Hoxa-9 represses transforming growth factor-beta-induced osteopontin gene transcription

Identification of a Hoxd10-regulated transcriptional network and combinatorial interactions with Hoxa10 during spinal cord development

Hoxd10 is expressed in the posterior spinal cord and hindlimbs of the mouse. Hoxd10, along with other Hox transcription factors, is thought to regulate the activity of genes involved in nervous system patterning and motor neuron development, but little is known about the downstream targets regulated by this gene. cDNA microarrays were used to investigate the transcriptional network regulated by Hoxd10 in homozygous knockout animals. Sixty-nine genes were identified with altered expression levels in mutant spinal cords. Among these were genes involved in such diverse cellular events as cellular communication, cell cycle control, development and differentiation, and neuronal survival. The expression of some of these genes was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. Nine genes showed changes in expression of the same sign and similar magnitude using RT-PCR in Hoxd10 single mutant animals, with additional changes in expression seen in Hoxa10/Hoxd10 double mutant animals. In situ hybridization studies also demonstrated changes in expression consistent with microarray results. Analysis of putative promoter regions for Hox protein binding sites suggested that some genes may be direct Hoxd10 targets, whereas others likely are regulated through intermediate steps. Using cDNA microarrays to study a single gene knockout during critical developmental stages has identified a large number of genes regulated by Hoxd10, many of which would not have been approached as candidates for Hox gene regulation based on function or expression.

Homeobox A9 transcriptionally regulates the EphB4 receptor to modulate endothelial cell migration and tube formation

Homeobox genes (Hox) encode for transcription factors, which regulate cell proliferation and migration and play an important role in the development of the cardiovascular system during embryogenesis. In this study, we investigated the role of HoxA9 for endothelial cell migration and angiogenesis in vitro and identified a novel target gene, the EphB4 receptor. Inhibition of HoxA9 expression decreased endothelial cell tube formation and inhibited endothelial cell migration, suggesting that HoxA9 regulates angiogenesis. Because Eph receptor tyrosine kinases importantly contribute to angiogenesis, we examined whether HoxA9 may transcriptionally regulate the expression of EphB4. Downregulation of HoxA9 reduced the expression of EphB4. Chromatin-immunoprecipitation revealed that HoxA9 interacted with the EphB4 promoter, whereas a deletion construct of HoxA9 without DNA-binding motif (Delta(aa) 206-272) did not bind. Consistently, HoxA9 wild-type overexpression activated the EphB4 promoter as determined by reporter gene expression. HoxA9 binds to the EphB4 promoter and stimulates its expression resulting in an increase of endothelial cell migration and tube forming activity. Thus, modulation of EphB4 expression may contribute to the proangiogenic effect of HoxA9 in endothelial cells.

Transcriptional regulation of human osteopontin promoter by C/EBPα and AML-1 in metastatic cancer cells

Osteopontin (OPN) is a secreted glycoprotein produced by osteoclasts, macrophages, T cells, hematopoietic cells, and vascular smooth muscle cells. It contributes to macrophage homing and cellular immunity. It also mediates neovascularization, inhibits apoptosis, and plays important roles in extracellular matrix remodeling and angiogenesis. These properties are also characteristics of metastatic cancer cells. Consequently, the OPN gene was found to be upregulated among various metastatic cancer cells. This suggests that OPN is involved in tumor metastasis. How the OPN gene is upregulated in metastatic cancer cells remains to be illustrated. Thus, we investigated the transcriptional activation of the OPN promoter in the human metastatic cancer cell line A2058. We cloned the OPN promoter, and serial deletion analysis of the OPN promoter showed that the region between -170 and -127 may act as an enhancer to control the OPN gene in metastatic tumor cells. This region was found to contain overlapped AML-1 and C/EBP binding site motifs. Gel-mobility-shift assays using the A2058 nuclear extract and AML-1a or C/EBPalpha (CCAAT/enhancer binding protein alpha) recombinant protein indicated that these two transcription factors can bind to the overlapped AML-1 /C/EBP binding site motifs on the OPN regulatory sequence from -147 to -127. Surprisingly, the gel-shift experiments did not show supershift complex formation between AML-1 and C/EBPalpha. Functional analysis showed that the C/EBPalpha was more potent than the complex of AML-1 and its cofactor CBFbeta to upregulate the OPN promoter. In addition, AML-1 and C/EBPalpha did not exhibit transactivation additively or synergistically. Our results suggest that AML-1 and C/EBPalpha play an important role in the upregulation of the OPN gene in metastatic tumor cells.

AP-1 is involved in UTP-induced osteopontin expression in arterial smooth muscle cells

Osteopontin (OPN), an RGD-containing extracellular matrix protein, is associated with arterial smooth muscle cell (SMC) activation in vitro and in vivo. Many cytokines and growth factors involved in vessel wall remodeling induce OPN overexpression. Moreover, we recently demonstrated that the extracellular nucleotide UTP also induces OPN expression and that OPN is essential for UTP-mediated SMC migration. Thus, we set out to investigate the mechanisms of OPN expression. The aim of this study was to identify transcription factors involved in the regulation of OPN expression in SMCs. First, we explored the contribution of mRNA stabilization and transcription in the increase of UTP-induced OPN mRNA levels. We show that UTP induced OPN mRNA increases via both OPN mRNA stabilization and OPN promoter activation. Then, to identify transcription factors involved in UTP-induced OPN transcription, we located a promoter element activated by UTP within the rat OPN promoter using a gene reporter assay strategy. The -96 to +1 region mediated UTP-induced OPN overexpression (+276+/-60%). Sequence analysis of this region revealed a potential site for AP-1 located at -76. When this AP-1 site was deleted, UTP-induced activation of the -96 to +1 region was totally inhibited. Thus, this AP-1 (-76) site is involved in UTP-induced OPN transcription. A supershift assay revealed that both c-Fos and c-Jun bind to this AP-1 site. Finally, we demonstrate that angiotensin II and platelet-derived growth factor, two main factors involved in vessel wall pathology, also modulated OPN expression via AP-1 activation.

TALE class homeodomain gene Irx5 is an immediate downstream target for Hoxb4 transcriptional regulation

The Hox genes are a family of homeodomain-containing transcription factors that determine anteroposterior identity early on in development. Although much is now known about their regulation and function, very little is known of their effector (downstream target) genes. Here, we show that the TALE class homeodomain transcription factor Irx5 is a direct, positively regulated target of Hoxb4.

A glucocorticoid-induced leucine-zipper protein, GILZ, inhibits adipogenesis of mesenchymal cells

Mesenchymal stem cells have the potential to differentiate into various cell lineages, including adipocytes and osteoblasts. The induction of adipocyte differentiation by glucocorticoids (GCs) not only causes the accumulation of fat cells in bone marrow, but also depletes the supply of osteoblasts for new bone formation, thus leading to osteoporosis. We have shown that a GC-induced leucine-zipper protein (GILZ) antagonizes adipocyte differentiation. GILZ binds to a tandem repeat of CCAAT/enhancer-binding protein (C/EBP) binding sites in the promoter of the gene encoding peroxisome-proliferator-activated receptor-gamma2 (PPAR-gamma2), and inhibits its transcription as a sequence-specific transcriptional repressor. We have also shown that ectopic expression of GILZ blocks GC-induced adipocyte differentiation. Furthermore, adipogenic marker genes (for example, those encoding PPAR-gamma2, C/EBP-alpha, lipoprotein lipase and adipsin) are also inhibited by GILZ. Our results reveal a novel GC antagonistic mechanism that has potential therapeutic applications for the inhibition of GC-induced adipocyte differentiation.

Gene expression profiling reveals progesterone-mediated cell cycle and immunoregulatory roles of Hoxa-10 in the preimplantation uterus

Human infertility and recurrent pregnancy loss caused by implantation defects are poorly understood. Hoxa-10-deficient female mice have severe infertility and recurrent pregnancy loss due to defective uterine implantation. Gene expression profiling experiments reveal that Hoxa-10 is an important regulator of two critical events in implantation: stromal cell proliferation and local immunosuppression. At the time of implantation, Hoxa-10 mediates the progesterone-stimulated proliferation of uterine stromal cells. Hoxa-10 mutants express a stromal cell proliferation defect that is accompanied by quantitative or spatial alterations in the expression of two cyclin-dependent kinase inhibitor genes, p57 and p15. Hoxa-10 deficiency also leads to a severe local immunological disturbance, characterized by a polyclonal proliferation of T cells, that occurs in place of the normal progesterone-mediated immunosuppression in the periimplantation uterus.

Two major Smad pathways in TGF-beta superfamily signalling

Members of the transforming growth factor-beta (TGF-beta) superfamily bind to two different serine/threonine kinase receptors, i.e. type I and type II receptors. Upon ligand binding, type I receptors specifically activate intracellular Smad proteins. R-Smads are direct substrates of type I receptors; Smads 2 and 3 are specifically activated by activin/nodal and TGF-beta type I receptors, whereas Smads 1, 5 and 8 are activated by BMP type I receptors. Nearly 30 proteins have been identified as members of the TGF-beta superfamily in mammals, and can be classified based on whether they activate activin/TGF-beta-specific R-Smads (AR-Smads) or BMP-specific R-Smads (BR-Smads). R-Smads form complexes with Co-Smads and translocate into the nucleus, where they regulate the transcription of target genes. AR-Smads bind to various proteins, including transcription factors and transcriptional co-activators or co-repressors, whereas BR-Smads interact with other proteins less efficiently than AR-Smads. Id proteins are induced by BR-Smads, and play important roles in exhibiting some biological effects of BMPs. Understanding the mechanisms of TGF-beta superfamily signalling is thus important for the development of new ways to treat various clinical diseases in which TGF-beta superfamily signalling is involved.

Persistent parity-induced changes in growth factors, TGF-beta3, and differentiation in the rodent mammary gland

Epidemiological studies have repeatedly demonstrated that women who undergo an early first full-term pregnancy have a significantly reduced lifetime risk of breast cancer. Similarly, rodents that have previously undergone a full-term pregnancy are highly resistant to carcinogen-induced breast cancer compared with age-matched nulliparous controls. Little progress has been made, however, toward understanding the biological basis of this phenomenon. We have used DNA microarrays to identify a panel of 38 differentially expressed genes that reproducibly distinguishes, in a blinded manner, between the nulliparous and parous states of the mammary gland in multiple strains of mice and rats. We find that parity results in the persistent down-regulation of multiple genes encoding growth factors, such as amphiregulin, pleiotrophin, and IGF-1, as well as the persistent up-regulation of the growth-inhibitory molecule, TGF-beta3, and several of its transcriptional targets. Our studies further indicate that parity results in a persistent increase in the differentiated state of the mammary gland as well as lifelong changes in the hematopoietic cell types resident within the gland. These findings define a developmental state of the mammary gland that is refractory to carcinogenesis and suggest novel hypotheses for the mechanisms by which parity may modulate breast cancer risk.

The small GTPase Rap1 is an immediate downstream target for Hoxb4 transcriptional regulation

The Hox genes are a family of homeodomain-containing transcription factors which determine anteroposterior identity early on in development. Although a lot is now known about their regulation and function, very little is known of their effector (downstream target) genes. Here we show that the small GTPase Rap1 is a direct, negatively regulated target of Hoxb4 and is excluded from Hoxb4 expressing cells.

Regulation of cell proliferation by Smad proteins

Transforming growth factor-beta (TGF-beta) family members which include TGF-betas, activins, and bone morphogenetic proteins (BMPs) regulate a broad spectrum of biological responses on a large variety of cell types. TGF-beta family members initiate their cellular responses by binding to distinct receptors with intrinsic serine/threonine kinase activity and activation of specific downstream intracellular effectors termed Smad proteins. Smads relay the signal from the cell membrane to the nucleus, where they affect the transcription of target genes. Smad activation, subcellular distribution, and stability have been found to be intricately regulated and a broad array of transcription factors have been identified as Smad partners. Important activities of TGF-beta are its potent anti-mitogenic and pro-apoptotic effects that, at least in part, are mediated via Smad proteins. Escape from TGF-beta/Smad-induced growth inhibition and apoptosis is frequently observed in tumors. Certain Smads have been found to be mutated in specific types of cancer and gene ablation of particular Smads in mice has revealed increased rate of tumorigenesis. In late stage tumors, TGF-beta has been shown to function as a tumor promoter. TGF-beta can stimulate the de-differentiation of epithelial cells to malignant invasive and metastatic fibroblastic cells. Interestingly, TGF-beta may mediate these effects directly on tumor cells via subverted Smad-dependent and/or Smad-independent pathways.

The metastasis gene osteopontin: a candidate target for cancer therapy

Malignant tumors are characterized by dysregulated growth control, overcoming of replicative senescence, and metastasis formation. Current therapeutic regimens mostly exert their effects through inhibition of cell cycle progression, leaving two major components of transformation untouched. The cytokine osteopontin is essential for the dissemination of various cancers. Past research has implied several modes in which osteopontin and its main receptors on tumor cells can be suppressed. Osteopontin expression is inhibitable on the levels of gene transcription and the RNA message, and the osteopontin protein can be blocked with antibodies or synthetic peptides. The osteopontin receptor CD44 has been targeted by diverse therapeutic strategies, including cytotoxic and immunotherapeutic approaches. The receptor integrin alpha(V)beta(3) contributes not only to tumor cell dissemination, but also to angiogenesis and osteolysis in bone metastases. Small molecule inhibitors of this receptor are under study as drug candidates. Because receptors and cytokine ligands that mediate metastasis formation are sparsely expressed in the adult healthy organism and are more readily reached by pharmaceuticals than intracellular drug targets they may represent a particularly suitable focus for therapeutic intervention.

Proliferation of primitive myeloid progenitors can be reversibly induced by HOXA10

Recent studies show that several Hox transcription factors are important for regulation of proliferation and differentiation in hematopoiesis. Among these is H0XA10, which is selectively expressed at high levels in the most primitive subpopulation of human CD34(+) bone marrow cells. When overexpressed, H0XA10 increases the proliferation of early progenitor cells and can lead to the development of myeloid leukemia. To study the effects of H0XA10 on primitive hematopoietic progenitors in more detail, transgenic mice were generated with regulatable H0XA10 expression. The transgenic mouse model, referred to as tetO-HOXA10, contains the H0XA10 gene controlled by a tetracycline-responsive element and a minimal promoter. Thus, the expression of H0XA10 is inducible and reversible depending on the absence or presence of tetracycline or its analog, doxycycline. A retroviral vector containing the tetracycline transactivator gene (tTA) was used to induce expression of the H0XA10 gene in bone marrow cells from the transgenic mice. Reverse transcription-polymerase chain reaction analysis confirmed regulatable H0XA10 expression in several transgenic lines. H0XA10 induction led to the formation of hematopoietic colonies containing blastlike cells and megakaryocytes. Moreover, the induction of H0XA10 resulted in significant proliferative advantage of primitive hematopoietic progenitors (spleen colony-forming units [CFU-S(12)]), which was reversible on withdrawal of induction. Activation of H0XA10 expression in tet0-H0XA10 mice will therefore govern proliferation of primitive myeloid progenitors in a regulated fashion. This novel animal model can be used to identify the target genes of HOXA10 and better clarify the specific role of HOXA10 in normal and malignant hematopoiesis.

Divergence and convergence of TGF-beta/BMP signaling

The transforming growth factor-beta (TGF-beta) superfamily includes more than 30 members which have a broad array of biological activities. TGF-beta superfamily ligands bind to type II and type I serine/threonine kinase receptors and transduce signals via Smad proteins. Receptor-regulated Smads (R-Smads) can be classified into two subclasses, i.e. those activated by activin and TGF-beta signaling pathways (AR-Smads), and those activated by bone morphogenetic protein (BMP) pathways (BR-Smads). The numbers of type II and type I receptors and Smad proteins are limited. Thus, signaling of the TGF-beta superfamily converges at the receptor and Smad levels. In the intracellular signaling pathways, Smads interact with various partner proteins and thereby exhibit a wide variety of biological activities. Moreover, signaling by Smads is modulated by various other signaling pathways allowing TGF-beta superfamily ligands to elicit diverse effects on target cells. Perturbations of the TGF-beta/BMP signaling pathways result in various clinical disorders including cancers, vascular diseases, and bone disorders.

Characteristics of the binding of aminoglycoside antibiotics to teichoic acids. A potential model system for interaction of aminoglycosides with polyanions

The binding of the aminoglycoside antibiotic dihydrostreptomycin to defined cell-wall teichoic acids and to lipoteichoic acid isolated from various gram-positive eubacteria was followed by equilibrium dialysis. Dihydrostreptomycin was used at a wide range of concentration under different conditions of ionic strength, concentration of teichoic acid, presence of cationic molecules like Mg2+, spermidine, other aminoglycoside antibiotics (gentamicin, neomycin, paromomycin). Interaction of dihydrostreptomycin with teichoic acid was found to be a cooperative binding process. The binding characteristics seem to be dependent on structural features of teichoic acid and are influenced by cationic molecules. Mg2+, spermidine and other aminoglycosides antibiotics inhibit the binding of dihydrostreptomycin to teichoic acid competitively. The binding of aminoglycosides to teichoic acids is considered as a model system for the interaction of aminoglycoside antibiotics with cellular polyanions. Conclusions of physiological significance are drawn.