The role of promyelocytic leukemia zinc finger and promyelocytic leukemia in leukemogenesis and development

Elucidating the Role of Pro-renin Receptors in Pancreatic Ductal Adenocarcinoma Progression: A Novel Therapeutic Target in Cancer Therapy

Pancreatic cancer is a highly aggressive malignancy with a very poor prognosis. The 5- year survival in these patients is very low, and most patients develop drug resistance to current therapies, so additional studies are needed to identify the potential role of new drug targets for the treatment of pancreatic cancer. Recent investigations have been performed regarding the roles of pro-renin receptors (PRR) in the initiation and development of cancers. PRR is a component of the local renin-angiotensin system (RAS). Local tissue RAS has been known in diverse organ systems, including the pancreas. Various investigations have implicated that PRRs are associated with the upregulation of various signaling pathways, like the renin-angiotensin system pathway, PI3K/Akt/mTOR, and the Wnt-signaling pathways, to contribute to pathological conditions, including cancer. In this review, we presented an overview of the role of PRR in the progression of pancreatic adenocarcinoma.

Zinc finger protein ZBTB20 is an independent prognostic marker and promotes tumor growth of human hepatocellular carcinoma by repressing FoxO1

Zinc finger and BTB domain-containing 20 (ZBTB20) is a new BTB/POZ-domain gene and a member of the POK family of transcriptional repressors. Notably, the role of ZBTB20 and its underlying mechanisms involved in hepatocarcinogenesis are poorly investigated. In this study, the expression of ZBTB20 was significantly overexpressed in hepatocellular carcinoma (HCC) tissues. The positive expression of ZBTB20 was associated with large tumor size, high Edmondson-Steiner grading and advanced tumor-node-metastasis (TNM) tumor stage. Additionally, HCC patients with positive expression of ZBTB20 had a poorer 5-year survival. Multivariate analyses revealed that ZBTB20 overexpression was an independent prognostic factor for HCC. Gain- and loss-of-function experiments demonstrated that ZBTB20 promoted HCC cell viability, proliferation, tumorigenicity, and cell cycle progression. Mechanistically, Cyclin D1 and Cyclin E were increased, while p21 and p27 were decreased by ZBTB20 in HCC cells. FoxO1 was inversely correlated with ZBTB20 protein expression in the same cohort of HCC specimens. We further revealed that FoxO1 was transcriptionally repressed by ZBTB20 in HCC. Moreover, restoration of FoxO1 expression partially abrogated ZBTB20-induced HCC cell proliferation and growth entry in vitro and in vivo. Collectively, these results indicate that ZBTB20 may serve as a prognostic marker and promotes tumor growth of HCC via transcriptionally repressing FoxO1.

Cyclic decidualization of the human endometrium in reproductive health and failure

Decidualization denotes the transformation of endometrial stromal fibroblasts into specialized secretory decidual cells that provide a nutritive and immunoprivileged matrix essential for embryo implantation and placental development. In contrast to most mammals, decidualization of the human endometrium does not require embryo implantation. Instead, this process is driven by the postovulatory rise in progesterone levels and increasing local cAMP production. In response to falling progesterone levels, spontaneous decidualization causes menstrual shedding and cyclic regeneration of the endometrium. A growing body of evidence indicates that the shift from embryonic to maternal control of the decidual process represents a pivotal evolutionary adaptation to the challenge posed by invasive and chromosomally diverse human embryos. This concept is predicated on the ability of decidualizing stromal cells to respond to individual embryos in a manner that either promotes implantation and further development or facilitates early rejection. Furthermore, menstruation and cyclic regeneration involves stem cell recruitment and renders the endometrium intrinsically capable of adapting its decidual response to maximize reproductive success. Here we review the endocrine, paracrine, and autocrine cues that tightly govern this differentiation process. In response to activation of various signaling pathways and genome-wide chromatin remodeling, evolutionarily conserved transcriptional factors gain access to the decidua-specific regulatory circuitry. Once initiated, the decidual process is poised to transit through distinct phenotypic phases that underpin endometrial receptivity, embryo selection, and, ultimately, resolution of pregnancy. We discuss how disorders that subvert the programming, initiation, or progression of decidualization compromise reproductive health and predispose for pregnancy failure.

Identification of promoter within the first intron of Plzf gene expressed in carp spermatogonial stem cells

Promyelocytic leukemia zinc finger (Plzf), a transcriptional repressor, is involved in survival and maintenance of pluripotent stem cells including embryonic and spermatogonial stem cells in mammals. Its cDNA was characterized and expression in proliferating spermatogonial stem cells of rohu (Labeo rohita), a farmed carp, was documented. In teleost, the information on its promoter activity is lacking. Here, we have isolated, sequenced and performed the first characterization of regulatory elements for Plzf being expressed in proliferating spermatogonial stem cells of rohu. About 3.2 kb of 5'-flanking region, relative to ATG start codon, derived by genome walking was sequenced. The 5'-RACE (rapid amplification of cDNA ends) analysis not only mapped the transcriptional start site but also detected non-coding exons. Interestingly, computational analysis detected several putative regulatory elements including TATA-box positioned in the first intron. Luciferase reporter assay was performed for serially deleted constructs to measure their promoter activities. The region containing putative TATA- and CAAT-boxes including GC-rich motif, positioned within first intron, was identified as a potential promoter; but its full promoter activity was dependent on upstream region containing a putative Evi-1-like element. Moreover, our findings also identified a region acting as transcriptional repressor. These findings could be used as roadmap for future understandings of its regulated expression during male germ cell development in fish species.

Distinct signal transduction pathways downstream of the (P)RR revealed by microarray and ChIP-chip analyses

The (pro)renin receptor ((P)RR) signaling is involved in different pathophysiologies ranging from cardiorenal end-organ damage via diabetic retinopathy to tumorigenesis. We have previously shown that the transcription factor promyelocytic leukemia zinc finger (PLZF) is an adaptor protein of the (P)RR. Furthermore, recent publications suggest that major functions of the (P)RR are mediated ligand-independently by its transmembrane and intracellular part, which acts as an accessory protein of V-ATPases. The transcriptome and recruitmentome downstream of the V-ATPase function and PLZF in the context of the (P)RR are currently unknown. Therefore, we performed a set of microarray and chromatin-immunoprecipitation (ChIP)-chip experiments using siRNA against the (P)RR, stable overexpression of PLZF, the PLZF translocation inhibitor genistein and the specific V-ATPase inhibitor bafilomycin to dissect transcriptional pathways downstream of the (P)RR. We were able to identify distinct and overlapping genetic signatures as well as novel real-time PCR-validated target genes of the different molecular functions of the (P)RR. Moreover, bioinformatic analyses of our data confirm the role of (P)RŔs signal transduction pathways in cardiovascular disease and tumorigenesis.

Identification of a novel promyelocytic leukemia zinc-finger isoform required for colorectal cancer cell growth and survival

Promyelocytic leukemia zinc-finger (PLZF) is a transcriptional repressor that regulates proliferation, differentiation and apoptosis among various cellular origins. PLZF expression is upregulated in colorectal cancer cell lines but its putative functional role in this context is unknown. Here, we report the identification of a novel p65 PLZF isoform that results from the usage of an evolutionarily conserved alternative translational initiation site. This isoform is devoid of the classical BTB/POZ domain required for nuclear localization and transcriptional repression. Depletion of p65 PLZF expression in colorectal cancer cell lines results in reduction of cell growth, loss of cell anchorage and increase in cell apoptosis. Overall, these results indicate that p65 PLZF is crucial to maintain colorectal cancer cell adhesion as well as survival and must occur independently of the traditionally viewed transcriptional role of PLZF in the course of these biological processes.

Zbtb16 has a role in brown adipocyte bioenergetics

Objective:

A better understanding of the processes influencing energy expenditure could provide new therapeutic strategies for reducing obesity. As the metabolic activity of the brown adipose tissue (BAT) and skeletal muscle is an important determinant of overall energy expenditure and adiposity, we investigated the role of genes that could influence cellular bioenergetics in these two tissues.

Design:

We screened for genes that are induced in both the BAT and skeletal muscle during acute adaptive thermogenesis in the mouse by microarray. We used C57BL/6J mice as well as the primary and immortalized brown adipocytes and C2C12 myocytes to validate the microarray data. Further characterization included gene expression, mitochondrial density, cellular respiration and substrate utilization. We also used a Hybrid Mouse Diversity Panel to assess in vivo effects on obesity and body fat content.

Results:

We identified the transcription factor Zbtb16 (also known as Plzf and Zfp14) as being induced in both the BAT and skeletal muscle during acute adaptive thermogenesis. Zbtb16 overexpression in brown adipocytes led to the induction of components of the thermogenic program, including genes involved in fatty acid oxidation, glycolysis and mitochondrial function. Enhanced Zbtb16 expression also increased mitochondrial number, as well as the respiratory capacity and uncoupling. These effects were accompanied by decreased triglyceride content and increased carbohydrate utilization in brown adipocytes. Natural variation in Zbtb16 mRNA levels in multiple tissues across a panel of >100 mouse strains was inversely correlated with body weight and body fat content.

Conclusion:

Our results implicate Zbtb16 as a novel determinant of substrate utilization in brown adipocytes and of adiposity in vivo.

Nuclear Kaiso expression is associated with high grade and triple-negative invasive breast cancer

Kaiso is a BTB/POZ transcription factor that is ubiquitously expressed in multiple cell types and functions as a transcriptional repressor and activator. Little is known about Kaiso expression and localization in breast cancer. Here, we have related pathological features and molecular subtypes to Kaiso expression in 477 cases of human invasive breast cancer. Nuclear Kaiso was predominantly found in invasive ductal carcinoma (IDC) (p = 0.007), while cytoplasmic Kaiso expression was linked to invasive lobular carcinoma (ILC) (p = 0.006). Although cytoplasmic Kaiso did not correlate to clinicopathological features, we found a significant correlation between nuclear Kaiso, high histological grade (p = 0.023), ERα negativity (p = 0.001), and the HER2-driven and basal/triple-negative breast cancers (p = 0.018). Interestingly, nuclear Kaiso was also abundant in BRCA1-associated breast cancer (p<0.001) and invasive breast cancer overexpressing EGFR (p = 0.019). We observed a correlation between nuclear Kaiso and membrane-localized E-cadherin and p120-catenin (p120) (p<0.01). In contrast, cytoplasmic p120 strongly correlated with loss of E-cadherin and low nuclear Kaiso (p = 0.005). We could confirm these findings in human ILC cells and cell lines derived from conditional mouse models of ILC. Moreover, we present functional data that substantiate a mechanism whereby E-cadherin controls p120-mediated relief of Kaiso-dependent gene repression. In conclusion, our data indicate that nuclear Kaiso is common in clinically aggressive ductal breast cancer, while cytoplasmic Kaiso and a p120-mediated relief of Kaiso-dependent transcriptional repression characterize ILC.

Far-infrared therapy induces the nuclear translocation of PLZF which inhibits VEGF-induced proliferation in human umbilical vein endothelial cells

Many studies suggest that far-infrared (FIR) therapy can reduce the frequency of some vascular-related diseases. The non-thermal effect of FIR was recently found to play a role in the long-term protective effect on vascular function, but its molecular mechanism is still unknown. In the present study, we evaluated the biological effect of FIR on vascular endothelial growth factor (VEGF)-induced proliferation in human umbilical vein endothelial cells (HUVECs). We found that FIR ranging 3∼10 µm significantly inhibited VEGF-induced proliferation in HUVECs. According to intensity and time course analyses, the inhibitory effect of FIR peaked at an effective intensity of 0.13 mW/cm² at 30 min. On the other hand, a thermal effect did not inhibit VEGF-induced proliferation in HUVECs. FIR exposure also inhibited the VEGF-induced phosphorylation of extracellular signal-regulated kinases in HUVECs. FIR exposure further induced the phosphorylation of endothelial nitric oxide (NO) synthase (eNOS) and NO generation in VEGF-treated HUVECs. Both VEGF-induced NO and reactive oxygen species generation was involved in the inhibitory effect of FIR. Nitrotyrosine formation significantly increased in HUVECs treated with VEGF and FIR together. Inhibition of phosphoinositide 3-kinase (PI3K) by wortmannin abolished the FIR-induced phosphorylation of eNOS and Akt in HUVECs. FIR exposure upregulated the expression of PI3K p85 at the transcriptional level. We further found that FIR exposure induced the nuclear translocation of promyelocytic leukemia zinc finger protein (PLZF) in HUVECs. This induction was independent of a thermal effect. The small interfering RNA transfection of PLZF blocked FIR-increased PI3K levels and the inhibitory effect of FIR. These data suggest that FIR induces the nuclear translocation of PLZF which inhibits VEGF-induced proliferation in HUVECs.

Activated leukemic oncogenes AML1-ETO and c-kit: role in development of acute myeloid leukemia and current approaches for their inhibition

Acute myeloid leukemia (AML) is a malignant blood disease caused by different mutations that enhance the proliferative activity and survival of blood cells and affect their differentiation and apoptosis. The most frequent disorders in AML are translocations between chromosomes 21 and 8 leading to production of a chimeric oncogene, AML1-ETO, and hyperexpression of the receptor tyrosine kinase KIT. Mutations in these genes often occur jointly. The presence in cells of two activated oncogenes is likely to trigger their malignization. The current approaches for treatment of oncologic diseases (bone marrow transplantation, radiotherapy, and chemotherapy) have significant shortcomings, and thus many laboratories are intensively developing new approaches against leukemias. Inhibiting expression of activated leukemic oncogenes based on the principle of RNA interference seems to be a promising approach in this field.

Zinc finger protein ZBTB20 expression is increased in hepatocellular carcinoma and associated with poor prognosis

Background

Our previous studies showed that ZBTB20, a new BTB/POZ-domain gene, could negatively regulate α feto-protein and other liver-specific genes, concerning such as bio-transformation, glucose metabolism and the regulation of the somatotropic hormonal axis. The aim of this study is to determine the potential clinical implications of ZBTB20 in hepatocellular carcinoma (HCC).

Methods

Quantitative real-time RT-PCR and Western blot analyses were used to detect expression levels of ZBTB20 in 50 paired HCC tumorous and nontumorous tissues and in 20 normal liver tissues. Moreover, expression of ZBTB20 was assessed by immunohistochemistry of paired tumor and peritumoral liver tissue from 102 patients who had undergone hepatectomy for histologically proven HCC. And its relationship with clinicopathological parameters and prognosis was investigated.

Results

Both messenger RNA and protein expression levels of ZBTB20 were elevated significantly in HCC tissues compared with the paired non-tumor tissues and normal liver tissues. Overexpressed ZBTB20 protein in HCC was significantly associated with vein invasion (P = 0.016). Importantly, the recurrence or metastasis rates of HCCs with higher ZBTB20 expression were markedly greater than those of HCCs with lower expression (P = 0.003, P = 0.00015, respectively). Univariate and multivariate analyses revealed that ZBTB20 overexpression was an independent prognostic factor for HCC. The disease-free survival period and over-all survival period in patients with overexpressed ZBTB20 in HCC was significantly reduced.

Conclusions

The expression of ZBTB20 is increased in HCC and associated with poor prognosis in patients with HCC, implicating ZBTB20 as a candidate prognostic marker in HCC.

An allele separating skeletal patterning and spermatogonial renewal functions of PLZF

Background

The promyelocytic leukemia zinc finger gene Plzf (also called Zbtb16, Zfp145 or Green's luxoid) belongs to the POZ/zinc-finger family of transcription factors. It contains a BTB/POZ domain that mediates epigenetic transcriptional repression. PLZF is essential for proper skeleton patterning and male germ cell renewal. Two alleles have been reported that display similar phenotypes: a targeted knock-out, and the spontaneous nonsense mutation luxoid.

Results

We describe a new ENU induced missense allele of Plzf called seven toes (Plzf^7t). Homozygous animals exhibit hindlimb and axial skeleton abnormalities. Whereas the skeletal abnormalities are similar to those of the other alleles, Plzf^7t differs in that it does not cause spermatogonial depletion and infertility. Positional cloning revealed a point mutation changing the evolutionarily conserved amino acid Glu44 to Gly, possibly altering the BTB domain's activity.

Conclusions

Plzf^7t is a separation-of-function allele that reveals differential requirements for domains of PLZF in different developmental milieus.

Signal transduction of the (pro)renin receptor as a novel therapeutic target for preventing end-organ damage

The (pro)renin receptor ((P)RR) not only represents a novel component of the renin-angiotensin system but is also a promising novel drug target because of its crucial involvement in the pathogenesis of renal and cardiac end-organ damage. This review discusses the signal transduction of the (P)RR with its adapter protein promyelocytic zinc-finger protein, the impact of this receptor, especially on cardiovascular disease, and its putative interaction with renin inhibitors such as aliskiren. Furthermore, the increasing complexity regarding the cellular function of the (P)RR is addressed, which arises by the intimate link with proton pumps and the phosphatase PRL-1, as well as by the presence of different subcellular localizations and of a soluble isoform of the (P)RR. Finally, the rationale and strategy for the development of small-molecule antagonists of the (P)RR, called renin/prorenin receptor blockers, are presented.

Adapter proteins and promoter regulation of the angiotensin AT2 receptor — implications for cardiac pathophysiology

The angiotensin AT 2 receptor (AT2R) represents an important component of the renin-angiotensin system since it is involved in the (patho) physiology of different cardiovascular and neuronal diseases. Furthermore, AT2 receptors can partly mediate beneficial effects of angiotensin AT 1 receptor (AT1R) blockers, and direct pharmacological AT 2 receptor agonism emerges as a novel therapeutic strategy. This review discusses the constitutive and ligand-mediated activity as well as the signal transduction of the AT2 receptor, focusing on adapter proteins which directly bind to this receptor. Direct protein-protein interaction partners of the AT2 receptor described so far include the transcription factor promyelocytic zinc finger protein, AT2 receptor binding protein and the AT1 receptor. In addition, the putative crosstalk of the AT2 receptor with the renin/ prorenin receptor (RER) via the promyelocytic zinc finger protein (PLZF) and the role of oestrogens on the regulation of the AT2 receptor are presented. Conceiving the coupling of the AT2 receptor to different adapter proteins with distinct and partly opposing cellular effects and the implications of its constitutive activity might help to overcome the current controversies on the (patho)physiological role of the AT2 receptor.

Cyclin-dependent kinase antagonizes promyelocytic leukemia zinc-finger through phosphorylation

Acute promyelocytic leukemia is associated with chromosomal translocations that involve the RARalpha gene and several distinct loci producing a variety of fusion proteins. One such fusion partner is promyelocytic leukemia zinc-finger gene (PLZF), a member of the POK (POZ and Krüppel) family of transcriptional repressors that is a key developmental regulator, stem cell maintenance factor and tumor suppressor. Overexpression of PLZF has been shown to induce cell cycle arrest at the G(1) to S transition and repress the expression of key pro-proliferative genes such as CCNA2 and MYC. However, given this data suggesting an important growth inhibitory role for PLZF, relatively little is known regarding regulation of its activity. Here we show that the main cyclin-dependent kinase involved at the G(1) to S transition (CDK2) phosphorylates PLZF at two consensus sites found within PEST domains present in the hinge region of the protein. This phosphorylation triggers the ubiquitination and subsequent degradation of PLZF, which impairs PLZF transcriptional repression ability and antagonizes its growth inhibitory effects. This critical mechanism of PLZF regulation may thus be relevant for cell cycle progression during the development and the pathogenesis of human cancer.

Repression of kit expression by Plzf in germ cells

Male mice lacking expression of Plzf, a DNA sequence-specific transcriptional repressor, show progressive germ cell depletion due to exhaustion of the spermatogonial stem cell population. This is likely due to the deregulated expression of genes controlling the switch between spermatogonial self-renewal and differentiation. Here we show that Plzf directly represses the transcription of kit, a hallmark of spermatogonial differentiation. Plzf represses both endogenous kit expression and expression of a reporter gene under the control of the kit promoter region. A discrete sequence of the kit promoter, required for Plzf-mediated kit transcriptional repression, is bound by Plzf both in vivo and in vitro. A 3-bp mutation in this Plzf binding site abolishes the responsiveness of the kit promoter to Plzf repression. A significant increase in kit expression is also found in the undifferentiated spermatogonia isolated from Plzf(-/-) mice. Thus, we suggest that one mechanism by which Plzf maintains the pool of spermatogonial stem cells is through a direct repression of kit expression.

Vitamins A and E: metabolism, roles and transfer to offspring

Vitamins A and E are essential, naturally occurring, fat-soluble nutrients that are involved in several important biological processes such as immunity, protection against tissue damage, reproduction, growth and development. They are extremely important during the early stages of life and must be transferred adequately to the young during gestation and lactation. The present article presents an overview of their biological functions, metabolism and dynamics of transfer to offspring in mammals. Among other topics, the review focuses on the biochemical aspects of their intestinal absorption, blood transport, tissue uptake, storage and catabolism. It also describes their different roles as well as their use as preventive and therapeutic agents. Finally, the mechanisms involved in their transfer during gestation and lactation are discussed.

A novel signal transduction cascade involving direct physical interaction of the renin/prorenin receptor with the transcription factor promyelocytic zinc finger protein

A human renin/prorenin receptor (RER) has recently been cloned. To gain insight into the molecular function of the RER, we studied its signal transduction mechanisms. Initially, we found a ubiquitous and intracellular expression pattern of the human RER. Consistently, we observed several transcriptional start sites and a high promoter activity of the human RER. We could identify the transcription factor promyelocytic zinc finger (PLZF) protein as a direct protein interaction partner of the C-terminal domain of the RER by yeast 2-hybrid screening and coimmunoprecipitation. Coimmunoprecipitation experiments also indicated homodimerization of the RER. On activation of the RER by renin, PLZF is translocated into the nucleus and represses transcription of the RER itself, thereby creating a very short negative feedback loop, but activates transcription of the p85alpha subunit of the phosphatidylinositol-3 kinase (PI3K-p85alpha). Small interfering RNA against the RER abolished these effects. A PLZF cis-element in the RER promoter was identified by site-directed mutagenesis and electrophoretic mobility-shift assay. Renin stimulation caused a 6-fold recruitment of PLZF to this promoter region as shown by chromatin immunoprecipitation. Moreover, renin stimulation of rat H9c2 cardiomyoblasts induced an increase of cell number and a decrease of apoptosis. These effects were partly abolished by PI3K inhibition and completely abrogated by small interfering RNA against PLZF. Finally, experiments in PLZF knockout mice confirmed the role of PLZF as an upstream regulator of RER and PI3K-p85alpha. Our data demonstrate the existence of a novel signal transduction pathway involving the ligand renin, RER, and the transcription factor PLZF, which is of physiological and putative pathophysiological relevance.

Reversible Kinetic Analysis of Myc Targets In vivo Provides Novel Insights into Myc-Mediated Tumorigenesis

Deregulated expression of the Myc transcription factor is a frequent causal mutation in human cancer. Thousands of putative Myc target genes have been identified in in vitro studies, indicating that Myc exerts highly pleiotropic effects within cells and tissues. However, the complexity and diversity of Myc gene targets has confounded attempts at identifying which of these genes are the critical targets mediating Myc-driven tumorigenesis in vivo. Acute activation of Myc in a reversibly switchable transgenic model of Myc-mediated beta cell tumorigenesis induces rapid tumor onset, whereas subsequent Myc deactivation triggers equally rapid tumor regression. Thus, sustained Myc activity is required for tumor maintenance. We have used this reversibly switchable kinetic tumor model in combination with high-density oligonucleotide microarrays to develop an unbiased strategy for identifying candidate Myc-regulated genes responsible for maintenance of Myc-dependent tumors. Consistent with known Myc functions, some Myc-regulated genes are involved in cell growth, cycle, and proliferation. In addition, however, many Myc-regulated genes are specific to beta cells, indicating that a significant component of Myc action is cell type specific. Finally, we identify a very restricted cadre of genes with expression that is inversely regulated upon Myc activation-induced tumor progression and deactivation-induced tumor regression. By definition, such genes are candidates for tumor maintenance functions. Combining reversibly switchable, transgenic models of tumor formation and regression with genomic profiling offers a novel strategy with which to deconvolute the complexities of oncogenic signaling pathways in vivo.

Inhibition of retinoic acid receptor signaling by Ski in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease with multiple different cytogenetic and molecular aberrations contributing to leukemic transformation. We compared gene expression profiles of 4608 genes using cDNA-arrays from 20 AML patients (nine with -7/del7q and 11 with normal karyotype) with 23 CD34+ preparations from healthy bone marrow donors. SKI, a nuclear oncogene, was highly up regulated. In a second set of 183 AML patients analyzed with real-time PCR, the highest expression level of SKI in AML with -7/del7q could be confirmed. As previously described, Ski associates with the retinoic acid receptor (RAR) complex and can repress transcription. We wanted to investigate the interference of Ski with RARalpha signaling in AML. Ski was co-immunoprecipitated and colocalized with RARalpha. We also found that overexpression of wild-type Ski inhibited the prodifferentiating effects of retinoic acid in U937 leukemia cells. Mutant Ski, lacking the N-CoR binding, was no more capable of repressing RARalpha signaling. The inhibition by wild-type Ski could partially be reverted by the histone deacetylase blocking agent valproic acid. In conclusion, Ski seems to be involved in the blocking of differentiation in AML via inhibition of RARalpha signaling.

A role for Kaiso-p120ctn complexes in cancer?

Kaiso belongs to the zinc finger and broad-complex, tramtrack and bric-a-brac/poxvirus and zinc finger (BTB/POZ) protein family that has been implicated in tumorigenesis. Kaiso was first discovered in a complex with the armadillo-domain protein p120ctn and later shown to function as a transcriptional repressor. As p120ctn seems to relieve Kaiso-mediated repression, its altered intracellular localization in some cancer cells might result in aberrant Kaiso nuclear activity. Intriguingly, Kaiso's target genes include both methylated and sequence-specific recognition sites. The latter include genes that are modulated by the canonical Wnt (beta-catenin-T-cell factor) signalling pathway. Further interest in Kaiso stems from findings that its cytoplasmic versus nuclear localization is modulated by complex cues from the microenvironment.

Sequence and structural analysis of BTB domain proteins

BACKGROUND

The BTB domain (also known as the POZ domain) is a versatile protein-protein interaction motif that participates in a wide range of cellular functions, including transcriptional regulation, cytoskeleton dynamics, ion channel assembly and gating, and targeting proteins for ubiquitination. Several BTB domain structures have been experimentally determined, revealing a highly conserved core structure.

RESULTS

We surveyed the protein architecture, genomic distribution and sequence conservation of BTB domain proteins in 17 fully sequenced eukaryotes. The BTB domain is typically found as a single copy in proteins that contain only one or two other types of domain, and this defines the BTB-zinc finger (BTB-ZF), BTB-BACK-kelch (BBK), voltage-gated potassium channel T1 (T1-Kv), MATH-BTB, BTB-NPH3 and BTB-BACK-PHR (BBP) families of proteins, among others. In contrast, the Skp1 and ElonginC proteins consist almost exclusively of the core BTB fold. There are numerous lineage-specific expansions of BTB proteins, as seen by the relatively large number of BTB-ZF and BBK proteins in vertebrates, MATH-BTB proteins in Caenorhabditis elegans, and BTB-NPH3 proteins in Arabidopsis thaliana. Using the structural homology between Skp1 and the PLZF BTB homodimer, we present a model of a BTB-Cul3 SCF-like E3 ubiquitin ligase complex that shows that the BTB dimer or the T1 tetramer is compatible in this complex.

CONCLUSION

Despite widely divergent sequences, the BTB fold is structurally well conserved. The fold has adapted to several different modes of self-association and interactions with non-BTB proteins.

The MTG proteins: chromatin repression players with a passion for networking

The human myeloid translocation genes (MTGs) encode a family of proteins with a modular structure that can be traced to the Drosophila protein nervy. The nuclear MTGs can mediate the formation of complex protein networks among nuclear corepressors (Sin3a, N-CoR, SMRT), chromatin-modifying enzymes (histone deacetylases), and DNA-binding transcription factors. Hierarchical modulation of repression at target genes by MTG protein complexes is likely required for fine spatial and temporal gene regulation during development and differentiation. Genomic changes can disrupt these sophisticated protein networks and underlie novel pathogenic causes of cancer and neurodegeneration.

Structure and expression of the gene encoding a Broad-Complex homolog in the silkworm, Bombyx mori

The steroid hormone ecdysone (20-hydroxyexdysone) initiates metamorphosis and also larval ecdysis in many insects by activating a cascade of genes that includes primary response genes (early genes), most of which encode transcriptional regulators, and secondary response genes (late genes) regulated by the early genes. One of the early genes, Broad-Complex (BR-C), a key regulator of the ecdysone cascade, shares a common amino-terminal BTB domain which is fused by alternative splicing to one of four pairs of C(2)H(2) zinc finger domains (Z1, Z2, Z3, and Z4). cDNAs for BR-C (BmBR-C) were isolated from the silkworm Bombyx mori. These genes showed 90.3% and 98.2% amino acid identity with the Drosophila BR-C and Manduca BR-C in the N-terminal BTB domain; 96.0%, 90.7%, and 85.2% identity with the three zinc finger domains of the Drosophila Z1, Z2, and Z4 isoforms; and 96.3% and 98.1% identity with the two zinc finger domains of the Manduca Z2 and Z4 isoforms, respectively. Partial genomic sequencing (from the 3' region of the core sequence to the 3' region of the Z3 class zinc finger-coding sequence) of the BmBR-C gene showed that four exons coding the zinc finger domains are arranged the same as the BR-C gene in Drosophila. The amino acid sequence predicted from the genomic sequence corresponding to the BmBR-C Z3 class zinc finger domain is 100% identical to the Z3 isoforms of Drosophila and Manduca. We examined expression patterns of the BmBR-C isoforms during late larval to pupal development in the epidermis, fatbody and silk gland. During the metamorphic transformation, the epidermis and silk gland are completely histolyzed; however, the fat body survives into the adult phase. Expression patterns of BmBR-C during development differed extensively between the histolyzed group and the survival group. The BmBR-C expression patterns in silk glands also differed between the anterior and other areas (the middle and posterior silk glands).

Casein Kinase II Alpha Subunit and C1-Inhibitor Are Independent Predictors of Outcome in Patients with Squamous Cell Carcinoma of the Lung

PURPOSE

Gene expression profiling has been shown to be a valuable tool for prognostication and identification of cancer-associated genes in human malignancies. We aimed to identify potential prognostic marker(s) in non-small cell lung cancers using global gene expression profiles.

EXPERIMENTAL DESIGN

Twenty-one previously untreated patients with non-small cell lung cancer were analyzed using the Affymetrix GeneChip high-density oligonucleotide array and comparative genomic hybridization. Identified candidate genes were validated in an independent cohort of 45 patients using quantitative real-time reverse transcription-PCR and Western blot analyses. Follow-up data for these patients was collected and used to assess outcome correlations.

RESULTS

Hierarchical clustering analysis yielded three distinct subgroups based on gene expression profiling. Cluster I consisted of 4 patients with adenocarcinoma and 1 with squamous cell carcinoma (squamous cell carcinoma); clusters II and III consisted of 6 and 10 patients with squamous cell carcinoma, respectively. Outcome analysis was performed on the cluster groups containing solely squamous cell carcinoma, revealing significant differences in disease-specific survival rates. Moreover, patients having a combination of advanced Tumor-Node-Metastasis stage and assigned to the poor prognosis cluster group (cluster II) had significantly poorer outcomes. Comparative genomic hybridization analysis showed recurrent chromosomal losses at 1p, 3p, 17, 19, and 22 and gains/amplifications at 3q, 5p, and 8q, which did not vary significantly between the cluster groups. We internally and externally validated a subset of 11 cluster II (poor prognosis)-specific genes having corresponding chromosomal aberrations identified by comparative genomic hybridization as prognostic markers in an independent cohort of patients with lung squamous cell carcinoma identifying CSNK2A1 and C1-Inh as independent predictors of outcome.

CONCLUSION

CSNK2A1 and C1-Inh are independent predictors of survival in lung squamous cell carcinoma patients and may be useful as prognostic markers.

Essential role of Plzf in maintenance of spermatogonial stem cells

Little is known of the molecular mechanisms whereby spermatogonia, mitotic germ cells of the testis, self-renew and differentiate into sperm. Here we show that Zfp145, encoding the transcriptional repressor Plzf, has a crucial role in spermatogenesis. Zfp145 expression was restricted to gonocytes and undifferentiated spermatogonia and was absent in tubules of W/W(v) mutants that lack these cells. Mice lacking Zfp145 underwent a progressive loss of spermatogonia with age, associated with increases in apoptosis and subsequent loss of tubule structure but without overt differentiation defects or loss of the supporting Sertoli cells. Spermatogonial transplantation experiments revealed a depletion of spermatogonial stem cells in the adult. Microarray analysis of isolated spermatogonia from Zfp145-null mice before testis degeneration showed alterations in the expression profile of genes associated with spermatogenesis. These results identify Plzf as a spermatogonia-specific transcription factor in the testis that is required to regulate self-renewal and maintenance of the stem cell pool.

Mechanism of SMRT Corepressor Recruitment by the BCL6 BTB Domain

BCL6 encodes a transcription factor that represses genes necessary for the terminal differentiation of lymphocytes within germinal centers, and the misregulated expression of this factor is strongly implicated in several types of B cell lymphoma. The homodimeric BTB domain of BCL6 (also known as the POZ domain) is required for the repression activity of the protein and interacts directly with the SMRT and N-CoR corepressors that are found within large multiprotein histone deacetylase-containing complexes. We have identified a 17 residue fragment from SMRT that binds to the BCL6 BTB domain, and determined the crystal structure of the complex to 2.2 A. Two SMRT fragments bind symmetrically to the BCL6 BTB homodimer and, in combination with biochemical and in vivo data, the structure provides insight into the basis of transcriptional repression by this critical B cell lymphoma protein.

VDUP1 upregulated by TGF-beta1 and 1,25-dihydorxyvitamin D3 inhibits tumor cell growth by blocking cell-cycle progression

Vitamin D(3) upregulated protein 1 (VDUP1) is a 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) upregulated protein, and it is induced by various stresses. In human tumor tissues, VDUP1 expression was downregulated. Upon stimulation by growth-inhibitory signals such as TGF-beta1 and 1,25(OH)(2)D(3), its expression was rapidly upregulated as the cell growth was retarded. The transfection of VDUP1 in tumor cells reduced cell growth. The VDUP1 expression was also increased when the cell-cycle progression was arrested. Transfection of VDUP1 induced cell-cycle arrest at the G0/G1 phase, indicating that VDUP1 possesses a tumor-suppressive activity. In addition, it was found that VDUP1 interacted with promyelocytic leukemia zinc-finger, Fanconi anemia zinc-finger, and histone deacetylase 1, which are known to be transcriptional corepressors. VDUP1 itself suppressed IL-3 receptor and cyclin A2 promoter activity. Taken together, these results suggest that VDUP1 is a novel antitumor gene which forms a transcriptional repressor complex.

Purified promyelocytic leukemia coiled-coil aggregates as a tetramer displaying low alpha-helical content

The promyelocytic leukemia (PML) gene is involved in the 15/17 chromosomal translocation of acute promyelocytic leukemia (APL). It encodes a nuclear phosphoprotein containing an alpha-helical coiled-coil domain with four heptad repeats. The heptad repeats consist of four clusters of hydrophobic amino acids that mediate in vivo the complex formation between PML and other PML molecules or PML-RARalpha mutant protein. In this report, we show the production of PML coiled-coil (fragment 223-360) as a fusion protein, its solubilization by the combined action of two different detergents, and its purification with affinity chromatography after column proteolytic cleavage. The FPLC chromatograms of the purified coiled-coils, carried out under non-denaturing conditions, show that the peptide elutes only in the presence of Sarkosyl detergent (conc. 0.1%) and, under these conditions, elutes as a tetrameric complex. This confirms the evidence from in vivo experiments that this region is responsible for protein complex formation. The HPLC analyses show the presence of a single peak eluting under highly hydrophobic conditions, indicating the high hydrophobicity of the peptide in accordance with the primary sequence analysis. Finally, the purified peptide was structurally characterized by means of circular dichroism (CD) measurements that were carried out with low Sarkosyl concentration (0.003%). The CD spectra indicate a low alpha-helical content (13.5%) with respect to predictions based on the primary sequence analysis (PSI-PRED, SS-PRO, and J-PRED), suggesting that the alpha-helix content could be modulated by coiled-coil surrounding domains and/or by other post-translational modifications, even if the effect of the Sarkosyl on the peptide secondary structure cannot be excluded.

The ETO (MTG8) gene family

Cloning and characterization of the 8;21 chromosomal breakpoint identified AML1 on chromosome 21 and ETO (MTG8) on chromosome 8, and the resultant chimeric gene product, AML-1/ETO. The ETO gene family now includes three human members encoding proteins composed of four evolutionarily conserved domains termed nervy homology regions (NHR) 1-4. ETO associates with N-CoR/Sin3a/HDAC complexes in vivo and acts as a corepressor for the promyelocytic zinc finger protein. Moreover, ETO is nuclear matrix attached at sites coincident with histone deacetylase enzymes and mSin3a. These data suggest that ETO proteins function as transcriptional corepressors. This review focuses on the ETO gene family in terms of expression and function. Specifically, the role of ETO as a co-repressor will be detailed. Additionally, the impact of this recent discovery on treatment of t(8;21)-containing leukemia will be discussed.

Genetics of myeloid leukemias

Human leukemias are typified by acquired recurring chromosomal translocations. Cloning of these translocation breakpoints has provided important insights into pathogenesis of disease as well as novel therapeutic approaches. Chronic myelogenous leukemias (CML) are caused by constitutively activated tyrosine kinases, such as BCR/ABL, that confer a proliferative and survival advantage to hematopoietic progenitors but do not affect differentiation. These activated kinases are validated targets for therapy with selective tyrosine kinase inhibitors, a paradigm that may have broad applications in treatment of hematologic malignancies as well as solid tumors. Chromosomal translocations in acute myeloid leukemias (AML) most often result in loss-of-function mutations in transcription factors that are required for normal hematopoietic development. These latter mutations, however, are not sufficient to cause AML. The available evidence indicates that activating mutations in the hematopoietic tyrosine kinases FLT3 and c-KIT, and in N-RAS and K-RAS, confer proliferative advantage to hematopoietic progenitors and cooperate with loss-of-function mutations in hematopoietic transcription factors to cause an acute leukemia phenotype characterized by proliferation and impaired differentiation. The data supporting this hypothesis and the clinical and therapeutic implications of these observations are reviewed.

Comprehensive genotypic analysis of leukemia: clinical and therapeutic implications

Over the past several years, the application of a spectrum of cytogenetic and molecular diagnostic techniques has dramatically improved our understanding of the pathophysiology of leukemia. These techniques include chromosomal translocations visualized by G-banding techniques, fluorescence in-situ hybridization, spectral karyotyping, comparative genomic hybridization, loss of heterozygosity analysis, and characterization of point mutations by DNA sequence analysis. We will review the application of these techniques, update novel findings utilizing these techniques over the past year as they apply to specific leukemias, and review the clinical and therapeutic implications of these findings.