Cooperative E-box regulation of human GLI1 by TWIST and USF

GLI1, a novel target of the ER stress regulator p97/VCP, promotes ATF6f-mediated activation of XBP1

Upon accumulation of improperly folded proteins in the Endoplasmic Reticulum (ER), the Unfolded Protein Response (UPR) is triggered to restore ER homeostasis. The induction of stress genes is a sine qua non condition for effective adaptive UPR. Although this requirement has been extensively described, the mechanisms underlying this process remain in part uncharacterized. Here, we show that p97/VCP, an AAA+ ATPase known to contribute to ER stress-induced gene expression, regulates the transcription factor GLI1, a primary effector of Hedgehog (Hh) signaling. Under basal (non-ER stress) conditions, GLI1 is repressed by a p97/VCP-HDAC1 complex while upon ER stress GLI1 is induced through a mechanism requiring both USF2 binding and increase histone acetylation at its promoter. Interestingly, the induction of GLI1 was independent of ligand-regulated Hh signaling. Further analysis showed that GLI1 cooperates with ATF6f to induce promoter activity and expression of XBP1, a key transcription factor driving UPR. Overall, our work demonstrates a novel role for GLI1 in the regulation of ER stress gene expression and defines the interplay between p97/VCP, HDAC1 and USF2 as essential players in this process.

Epigenetic landscape change analysis during human EMT sheds light on a key EMT mediator TRIM29

Epithelial to mesenchymal transition (EMT) is a key trans-differentiation process, which plays a critical role in physiology and pathology. Although gene expression changes in EMT have been scrutinized, study of epigenome is in its infancy. To understand epigenetic changes during TWIST-driven EMT, we used the AcceSssIble assay to study DNA methylation and chromatin accessibility in human mammary epithelial cells (HMECs). The DNA methylation changes were found to have functional significance in EMT - i.e. methylated genes were enriched for E-box motifs that can be recognized by TWIST, at the promoters suggesting a potential targeting phenomenon, whereas the demethylated regions were enriched for pro-metastatic genes, supporting the role of EMT in metastasis. TWIST-induced EMT triggers alterations in chromatin accessibility both independent of and dependent on DNA methylation changes, primarily resulting in closed chromatin conformation. By overlapping the genes, whose chromatin structure is changed during early EMT and a known "core EMT signature", we identified 18 driver candidate genes during EMT, 14 upregulated and 4 downregulated genes with corresponding chromatin structure changes. Among 18 genes, we focused on TRIM29 as a novel marker of EMT. Although loss of TRIM29 is insufficient to suppress CDH, it is enough to induce CDH2 and VIM. Gene functional annotation analysis shows the involvement of TRIM29 in epidermal development, cell differentiation and cell migration. Taken together, our results provide a robust snapshot of chromatin state during human EMT and identify TRIM29 as a core mediator of EMT.

The Heterodimeric TWIST1-E12 Complex Drives the Oncogenic Potential of TWIST1 in Human Mammary Epithelial Cells

The TWIST1 embryonic transcription factor displays biphasic functions during the course of carcinogenesis. It facilitates the escape of cells from oncogene-induced fail-safe programs (senescence, apoptosis) and their consequent neoplastic transformation. Additionally, it promotes the epithelial-to-mesenchymal transition and the initiation of the metastatic spread of cancer cells. Interestingly, cancer cells recurrently remain dependent on TWIST1 for their survival and/or proliferation, making TWIST1 their Achilles’ heel. TWIST1 has been reported to form either homodimeric or heterodimeric complexes mainly in association with the E bHLH class I proteins. These complexes display distinct, sometimes even antagonistic, functions during development and unequal prometastatic functions in prostate cancer cells. Using a tethered dimer strategy, we successively assessed the ability of TWIST1 dimers to cooperate with an activated version of RAS in human mammary epithelial cell transformation, to provide mice with the ability to spontaneously develop breast tumors, and lastly to maintain a senescence program at a latent state in several breast cancer cell lines. We demonstrate that the TWIST1-E12 complex, unlike the homodimer, is an oncogenic form of TWIST1 in mammary epithelial cells and that efficient binding of both partners is a prerequisite for its activity. The detection of the heterodimer in human premalignant lesions by a proximity ligation assay, at a stage preceding the initiation of the metastatic cascade, is coherent with such an oncogenic function. TWIST1-E protein heterodimeric complexes may thus constitute the main active forms of TWIST1 with regard to senescence inhibition over the time course of breast tumorigenesis.

TWIST1 drives cisplatin resistance and cell survival in an ovarian cancer model, via upregulation of GAS6, L1CAM, and Akt signalling

Epithelial ovarian cancer (EOC) is the most deadly gynaecologic malignancy due to late onset of symptoms and propensity towards drug resistance. Epithelial-mesenchymal transition (EMT) has been linked to the development of chemoresistance in other cancers, yet little is known regarding its role in EOC. In this study, we sought to determine the role of the transcription factor TWIST1, a master regulator of EMT, on cisplatin resistance in an EOC model. We created two Ovcar8-derived cell lines that differed only in their TWIST1 expression. TWIST1 expression led to increased tumour engraftment in mice, as well as cisplatin resistance in vitro. RNA sequencing analysis revealed that TWIST1 expression resulted in upregulation of GAS6 and L1CAM and downregulation of HMGA2. Knockdown studies of these genes demonstrated that loss of GAS6 or L1CAM sensitized cells to cisplatin, but that loss of HMGA2 did not give rise to chemoresistance. TWIST1, in part via GAS6 and L1CAM, led to higher expression and activation of Akt upon cisplatin treatment, and inhibition of Akt activation sensitized cells to cisplatin. These results suggest TWIST1- and EMT-driven increase in Akt activation, and thus tumour cell proliferation, as a potential mechanism of drug resistance in EOC.

Hedgehog pathway activation in T-cell acute lymphoblastic leukemia predicts response to SMO and GLI1 inhibitors

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive childhood leukemia that is caused by the accumulation of multiple genomic lesions resulting in transcriptional deregulation and increased cell proliferation and survival. Through analysis of gene expression data, we provide evidence that the hedgehog pathway is activated in 20% of T-ALL samples. Hedgehog pathway activation is associated with ectopic expression of the hedgehog ligands Sonic hedgehog (SHH) or Indian hedgehog (IHH), and with upregulation of the transcription factor GLI1 Ectopic expression of SHH or IHH in mouse T cells in vivo caused hedgehog pathway activation in both lymphoid and epithelial cells in the thymus and resulted in increased expression of important T-cell stimulatory ligands (Dll4, Il7, and Vegf) by thymic epithelial cells. In T-ALL cell lines, pharmacological inhibition or short interfering RNA-mediated knockdown of SMO or GLI1 led to decreased cell proliferation. Moreover, primary T-ALL cases with high GLI1 messenger RNA levels, but not those with low or undetectable GLI1 expression, were sensitive to hedgehog pathway inhibition by GANT61 or GDC-0449 (vismodegib) using ex vivo cultures and in vivo xenograft models. We identify the hedgehog pathway as a novel therapeutic target in T-ALL and demonstrate that hedgehog inhibitors approved by the US Food and Drug Administration could be used for the treatment of this rare leukemia.

Signal Transduction Pathways of EMT Induced by TGF-β, SHH, and WNT and Their Crosstalks

Epithelial-to-mesenchymal transition (EMT) is a key step in development, wound healing, and cancer development. It involves cooperation of signaling pathways, such as transformation growth factor-β (TGF-β), Sonic Hedgehog (SHH), and WNT pathways. These signaling pathways crosstalk to each other and converge to key transcription factors (e.g., SNAIL1) to initialize and maintain the process of EMT. The functional roles of multi-signaling pathway crosstalks in EMT are sophisticated and, thus, remain to be explored. In this review, we focused on three major signal transduction pathways that promote or regulate EMT in carcinoma. We discussed the network structures, and provided a brief overview of the current therapy strategies and drug development targeted to these three signal transduction pathways. Finally, we highlighted systems biology approaches that can accelerate the process of deconstructing complex networks and drug discovery.

Receptor activator for nuclear factor-κB ligand signaling promotes progesterone-mediated estrogen-induced mammary carcinogenesis

Breast cancer is a leading cause of cancer-related death in women. Prolonged exposure to the ovarian hormones estrogen and progesterone increases the risk of breast cancer. Although estrogen is known as a primary factor in mammary carcinogenesis, very few studies have investigated the role of progesterone. Receptor activator for nuclear factor-κB (NF-κB) ligand (RANKL) plays an important role in progesterone-induced mammary carcinogenesis. However, the molecular mechanism underlying RANKL-induced mammary carcinogenesis remains unknown. In our current study, we show that RANKL induces glioma-associated oncogene homolog 1 (GLI-1) in estrogen-induced progesterone-mediated mammary carcinogenesis. In vivo experiments were carried out using ACI rats and in vitro experiments were carried out in MCF-7 cells. In ACI rats, mifepristone significantly reduced the incidence of mammary tumors. Likewise, mifepristone also inhibited the proliferation of MCF-7 cells. Hormone treatments induced RANKL, receptor activator of NF-κB (RANK), and NF-κB in a protein kinase B-dependent manner and inhibited apoptosis by activation of anti-apoptotic protein Bcl2 in mammary tumors and MCF-7 cells. Mechanistic studies in MCF-7 cells reveal that RANKL induced upstream stimulatory factor-1 and NF-κB, resulting in subsequent activation of their downstream target GLI-1. We have identified that progesterone mediates estrogen-induced mammary carcinogenesis through activation of GLI-1 in a RANKL-dependent manner.

Prioritization of cancer-related genomic variants by SNP association network

We have developed a general framework to construct an association network of single nucleotide polymorphisms (SNPs) (SNP association network, SAN) based on the functional interactions of genes located in the flanking regions of SNPs. SAN, which was constructed based on protein-protein interactions in the Human Protein Reference Database (HPRD), showed significantly enriched signals in both linkage disequilibrium (LD) and long-range chromatin interaction (Hi-C). We used this network to further develop two methods for predicting and prioritizing disease-associated genes from genome-wide association studies (GWASs). We found that random walk with restart (RWR) using SAN (RWR-SAN) can greatly improve the prediction of lung-cancer-associated genes by comparing RWR with the use of network in HPRD (AUC 0.81 vs 0.66). In a reanalysis of the GWAS dataset of age-related macular degeneration (AMD), SAN could identify more potential AMD-associated genes that were previously ranked lower in the GWAS study. The interactions in SAN could facilitate the study of complex diseases.

Structural and logical analysis of a comprehensive hedgehog signaling pathway to identify alternative drug targets for glioma, colon and pancreatic cancer

Hedgehog is an evolutionarily conserved developmental pathway, widely implicated in controlling various cellular responses such as cellular proliferation and stem cell renewal in human and other organisms, through external stimuli. Aberrant activation of this pathway in human adult stem cell line may cause different types of cancers. Hence, targeting this pathway in cancer therapy has become indispensable, but the non availability of detailed molecular interactions, complex regulations by extra- and intra-cellular proteins and cross talks with other pathways pose a serious challenge to get a coherent understanding of this signaling pathway for making therapeutic strategy. This motivated us to perform a computational study of the pathway and to identify probable drug targets. In this work, from available databases and literature, we reconstructed a complete hedgehog pathway which reports the largest number of molecules and interactions to date. Using recently developed computational techniques, we further performed structural and logical analysis of this pathway. In structural analysis, the connectivity and centrality parameters were calculated to identify the important proteins from the network. To capture the regulations of the molecules, we developed a master Boolean model of all the interactions between the proteins and created different cancer scenarios, such as Glioma, Colon and Pancreatic. We performed perturbation analysis on these cancer conditions to identify the important and minimal combinations of proteins that can be used as drug targets. From our study we observed the under expressions of various oncoproteins in Hedgehog pathway while perturbing at a time the combinations of the proteins GLI1, GLI2 and SMO in Glioma; SMO, HFU, ULK3 and RAS in Colon cancer; SMO, HFU, ULK3, RAS and ERK12 in Pancreatic cancer. This reconstructed Hedgehog signaling pathway and the computational analysis for identifying new combinatory drug targets will be useful for future in-vitro and in-vivo analysis to control different cancers.

The proto-oncogene TWIST1 is regulated by microRNAs

Upregulation of the proto-oncogene Twist1 is highly correlated with acquired drug resistance and poor prognosis in human cancers. Altered expression of this multifunctional transcription factor is also associated with inherited skeletal malformations. The mammalian Twist1 3′UTRs are highly conserved and contain a number of potential regulatory elements including miRNA target sites. We analyzed the translational regulation of TWIST1 using luciferase reporter assays in a variety of cell lines. Among several miRNAs tested, miR-145a-5p, miR-151-5p and a combination of miR-145a-5p + miR-151-5p and miR-151-5p + miR-337-3p were able to significantly repress Twist1 translation. This phenomena was confirmed with both exogenous and endogenous miRNAs and was dependent on the presence of the predicted target sites in the 3′UTR. Furthermore, the repression was sensitive to LNA-modified miRNA antagonists and resulted in decreased migratory potential of murine embryonic fibroblast cells. Understanding the in vivo mechanisms of this oncogene's regulation might open up a possibility for therapeutic interference by gene specific cancer therapies.

Differential configurations involving binding of USF transcription factors and Twist1 regulate Alx3 promoter activity in mesenchymal and pancreatic cells

During embryonic development, the aristaless-type homeodomain protein Alx3 is expressed in the forehead mesenchyme and contributes to the regulation of craniofacial development. In the adult, Alx3 is expressed in pancreatic islets where it participates in the control of glucose homoeostasis. In the present study, we investigated the transcriptional regulation of Alx3 gene expression in these two cell types. We found that the Alx3 promoter contains two E-box regulatory elements, named EB1 and EB2, that provide binding sites for the basic helix-loop-helix transcription factors Twist1, E47, USF (upstream stimulatory factor) 1 and USF2. In primary mouse embryonic mesenchymal cells isolated from the forehead, EB2 is bound by Twist1, whereas EB1 is bound by USF1 and USF2. Integrity of both EB1 and EB2 is required for Twist1-mediated transactivation of the Alx3 promoter, even though Twist1 does not bind to EB1, indicating that binding of USF1 and USF2 to this element is required for Twist1-dependent Alx3 promoter activity. In contrast, in pancreatic islet insulin-producing cells, the integrity of EB2 is not required for proximal promoter activity. The results of the present study indicate that USF1 and USF2 are important regulatory factors for Alx3 gene expression in different cell types, whereas Twist1 contributes to transcriptional transactivation in mesenchymal, but not in pancreatic, cells.

Noncanonical regulation of the Hedgehog mediator GLI1 by c-MYC in Burkitt lymphoma

Although Hedgehog signaling plays a major role in GLI1 transcription, there is now evidence suggesting that other pathways/genes, such as c-MYC, may also regulate GLI1 expression. We initiated studies in Burkitt lymphoma cells, which constitutively express c-MYC due to a chromosomal translocation, to determine whether Hedgehog or c-MYC regulates GLI1 expression. We show that all Burkitt lymphoma cell lines tested express GLI1, PTCH1, and SMO and that five of six Burkitt lymphomas express GLI1. Exposure to Sonic or Indian Hedgehog or cyclopamine (SMO inhibitor) does not modulate GLI1 expression, cell proliferation, or apoptosis in most Burkitt lymphoma cell lines. Sequence analysis of PTCH1, SMO, and SuFu failed to show mutations that might explain the lack of Hedgehog responsiveness, and we did not detect primary cilia, which may contribute to it. We show that c-MYC interacts with the 5'-regulatory region of GLI1, using chromatin immunoprecipitation (ChIP) assay, and E-box-dependent transcriptional activation of GLI1 by c-MYC in NIH3T3 and HeLa cells. The c-MYC small-molecule inhibitor 10058-F4 downregulates GLI1 mRNA and protein and reduces the viability of Burkitt lymphoma cells. Inhibition of GLI1 by GANT61 increases apoptosis and reduces viability of some Burkitt lymphoma cells. Collectively, our data provide evidence that c-MYC directly regulates GLI1 and support an antiapoptotic role for GLI1 in Burkitt lymphoma. Burkitt lymphoma cells do not seem to be Hedgehog responsive. These findings suggest a mechanism for resistance to SMO inhibitors and have implications for using SMO inhibitors to treat human cancers.

The sonic hedgehog-GLI1 signaling pathway in brain tumor development

INTRODUCTION

The sonic hedgehog (Shh) pathway is a regulatory network involved in development and cancer. Proteins like Ptch, SMO, and Gli are central to the Shh pathway. Other proteins like HHIP, SUFU, Bmi-1, Cyclin D2, Plakoglobin, PAX6, Nkx2.2, and SFRP1 are not so well understood in Shh regulation as Gli-1 downstream target genes.

AREAS COVERED

In this review we try to explain the Shh pathway components and their role in development and cancer, mainly of the brain. A summary of each of the proteins is presented together with an overview of their involvement in cancer.

EXPERT OPINION

Genetic alterations of the Shh pathway have been detected in cancer stem cells, a subgroup of tumor cells implicated in the origin and maintenance of tumors, being responsible for cancer recurrence and chemotherapy resistance. Cancer stem cells constitute a novel target for biomedical researchers. Specifically, the Shh pathway is being explored as a new opportunity for targeted therapies against tumors. Therefore, a better knowledge of every of the regulators of the Shh pathway is needed.

Recent advances in the therapeutic applications of pyrazolines

Introduction: Pyrazolines are well-known and important nitrogen-containing five-membered ring heterocyclic compounds. Various methods have been worked out for their synthesis. Several pyrazoline derivatives have been found to possess diverse biological properties, which has stimulated research activity in this field.

Areas covered: The present review sheds light on the recent therapeutic patent literature (2000 – 2011) describing the applications of pyrazolines and their derivatives on selected activities. Many of the therapeutic applications of pyrazoline derivatives have been discussed, either in the patent or in the general literature areas in this review. In addition to selected biological data, a wide range of pharmaceutical applications and pharmaceutical compositions are also summarized.

Expert opinion: Pyrazoline derivatives have numerous prominent pharmacological effects, such as antimicrobial (antibacterial, antifungal, antiamoebic, antimycobacterial), anti-inflammatory, analgesic, antidepressant and anticancer. Further pharmacological effects include cannabinoid CB1 receptor antagonists, antiepileptic, antitrypanosomal, antiviral activity, MAO-inhibitory, antinociceptive activity, insecticidal, hypotensive, nitric oxide synthase inhibitor, antioxidant, steroidal and antidiabetic. Lastly, they also effect ACAT inhibition, urotensin II and somatostatin-5 receptors, TGF-β signal transduction inhibitors and neurocytotoxicity inhibitors activities. Many new pyrazoline derivatives have been synthesized and patented, but there are still new aspects to explore and work on.

Twist-1 is a PPARdelta-inducible, negative-feedback regulator of PGC-1alpha in brown fat metabolism

Brown fat is specialized for energy expenditure, a process that is principally controlled by the transcriptional coactivator PGC-1alpha. Here, we describe a molecular network important for PGC-1alpha function and brown fat metabolism. We find that twist-1 is selectively expressed in adipose tissue, interacts with PGC-1alpha, and is recruited to the promoters of PGC-1alpha's target genes to suppress mitochondrial metabolism and uncoupling. In vivo, transgenic mice expressing twist-1 in the adipose tissue are prone to high-fat-diet-induced obesity, whereas twist-1 heterozygous knockout mice are obesity resistant. These phenotypes are attributed to their altered mitochondrial metabolism in the brown fat. Interestingly, the nuclear receptor PPARdelta not only mediates the actions of PGC-1alpha but also regulates twist-1 expression, suggesting a negative-feedback regulatory mechanism. These findings reveal an unexpected physiological role for twist-1 in the maintenance of energy homeostasis and have important implications for understanding metabolic control and metabolic diseases.

Hedgehog signalling in breast cancer

Breast cancer is the most common cause of cancer death among women worldwide. In order to improve the treatment of this disease, a more complete understanding of its biological basis is necessary. Since the Hedgehog (Hh) pathway was recently found to be required for growth and propagation of a number of different cancers, we discuss here the possible involvement of this pathway in the normal biology and development of cancer in the mammary gland. The use of mouse mammary cancer models has assisted the process of dissecting the mechanisms behind Hh-driven mammary tumour formation and growth. Based on recent studies, we conclude that the inhibition of Hh signalling in breast tumours may interfere with the maintenance of a putative cancer stem cell compartment and the abnormal stimulation of tumour stroma. Therefore, the components of the Hh signalling cascade may provide a set of drug targets, which could be implemented into novel combinatorial strategies for the treatment of breast cancer.

GLI1 is a direct transcriptional target of EWS-FLI1 oncoprotein

Ewing sarcoma family of tumors (ESFT) is an undifferentiated neoplasm of the bone and soft tissue. ESFT is characterized by a specific chromosomal translocation occurring between chromosome 22 and (in most cases) chromosome 11, which generates an aberrant transcription factor, EWS-FLI1. The function of EWS-FLI1 is essential for the maintenance of ESFT cell survival and tumorigenesis. The Hedgehog pathway is activated in several cancers. Oncogenic potential of the Hedgehog pathway is mediated by increasing the activity of the GLI family of transcription factors. Recent evidence suggests that EWS-FLI1 increases expression of GLI1 by an unknown mechanism. Our data from chromatin immunoprecipitation and promoter reporter studies indicated GLI1 as a direct transcriptional target of EWS-FLI1. Expression of EWS-FLI1 in non-ESFT cells increased GLI1 expression and GLI-dependent transcription. We also detected high levels of GLI1 protein in ESFT cell lines. Pharmacological inhibition of GLI1 protein function decreased proliferation and soft agar colony formation of ESFT cells. Our results establish GLI1 as a direct transcriptional target of EWS-FLI1 and suggest a potential role for GLI1 in ESFT tumorigenesis.

Mechanism of transcriptional activation by the proto-oncogene Twist1

Mammalian Twist1, a master regulator in development and a key factor in tumorigenesis, is known to repress transcription by several mechanisms and is therefore considered to mediate its function mainly through inhibition. A role of Twist1 as transactivator has also been reported but, so far, without providing a mechanism for such an activity. Here we show that heterodimeric complexes of Twist1 and E12 mediate E-box-dependent transcriptional activation. We identify a novel Twist1 transactivation domain that coactivates together with the less potent E12 transactivation domain. We found three specific residues in the highly conserved WR domain to be essential for the transactivating function of murine Twist1 and suggest an alpha-helical structure of the transactivation domain.

VMD2 promoter requires two proximal E-box sites for its activity in vivo and is regulated by the MITF-TFE family

The retinal pigment epithelium (RPE) is crucial for the function and survival of retinal photoreceptors. VMD2 encodes bestrophin, an oligomeric chloride channel that is preferentially expressed in the RPE and, when mutated, causes Best macular dystrophy. Previously, we defined the VMD2 upstream region from -253 to +38 bp as being sufficient to direct RPE-specific expression in the eye, and we suggested microphthalmia-associated transcription factor (MITF) as a possible positive regulator. Here we show that in transgenic mice the -154 to +38 bp region is sufficient for RPE expression, and mutation of two E-boxes, 1 and 2, within this region leads to loss of promoter activity. A yeast one-hybrid screen using bait containing E-box 1 identified clones encoding MITF, TFE3, and TFEB, and chromatin immunoprecipitation with antibodies against these proteins enriched the VMD2 proximal promoter. Analysis using in vivo electroporation with constructs containing mutation of each E-box indicated that expression in native RPE requires both E-boxes, yet in vitro DNA binding studies suggested that MITF binds well to E-box 1 but only minimally to E-box 2. MITF knockdown by small interfering RNA (siRNA) in cell culture revealed a strong correlation between MITF and VMD2 mRNA levels. Sequential transfection of a luciferase construct with expression vectors following MITF siRNA revealed that TFE3 and TFEB can also transactivate the VMD2 promoter. Taken together, we suggest that VMD2 is regulated by the MITF-TFE family through two E-boxes, with E-box 1 required for a direct interaction of MITF-TFE factors and E-box 2 for binding of the as yet unidentified factor(s).

Clear cell sarcoma of the kidney: up-regulation of neural markers with activation of the sonic hedgehog and Akt pathways

PURPOSE AND EXPERIMENTAL DESIGN

Clear cell sarcoma of the kidney (CCSK), the second most common renal tumor in children, poses significant diagnostic challenges. No positive diagnostic markers are available, and the pathogenesis of CCSK remains an enigma. To address these challenges, the gene expression patterns of 14 CCSKs were compared with 15 Wilms tumors and 3 fetal kidney samples using oligonucleotide arrays.

RESULTS

Using unsupervised methods, the gene expression profile of CCSK was distinctive: differentially expressed genes could largely be grouped into four categories: (a) a wide variety of neural markers, (b) members of the Sonic hedgehog pathway, (c) members of the phosphoinositide-3-kinase/Akt cell proliferation pathway, and (d) known therapeutic targets. Corresponding changes in critical proteins using Western blot and/or immunohistochemistry confirmed the up-regulation of these pathways and proteins. In particular, CD117 and epidermal growth factor receptor are up-regulated at the protein level in many CCSKs, providing potential therapeutic targets. One of the neural markers, nerve growth factor receptor, represents a promising diagnostic tool for CCSK.

CONCLUSIONS

This study suggests that CCSKs arise within a renal mesenchymal cell that shows a wide variety of neural markers. As such, it seems to be susceptible to genetic changes also seen in a variety of other neuroectodermal and neuronal tumors, including activation of Sonic hedgehog and phosphoinositide-3-kinase/Akt pathways. Involvement of these pathways in CCSKs implicates their widening role in tumorigenesis.

Up-regulation of TWIST in prostate cancer and its implication as a therapeutic target

Androgen-independent metastatic prostate cancer is the main obstacle in the treatment of this cancer. Unlike a majority of solid cancers, prostate cancer usually shows poor response to chemotherapeutic drugs. In this study, we have shown a potential novel target, TWIST, a highly conserved bHLH transcription factor, in the treatment of prostate cancer. Using malignant and nonmalignant prostate tissues, we found that TWIST expression was highly expressed in the majority (90%) of prostate cancer tissues but only in a small percentage (6.7%) of benign prostate hyperplasia. In addition, the TWIST expression levels were positively correlated with Gleason grading and metastasis, indicating its role in the development and progression of prostate cancer. Furthermore, down-regulation of TWIST through small interfering RNA in androgen-independent prostate cancer cell lines, DU145 and PC3, resulted in increased sensitivity to the anticancer drug taxol-induced cell death which was associated with decreased Bcl/Bax ratio, leading to activation of the apoptosis pathway. More importantly, inactivation of TWIST suppressed migration and invasion abilities of androgen-independent prostate cancer cells, which was correlated with induction of E-cadherin expression as well as morphologic and molecular changes associated with mesenchymal to epithelial transition. These results were further confirmed on the androgen-dependent LNCaP cells ectopically expressing the TWIST protein. Our results have identified TWIST as a critical regulator of prostate cancer cell growth and suggest a potential therapeutic approach to inhibit the growth and metastasis of androgen-independent prostate cancer through inactivation of the TWIST gene.

Expression of the Transcription Factors Snail, Slug, and Twist and Their Clinical Significance in Human Breast Cancer

BACKGROUND

Slug, Snail, and Twist are transcription factors that regulate the expression of tumor suppressors such as E-cadherin. We examined the distribution and expression of these three molecules together with the methylation of the Twist gene promoter in human breast cancer to elucidate their clinical significance.

METHODS

Frozen sections from breast cancer primary tumors (tumor, n = 114; background, n = 30) were immunostained with Slug, Snail, and Twist antibodies. RNA was reverse-transcribed, quantified, and analyzed by quantitative polymerase chain reaction (Q-PCR). Results were expressed as copy number of transcript per 50 ng of RNA (standardized against beta-actin).

RESULTS

Immunohistochemistry revealed that all three molecules were stained in mammary tissues, with an increase in Twist within tumor tissues; this was supported by Q-PCR analysis. Q-PCR analysis showed that Slug was elevated with increasing tumor grade and prognostic indices. Twist was elevated with increasing nodal involvement (tumor-node-metastasis status). Conversely, Snail was reduced in expression corresponding with prognostic indices and tumor grade. Increased levels of Slug were associated with tumors from patients with metastatic disease or disease recurrence, and increased expression of Twist was associated with tumors from patients who had died from breast cancer. It is interesting to note that Snail expression was significantly reduced in patients with a poor outcome and those who had node-positive tumors. In addition, tumors exhibited methylation of the Twist promoter.

CONCLUSIONS

These data demonstrate that all three transcription factors have inappropriate expression in breast cancer and that this may play a part in the progression of human breast tumors.

Twist is an integrator of SHH, FGF, and BMP signaling

Development of vertebrate embryos is regulated by a number of different signaling pathways. These pathways are frequently not independent of each other but are connected by crosstalk between cells and tissues. Furthermore, different signaling pathways have been found to interact at the cellular level. Development of cranial and limb structures is an example, in which FGF, BMP, and SHH signaling interact. Mutations in the different signaling pathways may therefore result in complex but similar phenotypes. This indicates the existence of integrator molecules, which depend in their expression or activity on the combination of different signaling pathways. Here we show that expression of the bHLH transcription factor Twist in the paraxial mesoderm requires an induction from the notochord. This induction can only be substituted by a combination of FGF and SHH signaling, but not by individual application of FGF8 or SHH alone. Furthermore, the expression of Twist can be modified by BMP2 in a complex, age-dependent manner. We propose that Twist is one of the integrating parts of the three signaling pathways and mediates some of the common effects.

GLI2 is expressed in normal human epidermis and BCC and induces GLI1 expression by binding to its promoter

Sonic hedgehog (Shh) binds to its receptor patched (PTCH), leading to the activation and repression of target genes via the GLI family of zinc-finger transcription factors. Deregulation of the Shh pathway is associated with basal cell carcinoma (BCC) due to upregulation of GLI1 and GLI2. We recently demonstrated a positive feedback loop between GLI1 and GLI2, which revealed that GLI1 may be a direct target of GLI2. Using band shift and luciferase reporter assays, we now show that GLI2 binds the GLI-binding consensus sequence in the GLI1 promoter. These data suggest that GLI2 directly activates GLI1 and that retrovirally expressed GLI2 induces expression of endogenous GLI1 in human primary keratinocytes. Finally, using in situ hybridization, we show that GLI2 is expressed in the interfollicular epidermis and the outer root sheath of hair follicles in normal skin as well as in BCC tumor islands. These results suggest an important role for GLI2 in regulating epidermal proliferation and skin tumorigenesis.

Analysis of the VMD2 Promoter and Implication of E-box Binding Factors in Its Regulation

The retinal pigment epithelium (RPE) is crucial for the normal development and function of retinal photo-receptors, and mutations in several genes that are preferentially expressed in the RPE have been shown to cause retinal degeneration. We analyzed the 5'-up-stream region of human VMD2, a gene that is preferentially expressed in the RPE and, when mutated, causes Best macular dystrophy. Transgenic mouse studies with VMD2 promoter/lacZ constructs demonstrated that a-253 to +38 bp fragment is sufficient to direct RPE-specific expression in the eye. Transient transfection assays using the D407 human RPE cell line with VMD2 promoter/luciferase reporter constructs identified two positive regulatory regions, -585 to -541 bp for high level expression and -56 to -42 bp for low level expression. Mutation of a canonical E-box located in the -56 to -42 bp region greatly diminished luciferase expression in D407 cells and abolished the bands shifted with bovine RPE nuclear extract in electrophoretic mobility shift assays. Independently a candidate approach was used to select microphthalmia-associated transcription factor (MITF) for testing because it is expressed in the RPE and associated with RPE abnormalities when mutated. MITF-M significantly increased luciferase expression in D407 cells in an E-box-dependent manner. These studies define the VMD2 promoter region sufficient to drive RPE-specific expression in the eye, identify positive regulatory regions in vitro, and suggest that MITF as well as other E-box binding factors may act as positive regulators of VMD2 expression.

A HANDful of questions: the molecular biology of the heart and neural crest derivatives (HAND)-subclass of basic helix-loop-helix transcription factors

The HAND subclass of basic Helix-loop-helix factors is comprised of two members HAND1 and HAND2. HAND genes are present within the genomes of organisms ranging from flies to man. Experiments employing chick embryology, tissue culture, and gene targeting in mice show that HAND function is critical for the specification and/or differentiation of extraembryonic structures that include the yolk sac, placenta, and the cells of the trophoblast lineages. HAND factors also play key roles in cardiac, gut, sympathetic neuronal development and in the proper development of tissues populated by HAND-expressing neural crest cells, including regions of the developing vasculature, the limbs, the jaw, and teeth. Surprisingly, nearly 10 years after their initial identification and characterization, little is understood about the nature of the downstream target genes which HAND1 and HAND2 regulate, whether the nature of their transcriptional regulation is positive or negative, or if they modulate genetic programs common to these diverse tissue types or if they drive unique subsets of genes that contribute to tissue identity. At the core of these questions is by which mechanisms do HAND factors modulate biological activity? Do they behave like classical class B bHLH factors or is their function more complex requiring a rethinking of the dogma? What follows is a review of what is currently known about HAND factors and a reflection on why elucidating their role in the biological programs within which they participate has been so difficult.

Inhibition of skeletal muscle development: less differentiation gives more muscle

The fact that stem cells have to be protected from premature differentiation is true for many organs in the developing embryo and the adult organism. However, there are several arguments that this is particularly important for (skeletal) muscle. There are some evolutionary arguments that muscle is a "default" pathway for mesodermal cells, which has to be actively prevented in order to allow cells to differentiate into other tissues. Myogenic cells originate from very small areas of the embryo where only a minor portion of these cells is supposed to differentiate. Differentiated muscle fibres are unconditionally post-mitotic, leaving undifferentiated stem cells as the only source of regeneration. The mechanical usage of muscle and its superficial location in the vertebrate body makes regeneration a frequently used mechanism. Looking at the different inhibitory mechanisms that have been found within the past 10 or so years, it appears as if evolution has taken this issue very serious. At all possible levels we find regulatory mechanisms that help to fine tune the differentiation of myogenic cells. Secreted molecules specifying different populations of somitic cells, diffusing or membrane-bound signals among fellow myoblasts, modulating molecules within the extracellular matrix and last, but not least, a changing set of activating and repressing cofactors. We have come a long way from the simple model of MyoD just to be turned on at the right time in the right cell.

Twist plays an essential role in FGF and SHH signal transduction during mouse limb development

Loss of Twist gene function arrests the growth of the limb bud shortly after its formation. In the Twist(-/-) forelimb bud, Fgf10 expression is reduced, Fgf4 is not expressed, and the domain of Fgf8 and Fgfr2 expression is altered. This is accompanied by disruption of the expression of genes (Shh, Gli1, Gli2, Gli3, and Ptch) associated with SHH signalling in the limb bud mesenchyme, the down-regulation of Bmp4 in the apical ectoderm, the absence of Alx3, Alx4, Pax1, and Pax3 activity in the mesenchyme, and a reduced potency of the limb bud tissues to differentiate into osteogenic and myogenic tissues. Development of the hindlimb buds in Twist(-/-) embryos is also retarded. The overall activity of genes involved in SHH signalling is reduced.Fgf4 and Fgf8 expression is lost or reduced in the apical ectoderm, but other genes (Fgf10, Fgfr2) involved with FGF signalling are expressed in normal patterns. Twist(+/-);Gli3(+/XtJ) mice display more severe polydactyly than that seen in either Twist(+/-) or Gli3(+/XtJ) mice, suggesting that there is genetic interaction between Twist and Gli3 activity. Twist activity is therefore essential for the growth and differentiation of the limb bud tissues as well as regulation of tissue patterning via the modulation of SHH and FGF signal transduction.