferase reporter gene assay and chromatin immunoprecipitation, we reveal that HOXC8 binds to the EMB promoter at the region of nucleotides -2303 to -2315 and acts as a transcription inhibitor to suppress embigin expression. Depletion of embigin leads to increase in proliferation, anchorage-independent growth and migration of breast cancer cells, and the inhibitory effects mediated by HOXC8 knockdown on breast tumorigenesis can be largely rescued by depletion of embigin expression in breast cancer cells, suggesting that HOXC8 regulates breast tumorigenesis, at least partly, through regulating embigin expression. Moreover, we show that loss of embigin promotes proliferation, anchorage-independent growth, and migration ability of normal mammary epithelial MCF10A cells. The analyses of publically available human breast tumor microarray gene expression database show that low embigin levels correlate with short survival of breast tumor patients, particularly with basal-like tumor patients, and embigin expression is low specifically in patients with basal-like, ER-/HER2- tumors. Taken together, our study demonstrates that low/loss of embigin plays an important role in the progression of breast tumors.

Genes Frequently Coexpressed with Hoxc8 Provide Insight into the Discovery of Target Genes

Identifying Hoxc8 target genes is at the crux of understanding the Hoxc8-mediated regulatory networks underlying its roles during development. However, identification of these genes remains difficult due to intrinsic factors of Hoxc8, such as low DNA binding specificity, context-dependent regulation, and unknown cofactors. Therefore, as an alternative, the present study attempted to test whether the roles of Hoxc8 could be inferred by simply analyzing genes frequently coexpressed with Hoxc8, and whether these genes include putative target genes. Using archived gene expression datasets in which Hoxc8 was differentially expressed, we identified a total of 567 genes that were positively coexpressed with Hoxc8 in at least four out of eight datasets. Among these, 23 genes were coexpressed in six datasets. Gene sets associated with extracellular matrix and cell adhesion were most significantly enriched, followed by gene sets for skeletal system development, morphogenesis, cell motility, and transcriptional regulation. In particular, transcriptional regulators, including paralogs of Hoxc8, known Hox co-factors, and transcriptional remodeling factors were enriched. We randomly selected Adam19, Ptpn13, Prkd1, Tgfbi, and Aldh1a3, and validated their coexpression in mouse embryonic tissues and cell lines following TGF-β2 treatment or ectopic Hoxc8 expression. Except for Aldh1a3, all genes showed concordant expression with that of Hoxc8, suggesting that the coexpressed genes might include direct or indirect target genes. Collectively, we suggest that the coexpressed genes provide a resource for constructing Hoxc8-mediated regulatory networks.

HOXC8 promotes breast tumorigenesis by transcriptionally facilitating cadherin-11 expression

Cell-cell adhesion molecule cadherin-11(CDH11) is preferentially expressed in basal-like breast cancer cells and facilitates breast cancer cell migration by promoting small GTPase Rac activity. However, how the expression of CDH11 is regulated in breast cancer cells is not understood. Here, we show that CDH11 is transcriptionally controlled by homeobox C8 (HOXC8) in human breast cancer cells. HOXC8 serves as a CDH11-specific transcription factor and binds to the site of nucleotides −196 to −191 in the CDH11 promoter. Depletion of HOXC8 leads to the decrease in anchorage-independent cell growth, cell migration/invasion and spontaneous metastasis of breast cancer cells; however, suppressed tumorigenic events were fully rescued by ectopic CDH11 expression in HOXC8-knockdown cells. These results indicate that HOXC8 impacts breast tumorigenesis through CDH11. The analysis of publically available human breast tumor microarray gene expression database demonstrates a strong positive linear association between HOXC8 and CDH11 expression (ρ = 0.801, p < 0.001). Survival analysis (Kaplan-Meier method, log-rank test) shows that both high HOXC8 and CDH11 expression correlate with poor recurrence-free survival rate of patients. Together, our study suggests that HOXC8 promotes breast tumorigenesis by maintaining high level of CDH11 expression in breast cancer cells.

Chronic inhibition of cyclic guanosine monophosphate-specific phosphodiesterase 5 prevented cardiac fibrosis through inhibition of transforming growth factor β-induced Smad signaling

Recent evidences suggested that cyclic guanosine monophosphate-specific phosphodiesterase 5 (PDE5) inhibitor represents an important therapeutic target for cardiovascular diseases. Whether and how it ameliorates cardiac fibrosis, a major cause of diastolic dysfunction and heart failure, is unknown. The purpose of this study was to investigate the effects of PDE5 inhibitor on cardiac fibrosis. We assessed cardiac fibrosis and pathology in mice subjected to transverse aortic constriction (TAC). Oral sildenafil, a PDE5 inhibitor, was administered in the therapy group. In control mice, 4 weeks of TAC induced significant cardiac dysfunction, cardiac fibrosis, and cardiac fibroblast activation (proliferation and transformation to myofibroblasts). Sildenafil treatment markedly prevented TAC-induced cardiac dysfunction, cardiac fibrosis and cardiac fibroblast activation but did not block TAC-induced transforming growth factor-β1 (TGF-β1) production and phosphorylation of Smad2/3. In isolated cardiac fibroblasts, sildenafil blocked TGF-β1-induced cardiac fibroblast transformation, proliferation and collagen synthesis. Furthermore, we found that sildenafil induced phosphorylated cAMP response element binding protein (CREB) and reduced CREB-binding protein 1 (CBP1) recruitment to Smad transcriptional complexes. PDE5 inhibition prevents cardiac fibrosis by reducing CBP1 recruitment to Smad transcriptional complexes through CREB activation in cardiac fibroblasts.

Characterization of novel MSX1 mutations identified in Japanese patients with nonsyndromic tooth agenesis

Since MSX1 and PAX9 are linked to the pathogenesis of nonsyndromic tooth agenesis, we performed detailed mutational analysis of these two genes sampled from Japanese patients. We identified two novel MSX1 variants with an amino acid substitution within the homeodomain; Thr174Ile (T174I) from a sporadic hypodontia case and Leu205Arg (L205R) from a familial oligodontia case. Both the Thr174 and Leu205 residues in the MSX1 homeodomain are highly conserved among different species. To define possible roles of mutations at these amino acids in the pathogenesis of nonsyndromic tooth agenesis, we performed several functional analyses. It has been demonstrated that MSX1 plays a pivotal role in hard tissue development as a suppressor for mesenchymal cell differentiation. To evaluate the suppression activity of the variants in mesenchymal cells, we used the myoD-promoter, which is one of convenient reporter assay system for MSX1. Although the gene products of these MSX1 variants are stable and capable of normal nuclear localization, they do not suppress myoD-promoter activity in differentiated C2C12 cells. To clarify the molecular mechanisms underlying our results, we performed further analyses including electrophoretic mobility shift assays, and co-immunoprecipitation assays to survey the molecular interactions between the mutant MSX1 proteins and the oligonucleotide DNA with MSX1 consensus binding motif or EZH2 methyltransferase. Since EZH2 is reported to interact with MSX1 and regulate MSX1 mediated gene suppression, we hypothesized that the T174I and L205R substitutions would impair this interaction. We conclude from the results of our experiments that the DNA binding ability of MSX1 is abolished by these two amino acid substitutions. This illustrates a causative role of the T174I and L205R MSX1 homeodomain mutations in tooth agenesis, and suggests that they may influence cell proliferation and differentiation resulting in lesser tooth germ formation in vivo.

Osteogenic gene expression correlates with development of heterotopic ossification in war wounds

BACKGROUND

Heterotopic ossification (HO) is a frequent complication of modern wartime extremity injuries. The biological mechanisms responsible for the development of HO in traumatic wounds remain elusive.

QUESTION/PURPOSES

The aims of our study were to (1) characterize the expression profile of osteogenesis-related gene transcripts in traumatic war wounds in which HO developed; and (2) determine whether expression at the mRNA level correlated with functional protein expression and HO formation.

METHODS

Biopsy specimens from 54 high-energy penetrating extremity wounds obtained at the initial and final surgical débridements were evaluated. The levels of selected osteogenic-related gene transcripts from RNA extracts were assessed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. As a result of its key role in osteogenesis, the concentration of BMP-2 in the effluent of 29 wounds also was determined.

RESULTS

The transcripts of 13 genes (ALPL [p = 0.006], BMP-2 [p < 0.001], BMP-3 [p = 0.06], COL2A1 [p < 0.001], COLL10A1 [p < 0.001], COL11A1 [p = 0.006], COMP [p = 0.02], CSF2 [p = 0.003], CSF3 [p = 0.012], MMP8 [p < 0.001], MMP9 [p = 0.014], SMAD1 [p = 0.024], and VEGFA [p = 0.017]) were upregulated greater than twofold in wounds in which HO developed compared with wounds in which it did not develop. Gene transcript expression of BMP-2 also correlated directly with functional protein expression in the wounds that formed HO (p = 0.029).

CONCLUSIONS

Important differences exist in the osteogenic gene expression profile of wounds in which HO developed compared with wounds in which it did not develop. The upregulation of multiple osteogenesis-related gene transcripts indicates the presence of a proosteogenic environment necessary for ectopic bone formation in traumatic wounds.

CLINICAL RELEVANCE

Understanding the osteogenic environment associated with war wounds may allow for the development of novel therapeutic strategies for HO.

Smad7 regulates terminal maturation of chondrocytes in the growth plate

Members of the bone morphogenetic protein (BMP) superfamily, including transforming growth factor-betas (TGFβ), regulate multiple aspects of chondrogenesis. Smad7 is an intracellular inhibitor of BMP and TGFβ signaling. Studies in which Smad7 was overexpressed in chondrocytes demonstrated that Smad7 can impact chondrogenesis by inhibiting BMP signaling. However, whether Smad7 is actually required for endochondral ossification in vivo is unclear. Moreover, whether Smad7 regulates TGFβ in addition to BMP signaling in developing cartilage is unknown. In this study, we found that Smad7 is required for both axial and appendicular skeletal development. Loss of Smad7 led to impairment of the cell cycle in chondrocytes and to defects in terminal maturation. This phenotype was attributed to upregulation of both BMP and TGFβ signaling in Smad7 mutant growth plates. Moreover, Smad7-/- mice develop hypocellular cores in the medial growth plates, associated with elevated HIF1α levels, cell death, and intracellular retention of types II and X collagen. Thus, Smad7 may be required to mediate cell stress responses in the growth plate during development.

Misexpression of Pknox2 in mouse limb bud mesenchyme perturbs zeugopod development and deltoid crest formation

The TALE (Three Amino acid Loop Extension) family consisting of Meis, Pbx and Pknox proteins is a group of transcriptional co-factors with atypical homeodomains that play pivotal roles in limb development. Compared to the in-depth investigations of Meis and Pbx protein functions, the role of Pknox2 in limb development remains unclear. Here, we showed that Pknox2 was mainly expressed in the zeugopod domain of the murine limb at E10.5 and E11.5. Misexpression of Pknox2 in the limb bud mesenchyme of transgenic mice led to deformities in the zeugopod and forelimb stylopod deltoid crest, but left the autopod and other stylopod skeletons largely intact. These malformations in zeugopod skeletons were recapitulated in mice overexpressing Pknox2 in osteochondroprogenitor cells. Molecular and cellular analyses indicated that the misexpression of Pknox2 in limb bud mesenchyme perturbed the Hox10-11 gene expression profiles, decreased Col2 expression and Bmp/Smad signaling activity in the limb. These results indicated that Pknox2 misexpression affected mesenchymal condensation and early chondrogenic differentiation in the zeugopod skeletons of transgenic embryos, suggesting Pknox2 as a potential regulator of zeugopod and deltoid crest formation.

Cross-analysis of gene and miRNA genome-wide expression profiles in human fibroblasts at different stages of transformation

We have developed a cellular system constituted of human telomerase immortalized fibroblasts that gradually underwent neoplastic transformation during propagation in culture. We exploited this cellular system to investigate gene and miRNA transcriptional programs in cells at different stages of propagation, representing five different phases along the road to transformation, from non-transformed cells up to tumorigenic and metastatic ones. Here we show that gene and miRNA expression profiles were both able to divide cells according to their transformation phase. We identified more than 1,700 genes whose expression was highly modulated in cells at at least one propagation stage and we found that the number of modulated genes progressively increased at successive stages of transformation. These genes identified processes significantly deregulated in tumorigenic cells, such as cell differentiation, cell movement and extracellular matrix remodeling, cell cycle and apoptosis, together with upregulation of several cancer testis antigens. Alterations in cell cycle, apoptosis, and cancer testis antigen expression were particular hallmarks of metastatic cells. A parallel deregulation of a panel of 43 miRNAs strictly connected to the p53 and c-Myc pathways and with oncogenic/oncosuppressive functions was also found. Our results indicate that cen3tel cells can be a useful model for human fibroblast neoplastic transformation, which appears characterized by complex and peculiar alterations involving both genetic and epigenetic reprogramming, whose elucidation could provide useful insights into regulatory networks underlying cancerogenesis.

Submicroscopic deletion of 12q13 including HOXC gene cluster with skeletal anomalies and global developmental delay

We report on a patient with a submicroscopic deletion of 12q13 detected by array-CGH and confirmed by FISH. He was haploinsufficient for the HOXC gene cluster and some other neighboring genes. HOX genes have an important role in the initial formation of the body. The patient showed characteristic features including severe kyphoscoliosis, digital abnormalities, cardiac anomaly, expressive language, and global developmental delay. Radiologic features of the fingers had some similarities with those for multiple synostosis syndrome. No human genetic disorders due to HOXC abnormalities are yet known. We tentatively assume that his skeletal anomalies are associated with haploinsufficiency of the HOXC gene cluster. Further studies are necessary to determine the clinical importance of haploinsufficiency of the HOXC gene cluster.

Smad6 is essential to limit BMP signaling during cartilage development

Bone morphogenetic protein (BMP) signaling pathways regulate multiple aspects of endochondral bone formation. The importance of extracellular antagonists as regulators of BMP signaling has been defined. In vitro studies reveal that the intracellular regulators, inhibitory Smads 6 and 7, can regulate BMP-mediated effects on chondrocytes. Although in vivo studies in which inhibitory Smads were overexpressed in cartilage have shown that inhibitory Smads have the potential to limit BMP signaling in vivo, the physiological relevance of inhibitory Smad activity in skeletal tissues is unknown. In this study, we have determined the role of Smad6 in endochondral bone formation. Loss of Smad6 in mice leads to defects in both axial and appendicular skeletal development. Specifically, Smad6-/- mice exhibit a posterior transformation of the seventh cervical vertebra, bilateral ossification centers in lumbar vertebrae, and bifid sternebrae due to incomplete sternal band fusion. Histological analysis of appendicular bones revealed delayed onset of hypertrophic differentiation and mineralization at midgestation in Smad6-/- mice. By late gestation, however, an expanded hypertrophic zone, associated with an increased pool of proliferating cells undergoing hypertrophy, was evident in Smad6 mutant growth plates. The mutant phenotype is attributed, at least in part, to increased BMP responsiveness in Smad6-deficient chondrocytes. Overall, our results show that Smad6 is required to limit BMP signaling during endochondral bone formation.

Quantitative proteomic analysis of dexamethasone-induced effects on osteoblast differentiation, proliferation, and apoptosis in MC3T3-E1 cells using SILAC

SUMMARY

The impairment of osteoblast differentiation is one cause of the glucocorticoid-induced osteoporosis (GCOP). The quantitative proteomic analysis of the dexamethasone (DEX)-induced effects of osteoblast differentiation, proliferation, and apoptosis using stable-isotope labeling by amino acids in cell culture (SILAC) demonstrated drastic changes of some key proteins in MC3T3-E1 cells.

INTRODUCTION

The impairment of osteoblast differentiation is one of the main explanations of GCOP. SILAC enables accurate quantitative proteomic analysis of protein changes in cells to explore the underlying mechanism of GCOP.

METHODS

Osteoprogenitor MC3T3-E1 cells were treated with or without 10(−6) M DEX for 7 days, and the differentiation ability, proliferation, and apoptosis of the cells were measured. The protein level changes were analyzed using SILAC and liquid chromatography-coupled tandem mass spectrometry.

RESULTS

In this study, 10(−6) M DEX inhibited both osteoblast differentiation and proliferation but induced apoptosis in osteoprogenitor MC3T3-E1 cells on day 7. We found that 10(−6) M DEX increased the levels of tubulins (TUBA1A, TUBB2B, and TUBB5), IQGAP1, S100 proteins (S100A11, S100A6, S100A4, and S100A10), myosin proteins (MYH9 and MYH11), and apoptosis and stress proteins, while inhibited the protein levels of ATP synthases (ATP5O, ATP5H, ATP5A1, and ATP5F1), G3BP-1, and Ras-related proteins (Rab-1A, Rab-2A, and Rab-7) in MC3T3-E1 cells.

CONCLUSIONS

Several members of the ATP synthases, myosin proteins, small GTPase superfamily, and S100 proteins may participate in functional inhibition of osteoblast progenitor cells by GCs. Such protein expression changes may be of pathological significance in coping with GCOP.

Up-regulation of homeodomain genes, DLX1 and DLX2, by FLT3 signaling

BACKGROUND

Activating mutations in fms-like tyrosine kinase-3 (FLT3) are frequent in acute myeloid leukemia and represent both a poor prognostic feature and a therapeutic target. We have identified a previously unrecognized downstream effect of FLT3 activation, namely up-regulation of the homeodomain genes, DLX1 and DLX2.

DESIGN AND METHODS

MV4;11 cells with FLT3-internal tandem duplication mutation, RS4;11 cells with wild-type FLT3 and blasts from patients with acute myeloid leukemia were used to pursue the relation between FLT3, DLX1/2 and transforming growth factor-β (TGFβ). Real-time quantitative reverse transcriptase polymerase chain reaction, western blot and reverse-phase protein array were performed to detect changes in gene and protein expression. RNA interference and MTS assays were used to study the interaction of PKC412, FLT3 inhibitor and TGFβ1.

RESULTS

A direct relationship between FLT3 activity and DLX1/2 expression was revealed by both inhibition and up-regulation of FLT3 signaling in MV4;11 and RS4;11 cell lines, respectively, in isolated blast cells from patients with acute myeloid leukemia, and in reverse-phase protein array assays of samples from patients with acute myeloid leukemia. Mechanistically, the link between FLT3 and DLX1 expression appears to involve MAPK signaling through the ERK and JNK pathways. To determine whether elevated DLX1 had a functional consequence, we explored the reported inhibition by DLX1 on TGFβ/Smad signaling. Indeed, TGFβ responses were blunted by FLT3 activation in a DLX1-dependent manner and FLT3 inhibition resulted in a time-dependent increase in nuclear phospho-Smad2.

CONCLUSIONS

These findings suggest that alterations in DLX1/2 contribute to the biological consequences of FLT3 activation.

Polymorphisms in the HOXD4 gene are not associated with peak bone mineral density in Chinese nuclear families

AIM

To determine the associations between HOXD4 gene polymorphisms with peak bone mineral density (BMD) throughing measuring three tagging single nucleotide polymorphisms (tagSNPs), including rs1867863, rs13418078, and rs4972504, in HOXD4.

METHODS

Four hundred Chinese nuclear families with male offspring (1215 subjects) and 401 Chinese nuclear families with female offspring (1260 subjects) were recruited. BMD of the lumbar spine 1-4 (L1-4) and left proximal femur including total hip and femoral neck were measured by dual-energy X-ray absorptiometry. The quantitative transmission disequilibrium test (QTDT) was performed to investigate the association among the tagging SNPs, haplotypes and peak BMD.

RESULTS

Only the CC genotype was identified in rs13418078 in the Chinese population, unlike other populations. We failed to find significant within-family association among these SNPs, haplotypes and peak BMD at any bone site in either male- or female-offspring nuclear families.

CONCLUSION

The results suggest that genetic polymorphisms in HOXD4 may not be a major contributor to the observed variability in peak BMD in the lumbar spine and the hip in Chinese men and women.

Microarray Analysis of Defective Cartilage in Hoxc8- and Hoxd4-Transgenic Mice

OBJECTIVE

Homeobox genes of the Hox class are required for proper patterning of skeletal elements and play a role in cartilage differentiation. In transgenic mice with overexpression of Hoxc8 and Hoxd4 during cartilage development, the authors observed severe defects, namely, physical instability of cartilage, accumulation of immature chondrocytes, and decreased maturation to hypertrophy. To define the molecular basis underlying these defects, the authors performed gene expression profiling using the Affymetrix microarray platform.

RESULTS

Primary chondrocytes were isolated from Hoxc8- and Hoxd4-transgenic mouse embryo rib cartilage at 18.5 days of gestation. In both cases, differentially expressed genes were identified that have a role in cell proliferation and cell cycle regulation. A comparison between the controls for both experimental groups did not reveal significant differences, as expected. However, the repertoires of differentially expressed genes were found not to overlap between Hoxc8- and Hoxd4-transgenic cartilage. This included different Wnt genes, cell cycle, and apoptosis regulators.

CONCLUSION

Overexpression of Hoxc8 and Hoxd4 transcription factors alters transcriptional profiles in chondrocytes at E18.5. The differences in repertoires of altered gene expression between the 2 transgenic conditions suggest that the molecular mechanisms underlying the cartilage defects may be different in both transgenic paradigms, despite apparently similar phenotypes.

Ex vivo transfer of the Hoxc-8-interacting domain of Smad1 by a tropism-modified adenoviral vector results in efficient bone formation in a rabbit model of spinal fusion

STUDY DESIGN

Ex vivo gene transfer for spinal fusion.

OBJECTIVE

This study aimed to evaluate ex vivo transfer of the nuclear-localized Hoxc-8-interacting domain of Smad1 (termed Smad1C) to rabbit bone marrow stromal cells (BMSCs) by a tropism-modified human adenovirus serotype 5 (Ad5) vector as a novel therapeutic approach for spinal fusion.

SUMMARY OF BACKGROUND DATA

Novel approaches are needed to improve the success of bone union after spinal fusion. One such approach is the ex vivo transfer of a gene encoding an osteoinductive factor to BMSCs which are subsequently reimplanted into the host. We have previously shown that heterologous expression of the Hoxc-8-interacting domain of Smad1 in the nuclei of osteoblast precursor cells is able to stimulate the expression of genes related to osteoblast differentiation and induce osteogenesis in vivo. Gene delivery vehicles based on human Ad5 are well suited for gene transfer for spinal fusion because they can mediate high-level, short-term gene expression. However, Ad5-based vectors with native tropism poorly transduce BMSCs, necessitating the use of vectors with modified tropism to achieve efficient gene transfer.

METHODS

The gene encoding Smad1C was transferred to rabbit BMSCs by an Ad5 vector with native tropism or a vector retargeted to alphav integrins, which are abundantly expressed on rabbit BMSCs. Transduced BMSCs were maintained in osteoblastic differentiation medium for 30 days. Alkaline phosphatase activity was determined and cells stained for calcium deposition. As positive controls for osteogenesis, we used Ad5 vectors expressing bone morphogenetic protein 2. As negative controls, BMSCs were mock-transduced or transduced with an Ad5 vector expressing beta-galactosidase. In an immunocompetent rabbit model of spinal fusion, transduced BMSCs were coated onto absorbable gelatin sponge and implanted between decorticated transverse processes L6 and L7 of 8-week-old female New Zealand white rabbits. Animals were killed 4 weeks after implantation of the sponges, the fusion masses harvested and the area of new bone quantified using image analysis software.

RESULTS

The Smad1C-expressing tropism-modified Ad5 vector mediated a significantly higher level of alkaline phosphatase activity and calcium deposition in transduced rabbit BMSCs than all other vectors. The rabbit BMSCs transduced ex vivo with the Smad1C-expressing tropism-modified Ad5 vector mediated a greater amount of new bone formation than BMSCs transduced with any other vector.

CONCLUSIONS

Delivery of the Smad1C gene construct to BMSCs by an alphav integrin-targeted Ad5 vector shows promise for spinal fusion and other applications requiring the formation of new bone in vivo.

20ns molecular dynamics simulation of the antennapedia homeodomain-DNA complex: water interaction and DNA structure analysis

Homeodomains are one of the important families of eukaryotic DNA-binding motifs and provide an important model system for studying protein-DNA interactions. The crystal structure and NMR structure of the antennapedia homeodomain-DNA complex and comparison between them is available. Although earlier works have shown that the direct contacts and water mediated contacts are important for the binding and specificity. The detail dynamical structural characteristics of the complex, water mediating interactions in the complex and also the detail study of the free DNA and protein has not done. In the present paper we have reported the results of 20ns MD simulation of this complex with the presence of explicit water and also the 20ns MD simulation of the protein and the DNA separately in explicit water. The results show that the complex remains stable during the last 8ns of the simulation. The part of the protein which is interacting with the DNA has fewer fluctuations than other part of the protein. The pattern of water distribution around the interacting center has a typical pattern for this complex and it is quite different from the free protein and the free DNA. Water molecules penetrate into the interacting center during the simulation. Several water bridges have been identified which is responsible for recognition but not observed in the crystal structure. The recognized DNA sequence (14 mer) has been characterized by helical and step parameters. The correlated motions of the DNA and the protein in the complexed form and the free form has been analyzed.

Hoxc8 represses BMP-induced expression of Smad6

Proper regulation of bone morphogenetic protein (BMP) signaling is critical for correct patterning and morphogenesis of various tissues and organs. A well known feedback mechanism is a BMP-mediated induction of Smad6, an inhibitor of BMP signaling. Hoxc8, one of the Hox family transcription factors, has also been shown to negatively regulate BMP-mediated gene expression. Here we add another level of Hoxc8 regulation on BMP signaling. Our results show that Hoxc8, when over-expressed in C3H10T1/2 or C2C12 cells, suppressed basal Smad6 promoter activity and its mRNA expression. Activation of Smad6 transcription either by BMP2 treatment or Smad1 over-expression was also abolished by Hoxc8. When chromatin was precipitated from mouse embryos with anti-Smad1 or anti-Hoxc8 antibody, Smad6 promoter sequence was enriched, suggesting that Hoxc8 proteins make complexes with Smad1 in the Smad6 promoter region. Yet, a lack of Hox binding motifs in the Smad6 promoter sequence suggests that instead of directly binding to the DNA, Hoxc8 may regulate Smad6 expression via an indirect mechanism. Our results suggest that the Smad6-mediated negative feedback mechanism on BMP signaling may be balanced by the repression of Smad6 expression by Hoxc8.

Finding partners: how BMPs select their targets

The bone morphogenetic protein (BMP) signaling pathway is a conserved and evolutionarily ancient regulatory module affecting a large variety of cellular behaviors. The evolutionary flexibility in using BMP responses presumably arose by co-option of a canonical BMP signaling cascade to regulate the transcription of diverse batteries of target genes. This begs the question of how seemingly interchangeable BMP signaling components elicit widely different outputs in different cell types, an important issue in the context of understanding how BMP signaling integrates with gene regulatory networks to control development. Because a molecular understanding of how BMP signaling activates different batteries of target genes is an essential prerequisite to comprehending the roles of BMPs in regulating cellular responses, here we review the current knowledge of how BMP-regulated target genes are selected by the signal transduction machinery. We highlight recent studies suggesting the evolutionary conservation of BMP target gene regulation signaling by Schnurri family zinc finger proteins. Developmental Dynamics 238:1321-1331, 2009. (c) 2009 Wiley-Liss, Inc.

Interplay between activin and Hox genes determines the formation of the kidney morphogenetic field

The kidney develops in a specific position along the anterior-posterior axis. All vertebrate kidney tissues are derived from the intermediate mesoderm (IM), and early kidney genes such as Lim1 and Pax2 are expressed in amniotes posterior to the sixth somite axial level. IM cells anterior to this level do not express kidney genes owing to changes in their competence to respond to kidney-inductive signals present along the entire axis. We aimed to understand the molecular mechanisms governing the loss of competence of anterior IM cells and the formation of the anterior border of the kidney morphogenetic field. We identified the dorsal neural tube as the potential kidney-inductive tissue and showed that activin, a secreted morphogen, is necessary but insufficient for Lim1 induction and establishment of the kidney field. Activin or activin-like and BMP signaling cascades are activated along the entire axis, including in anterior non-kidney IM, suggesting that competence to respond to these signals involves downstream or other components. Detailed expression pattern analysis of Hox genes during early chick development revealed that paralogous group four genes share the same anterior border as the kidney genes. Ectopic expression of Hoxb4 in anterior non-kidney IM, either by retinoic acid (RA) administration or plasmid-mediated overexpression, resulted in ectopic kidney gene expression. The anterior expansion of Lim1 expression was restrained when Hoxb4 was co-expressed with a truncated form of activin receptor. We suggest a model in which the competence of IM cells to respond to TGFbeta signaling and express kidney genes is driven by RA and mediated by Hoxb4.

In vitro osteoblast differentiation is negatively regulated by Hoxc8

Hoxc8 has multiple roles in normal skeletal development. In this paper, a MC3T3-E1 subclone 4 osteogenic cell differentiation model was used to examine expression of Hoxc8 at multiple stages of osteogenesis. We found that Hoxc8 expression levels do not change in the early stage but increase in the middle stage and decrease in the late stage of osteogenesis. A knockdown of Hoxc8 by small-interfering RNA transfection in C2C12 cells indicated that Hoxc8 is a negative regulator of osteogenesis. Similarly, expression of Hoxc8 in C2C12 cells decreases alkaline phosphatase levels induced by bone morphogenetic protein-2 (BMP-2). The results of this study showed that Hoxc8 is involved in BMP-2-induced osteogenesis, and osteoblast differentiation in vitro is negatively regulated by Hoxc8, suggesting that Hoxc8 regulation is essential for osteoblast differentiation.

Hox specificity unique roles for cofactors and collaborators

Hox proteins are well known for executing highly specific functions in vivo, but our understanding of the molecular mechanisms underlying gene regulation by these fascinating proteins has lagged behind. The premise of this review is that an understanding of gene regulation-by any transcription factor-requires the dissection of the cis-regulatory elements that they act upon. With this goal in mind, we review the concepts and ideas regarding gene regulation by Hox proteins and apply them to a curated list of directly regulated Hox cis-regulatory elements that have been validated in the literature. Our analysis of the Hox-binding sites within these elements suggests several emerging generalizations. We distinguish between Hox cofactors, proteins that bind DNA cooperatively with Hox proteins and thereby help with DNA-binding site selection, and Hox collaborators, proteins that bind in parallel to Hox-targeted cis-regulatory elements and dictate the sign and strength of gene regulation. Finally, we summarize insights that come from examining five X-ray crystal structures of Hox-cofactor-DNA complexes. Together, these analyses reveal an enormous amount of flexibility into how Hox proteins function to regulate gene expression, perhaps providing an explanation for why these factors have been central players in the evolution of morphological diversity in the animal kingdom.

Mesenchymal stem cells from different organs are characterized by distinct topographic Hox codes

Mesenchymal stem cells (MSC) are multipotent cells found as part of the stromal compartment of the bone marrow and in many other organs. They can be identified in vitro as CFU-F (colony forming unit-fibroblast) based on their ability to form adherent colonies of fibroblast-like cells in culture. MSC expanded in vitro retain characteristics appropriate to their tissue of origin. This is reflected in their propensity for differentiating towards specific lineages, and their capacity to generate, upon retransplantation in vivo, a stroma supporting typical lineages of hematopoietic cells. Hox genes encode master regulators of regional specification and organ development in the embryo and are widely expressed in the adult. We investigated whether they could be involved in determining tissue-specific properties of MSC. Hox gene expression profiles of individual CFU-F colonies derived from various organs and anatomical locations were generated, and the relatedness between these profiles was determined using hierarchical cluster analysis. This revealed that CFU-F have characteristic Hox expression signatures that are heterogeneous but highly specific for their anatomical origin. The topographic specificity of these Hox codes is maintained during differentiation, suggesting that they are an intrinsic property of MSC. Analysis of Hox codes of CFU-F from vertebral bone marrow suggests that MSC originate over a large part of the anterioposterior axis, but may not originate from prevertebral mesenchyme. These data are consistent with a role for Hox proteins in specifying cellular identity of MSC.

PPARgamma-2 and BMPR2 genes were differentially expressed in peripheral blood of SLE patients with osteonecrosis

Most researchers believe that the peroxisome proliferative activated receptor gamma (PPARgamma-2) and bone morphogenetic protein receptor type II (BMPR2) play important roles in steroid-induced osteonecrosis (ON). However, the molecular mechanism of this process is still unclear. Recent studies indicate that steroid treatments cause adipocyte formation due to differentiation of mesenchymal stem cells, which then prevents osteoblast formation. This study examined PPARgamma-2, bone morphogenetic protein 2 (BMP2), and BMPR2 in patients with systemic lupus erythromatosus (SLE) who eventually developed ON after prolonged steroid treatment. The subjects of this experiment included 220 SLE patients who had undergone steroid treatment for at least 2 years. Fifty-five of the 220 patients were ON patients, and 165 were non-ON patients. Real-time PCR was performed to analyze the expression of the PPARgamma-2, BMP2, and BMPR2 mRNA in the peripheral blood of these patients. The results indicated that the expression of PPARgamma-2 mRNA increased 37% in the ON patients' peripheral blood, but the expression of BMPR2 mRNA decreased 57%. The average expression of the PPARgamma-2 mRNA in the ON patients was significantly higher than that in the non-ON patients (p = 0.044). Conversely, the expression of BMPR2 mRNA was significantly lower than that in non-ON patients (p = 0.036), but the expression of BMP2 mRNA did not significantly differ. This study demonstrated that the PPARgamma-2 and BMPR2 have important roles in the ON process after prolonged steroid administration in SLE patients; however, the detailed molecular mechanisms of this process require further study.

Bone morphogenetic proteins in tissue engineering: the road from the laboratory to the clinic, part I (basic concepts)

Discovered in 1965, bone morphogenetic proteins (BMPs) are a group of cytokines from the transforming growth factor-beta (TGFbeta) superfamily with significant roles in bone and cartilage formation. BMPs are used as powerful osteoinductive components of diverse tissue-engineering products for the healing of bone. Several BMPs with different physiological roles have been identified in humans. The purpose of this review is to cover the biological function of the main members of BMP family, the latest research on BMPs signalling pathways and advances in the production of recombinant BMPs for tissue engineering purposes.

MH1 domain of SMAD4 binds N-terminal residues of the homeodomain of Hoxc9

Smad family proteins mediate signaling initiated by bone morphogenetic proteins (BMPs). Upon BMP stimulation, the Smads such as Smad4 can interact directly with Hox proteins and suppress their DNA-binding activity. Although the interaction between the MAD-homology 1 (MH1) domain of Smad4 and Hox was found to regulate the transcription activity of Hox proteins, the molecular mechanism is not well characterized and direct contact residues remain to be elucidated. In the present study, the interaction between the recombinant homeodomain (HD) of Hoxc9 and MH1 domain of Smad4 was investigated with the use of the GST pull-down assay, surface plasmon resonance (SPR) analysis as well as multidimensional nuclear magnetic resonance (NMR) techniques. The Hoxc9-HD was precipitated with the GST-fused Smad4-MH1 but not with GST alone, demonstrating a direct interaction between Hoxc9-HD and Smad4-MH1 in vitro. SPR measurement further confirmed a moderately strong interaction (K(d) approximately 400 nM) between these two domains. Moreover, NMR titration experiments showed that a strong and specific binding occurred between Smad4-MH1 and Hoxc9-HD. NMR triple-resonance experiments and backbone assignments revealed that the N-terminal arm of Hoxc9-HD, spanning the positive-charged DNA-binding segment of Arg190-Arg196, was intimately involved in the interaction with Smad4-MH1. Ala-substitutions of Arg190-Arg196 led to the loss of interaction between Hoxc9-HD and Smad4-MH1 in both GST-pull down assay and SPR analysis; further provided functional evidence for the critical role of this positive-charged region in binding to Smad4-MH1. This suggested that Smad4-MH1 could occupy one of the DNA binding sites of Hoxc9 and consequently inhibits its transcription activity. The above results are in good agreement and yield the first insight into the interaction between the homeodomain of Hox proteins and the conserved MH1 domain of Smad family proteins.

Osteogenic differentiation of human adipose tissue-derived stem cells is modulated by the miR-26a targeting of the SMAD1 transcription factor

The molecular mechanisms that regulate hADSC differentiation toward osteogenic precursors and subsequent bone-forming osteoblasts is unknown. Using osteoblast precursors obtained from subcutaneous human adipose tissue, we observed that microRNA-26a modulated late osteoblasts differentiation by targeting the SMAD1 transcription factor.

INTRODUCTION

Elucidation of the molecular mechanisms guiding human adipose tissue-derived stem cells (hADSCs) differentiation is of extreme importance for improving the treatment of bone-related diseases such as osteoporosis. The aim of this study was to identify microRNA as a regulator of the osteogenic differentiation of hADSCs.

MATERIALS AND METHODS

Osteoblast differentiation of hADSCs was induced by treatment with dexamethasone, ascorbic acid, and beta-glycerol phosphate. The expression of osteoblastic phenotype was evaluated after the induction by simultaneous monitoring of alkaline phosphatase activity, the expression of genes involved in osteoblastic differentiation by real-time RT-PCR, and mineralization at the same time. MicroRNA expression was determined by Northern blot, and transfection of both antisense miR-RNA and sensor plasmids was done to validate the inhibitory role of microRNA during hADSC osteogenesis. Western blot was used to determine the expression levels of the SMAD1 protein. qRT-PCR analysis was used to compare the expression patterns of osteoblastic markers in transfected cells.

RESULTS AND CONCLUSIONS

We analyzed the role of microRNA 26a (miR-26a) during differentiation of hADSCs. Northern blot analysis of miR-26a during hADSC differentiation showed increased expression, whereas expression of the SMAD1 protein was complementary to that of miR-26a. Because the highest expression of miR-26a and the lowest expression of SMAD1 protein were reached at hADSC terminal differentiation, we carried out our study during the late stages of hADSC differentiation. The inhibition of miR-26a, by 2'-O-methyl-antisense RNA, increased protein levels of its predicted target, SMAD1 transcription factor, in treated osteoblasts, upregulating bone marker genes and thus enhancing osteoblast differentiation. Our data suggest a role for miR-26a in the differentiation induced by treatment with dexamethasone, ascorbic acid, and beta-glycerol phosphate of hADSCs toward the osteogenic lineage by targeting its predicted target, the SMAD1 protein. This study contributes to a better knowledge of molecular mechanisms governing hADSC differentiation by proposing a microRNA-based control of late differentiation.

Molecular basis for skeletal variation: insights from developmental genetic studies in mice

Skeletal variations are common in humans, and potentially are caused by genetic as well as environmental factors. We here review molecular principles in skeletal development to develop a knowledge base of possible alterations that could explain variations in skeletal element number, shape or size. Environmental agents that induce variations, such as teratogens, likely interact with the molecular pathways that regulate skeletal development.

Atrial natriuretic peptide inhibits transforming growth factor beta-induced Smad signaling and myofibroblast transformation in mouse cardiac fibroblasts

This study tested the hypothesis that activation of atrial natriuretic peptide (ANP)/cGMP/protein kinase G signaling inhibits transforming growth factor (TGF)-beta1-induced extracellular matrix expression in cardiac fibroblasts and defined the specific site(s) at which this molecular merging of signaling pathways occurs. Left ventricular hypertrophy and fibrosis, collagen deposition, and myofibroblast transformation of cardiac fibroblasts in response to pressure overload by transverse aortic constriction were exaggerated in ANP-null mice compared with wild-type controls. ANP and cGMP inhibited TGF-beta1-induced myofibroblast transformation, proliferation, collagen synthesis, and plasminogen activator inhibitor-1 expression in cardiac fibroblasts isolated from wild-type mice. Following pretreatment with cGMP, TGF-beta1 induced phosphorylation of Smad3, but the resultant pSmad3 could not be translocated to the nucleus. pSmad3 that had been phosphorylated with recombinant protein kinase G-1alpha was analyzed by use of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and ion trap tandem mass spectrometry. The analysis revealed phosphorylation of Ser309 and Thr388 residues, sites distinct from the C-terminal Ser423/425 residues that are phosphorylated by TGF-beta receptor kinase and are critical for the nuclear translocation and down-stream signaling of pSmad3. These results suggest that phosphorylation of Smad3 by protein kinase G is a potential molecular mechanism by which activation of ANP/cGMP/protein kinase G signaling disrupts TGF-beta1-induced nuclear translocation of pSmad3 and downstream events, including myofibroblast transformation, proliferation, and expression of extracellular matrix molecules in cardiac fibroblasts. We postulate that this process contributes to the antifibrogenic effects of the natriuretic peptide in heart.

Mouse naked cuticle 2 (mNkd2) as a direct transcriptional target of Hoxc8 in vivo

Mouse naked cuticle 2 (mNkd2), the mammalian homolog of the Drosophila segment polarity gene naked cuticle (nkd), encodes an EF hand protein that regulates early Wg activity by acting as an inducible antagonist. The transcription factor, Hoxc8, a member of the homeobox gene family, is vital for growth and differentiation. Chromatin immunoprecipitation (ChIP) assay, an electrophoretic mobility shift assay (EMSA), and a reporter assay demonstrated that endogenous Hoxc8 protein binds directly to the enhancer region of the mNkd2 gene, implying a Hoxc8-dependent transcriptional activity. Introduction of exogenous Hoxc8 into NIH3T3 cell lines lacking wild-type Hoxc8 dramatically reduced expression of mNkd2 mRNA. If, as the results suggest, mNkd2 is a direct target of Hoxc8, it represents a novel mechanism by which Hoxc8 might cross-talk with the Wnt signaling pathway by regulating mNkd2.

Comparative roles of Twist-1 and Id1 in transcriptional regulation by BMP signaling

Basic helix-loop-helix (bHLH) transcription factors are known as key regulators for mesenchymal differentiation. The present study showed that overexpression of Twist-1, a bHLH transcription factor, suppresses bone morphogenetic protein (BMP)-induced osteoblast differentiation, and downregulation of endogenous Twist-1 enhances BMP signaling. Maximal inhibition of BMP signaling was observed when Twist-1 was bound to E47, which markedly enhanced the stability of Twist-1. Co-immunoprecipitation assays revealed that Twist-1 formed a complex with Smad4 and histone deacetylase (HDAC) 1 in MC3T3-E1 cells stably expressing Twist-1. With trichostatin, an HDAC inhibitor, osteogenic factors such as alkaline phosphatase, Runx2 and osteopontin increased. Those results suggested that Twist-1 inhibited BMP signaling by recruiting HDAC1 to Smad4. Furthermore, the inhibitory effects of Twist-1 on BMP signaling were overcome by Id1 through induction of Twist-1 degradation. These findings suggest that Twist-1 can act as an inhibitor of BMP signaling, and Id1 can regulate BMP signaling through a positive feedback loop repressing Twist-1 function. These two molecules may therefore regulate differentiation of mesenchymal cells into progeny such as osteoblasts by controlling BMP signaling.

The MH1 domain of Smad3 interacts with Pax6 and represses autoregulation of the Pax6 P1 promoter

Pax6 transcription is under the control of two main promoters (P0 and P1), and these are autoregulated by Pax6. Additionally, Pax6 expression is under the control of the TGFβ superfamily, although the precise mechanisms of such regulation are not understood. The effect of TGFβ on Pax6 expression was studied in the FHL124 lens epithelial cell line and was found to cause up to a 50% reduction in Pax6 mRNA levels within 24 h. Analysis of luciferase reporters showed that Pax6 autoregulation of the P1 promoter, and its induction of a synthetic promoter encoding six paired domain-binding sites, were significantly repressed by both an activated TGFβ receptor and TGFβ ligand stimulation. Subsequently, a novel Pax6 binding site in P1 was shown to be necessary for autoregulation, indicating a direct influence of Pax6 protein on P1. In transfected cells, and endogenously in FHL124 cells, Pax6 co-immunoprecipitated with Smad3 following TGFβ receptor activation, while in GST pull-down experiments, the MH1 domain of Smad3 was observed binding the RED sub-domain of the Pax6 paired domain. Finally, in DNA adsorption assays, activated Smad3 inhibited Pax6 from binding the consensus paired domain recognition sequence. We hypothesize that the Pax6 autoregulatory loop is targeted for repression by the TGFβ/Smad pathway, and conclude that this involves diminished paired domain DNA-binding function resulting from a ligand-dependant interaction between Pax6 and Smad3.

BMP signaling and skeletogenesis

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-beta superfamily of signal molecules that mediate many diverse biological processes ranging from early embryonic tissue patterning to postnatal tissue homeostasis. BMPs trigger cell responses mainly through the canonical signaling pathway where intracellular Smads play central roles in delivering the extracellular signals to the nucleus. While the same Smads are used by BMPs in all types of cells, different transcription factors account in part for the functional diversity of BMPs. These transcription factors are recruited by Smads to regulate the expression of specific subsets of target genes depending on the cell types. Among the transcription factors are Hox proteins. Experimental gain and loss-of-function studies as well as naturally occurring mutations in Hox genes demonstrate their central roles in embryonic skeletal patterning. In addition to the interactions with Smads observed for several Hox proteins, there is also evidence that the expression of a number of Hox genes is regulated by BMPs. It is suggested that Hox proteins play an important role in the BMP pathway.

Components of both major axial patterning systems of the Bilateria are differentially expressed along the primary axis of a 'radiate' animal, the anthozoan cnidarian Acropora millepora

Cnidarians are animals with a single (oral/aboral) overt body axis and with origins that nominally predate bilaterality. To better understand the evolution of axial patterning mechanisms, we characterized genes from the coral, Acropora millepora (Class Anthozoa) that are considered to be unambiguous markers of the bilaterian anterior/posterior and dorsal/ventral axes. Homologs of Otx/otd and Emx/ems, definitive anterior markers across the Bilateria, are expressed at opposite ends of the Acropora larva; otxA-Am initially around the blastopore and later preferentially toward the oral end in the ectoderm, and emx-Am predominantly in putative neurons in the aboral half of the planula larva, in a domain overlapping that of cnox-2Am, a Gsh/ind gene. The Acropora homologs of Pax-3/7, NKX2.1/vnd and Msx/msh are expressed in axially restricted and largely non-overlapping patterns in larval ectoderm. In Acropora, components of both the D/V and A/P patterning systems of bilateral animals are therefore expressed in regionally restricted patterns along the single overt body axis of the planula larva, and two 'anterior' markers are expressed at opposite ends of the axis. Thus, although some specific gene functions appear to be conserved between cnidarians and higher animals, no simple relationship exists between axial patterning systems in the two groups.

Identification of a Hoxc8-regulated transcriptional network in mouse embryo fibroblast cells

The transcription factor, Hoxc8, is a member of the homeobox gene family that is vital for growth and differentiation. Previously, we identified 34 genes whose expression levels were changed at least 2-fold by forced expression of Hoxc8 in C57BL/6J mouse embryo fibroblast cells using a mouse 16,463-gene oligonucleotide microarray. In the present study, we used the combined power of microarray profiling, global Hoxc8 DNA-binding site analysis, and high-throughput chromatin immunoprecipitation assays to identify direct and biologically relevant targets of Hoxc8 in vivo. Here we show that 19 of the 34 responsive genes contain Hoxc8 consensus DNA-binding sequence(s) in their regulatory regions. Chromatin immunoprecipitation analysis indicated that Hoxc8-DNA interaction was detected in five of the 19 candidate genes. All of these five target genes have been implicated in oncogenesis, cell adhesion, proliferation, and apoptosis. Overall, the genes described here should aid in the understanding of global regulatory networks of Hox genes and to provide valuable insight into the molecular basis of Hoxc8 in development and carcinogenesis.