DEC1 is a downstream target of TGF-beta with sequence-specific transcriptional repressor activities

BHLHE41, a transcriptional repressor involved in physiological processes and tumor development

BHLHE41 is a nuclear transcriptional repressor that belongs to the basic helix-loop-helix protein superfamily. BHLHE41 expression tends to be restricted to specific tissues and is regulated by environmental cues and biological events. BHLHE41 homodimerizes or heterodimerizes with various partners, influencing its transcription factor function. BHLHE41 is involved in the regulation of many physiological processes implicated in tissue/organ homeostasis, such as myogenesis, adipogenesis, circadian rhythms and DNA repair. At cellular level, BHLHE41 is involved in the regulation of mesenchymal stem cell properties, tissue-specific macrophage functions and lymphoid lineage physiology. In several cancer types, BHLHE41 modulates the expression of different transcriptional programs influencing cell cycle control, apoptosis, invasiveness, epithelial to mesenchymal transition and hypoxia response in the tumor environment. Depending on the cancer cell type, BHLHE41 can act as a tumor suppressor or an oncogene, and could be a target for innovative therapies. This review summarizes the available knowledge on BHLHE41 structure, biological functions, regulation and potential partners, as well as its role in physiological processes, and its implication in major cancer steps.

DEC1 is involved in TGF-β1-induced epithelial-mesenchymal transition of gastric cancer

DEC1 is a helix-loop-helix (bHLH) transcription factor, whose deregulation has been observed in several tumors. However, the effects of the dysregulation of this gene on epithelial-mesenchymal transition (EMT) are controversial, with its roles in gastric cancer (GC) remaining unclear. In the present study, we focused on the impact of DEC1 on EMT and cell mobility in gastric cancer. We found that DEC1 expression positively correlated with TGF-β1 and EMT markers in tumor issues, and that DEC1 facilitated TGF-β1-induced EMT in gastric cancer. In addition, gastric cancer cell migration potential was reduced after DEC1 knockdown. Using murine metastasis models, we confirmed that DEC1 promoted GC metastasis and further explored the correlation of DEC1 with TGF-β1 and E-cadherin in vivo. Chromatin immunoprecipitation (ChIP) assays revealed that DEC1 could directly interact with the promoter region of TGF-β1. These results suggest that DEC1 functions as a tumor enhancer that partially participates in TGF-β1-mediated EMT processes in GC, thus contributing to tumor metastasis.

Integrative dissection of gene regulatory elements at base resolution

Although vast numbers of putative gene regulatory elements have been cataloged, the sequence motifs and individual bases that underlie their functions remain largely unknown. Here, we combine epigenetic perturbations, base editing, and deep learning to dissect regulatory sequences within the exemplar immune locus encoding CD69. We converge on a ∼170 base interval within a differentially accessible and acetylated enhancer critical for CD69 induction in stimulated Jurkat T cells. Individual C-to-T base edits within the interval markedly reduce element accessibility and acetylation, with corresponding reduction of CD69 expression. The most potent base edits may be explained by their effect on regulatory interactions between the transcriptional activators GATA3 and TAL1 and the repressor BHLHE40. Systematic analysis suggests that the interplay between GATA3 and BHLHE40 plays a general role in rapid T cell transcriptional responses. Our study provides a framework for parsing regulatory elements in their endogenous chromatin contexts and identifying operative artificial variants.

Differentiated Embryo-Chondrocyte Expressed Gene1 and Parkinson's Disease: New Insights and Therapeutic Perspectives

Differentiated embryo-chondrocyte expressed gene1 (DEC1), an important transcription factor with a basic helix-loop-helix domain, is ubiquitously expressed in both human embryonic and adult tissues. DEC1 is involved in neural differentiation and neural maturation in the central nervous system (CNS). Recent studies suggest that DEC1 protects against Parkinson's disease (PD) by regulating apoptosis, oxidative stress, lipid metabolism, immune system, and glucose metabolism disorders. In this review, we summarize the recent progress on the role of DEC1 in the pathogenesis of PD and provide new insights into the prevention and treatment of PD and neurodegenerative diseases.

Novel Thioether-Bridged 2,6-Disubstituted and 2,5,6-Trisubstituted Imidazothiadiazole Analogues: Synthesis, Antiproliferative Activity, ADME, and Molecular Docking Studies

In this study, starting from 2-amino-1,3,4-thiadiazole derivatives (3-5), a new series of 2,6-disubstituted (compounds 7-15) and 2,5,6-trisubstituted (compounds 16-33) imidazo[2,1-b][1,3,4]-thiadiazole derivatives were synthesized using cyclization and Mannich reaction mechanisms, respectively. All synthesized compounds were characterized by ¹ H-NMR, ¹³ C-NMR, FT-IR, elemental analysis, and mass spectroscopy techniques. Also, X-ray diffraction analysis were used for compounds 4, 7, 11, 17, and 19. The cytotoxic effects of the new compounds on the viability of colon cancer cells (DLD-1), lung cancer cells (A549), and liver cancer cells (HepG2) were investigated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method in vitro. Compound 15 was found to be the most potent anticancer drug candidate in this series with an IC₅₀ value of 3.63 μM against HepG2 for 48 h. Moreover, the absorption, distribution, metabolism, and excretion (ADME) parameters of the synthesized compounds were calculated and thus, their potential to be safe drugs was evaluated. Finally, to support the biological activity experiments, molecular docking studies of these compounds were carried out on three different target cancer protein structures (PDB IDs: 5ETY, 1M17, and 3GCW), and the amino acids that play key roles in the binding of the compounds to these proteins were determined.

Promotion of colorectal cancer by transcription factor BHLHE40 involves upregulation of ADAM19 and KLF7

BHLHE40 is a transcription factor, whose role in colorectal cancer has remained elusive. We demonstrate that the BHLHE40 gene is upregulated in colorectal tumors. Transcription of BHLHE40 was jointly stimulated by the DNA-binding ETV1 protein and two associated histone demethylases, JMJD1A/KDM3A and JMJD2A/KDM4A, which were shown to also form complexes on their own and whose enzymatic activity was required for BHLHE40 upregulation. Chromatin immunoprecipitation assays revealed that ETV1, JMJD1A and JMJD2A interacted with several regions within the BHLHE40 gene promoter, suggesting that these three factors directly control BHLHE40 transcription. BHLHE40 downregulation suppressed both growth and clonogenic activity of human HCT116 colorectal cancer cells, strongly hinting at a pro-tumorigenic role of BHLHE40. Through RNA sequencing, the transcription factor KLF7 and the metalloproteinase ADAM19 were identified as putative BHLHE40 downstream effectors. Bioinformatic analyses showed that both KLF7 and ADAM19 are upregulated in colorectal tumors as well as associated with worse survival and their downregulation impaired HCT116 clonogenic activity. In addition, ADAM19, but not KLF7, downregulation reduced HCT116 cell growth. Overall, these data have revealed a ETV1/JMJD1A/JMJD2A→BHLHE40 axis that may stimulate colorectal tumorigenesis through upregulation of genes such as KLF7 and ADAM19, suggesting that targeting this axis represents a potential novel therapeutic avenue.

A novel role of helix-loop-helix transcriptional factor Bhlhe40 in osteoclast activation

The basic helix-loop-helix transcriptional factor, Bhlhe40 has been shown as a crucial regulator of immune response, tumorigenesis, and circadian rhythms. We identified Bhlhe40 as a possible regulator of osteoclast differentiation and function by shRNA library screening and found that Bhlhe40 was required for osteoclast activation. Bhlhe40 expression was induced in bone marrow macrophages (BMMs) by RANKL, whereas the expression of its homolog Bhlhe41 was decreased in osteoclastogenesis. μCT analysis of tibias revealed that Bhlhe40 knockout (KO) mice exhibited increased bone volume phenotype. Bone morphometric analysis showed that osteoclast number and bone resorption were decreased in Bhlhe40 KO mice, whereas significant differences in the osteoblast parameters were not seen between wild-type (WT) and Bhlhe40 KO mice. In vitro culture of BMMs showed that Bhlhe40 deficiency did not cause difference in osteoclast formation. In contrast, bone resorption activity of Bhlhe40 KO osteoclasts was markedly reduced in comparison with that of WT osteoclasts. Analysis of potential target genes of Bhlhe40 using data-mining platform ChIP-Atlas (http://chip-atlas.org) revealed that predicted target genes of Bhlhe40 were related to proton transport and intracellular vesicle acidification. We then analyzed the expression of proton pump, the vacuolar (V)-ATPases which are responsible for bone resorption. The expression of V-ATPases V1c1 and V0a3 was suppressed in Bhlhe40 KO osteoclasts. In addition, Lysosensor yellow/blue DND 160 staining demonstrated that vesicular acidification was attenuated in vesicles of Bhlhe40 KO osteoclasts. Furthermore, analysis with pH-sensitive fluorescent probe showed that proton secretion was markedly suppressed in Bhlhe40 KO osteoclasts compared to that in WT osteoclasts. Our findings suggest that Bhlhe40 plays a novel important role in the regulation of acid production in osteoclastic bone resorption.

Differential immunohistochemical expression of DEC1, CK‑1ε, and CD44 in oral atypical squamous epithelium and carcinoma in situ

Presence of nuclear atypia during histological investigation is often a cause of concern for pathologists while identifying tumor and non-tumor cells in a biopsy sample of oral mucosa. Nuclear atypia is observed in severe inflammation, ulcers and reactive changes. Therefore, additional methods, such as immunohistochemistry, may help precise diagnosis. When the atypia is suggestive of tumorous or reactive origin, the lesion is diagnosed as atypical squamous epithelium (ASE). When there is severe nuclear atypia in the mucosa, such as in disorders of nuclear polarity, large nuclei, and clear nucleolus, the lesion is diagnosed as carcinoma in situ (CIS). However, it is not easy to distinguish ASE and CIS using hematoxylin and eosin staining. The present study aimed to distinguish ASE from CIS using immunohistochemistry. A total of 32 biopsy samples of either ASE or CIS cases were selected and the level of casein kinase 1ε (CK-1ε), differentiated embryonic chondrocyte gene 1 (DEC1), proliferating cell nuclear antigen (PCNA) and CD44, which are four protein markers which have been previously linked to cancer progression, were analyzed. CK-1ε and CD44 expression was higher in CIS samples than in ASE samples. However, DEC1 expression was lower in CIS samples than in ASE samples. PCNA expression was not markedly different between the two groups. Additionally, it was found that DEC1-overexpressing cells had decreased levels of CK-1ε and CD44 compared with control cells, while CK-1ε-overexpressing cells had relatively unchanged levels of CD44, DEC1 and PCNA. These results suggested that DEC1 negatively regulates the expression of CK-1ε and CD44. Thus, DEC1, CK-1ε, and CD44 were identified as mechanistically linked and clinically relevant protein biomarkers, which could help distinguish ASE and CIS.

Circadian Dysregulation of the TGFβ/SMAD4 Pathway Modulates Metastatic Properties and Cell Fate Decisions in Pancreatic Cancer Cells

Impairment of circadian rhythms impacts carcinogenesis. SMAD4, a clock-controlled gene and central component of the TGFβ canonical pathway, is frequently mutated in pancreatic ductal adenocarcinoma (PDA), leading to decreased survival. Here, we used an in vitro PDA model of SMAD4-positive and SMAD4-negative cells to investigate the interplay between circadian rhythms, the TGFβ canonical signaling pathway, and its impact on tumor malignancy. Our data show that TGFβ1, SMAD3, SMAD4, and SMAD7 oscillate in a circadian fashion in SMAD4-positive PDA cells, whereas altering the clock impairs the mRNA dynamics of these genes. Furthermore, the expression of the clock genes DEC1, DEC2, and CRY1 varied depending on SMAD4 status. TGFβ pathway activation resulted in an altered clock, cell-cycle arrest, accelerated apoptosis rate, enhanced invasiveness, and chemosensitivity. Our data suggest that the impact of TGFβ on the clock is SMAD4-dependent, and S MAD3, SMAD4, DEC1, and CRY1 involved in this cross-talk affect PDA patient survival.

Non-circadian aspects of BHLHE40 cellular function in cancer

While many genes specifically act as oncogenes or tumor suppressors, others are tumor promoters or suppressors in a context-dependent manner. Here we will review the basic-helix-loop-helix (BHLH) protein BHLHE40, (also known as BHLHB2, STRA13, DEC1, or SHARP2) which is overexpressed in gastric, breast, and brain tumors; and downregulated in colorectal, esophageal, pancreatic and lung cancer. As a transcription factor, BHLHE40 is expressed in the nucleus, where it binds to target gene promoters containing the E-box hexanucleotide sequence, but can also be expressed in the cytoplasm, where it stabilizes cyclin E, preventing cyclin E-mediated DNA replication and cell cycle progression. In different organs BHLHE40 regulates different targets; hence may have different impacts on tumorigenesis. BHLHE40 promotes PI3K/Akt/mTOR activation in breast cancer, activating tumor progression, but suppresses STAT1 expression in clear cell carcinoma, triggering tumor suppression. Target specificity likely depends on cooperation with other transcription factors. BHLHE40 is activated in lung and esophageal carcinoma by the tumor suppressor p53 inducing senescence and suppressing tumor growth, but is also activated under hypoxic conditions by HIF-1α in gastric cancer and hepatocellular carcinomas, stimulating tumor progression. Thus, BHLHE40 is a multi-functional protein that mediates the promotion or suppression of cancer in a context dependent manner.

Extracellular vesicle cross-talk between pulmonary artery smooth muscle cells and endothelium during excessive TGF-β signalling: implications for PAH vascular remodelling

BACKGROUND

Excessive TGF-β signalling has been shown to underlie pulmonary hypertension (PAH). Human pulmonary artery smooth muscle cells (HPASMCs) can release extracellular vesicles (EVs) but their contents and significance have not yet been studied. Here, we aimed to analyse the contents and biological relevance of HPASMC-EVs and their transport to human pulmonary arterial endothelial cells (HPAECs), as well as the potential alteration of these under pathological conditions.

METHODS

We used low-input RNA-Seq to analyse the RNA cargoes sorted into released HPASMC-EVs under basal conditions. We additionally analysed the effects of excessive TGF-β signalling, using TGF-β1 and BMP4, in the transcriptome of HPASMCs and their EVs. We then, for the first time, optimised Cre-loxP technology for its use with primary cells in vitro, directly visualising HPASMC-to-HPAEC communication and protein markers on cells taking up EVs. Furthermore we could analyse alteration of this transport with excessive TGF-β signalling, as well as by other cytokines involved in PAH: IL-1β, TNF-α and VEGFA.

RESULTS

We were able to detect transcripts from 2417 genes in HPASMC-EVs. Surprisingly, among the 759 enriched in HPASMC-EVs compared to their donor cells, we found Zeb1 and 2 TGF-β superfamily ligands, GDF11 and TGF-β3. Moreover, we identified 90 genes differentially expressed in EVs from cells treated with TGF-β1 compared to EVs in basal conditions, including a subset involved in actin and ECM remodelling, among which were bHLHE40 and palladin. Finally, using Cre-loxP technology we showed cell-to-cell transfer and translation of HPASMC-EV Cre mRNA from HPASMC to HPAECs, effectively evidencing communication via EVs. Furthermore, we found increased number of smooth-muscle actin positive cells on HPAECs that took up HPASMC-EVs. The uptake and translation of mRNA was also higher in activated HPAECs, when stimulated with TGF-β1 or IL-1β.

CONCLUSIONS

HPASMC-EVs are enriched in RNA transcripts that encode genes that could contribute to vascular remodelling and EndoMT during development and PAH, and TGF-β1 up-regulates some that could enhance this effects. These EVs are functionally transported, increasingly taken up by activated HPAECs and contribute to EndoMT, suggesting a potential effect of HPASMC-EVs in TGF-β signalling and other related processes during PAH development.

Interaction with SP1, but not binding to the E-box motifs, is responsible for BHLHE40/DEC1-induced transcriptional suppression of CLDN1 and cell invasion in MCF-7 cells

Basic helix-loop-helix family member e40 (BHLHE40) is located in 3p26.1 and acts as a transcriptional repressor of the circadian rhythm by suppressing the expression of the clock genes and clock-controlled genes. Recent research indicated that BHLHE40 may be involved in regulating tumor cell progression. However the mechanism by which BHLHE40 regulates the invasion and metastasis of tumor cells is unclear. Our in vitro assays showed that BHLHE40 promoted tumor cell invasion while BHLHE40 silencing by siRNA suppressed tumor cell invasion of MCF-7 cells. BHLHE40 suppressed the mRNA and protein expression of CLDN1 CLDN4 and CDH1 and promoted the expression of SNAI1 and SNAI2. Reporter assays demonstrated that BHLHE40 suppressed CLDN1 transcription but not through direct binding to the E-box motifs in the CLDN1 promoter. Further studies demonstrated BHLHE40 suppressed CLDN1 transcription by preventing the interaction between SP1 and a specific motif within the promoter region of CLDN1. BHLHE40 could not further suppress CLDN1 transactivation after SP1 siRNA transfection that is, BHLHE40-induced suppression of CLDN1 relied on SP1. Furthermore our data indicated that SP1 was a major regulator of CLDN1 transcription by binding to a specific motif that was located at -233 to -61 bp upstream of the transcription start site. Immunoprecipitation and co-localization data revealed an interaction between BHLHE40 and SP1. By constructing deletion mutants we found that the BHLH and Orange regions are both essential for the BHLHE40-SP1 interaction. BHLHE40 probably acts as an inhibitory nuclear cofactor or perhaps recruits other inhibitory cofactors to inhibit the SP1-mediated CLDN1 transactivation. These results suggest that BHLHE40 facilitates cell invasion and may be used as a novel target for breast cancer prevention and treatment.

Calpain inhibition attenuates bleomycin-induced pulmonary fibrosis via switching the development of epithelial-mesenchymal transition

Calpains are intracellular calcium-dependent cysteine proteases, which cleave several substrates proteins, have been proven to play important roles in lung fibrosis. The aim of this study was to investigate the effects of calpain on bleomycin (BLM)-induced pulmonary fibrosis. A lung fibrosis mice model was established successfully by intraperitoneal injection of bleomycin. Calpeptin, a highly selective inhibitor of calpain activation, was administered three times weekly after bleomycin injection. Histological examination was used to assess the fibrosis. Quantitative-PCR and Western blotting were used to assess the development of epithelial-mesenchymal transition (EMT). We found calpeptin treatment decreased the BLM-induced EMT-associated markers, such as muscle actin (α-SMA) and collagen-I, while increased E-cadherin (E-cad). Calpeptin also suppressed the activation of transforming growth factor β1 (TGFβ1)-Smad2/3 signaling pathway, which plays crucial role in lung fibrosis and EMT. Furthermore, we found differentiated embryonic chondrocyte-expressed gene 1 (DEC1), an important transcription factor, was upregulated in both patients with idiopathic pulmonary fibrosis and in bleomycin-induced lung fibrosis. DEC1 was suppressed by calpeptin in bleomycin-induced mice model. Collectively, these findings indicated that calpeptin had a potential anti-fibrosis effect, which focus on the development of EMT.

Hypoxia stimulates microenvironment in human embryonic stem cell through inflammatory signalling: An integrative analysis

Despite, several lines of evidence suggesting the possible role of hypoxia in stem cell development and differentiation its significance in conferring the stemness and pluripotency remains elusive. In the present study we sought to delineate the candidate genes and molecular pathways imposed during hypoxic microenvironment and its physiological relevance in tipping the balance between the niche and cellular differentiation. Integrated meta-analysis was performed between the hypoxia exposed and normal human embryonic stem cells, employing three transcriptomic cohorts (GSE35819, GSE9510 and GSE37761) retrieved from Gene expression omnibus (GEO) database. Results reveal that a total number of 12 genes were consistently differentially expressed (6up regulated and 6 down regulated) with FDR <0.05 and fold change >1.5. The Gene Ontology (GO) functions and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis was performed using DAVID. The GO analysis showed DEG significantly enriched in terms of Cellular process (GO:0009987), protein binding (GO:0005515) and cell part (GO:0044464). KEGG analysis indicated participation of genes associated with circadian rthyum regulation and PPAR signalling pathway. Further, gene-set signature (MsigDB) enrichment analysis showed positive regulation with inflammatory signals and negative association with PPAR and p53 pathway. Protein-protein network of gene modules suggests significant hub proteins viz. CTTNB1 (Degree = 18), IL8 (Degree = 15), NFKB1 (Degree = 15) and RELA (Degree = 15) in the PPI network. MCODE algorithm was used for subnetworks of the PPI network. Our integrative analysis documents the potential candidate genes which serves distinct roles influencing metabolic shift and induce inflammatory effectors contributing to hypoxic mediated stem cell niche.

SMAD transcription factors are altered in cell models of HD and regulate HTT expression

Transcriptional dysregulation is observable in multiple animal and cell models of Huntington's disease, as well as in human blood and post-mortem caudate. This contributes to HD pathogenesis, although the exact mechanism by which this occurs is unknown. We therefore utilised a dynamic model in order to determine the differential effect of growth factor stimulation on gene expression, to highlight potential alterations in kinase signalling pathways that may be in part responsible for the transcriptional dysregulation observed in HD, and which may reveal new therapeutic targets. We demonstrate that cells expressing mutant huntingtin have a dysregulated transcriptional response to epidermal growth factor stimulation, and identify the transforming growth factor-beta pathway as a novel signalling pathway of interest that may regulate the expression of the Huntingtin (HTT) gene itself. The dysregulation of HTT expression may contribute to the altered transcriptional phenotype observed in HD.

Transcriptional regulator Bhlhe40 works as a cofactor of T-bet in the regulation of IFN-γ production in iNKT cells

Invariant natural killer T (iNKT) cells are a subset of innate-like T cells that act as important mediators of immune responses. In particular, iNKT cells have the ability to immediately produce large amounts of IFN-γ upon activation and thus initiate immune responses in various pathological conditions. However, molecular mechanisms that control IFN-γ production in iNKT cells are not fully understood. Here, we report that basic helix-loop-helix transcription factor family, member e40 (Bhlhe40), is an important regulator for IFN-γ production in iNKT cells. Bhlhe40 is highly expressed in stage 3 thymic iNKT cells and iNKT1 subsets, and the level of Bhlhe40 mRNA expression is correlated with Ifng mRNA expression in the resting state. Although Bhlhe40-deficient mice show normal iNKT cell development, Bhlhe40-deficient iNKT cells show significant impairment of IFN-γ production and antitumor effects. Bhlhe40 alone shows no significant effects on Ifng promoter activities but contributes to enhance T-box transcription factor Tbx21 (T-bet)-mediated Ifng promoter activation. Chromatin immunoprecipitation analysis revealed that Bhlhe40 accumulates in the T-box region of the Ifng locus and contributes to histone H3-lysine 9 acetylation of the Ifng locus, which is impaired without T-bet conditions. These results indicate that Bhlhe40 works as a cofactor of T-bet for enhancing IFN-γ production in iNKT cells.

Regulation of the Mechanism of TWIST1 Transcription by BHLHE40 and BHLHE41 in Cancer Cells

BHLHE40 and BHLHE41 (BHLHE40/41) are basic helix-loop-helix type transcription factors that play key roles in multiple cell behaviors. BHLHE40/41 were recently shown to be involved in an epithelial-to-mesenchymal transition (EMT). However, the precise mechanism of EMT control by BHLHE40/41 remains unclear. In the present study, we demonstrated that BHLHE40/41 expression was controlled in a pathological stage-dependent manner in human endometrial cancer (HEC). Our in vitro assays showed that BHLHE40/41 suppressed tumor cell invasion. BHLHE40/41 also suppressed the transcription of the EMT effectors SNAI1, SNAI2, and TWIST1. We identified the critical promoter regions of TWIST1 for its basal transcriptional activity. We elucidated that the transcription factor SP1 was involved in the basal transcriptional activity of TWIST1 and that BHLHE40/41 competed with SP1 for DNA binding to regulate gene transcription. This study is the first to report the detailed functions of BHLHE40 and BHLHE41 in the suppression of EMT effectors in vitro. Our results suggest that BHLHE40/41 suppress tumor cell invasion by inhibiting EMT in tumor cells. We propose that BHLHE40/41 are promising markers to predict the aggressiveness of each HEC case and that molecular targeting strategies involving BHLHE40/41 and SP1 may effectively regulate HEC progression.

Hypoxia Inhibits Myogenic Differentiation through p53 Protein-dependent Induction of Bhlhe40 Protein

Satellite cells are muscle-resident stem cells capable of self-renewal and differentiation to repair injured muscles. However, muscle injury often leads to an ischemic hypoxia environment that impedes satellite cell differentiation and reduces the efficiency of muscle regeneration. Here we performed microarray analyses and identified the basic helix-loop-helix family transcription factor Bhlhe40 as a candidate mediator of the myogenic inhibitory effect of hypoxia. Bhlhe40 is strongly induced by hypoxia in satellite cell-derived primary myoblasts. Overexpression of Bhlhe40 inhibits Myog expression and mimics the effect of hypoxia on myogenesis. Inhibition of Bhlhe40, conversely, up-regulates Myog expression and promotes myogenic differentiation. Importantly, Bhlhe40 knockdown rescues myogenic differentiation under hypoxia. Mechanistically, Bhlhe40 binds to the proximal E-boxes of the Myog promoter and reduces the binding affinity and transcriptional activity of MyoD on Myog. Interestingly, hypoxia induces Bhlhe40 expression independent of HIF1α but through a novel p53-dependent signaling pathway. Our study establishes a crucial role of Bhlhe40 in mediating the repressive effect of hypoxia on myogenic differentiation and suggests that inhibition of Bhlhe40 or p53 may facilitate muscle regeneration after ischemic injuries.

DEC1 regulates breast cancer cell proliferation by stabilizing cyclin E protein and delays the progression of cell cycle S phase

Breast cancer that is accompanied by a high level of cyclin E expression usually exhibits poor prognosis and clinical outcome. Several factors are known to regulate the level of cyclin E during the cell cycle progression. The transcription factor DEC1 (also known as STRA13 and SHARP2) plays an important role in cell proliferation and apoptosis. Nevertheless, the mechanism of its role in cell proliferation is poorly understood. In this study, using the breast cancer cell lines MCF-7 and T47D, we showed that DEC1 could inhibit the cell cycle progression of breast cancer cells independently of its transcriptional activity. The cell cycle-dependent timing of DEC1 overexpression could affect the progression of the cell cycle through regulating the level of cyclin E protein. DEC1 stabilized cyclin E at the protein level by interacting with cyclin E. Overexpression of DEC1 repressed the interaction between cyclin E and its E3 ligase Fbw7α, consequently reducing the level of polyunbiquitinated cyclin E and increased the accumulation of non-ubiquitinated cyclin E. Furthermore, DEC1 also promoted the nuclear accumulation of Cdk2 and the formation of cyclin E/Cdk2 complex, as well as upregulating the activity of the cyclin E/Cdk2 complex, which inhibited the subsequent association of cyclin A with Cdk2. This had the effect of prolonging the S phase and suppressing the growth of breast cancers in a mouse xenograft model. These events probably constitute the essential steps in DEC1-regulated cell proliferation, thus opening up the possibility of a protein-based molecular strategy for eliminating cancer cells that manifest a high-level expression of cyclin E.

Involvement of c-Myc in the proliferation of MCF-7 human breast cancer cells induced by bHLH transcription factor DEC2

Differentiated embryonic chondrocyte expressed gene 1 (DEC1; BHLHE40/Stra13/Sharp2) and differentiated embryonic chondrocyte expressed gene 2 (DEC2; BHLHE41/Sharp1) are basic helix-loop-helix (bHLH) transcriptional factors that are involved in the regulation of cell differentiation, circadian rhythms, response to hypoxia and carcinogenesis. Previous studies have demonstrated that the expression of DECs is induced under hypoxic conditions in various normal and cancer cell lines. In the present study, using RT-qPCR and western blot analysis, we demonstrated that hypoxia induced the expression of DEC1 and DEC2 in MCF-7 human breast cancer cells; their expression levels reached a peak at different time points. In particular, we found that the expression pattern of the hypoxia-inducible factor (HIF)-1α protein was similar to DEC1, and that of the HIF-2α protein was identical to that of DEC2. The knockdown of HIF-2α using siRNA suppressed the phosphorylation of Akt, as well as the expression of DEC2 and c-Myc. Hypoxia failed to affect the expression of DEC2 and c-Myc when the PI3K/Akt signaling pathway was blocked. In addition, the overexpression of DEC1 and DEC2 was induced by transfecting the cells with a pcDNA vector. The overexpression of DEC2, but not that of DEC1, increased the proliferation of the MCF-7 cells under both normoxic and hypoxic conditions. Concomitantly, the expression of c-Myc was upregulated by exposure to hypoxia and by the overexpression of DEC2. In conclusion, DEC2 participates in hypoxia-induced cell proliferation by functioning as a target gene of the PI3K/Akt signaling pathway and regulating the expression of c-Myc.

DEC1 coordinates with HDAC8 to differentially regulate TAp73 and ΔNp73 expression

P73, a member of the p53 family, plays a critical role in neural development and tumorigenesis. Due to the usage of two different promoters, p73 is expressed as two major isoforms, TAp73 and ΔNp73, often with opposing functions. Here, we reported that transcriptional factor DEC1, a target of the p53 family, exerts a distinct control of TAp73 and ΔNp73 expression. In particular, we showed that DEC1 was able to increase TAp73 expression via transcriptional activation of the TAp73 promoter. By contrast, Np73 transcription was inhibited by DEC1 via transcriptional repression of the ΔNp73 promoter. To further explore the underlying mechanism, we showed that DEC1 was unable to increase TAp73 expression in the absence of HDAC8, suggesting that HDAC8 is required for DEC1 to enhance TAp73 expression. Furthermore, we found that DEC1 was able to interact with HDAC8 and recruit HDAC8 to the TAp73, but not the ΔNp73, promoter. Together, our data provide evidence that DEC1 and HDAC8 in differentially regulate TAp73 and ΔNp73 expression, suggesting that this regulation may lay a foundation for a therapeutic strategy to enhance the chemosensitivity of tumor cells.

DEC1/STRA13/SHARP2 and DEC2/SHARP1 coordinate physiological processes, including circadian rhythms in response to environmental stimuli

Daily physiological and behavioral rhythms are regulated by endogenous circadian molecular clocks. Clock proteins DEC1 (BHLHe40) and DEC2 (BHLHe41) belong to the basic helix-loop-helix protein superfamily, which contains other clock proteins CLOCK and BMAL1. DEC1 and DEC2 are induced by CLOCK:BMAL1 heterodimer via the CACGTG E-box in the promoter and, thereafter, suppress their own expression by competing with CLOCK:BMAL1 for the DNA binding. This negative feedback DEC loop together with the PER loop involving PER and CRY, the other negative clock regulators, maintains the circadian rhythm of Dec1 and Dec2 expression. DEC1 is induced by light pulse and adjusts the circadian phase of the central clock in the suprachiasmatic nucleus, whereas DEC1 upregulation by TGF-β resets the circadian phase of the peripheral clocks in tissues. Furthermore, DEC1 and DEC2 modulate the clock output signals to control circadian rhythms in behavior and metabolism. In addition to the functions in the clocks, DEC1 and DEC2 are involved in hypoxia responses, immunological reactions, and carcinogenesis. These DEC actions are mediated by the direct binding to the E-box elements in target genes or by protein-protein interactions with transcription factors such as HIF-1α, RXRα, MyoD, and STAT. Notably, numerous growth factors, hormones, and cytokines, along with ionizing radiation and DNA-damaging agents, induce Dec1 and/or Dec2 in a tissue-specific manner. These findings suggest that DEC1 and DEC2 play a critical role in animal adaptation to various environmental stimuli.

The gene for the transcription factor BHLHE40/DEC1/stra13 is a dynamically regulated primary target of the vitamin D receptor

The basic helix-loop-helix protein BHLHE40 functions as a transcriptional repressor and is involved in the control of cellular growth, development and circadian rhythms. By the use of genome-wide data on vitamin D receptor (VDR) location, open chromatin and histone modification backed-up by gene-specific mRNA expression studies we show that the human BHLHE40 gene is dynamically up-regulated by the VDR ligand 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) and down-regulated by the histone deactylase inhibitor trichostatin A. The VDR binding site is located 1.7kb upstream of the transcription start site of the BHLHE40 gene and the chromatin at this genomic site is significantly opened by treatment with 1α,25(OH)2D3. The stair case style fluctuations in the BHLHE40 mRNA accumulation relate to the short half-life of the gene's mRNA of 0.9h. The identification of the widely expressed BHLHE40 gene as a primary VDR target may explain secondary effects of 1α,25(OH)2D3 on BHLHE40 responding genes. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Differentiated embryonic chondrocyte-expressed gene 1 is associated with hypoxia-inducible factor 1α and Ki67 in human gastric cancer

Background

Gastric cancer is a leading causes of cancer-related deaths ,but the underlying molecular mechanisms of its progression are largely unknown. Differentiated embryonic chondrocyte-expressed gene 1 (DEC1), is an important transcription factor involved in the progression of tumors and has recently been identified to be strongly inducible by hypoxia. Little is known about the contribution of DEC1 to the intracellular hypoxia and proliferation signaling events in gastric cancer.

Methods

Immunohistochemistry was used to detect the expression of DEC1, hypoxia-inducible factor 1(HIF-1α) and Ki67 in 173 human gastric cancer samples and adjacent non-tumor tissues samples. The relationship between DEC1, HIF-1α and Ki67 was evaluated.

Results

DEC1 protein was persistently expressed in the nucleus and cytoplasm of gastric cancer tissue. The protein expression of DEC1 and HIF-1α in tumour tissues was 83.8% and 54.3%, respectively, and was significantly higher than that in adjacent normal tissues (83.8% vs 23.7%, P <0.001; 54.3% vs 12.7%, P< 0.001). The expression of DEC1 and HIF-1α was associated with poor histological differentiation. (P < 0. 01). Furthermore, DEC1 level was positively correlated with HIF-1α (P < 0. 01, r=0.290) and Ki67 expression (P < 0. 01, r=0.249).

Conclusion

The upregulation of DEC1 may play an important role in hypoxia regulation and cell proliferation in gastric cancer. The relevant molecular mechanism requires further investigation.

Virtual Slides

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Transforming growth factor-beta inhibits the expression of clock genes

Disturbances of sleep-wake rhythms are an important problem in Alzheimer's disease (AD). Circadian rhythms are regulated by clock genes. Transforming growth factor-beta (TGF-β) is overexpressed in neurons in AD and is the only cytokine that is increased in cerebrospinal fluid (CSF). Our data show that TGF-β2 inhibits the expression of the clock genes Period (Per)1, Per2, and Rev-erbα, and of the clock-controlled genes D-site albumin promoter binding protein (Dbp) and thyrotroph embryonic factor (Tef). However, our results showed that TGF-β2 did not alter the expression of brain and muscle Arnt-like protein-1 (Bmal1). The concentrations of TGF-β2 in the CSF of 2 of 16 AD patients and of 1 of 7 patients with mild cognitive impairment were in the dose range required to suppress the expression of clock genes. TGF-β2-induced dysregulation of clock genes may alter neuronal pathways, which may be causally related to abnormal sleep-wake rhythms in AD patients.

The increased expression of DEC1 gene is related to HIF-1α protein in gastric cancer cell lines

Overexpression of differentiated embryo chondrocyte 1 (DEC1) has been reported to contribute to the cellular differentiation, proliferation, and apoptosis of various cancers. Our previous studies have shown that DEC1 was highly expressed in gastric cancer (GCa) tissues. However, there is no report about the expression of DEC1 in GCa cell lines until now. In this study, We evaluated the mRNA and protein expression of DEC1 and hypoxia-inducible factor 1α (HIF-1α) under normoxic and hypoxic conditions in six GCa cell lines: BGC-823, MGC80-3, MKN1, AGS, FU97 and SGC-7901. An HIF-1α protein inhibitor was used to analyze the association of DEC1 and HIF-1α expression. Under normoxia, the mRNA expression of both HIF-1α and DEC1 was moderate, whereas the protein expression of DEC1 was higher than that of HIF-1α. Hypoxia induced the mRNA expression of DEC1 and the protein expression of HIF-1α and DEC1 in a time-dependent manner but had no effect on the mRNA expression of HIF-1α. Furthermore, inhibition of HIF-1α protein expression resulted in a significant decrease in both the mRNA and protein expression of DEC1. Taken together, DEC1 expression is correlated with HIF-1α protein in GCa cell line, blockage of HIF-1α protein led to reduced DEC1 expression. The efficacy of inhibiting HIF-1α and DEC1 expression should be tested in clinical trials as possible treatment for GCa.

DeltaNp63, a target of DEC1 and histone deacetylase 2, modulates the efficacy of histone deacetylase inhibitors in growth suppression and keratinocyte differentiation

The p63 gene, a member of the p53 family, is expressed as TA and ΔN isoforms. ΔNp63 is the predominant isoform expressed in cells of epithelial origin and frequently overexpressed in cancers. However, what regulates p63 expression is uncertain. Here, we showed that ΔNp63 is regulated by the transcription factor DEC1, a p53 family target. We also showed that the ability of DEC1 to regulate ΔNp63 is enhanced by histone deacetylase (HDAC) inhibitors or knockdown of histone deacetylase 2 (HDAC2). Consistent with this, we found that DEC1 and HDAC2 physically interact and knockdown of HDAC2 leads to increased binding of DEC1 to the ΔNp63 promoter. Interestingly, we found that growth suppression induced by HDAC inhibitors is attenuated by ectopic expression of DEC1 in a ΔNp63-dependent manner. In addition, we showed that ectopic expression of DEC1 inhibits, whereas knockdown of DEC1 promotes, keratinocyte differentiation via modulating ΔNp63 expression. Finally, we showed that DEC1 cooperates with HDAC inhibitors to further decrease keratinocyte differentiation. Together, we conclude that ΔNp63 is a novel target of DEC1 and HDAC2 and modulates the efficacy of HDAC inhibitors in growth suppression and keratinocyte differentiation.

The role of the basic helix-loop-helix transcription factor Dec1 in the regulatory T cells

Naturally occurring regulatory T (Treg) cells play a central role in the maintenance of immune homeostasis and in restraining the development of spontaneous inflammatory responses. However, the underlying mechanisms of Treg homeostasis remain incompletely understood. Of particular note, the IL-2Rα (CD25) is crucial for the homeostasis of Treg cells and the prevention of lymphoproliferative autoimmune disease. In this paper, we report that the basic helix-loop-helix transcription factor Dec1 is involved in the homeostasis of Treg cells and plays a role in their survival or expansion after adoptive transfer to lymphopenic recipients. Hence, it is crucial for the suppression of effector T cell-mediated inflammatory responses. Enforced expression of Dec1 upregulates CD25 expression during thymocyte development and increases the number of Treg cells in the periphery. Dec1 binds the transcription factor Runx1 and colocalizes with Runx1 in Treg cells. Specifically, we demonstrate that in Treg cells the Dec1/Runx1 complex binds to regulatory elements present in the Il-2rα locus. Collectively, these data show how Dec1 mechanistically acts in Treg cells.

Hypoxia inducible BHLHB2 is a novel and independent prognostic marker in pancreatic ductal adenocarcinoma

AIMS

The cyclic adenosine monophosphate-inducible basic helix-loop-helix (bHLH) domain containing class-B2 transcriptional factor BHLHB2 is differentially expressed in a number of human malignancies. In the present study, the expression, regulation, functions and prognostic impact of BHLHB2 in pancreatic cancer were investigated.

METHODS

Expression analyses were carried out in tissues of the normal pancreas (n=10) and pancreatic ductal adenocarcinoma (n=77) as well as in eight pancreatic cancer cell lines using quantitative RT-PCR, semiquantitative immunohistochemistry, and immunoblot analyses. In vitro functional experiments were conducted using siRNA transfection, hypoxia, serum starvation, apoptosis induction with gemcitabine and actinomycin-D, and invasion assays. Survival analysis was performed using the Kaplan-Meier method. Prognostic factors were determined in a multivariable analysis using a Cox proportional hazards model.

RESULTS

BHLHB2 mRNA and protein expressions were strongly induced by hypoxia and by serum starvation in pancreatic cancer cell lines. BHLHB2 silencing with RNAi had no significant effects on growth and invasion but increased apoptosis resistance against gemcitabine by reducing caspace-3 cleavage. In BHLHB2 silenced cells the ED50 of gemcitabine increased from 13.95 ± 1.353 to 38.70 ± 5.262 nM (p<0.05). Ex vivo, the weak/absent nuclear staining in normal pancreatic ducts and acinar cells was replaced by moderate to strong nuclear/cytoplasmic staining in PanIN lesions and pancreatic cancer cells. Patients with weak/absent nuclear BHLHB2 staining had significantly worse median survival compared to those with strong staining (13 months vs. 27 months, p=0.03). In a multivariable analysis, BHLHB2 staining was an independent prognostic factor (Hazard-Ratio=2.348, 95% CI=1.250-4.411, p=0.008).

CONCLUSIONS

Hypoxia-inducible BHLHB2 expression is a novel independent prognostic marker in pancreatic cancer patients and indicates increased chemosensitivity towards gemcitabine.

The rexinoid bexarotene represses cyclin D1 transcription by inducing the DEC2 transcriptional repressor

Bexarotene is an RXR-selective vitamin A analog that has been shown to prevent ER-negative mammary tumorigenesis in animal models. While investigating the mechanism by which bexarotene prevents ER-negative breast cancer development, we found that the expression of cyclin D1, a critical cell cycle promoter, was repressed by bexarotene in vitro and in vivo. Time course and cycloheximide experiments show that repression of cyclin D1 is a late effect and requires new protein synthesis. Previously we discovered that DEC2 (differentially expressed in chondrocytes-2), a helix-loop-helix transcription repressor, was induced by bexarotene in human mammary epithelial cells. Therefore, we hypothesized that bexarotene represses the transcription of cyclin D1 through induction of DEC2. Luciferase reporter studies demonstrated that either bexarotene treatment or forced expression of DEC2 can repress the transcription of a cyclin D1 promoter reporter by affecting the basal transcriptional activity. Results from chromatin immunoprecipitation experiments showed that bexarotene treatment causes the recruitment of DEC2 and HDAC1 (histone deacetylase 1) to the cyclin D1 promoter. Co-immunoprecipitation confirms the interaction between DEC2 and HDAC1, suggesting that the recruitment of HDAC1 to the cyclin D1 promoter is through DEC2. Trichostatin A, a HDAC inhibitor, reverses the cyclin D1 repression by bexarotene, suggesting that repression of cyclin D1 involves histone deacetylation. Knock-down of DEC2 by siRNA abolishes the cyclin D1 repression, further supporting our hypothesis. Finally, we demonstrated that overexpression of DEC2 dramatically inhibited cell proliferation and repressed the expression of cyclin D1 in human mammary epithelial cells. These results suggest that bexarotene down-regulates cyclin D1 through induction of DEC2, followed by recruitment of HDAC1 to the cyclin D1 promoter causing transcriptional repression. By elucidating the mechanism by which rexinoids inhibit cell proliferation, it will be possible to develop more effective and less toxic drugs to prevent ER-negative breast cancers.

Tumor suppression by p53: making cells senescent

Cellular senescence is a permanent cell cycle arrest and a potent tumor suppression mechanism. The p53 tumor suppressor is a sequence-specific transcription factor and acts as a central hub sensing various stress signals and activating an array of target genes to induce cell cycle arrest, apoptosis, and senescence. Recent reports showed that restoration of p53 induces premature senescence and tumor regression in mice with hepatocarcinomas or sarcomas. Thus, p53-mediated senescence is capable of eliminating cancer cells in vivo. p63 and p73, two homologues of p53, have similar function in cell cycle arrest and apoptosis. However, the role of p63 and p73 in cellular senescence is elusive. In this review, we will discuss how p53 regulates senescence and future studies about p53 family members in senescence.

The hypoxia-regulated transcription factor DEC1 (Stra13, SHARP-2) and its expression in gastric cancer

Differentiated embryo-chondrocyte expressed gene 1 (DEC1), as a bHLH transcriptional factor, plays important roles in cell differentiation, proliferation, and apoptosis. The expression of DEC1 and its role in human gastric cancer are unknown. This study was designed to characterize the DEC1 gene profiling of human gastric cancer tissues. The expression of DEC1 in gastric cancer tissues was analyzed by cDNA microarray, reverse-transcriptase polymerase chain reaction (RT-PCR), Western blot, and immunohistochemical studies. Microarray assay demonstrated that DEC1 was one of the upregulated genes in gastric cancer when compared with normal tissues. The expression of DEC1 mRNA was increased in gastric cancer as determined by RT-PCR. An increased DEC1 protein expression in gastric cancer was verified by Western blot analysis. Immunohistochemical studies showed that the 83.02% gastric cancer tissues (44/53) were stained positive for DEC1. The DEC1 expression was increased during the tumor progression from well differentiated (50%, 4/8) to moderately differentiated (76%, 13/17), and poorly differentiated (96%, 27/28) tumor tissues. In contrast, a weak staining for DEC1 (low expression) was observed in 10 % normal tissues (1/10). Statistical analysis found a significant correlation between increased DEC1 expression and poorly differentiated cancer tissues. These data characterized DEC1 expression in gastric cancer and identified a correlation between upregulation of DEC1 expression and differentiation of gastric cancer, suggesting that DEC1 may play an important role in the differentiation and progression of gastric cancer.

PI-3 kinase pathway can mediate the effect of TGF-beta1 in inducing the expression of SHARP-2 in LLC-PK1 cells

We aim to investigate the effect of transforming growth factor (TGF)-beta1 on the expression of enhancer of split- and hairy-related protein-2 (SHARP-2) messenger RNA (mRNA) and its signaling pathway. In this study, several cell lines including LLC-PK1 (a porcine kidney tubular epithelial cell line), MDCK (Madin-Darby canine kidney) and CTLL-2 (cytotoxic T-lymphocyte line) were treated with recombinant human TGF-beta1, and a series of experiments were carried out, involving Northern blot analysis of total RNA from these cells. Further, several specific chemical inhibitors were applied before TGF-beta1 treatment to probe the signaling pathway. The results showed that TGF-beta1 can significantly up-regulate SHARP-2 mRNA expression in the LLC-PK1 cell line. The peak level of induction was found 2 h after TGF-beta1 stimulation. While one phosphoinositide 3-kinases (PI-3) kinase inhibitor, LY294002, completely blocked the effect of TGF-beta1 on SHARP-2 mRNA expression in LLC-PK1 cells at a low concentration, other inhibitors, including PD98059, staurosporine, AG490, wortmannin, okadaic acid and rapamycin, had no effect. The effect of LY294002 was dose-dependent. We conclude that, in LLC-PK1 cells at least, TGF-beta1 can effectively induce the SHARP-2 mRNA expression and that the PI-3 kinase pathway can mediate this effect.

Clock Gene Modulation by TNF-α Depends on Calcium and p38 MAP Kinase Signaling

A 24-h treatment with the cytokine tumor necrosis factor-α (TNF-α) suppresses transcription of E-box—driven clock genes (D-site albumin promoter binding protein, Dbp; Tyrotroph embryonic factor, Tef ; Hepatic leukemia factor, Hlf; Period homolog to Drosophila 1/2/3, Per1, Per2, and Per3) by yet unknown molecular mechanisms. The attenuation of clock genes has been suggested as a putative cause for the development of sickness behavior syndrome in infectious and autoimmune diseases. Here, the authors studied the effect of TNF-α at early time points (<3 h) on intracellular signaling events and clock gene expression in fibroblasts. Interaction of TNF-α with TNFR1 ( Tnfrsf1a , CD120a, p55), but not TNFR2 ( Tnfrsf1b, CD120b , p75), leads to fast downregulation of gene expression of Dbp and upregulation of negative regulators of the molecular clock, Per1 and Per2, Cryptochrome-1 ( Cry1), and Differentiated embryo chondrocytes-1 ( Dec1). Since the decrease of Dbp is also observed in cells deficient for Per1/Per2, Cry1/ Cry2 , or Dec1, these genes are unlikely to be responsible for inhibition of Dbp. The early effect of TNF-α on the clock gene Per1 is dependent on p38, mitogen-activated protein kinase (MAPK), and/or calcium signaling, whereas the effect on Dbp is independent of p38 MAPK, but also involves calcium signaling. Both genes remain unaffected by the NF-κB and AP-1 pathway. Taken collectively these data show p38 MAPK- and calcium-dependent TNFR1-mediated transient increase of the negative regulator Per1 and an independent decrease of Dbp.

A regulatory pathway involving Notch1/beta-catenin/Isl1 determines cardiac progenitor cell fate

Regulation of multipotent cardiac progenitor cell (CPC) expansion and subsequent differentiation into cardiomyocytes, smooth muscle or endothelial cells is a fundamental aspect of basic cardiovascular biology and cardiac regenerative medicine. However, the mechanisms governing these decisions remain unclear. Here, we show that Wnt/beta-catenin signalling, which promotes expansion of CPCs, is negatively regulated by Notch1-mediated control of phosphorylated beta-catenin accumulation within CPCs, and that Notch1 activity in CPCs is required for their differentiation. Notch1 positively, and beta-catenin negatively, regulated expression of the cardiac transcription factors, Isl1, Myocd and Smyd1. Surprisingly, disruption of Isl1, normally expressed transiently in CPCs before their differentiation, resulted in expansion of CPCs in vivo and in an embryonic stem (ES) cell system. Furthermore, Isl1 was required for CPC differentiation into cardiomyocyte and smooth muscle cells, but not endothelial cells. These findings reveal a regulatory network controlling CPC expansion and cell fate that involves unanticipated functions of beta-catenin, Notch1 and Isl1 that may be leveraged for regenerative approaches involving CPCs.

Singular value decomposition-based regression identifies activation of endogenous signaling pathways in vivo

Singular value decomposition regression can detect the activation of endogenous signaling pathways, allowing the identification of pathway cross-talk.

The ability to detect activation of signaling pathways based solely on gene expression data represents an important goal in biological research. We tested the sensitivity of singular value decomposition-based regression by focusing on functional interactions between the Ras and transforming growth factor beta signaling pathways. Our findings demonstrate that this approach is sufficiently sensitive to detect the secondary activation of endogenous signaling pathways as it occurs through crosstalk following ectopic activation of a primary pathway.

Activation of TGF-beta/activin signalling resets the circadian clock through rapid induction of Dec1 transcripts

The circadian clock is reset by external time cues for synchronization to environmental changes. In mammals, the light-input signalling pathway mediated by Per gene induction has been extensively studied. On the other hand, little is known about resetting mechanisms that are independent of Per induction. Here we show that activation of activin receptor-like kinase (ALK), triggered by TGF-beta, activin or alkali signals, evoked resetting of the cellular clock independently of Per induction. The resetting was mediated by an immediate-early induction of Dec1, a gene whose physiological role in the function of the circadian clock has been unclear. Acute Dec1 induction was a prerequisite for ALK-mediated resetting and upregulation was dependent on SMAD3, which was phosphorylated for activation in response to the resetting stimuli. Intraperitoneal injection of TGF-beta into wild-type or Dec1-deficient mice demonstrated that Dec1 has an essential role in phase-shift of clock gene expression in the kidney and adrenal gland. These results indicate that ALK-SMAD3-Dec1 signalling provides an input pathway in the mammalian molecular clock.

ID1, inhibitor of differentiation/DNA binding, is an effector of the p53-dependent DNA damage response pathway

ID1, inhibitor of differentiation/DNA binding, plays an important role in cell proliferation, differentiation, and tumorigenesis. It has been shown that ID1 is de-regulated in multiple cancers and up-regulation of ID1 is correlated with high grades and poor prognosis of human cancers. In contrast, the p53 tumor suppressor was found to be mutated or inactivated in most human cancers and loss of p53 results in early onset of multiple cancers. Although the biological functions of the ID1 oncogene and the p53 tumor suppressor have been intensively investigated, little is known about the upstream regulators of ID1 and the cross-talk between ID1 and p53. Here, we showed that ID1 is down-regulated in cells treated with various DNA damage agents in a p53-dependent manner. Interestingly, we found that DEC1, which was recently identified as a p53 target and mediates p53-dependent cell cycle arrest and senescence, is capable of inhibiting ID1 expression. Conversely, we found that knockdown of DEC1 attenuates DNA damage-induced ID1 repression. In addition, we identified several potential DEC1 responsive elements in the proximal promoter region of the ID1 gene. Moreover, we showed that overexpression of ID1 or ID1', an isoform of ID1, promotes cell proliferation potentially through inhibition of p21 expression. Finally, we found that the extent of DNA damage-induced premature senescence was substantially decreased by overexpression of ID1 or ID1'. Taken together, our study suggests that p53 trans-repressional activity can be mediated by its own target DEC1 and ID1 is an effector of the p53-dependent DNA damage response pathway.

Two novel VHL targets, TGFBI (BIGH3) and its transactivator KLF10, are up-regulated in renal clear cell carcinoma and other tumors

Mutations in the VHL gene are associated with highly vascular tumors of kidney, brain, retina, and adrenal gland. The inability of the mutant VHL protein to destabilize HIF-1 plays a crucial role in malignant angiogenesis. VHL is also associated with ECM assembly but the molecular mechanisms of this activity remain unclear. We used expression arrays and cell lines with different VHL status to identify ECM-associated genes controlled by VHL. One of them, adhesion-associated TGFBI, was repressed by VHL and overexpressed in renal, gastrointestinal, brain, and other tumors. Analyzing the mechanism of TGFBI up-regulation in clear cell carcinoma, we identified a novel VHL target, a Kruppel-like transcriptional factor 10 (KLF10). The TGFBI promoter, which we isolated and studied in Luc-reporter assay, was induced by KLF10 but not hypoxia. These data provide the molecular basis for the observed VHL effect on TGFBI and stimulate further research into the KLF10 and TGFBI roles in cancer.

Human somatic cell gene targeting

Human somatic cell gene targeting provides a powerful tool to scientists studying gene function in cultured human cells. This technology allows scientists to knock out genes in human somatic cells in a fashion analogous to the creation of knockout mice. Human somatic cell gene targeting brings the power of genetics to the study of human genes in human cells by making it possible to compare cells or individuals that are genetically identical except for a single, well-defined mutation in an endogenous gene. These modified cells can be studied both in vitro and in vivo. This unit presents protocols for human somatic cell gene targeting.

Transforming growth factor-beta promotes survival of mammary carcinoma cells through induction of antiapoptotic transcription factor DEC1

Transforming growth factor-beta (TGF-beta) signaling facilitates tumor growth and metastasis in advanced cancer. In the present study, we identified differentially expressed in chondrocytes 1 (DEC1, also known as SHARP2 and Stra13) as a downstream target of TGF-beta signaling, which promotes the survival of breast cancer cells. In the mouse mammary carcinoma cell lines JygMC(A) and 4T1, the TGF-beta type I receptor kinase inhibitors A-44-03 and SB431542 induced apoptosis of cells under serum-free conditions. Oligonucleotide microarray and real-time reverse transcription-PCR analyses revealed that TGF-beta induced DEC1 in these cells, and the increase of DEC1 was suppressed by the TGF-beta type I receptor kinase inhibitors as well as by expression of dominant-negative TGF-beta type II receptor. Overexpression of DEC1 prevented the apoptosis of JygMC(A) cells induced by A-44-03, and knockdown of endogenous DEC1 abrogated TGF-beta-promoted cell survival. Moreover, a dominant-negative mutant of DEC1 prevented lung and liver metastasis of JygMC(A) cells in vivo. Our observations thus provide new insights into the molecular mechanisms governing TGF-beta-mediated cell survival and metastasis of cancer.

bHLH-Orange Transcription Factors in Development and Cancer

Basic helix-loop-helix (bHLH) proteins are a large superfamily of transcription factors that play critical roles in many physiological processes including cellular differentiation, cell cycle arrest and apoptosis. Based on structural and phylogenetic analysis, mammalian bHLH-Orange (bHLH-O) proteins, which constitute the repressor family of bHLH factors, can be grouped into four subfamilies: Hes, Hey, Helt and Stra13/Dec. In addition to the bHLH domain that mediates DNA-binding and protein dimerization, all members of this family are characterized by a distinctive motif called the "Orange domain" which is present exclusively in these factors. Genetic studies using targeted mutagenesis in mice have revealed essential roles for many bHLH-O genes in embryonic development, cell fate decisions, differentiation of a number of cell types and in apoptosis. Furthermore, growing evidence of crosstalk between bHLH-O proteins with the tumor suppressors p53 and hypoxia-inducible factor, have started to shed light on their possible roles in oncogenesis. Consistently, deregulated expression of several bHLH-O factors is associated with various human cancers. Here, we review the structure and biological functions of bHLH-O factors, and discuss recent studies that suggest a potential role for these factors in tumorigenesis and tumor progression.

DEC1, a basic helix-loop-helix transcription factor and a novel target gene of the p53 family, mediates p53-dependent premature senescence

Cellular senescence plays an important role in tumor suppression. p53 tumor suppressor has been reported to be crucial in cellular senescence. However, the underlying mechanism is poorly understood. In this regard, a cDNA microarray assay was performed to identify p53 targets involved in senescence. Among the many candidates is DEC1, a basic helix-loop-helix transcription factor that has been recently shown to be up-regulated in K-ras-induced premature senescence. However, it is not clear whether DEC1 is capable of inducing senescence. Here, we found that DEC1 is a novel target gene of the p53 family and mediates p53-dependent premature senescence. Specifically, we showed that DEC1 is induced by the p53 family and DNA damage in a p53-dependent manner. We also found that the p53 family proteins bind to, and activate, the promoter of the DEC1 gene. In addition, we showed that overexpression of DEC1 induces G(1) arrest and promotes senescence. Moreover, we found that targeting endogenous DEC1 attenuates p53-mediated premature senescence in response to DNA damage. Furthermore, overexpression of DEC1 induces cellular senescence in p53-knockdown cells, albeit to a lesser extent. Finally, we showed that DEC1-induced senescence is p21-independent. Taken together, our data provided strong evidence that DEC1 is one of the effectors downstream of p53 to promote premature senescence.

Unraveling the molecular targets pertinent to junction restructuring events during spermatogenesis using the Adjudin-induced germ cell depletion model

During spermatogenesis, extensive restructuring takes place at the Sertoli-Sertoli and Sertoli-germ cell interface, which is regulated via intriguing interactions among cytokines, proteases, protease inhibitors, kinases, phosphatases, and transcription factors. This in turn determines the steady-state levels of integral membrane proteins at the cell junctions. We sought to further expand these observations using the Adjudin model. Adjudin is a potential male contraceptive that targets Sertoli-germ cell adhesion, causing exfoliation of spermatids and spermatocytes, but not spermatogonia, from the seminiferous epithelium. This model thus provides the means to identify crucial regulatory molecules and signaling pathways pertinent to junction restructuring events during spermatogenesis. In this study, genome-wide expression profiling of rat testes after treatment with Adjudin at the time of extensive junction restructuring was performed. Differentially regulated genes, such as cytokines, proteases, protease inhibitors, cell junction-associated proteins, and transcription factors pertinent to junction restructuring were identified. These data were consistent with earlier findings; however, much new information was obtained which has been deposited at the Gene Expression Omnibus data repository website: http://www.ncbi.nih.gov/geo/ with Accession number: GSE5131. The primary signaling events pertinent to junction restructuring in the testis induced by Adjudin were also delineated using bioinformatics. These findings were also consistent with recently published reports. The identified molecular signatures or targets pertinent to junction dynamics in the testis as reported herein, many of which have not been investigated, thus offer a framework upon which the regulation of junction restructuring events at the Sertoli-Sertoli and Sertoli-germ cell interface pertinent to spermatogenesis can be further studied.

A new inducible RNAi xenograft model for assessing the staged tumor response to mTOR silencing

Human xenograft tumor models are widely used for efficacy evaluation of potential cancer targets. siRNA is usually stably introduced into tumor cells prior to transplantation. However, silencing of the cancer therapeutic target usually results in reduced cell growth/survival in vitro and/or failure to establish tumors in vivo, thus hindering tumor response-based efficacy evaluation. The present study explored a new tumor response model based on regulated RNAi, which is more relevant from a clinical standpoint. As a proof of principle, an inducible lentiviral RNAi vector was used to silence the known cancer therapeutic target mTOR upon induction with Doxycycline (DOX). The responses to DOX-induced mTOR silencing were tested both in vitro and in vivo for prostate cancer PC3 models. Significant reduction in cancer cell survival was observed due to cell cycle arrest and apoptosis when mTOR silencing was induced in vitro. mTOR silencing also caused tumor regression for the early-staged PC3 tumors (100% tumor regressed and 45% became tumor-free). The advanced-staged tumors also demonstrated significant responses (100% regressed). Therefore, our results demonstrate the powerful utility of this new inducible xenograft tumor model for efficacy evaluation of cancer targets, and it provides a direct in vivo efficacy validation of mTOR as a cancer therapeutic target.

Hypoxic repression of STAT1 and its downstream genes by a pVHL/HIF-1 target DEC1/STRA13

DEC1/STRA13 is a bHLH type transcriptional regulator involved with immune regulation, hypoxia response and carcinogenesis. We recently demonstrated that STRA13 interacts with STAT3 in the transcriptional activation of STAT-dependent promoters. Here, we pursue STRA13 involvement in the JAK/STAT pathway by studying its role in STAT1 expression. First, we showed that VHL deficiency or HIF-1 activation resulted in the repression of endogenous STAT1 mediated by STRA13. We then characterized the STAT1 proximal promoter to assess its response to STRA13 by transient coexpression in a luciferase reporter assay. Using sequential truncation and site-directed mutagenesis of the STAT1 promoter with STRA13 deletion constructs, we showed that the STRA13 C-terminal trans-activation domain, which is known to bind HDAC1, mostly determines the repressive activity. Involvement of HDAC activity in STAT1 regulation was validated by TSA inhibition and chromatin immunoprecipitation (ChIP) assay. Thus, we demonstrate that STRA13-mediated repression of STAT1 transcription utilizes an HDAC1-dependent mechanism. Furthermore, we show that targets of unphosphorylated STAT1, such as antigen presenting genes and CASP1, are also repressed by hypoxia possibly through the same STRA13-mediated mechanism. Thus, the newly discovered link between HIF-1 and STAT1 reveals a previously unknown role of STRA13 in hypoxia and carcinogenesis.