Potential involvement of the AML1-MTG8 fusion protein in the granulocytic maturation characteristic of the t(8;21) acute myelogenous leukemia revealed by microarray analysis

AU-Rich Element RNA Binding Proteins: At the Crossroads of Post-Transcriptional Regulation and Genome Integrity

Genome integrity must be tightly preserved to ensure cellular survival and to deter the genesis of disease. Endogenous and exogenous stressors that impose threats to genomic stability through DNA damage are counteracted by a tightly regulated DNA damage response (DDR). RNA binding proteins (RBPs) are emerging as regulators and mediators of diverse biological processes. Specifically, RBPs that bind to adenine uridine (AU)-rich elements (AREs) in the 3' untranslated region (UTR) of mRNAs (AU-RBPs) have emerged as key players in regulating the DDR and preserving genome integrity. Here we review eight established AU-RBPs (AUF1, HuR, KHSRP, TIA-1, TIAR, ZFP36, ZFP36L1, ZFP36L2) and their ability to maintain genome integrity through various interactions. We have reviewed canonical roles of AU-RBPs in regulating the fate of mRNA transcripts encoding DDR genes at multiple post-transcriptional levels. We have also attempted to shed light on non-canonical roles of AU-RBPs exploring their post-translational modifications (PTMs) and sub-cellular localization in response to genotoxic stresses by various factors involved in DDR and genome maintenance. Dysfunctional AU-RBPs have been increasingly found to be associated with many human cancers. Further understanding of the roles of AU-RBP_S in maintaining genomic integrity may uncover novel therapeutic strategies for cancer.

Multidimensional study of the heterogeneity of leukemia cells in t(8;21) acute myelogenous leukemia identifies the subtype with poor outcome

t(8;21)(q22;q22) acute myelogenous leukemia (AML) is morphologically characterized by a continuum of heterogeneous leukemia cells from myeloblasts to differentiated myeloid elements. Thus, t(8;21) AML is an excellent model for studying heterogeneous cell populations and cellular evolution during disease progression. Using integrative analyses of immunophenotype, RNA-sequencing (RNA-seq), and single-cell RNA-sequencing (scRNA-seq), we identified three distinct intrapatient leukemic cell populations that were arrested at different stages of myeloid differentiation: CD34⁺CD117^dim blasts, CD34⁺CD117^bri blasts, and abnormal myeloid cells with partial maturation (AM). CD117 is also known as c-KIT protein. CD34⁺CD117^dim cells were blocked in the G0/G1 phase at disease onset, presenting with the regular morphology of myeloblasts showing features of granulocyte-monocyte progenitors (GMP), and were drug-resistant to chemotherapy. Genes associated with cell migration and adhesion (LGALS1, EMP3, and ANXA 2) were highly expressed in the CD34⁺CD117^dim population. CD34⁺CD117^bri blasts were blocked a bit later than the CD34⁺CD117^dim population in the hematopoietic differentiation stage and displayed high proliferation ability. AM cells, which bear abnormal myelocyte morphology, especially overexpressed granule genes AZU1, ELANE, and PRTN3 and were sensitive to chemotherapy. scRNA-seq at different time points identified CD34⁺CD117^dim blasts as an important leukemic cluster that expanded at postrelapse refractory stage after several cycles of chemotherapy. Patients with t(8;21) AML with a higher proportion of CD34⁺CD117^dim cells had significantly worse clinical outcomes than those with a lower CD34⁺CD117^dim proportion. Univariate and multivariate analyses identified CD34⁺CD117^dim proportion as an independent factor for poor disease outcome. Our study provides evidence for the multidimensional heterogeneity of t(8;21)AML and may offer new tools for future disease stratification.

Implication and role of neutrophil gelatinase-associated lipocalin in cancer: lipocalin-2 as a potential novel emerging comprehensive therapeutic target for a variety of cancer types

Cancer is a leading cause of mortalities worldwide. Over the past few decades, exploration of molecular mechanisms behind cancer initiation and progression has been of great interest in the viewpoint of both basic and clinical scientists. It is generally believed that identification of key molecules implicated in cancer pathology not only improves our understanding of the disease, but also could result in introduction of novel therapeutic strategies. Neutrophil gelatinase-associated lipocalin (NGAL)/lipocalin-2 (LCN2) is a member of lipocalin superfamily with a variety of functions. Although the main function of LCN2 is still unknown, many studies confirmed its significant role in the initiation, progression, and metastasis of various types of cancer. Furthermore, aberrant expression of LCN2 is also concerned with the chemo- and radio-resistant phenotypes of tumors. Here, we will review the contribution of known functions of LCN2 to the pathophysiology of cancer. We also highlight how the deregulated expression of LCN2 is associated with a variety of fatal types of cancer for which there are no effective therapeutic modalities. The unique and multiple functions of LCN2 and its widespread expression in different types of cancer prompted us to suggest LCN2 could be considered either as a valuable diagnostic and prognostic biomarker or as a potential novel therapeutic target.

Expression of myeloperoxidase in acute myeloid leukemia blasts mirrors the distinct DNA methylation pattern involving the downregulation of DNA methyltransferase DNMT3B

Myeloperoxidase (MPO) has been associated with both a myeloid lineage commitment and favorable prognosis in patients with acute myeloid leukemia (AML). DNA methyltransferase inhibitors (decitabine and zeburaline) induced MPO gene promoter demethylation and MPO gene transcription in AML cells with low MPO activity. Therefore, MPO gene transcription was directly and indirectly regulated by DNA methylation. A DNA methylation microarray subsequently revealed a distinct methylation pattern in 33 genes, including DNA methyltransferase 3 beta (DNMT3B), in CD34-positive cells obtained from AML patients with a high percentage of MPO-positive blasts. Based on the inverse relationship between the methylation status of DNMT3B and MPO, we found an inverse relationship between DNMT3B and MPO transcription levels in CD34-positive AML cells (P=0.0283). In addition, a distinct methylation pattern was observed in five genes related to myeloid differentiation or therapeutic sensitivity in CD34-positive cells from AML patients with a high percentage of MPO-positive blasts. Taken together, the results of the present study indicate that MPO may serve as an informative marker for identifying a distinct and crucial DNA methylation profile in CD34-positive AML cells.

svapls: an R package to correct for hidden factors of variability in gene expression studies

Background

Hidden variability is a fundamentally important issue in the context of gene expression studies. Collected tissue samples may have a wide variety of hidden effects that may alter their transcriptional landscape significantly. As a result their actual differential expression pattern can be potentially distorted, leading to inaccurate results from a genome-wide testing for the important transcripts.

Results

We present an R package svapls that can be used to identify several types of unknown sample-specific sources of heterogeneity in a gene expression study and adjust for them in order to provide a more accurate inference on the original expression pattern of the genes over different varieties of samples. The proposed method implements Partial Least Squares regression to extract the hidden signals of sample-specific heterogeneity in the data and uses them to find the genes that are actually correlated with the phenotype of interest. We also compare our package with three other popular softwares for testing differential gene expression along with a detailed illustration on the widely popular Golub dataset. Results from the sensitivity analyes on simulated data with widely different hidden variation patterns reveal the improved detection power of our R package compared to the other softwares along with reasonably smaller error rates. Application on the real-life dataset exhibits the efficacy of the R package in detecting potential batch effects from the dataset.

Conclusions

Overall, Our R package provides the user with a simplified framework for analyzing gene expression data with a wide range of hidden variation patterns and delivering a differential gene expression analysis with substantially improved power and accuracy.

The R package svapls is freely available at http://cran.r-project.org/web/packages/svapls/index.html.

AML1-ETO targets and suppresses cathepsin G, a serine protease, which is able to degrade AML1-ETO in t(8;21) acute myeloid leukemia

Although the significance of cathepsin G (CTSG) in host defense has been intensively investigated, little is known about its potential roles in granulopoiesis or leukemogenesis. We report here that CTSG is directly targeted and suppressed by AML1-ETO in t(8;21) acute myeloid leukemia (AML). Luciferase assays demonstrate that the CTSG promoter is strongly transactivated by AML1 and the AML1-dependent transactivation is suppressed by AML1-ETO. We also define a novel regulatory mechanism by which AML1-ETO-mediated transrepression requires both AML1-ETO and AML1 binding at adjacent sites, instead of the replacement of AML1 by AML1-ETO, and wild-type AML1 binding is a prerequisite for the repressive effect caused by AML1-ETO. Further evidence shows that CTSG, as a hematopoietic serine protease, can degrade AML1-ETO both in vitro and in vivo. Restoration of CTSG induces partial differentiation, growth inhibition and apoptosis in AML1-ETO-positive cells. In addition to t(8;21) AML, CTSG downregulation is observed in AML patients with other cytogenetic/genetic abnormalities that potentially interrupt normal AML1 function, that is, inv(16) and EVI1 overexpression. Thus, the targeting and suppression of CTSG by AML1-ETO in t(8;21) AML may provide a mechanism for leukemia cells to escape from the intracellular surveillance system by preventing degradation of foreign proteins.

The novel RUNX3/p33 isoform is induced upon monocyte-derived dendritic cell maturation and downregulates IL-8 expression

RUNX proteins are heterodimeric factors that play crucial roles during development and differentiation of cells of the immune system. The RUNX3 transcription factor controls lineage decisions during thymopoiesis and T-cell differentiation, and modulates myeloid cell effector functions. We now report the characterization of the human RUNX3/p33 isoform, generated by splicing out a Runt DNA-binding domain-encoding exon, and whose transcriptional activities differ from those of the prototypic RUNX3/p44 molecule. Unlike RUNX3/p44, RUNX3/p33 is induced upon maturation of monocyte-derived dendritic cells (MDDC), and is unable to transactivate the regulatory regions of the CD11a, CD11c and CD49e integrin genes. Overexpression of RUNX3/p33 in myeloid cell lines led to diminished expression of genes involved in inflammatory responses. Moreover, overexpression of RUNX3/p33 down-modulated the basal level of IL-8 production from immature monocyte-derived dendritic cells (MDDC). Besides, siRNA-mediated knock-down of RUNX3 led to diminished levels of IL-8 RNA in immature MDDC, and modulated the neutrophil-recruiting capacity of myeloid cell line supernatants. Since IL-8 promotes neutrophil chemotaxis and degranulation during inflammatory responses, and exerts mitogenic and angiogenic actions within tumor microenvironment, our results imply that myeloid RUNX3 expression regulates the recruitment of leukocytes towards inflammatory foci and might also contribute to human cancer progression.

POU4F1 is associated with t(8;21) acute myeloid leukemia and contributes directly to its unique transcriptional signature

The t(8;21)(q22;q22) translocation, present in ~5% of adult acute myeloid leukemia (AML) cases, produces the AML1/ETO fusion protein. Dysregulation of the POU domain-containing transcription factor POU4F1 is a recurring abnormality in t(8;21) AML. Here, we show that POU4F1 over-expression is highly correlated with, but not caused by AML1/ETO. AML1/ETO markedly increases the self-renewal capacity of myeloid progenitors from murine bone marrow or fetal liver and drives expansion of these cells in liquid culture. POU4F1 is neither necessary nor sufficient for these AML1/ETO-dependent properties, suggesting that it contributes to leukemia through novel mechanisms. To identify targets of POU4F1, we performed gene expression profiling in primary mouse cells with genetically defined levels of POU4F1 and identified 140 differentially expressed genes. This expression signature was significantly enriched in human t(8;21) AML samples and was sufficient to cluster t(8;21) AML samples in an unsupervised hierarchical analysis. Among the most highly differentially expressed genes, half are known AML1/ETO targets, implying that the unique transcriptional signature of t(8;21) AML is, in part, attributable to POU4F1 and not AML1/ETO itself. These genes provide novel candidates for understanding the biology and developing therapeutic approaches for t(8;21) AML.

Proleukemic RUNX1 and CBFbeta mutations in the pathogenesis of acute leukemia

The existence of non-random mutations in critical regulators of cell growth and differentiation is a recurring theme in cancer pathogenesis and provides the basis for our modern, molecular approach to the study and treatment of malignant diseases. Nowhere is this more true than in the study of leukemogenesis, where research has converged upon a critical group of genes involved in hematopoietic stem and progenitor cell self-renewal and fate specification. Prominent among these is the heterodimeric transcriptional regulator, RUNX1/CBFbeta. RUNX1 is a site-specific DNA-binding protein whose consensus response element is found in the promoters of many hematopoietically relevant genes. CBFbeta interacts with RUNX1, stabilizing its interaction with DNA to promote the actions of RUNX1/CBFbeta in transcriptional control. Both the RUNX1 and the CBFbeta genes participate in proleukemic chromosomal alterations. Together they contribute to approximately one-third of acute myelogenous leukemia (AML) and one-quarter of acute lymphoblastic leukemia (ALL) cases, making RUNX1 and CBFbeta the most frequently affected genes known in the pathogenesis of acute leukemia. Investigating the mechanisms by which RUNX1, CBFbeta, and their proleukemic fusion proteins influence leukemogenesis has contributed greatly to our understanding of both normal and malignant hematopoiesis. Here we present an overview of the structural features of RUNX1/CBFbeta and their derivatives, their roles in transcriptional control, and their contributions to normal and malignant hematopoiesis.

Transcriptional dysregulation mediated by RUNX1-RUNX1T1 in normal human progenitor cells and in acute myeloid leukaemia

The t(8;21)(q22;q22) occurs frequently in acute myelogenous leukaemia and gives rise to the transcription factor fusion protein, RUNX1-RUNX1T1 (also known as AML1-ETO). To identify the genes dysregulated by the aberrant transcriptional activity of RUNX1-RUNX1T1, we used microarrays to determine the effect of this mutation on gene expression in human progenitor cells and during subsequent development. Gene signatures of these developmental subsets were very dissimilar indicating that effects of RUNX1-RUNX1T1 are highly context dependent. We focused on gene changes associated with the granulocytic lineage and identified a clinically relevant subset of these by comparison with 235 leukaemia patient transcriptional signatures. We confirmed the overexpression of a number of significant genes (Sox4, IL-17BR, CD200 and gamma-catenin). Further, we show that overexpression of CD200 and gamma-catenin is also associated with the inv(16) abnormality which like RUNX1-RUNX1T1 disrupts core binding factor activity. We investigated the functional significance of CD200 and gamma-catenin overexpression in normal human progenitor cells. The effect of IL17 on growth was also assessed. Individually, none of these changes were sufficient to recapitulate the effects of RUNX1-RUNX1T1 on normal development. These data provide the most comprehensive and pertinent assessment of the effect of RUNX1-RUNX1T1 on gene expression and demonstrate the highly context-dependent effects of this fusion gene.

The multi-functional cellular adhesion molecule CD44 is regulated by the 8;21 chromosomal translocation

The 8;21 translocation is a common chromosomal abnormality in acute myeloid leukemia (AML). We recently identified a naturally occurring leukemogenic splice variant, AML1-ETO9a (acute myeloid leukemia-1 transcription factor and the eight-twenty-one corepressor-9a), of t(8;21). To understand the leukemic potential of AML1-ETO9a, we performed microarray analysis with the murine multipotential hematopoietic FDCP-mix A4 cell line. We identified changes in expression of various genes including CD44. CD44 is a type I transmembrane protein and functions as the major cellular adhesion molecule for hyaluronic acid, a component of the extracellular matrix. CD44 is expressed in most human cell types and is implicated in myeloid leukemia pathogenesis. We show that the presence of AML1-ETO9a significantly increased the expression of CD44 at both RNA and protein levels. Furthermore, the CD44 promoter is bound by AML1-ETO9a and AML1-ETO at the chromatin level. In addition, in the AML1-ETO9a leukemia mouse model CD44 is regulated in a cell context-dependent manner. Thus, our observations suggest that AML1-ETO and its splice variant AML1-ETO9a are able to regulate the expression of the CD44 gene, linking the 8;21 translocation to the regulation of a cell adhesion molecule that is involved in the growth and maintenance of the AML blast/stem cells.

The p21Waf1 pathway is involved in blocking leukemogenesis by the t(8;21) fusion protein AML1-ETO

The 8;21 translocation is a major contributor to acute myeloid leukemia (AML) of the M2 classification occurring in approximately 40% of these cases. Multiple mouse models using this fusion protein demonstrate that AML1-ETO requires secondary mutagenic events to promote leukemogenesis. Here, we show that the negative cell cycle regulator p21(WAF1) gene is up-regulated by AML1-ETO at the protein, RNA, and promoter levels. Retroviral transduction and hematopoietic cell transplantation experiments with p21(WAF1)-deficient cells show that AML1-ETO is able to promote leukemogenesis in the absence of p21(WAF1). Thus, loss of p21(WAF1) facilitates AML1-ETO-induced leukemogenesis, suggesting that mutagenic events in the p21(WAF1) pathway to bypass the growth inhibitory effect from AML1-ETO-induced p21(WAF1) expression can be a significant factor in AML1-ETO-associated acute myeloid leukemia.

A distinct epigenetic signature at targets of a leukemia protein

Background

Human myelogenous leukemia characterized by either the non random t(8; 21)(q22; q22) or t(16; 21)(q24; q22) chromosome translocations differ for both their biological and clinical features. Some of these features could be consequent to differential epigenetic transcriptional deregulation at AML1 targets imposed by AML1-MTG8 and AML1-MTG16, the fusion proteins deriving from the two translocations. Preliminary findings showing that these fusion proteins lead to transcriptional downregulation of AML1 targets, marked by repressive chromatin changes, would support this hypothesis. Here we show that combining conventional global gene expression arrays with the power of bioinformatic genomic survey of AML1-consensus sequences is an effective strategy to identify AML1 targets whose transcription is epigenetically downregulated by the leukemia-associated AML1-MTG16 protein.

Results

We interrogated mouse gene expression microarrays with probes generated either from 32D cells infected with a retroviral vector carrying AML1-MTG16 and unable of granulocyte differentiation and proliferation in response to the granulocyte colony stimulating factor (G-CSF), or from 32D cells infected with the cognate empty vector. From the analysis of differential gene expression alone (using as criteria a p value < 0.01 and an absolute fold change > 3), we were unable to conclude which of the 37 genes downregulated by AML1-MTG16 were, or not, direct AML1 targets. However, when we applied a bioinformatic approach to search for AML1-consensus sequences in the 10 Kb around the gene transcription start sites, we closed on 17 potential direct AML1 targets. By focusing on the most significantly downregulated genes, we found that both the AML1-consensus and the transcription start site chromatin regions were significantly marked by aberrant repressive histone tail changes. Further, the promoter of one of these genes, containing a CpG island, was aberrantly methylated.

Conclusion

This study shows that a leukemia-associated fusion protein can impose a distinct epigenetic repressive signature at specific sites in the genome. These findings strengthen the conclusion that leukemia-specific oncoproteins can induce non-random epigenetic changes.

Inducible expression of AML1-ETO fusion protein endows leukemic cells with susceptibility to extrinsic and intrinsic apoptosis

AML1-ETO, a leukemia-associated fusion protein generated by the frequently occurred chromosome translocation t(8;21) in acute myeloid leukemia, was shown to exert dichotomous functions in leukemic cells, that is, growth arrest versus differentiation block. By the analysis of oligonucleotide microarray, AML1-ETO was shown to modulate the expressions of an impressive array of pro- and anti-apoptotic genes. Here, we investigate potential effects of the ecdysone inducible AML1-ETO expression on apoptosis of leukemic U937 cell line. We show that AML1-ETO significantly stabilizes death receptor Fas protein and increases proapoptotic Bak in addition to reducing Bcl-2 expression. Accordingly, inducible AML1-ETO expression is followed by apoptosis to a lower degree. Especially, AML1-ETO endows leukemic cells with the susceptibility to anti-Fas agonist antibody, ultraviolet light and camptothecin analog NSC606985-induced apoptosis with increased activation of caspase-3/8. Considering that apoptosis-enhancing effect of AML1-ETO would not be favorable to the leukemogenesis harboring the t(8;21) translocation, it must be overcome to fulfill their leukemogenic potential. Complementary to this prediction is that two AML1-ETO-carrying leukemic cells, Kasumi-1 and SKNO-1, present similar sensitivity to apoptosis induction with AML1-ETO-negative leukemic cells. Therefore, genetic and/or epigenetic screenings of apoptosis-related genes modulated by AML1-ETO deserve to be explored for understanding the mechanisms of AML1-ETO-induced leukemogenesis.

Leukemogenic AML1-ETO fusion protein upregulates expression of connexin 43: the role in AML 1-ETO-induced growth arrest in leukemic cells

AML1-ETO, a fusion protein generated by the chromosomal translocation t(8;21), is frequently associated with acute myeloid leukemia (AML). In addition to blocking differentiation, AML1-ETO is also shown to induce growth arrest in AML cells, which is unfavorable for leukemogenesis harboring the t(8;21) translocation. However, its precise mechanism is still unclear. Here we provide the first demonstration that the conditional expression of AML1-ETO by the ecdysone-inducible system dramatically increases the expression of connexin 43 (CX43), together with growth arrest at G1 phase in leukemic U937 cells. We also show that the CX43 induction inhibits the proliferation of U937 cells at G1 phase, while the suppression of CX43 expression by small interfering RNA (siRNA) effectively overcomes the growth-inhibitory effect of AML1 -ETO in leukemic cells. Furthermore, either AML1-ETO or CX43 induction elevates cell-cycle negative regulator P27(kip1) protein by inhibiting its degradation, which is antagonized by siRNA against CX43. Taken together, our data indicate that CX43 plays a role in AML1-ETO-induced growth arrest possibly through the accumulation of P27(kip1) protein. The potential mutation or/and epigenetic alterations of CX43 and its related gene(s) deserve to be explored in AML1-ETO-positive AML patients.

Genomics and proteomics: emerging technologies in clinical cancer research

Fueled by the complete genomic data acquired from the human genome project and the desperate clinical need of comprehensive analytical tools to study a heterogeneous disease like cancer, genomic and proteomic technologies have evolved rapidly, accelerating the rate and number of discoveries in clinical cancer research. These discoveries include mechanistic understanding of cancer biology as well as the identification of biomarkers supporting early detection, molecular classification of tumors, molecular predictors of metastasis, treatment response, and prognosis. While the technical advances have been significant, clinical researchers and practicing physicians are now confronted with the challenges of understanding technically and statistically complex data sets, translating this complex information to fit clinical contexts and incorporating it into clinical studies. In this review, we will summarize the available technologies and associated bioinformatics, discuss studies that are clinically relevant, and discuss the limitations we are still facing. We will present a framework for future directions of these technologies and how we believe they should be applied in clinical studies.

Gene expression profiling data in lymphoma and leukemia: review of the literature and extrapolation of pertinent clinical applications

CONTEXT

Gene expression (GE) analyses using microarrays have become an important part of biomedical and clinical research in hematolymphoid malignancies. However, the methods are time-consuming and costly for routine clinical practice.

OBJECTIVES

To review the literature regarding GE data that may provide important information regarding pathogenesis and that may be extrapolated for use in diagnosing and prognosticating lymphomas and leukemias; to present GE findings in Hodgkin and non-Hodgkin lymphomas, acute leukemias, and chronic myeloid leukemia in detail; and to summarize the practical clinical applications in tables that are referenced throughout the text.

DATA SOURCE

PubMed was searched for pertinent literature from 1993 to 2005.

CONCLUSIONS

Gene expression profiling of lymphomas and leukemias aids in the diagnosis and prognostication of these diseases. The extrapolation of these findings to more timely, efficient, and cost-effective methods, such as flow cytometry and immunohistochemistry, results in better diagnostic tools to manage the diseases. Flow cytometric and immunohistochemical applications of the information gained from GE profiling assist in the management of chronic lymphocytic leukemia, other low-grade B-cell non-Hodgkin lymphomas and leukemias, diffuse large B-cell lymphoma, nodular lymphocyte-predominant Hodgkin lymphoma, and classic Hodgkin lymphoma. For practical clinical use, GE profiling of precursor B acute lymphoblastic leukemia, precursor T acute lymphoblastic leukemia, and acute myeloid leukemia has supported most of the information that has been obtained by cytogenetic and molecular studies (except for the identification of FLT3 mutations for molecular analysis), but extrapolation of the analyses leaves much to be gained based on the GE profiling data.

The tetramer structure of the Nervy homology two domain, NHR2, is critical for AML1/ETO's activity

AML1/ETO is the chimeric protein resulting from the t(8;21) in acute myeloid leukemia. The Nervy homology 2 (NHR2) domain in ETO mediates oligomerization and AML1/ETO's interactions with ETO, MTGR1, and MTG16, and with the corepressor molecules mSin3A and HDAC1 and HDAC3. We solved the NHR2 domain structure and found it to be an alpha-helical tetramer. We show that oligomerization contributes to AML1/ETO's inhibition of granulocyte differentiation, is essential for its ability to enhance the clonogenic potential of primary mouse bone marrow cells, and affects AML1/ETO's activity on several endogenous genes. Oligomerization is also required for AML1/ETO's interactions with ETO, MTGR1, and MTG16, but not with other corepressor molecules.

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.

Genome-wide profiling of papillary thyroid cancer identifies MUC1 as an independent prognostic marker

Clinicopathological variables used at present for prognostication and treatment selection for papillary thyroid carcinomas (PTCs) do not uniformly predict tumor behavior, necessitating identification of novel prognostic markers. Complicating the assessment is the long natural history of PTC and our rudimentary knowledge of its genetic composition. In this study we took advantage of differences in clinical behavior of two distinct variants of PTC, the aggressive tall-cell variant (TCV) and indolent conventional PTC (cPTC), to identify molecular prognosticators of outcome using complementary genome wide analyses. Comparative genome hybridization (CGH) and cDNA microarray (17,840 genes) analyses were used to detect changes in DNA copy number and gene expression in pathological cPTC and TCV. The findings from CGH and cDNA microarray analyses were correlated and validated by real-time PCR and immunohistochemical analyses on a series of 100 cases of cPTC and TCV. Genes identified by this approach were evaluated as prognostic markers in cPTC by immunohistochemistry on tissue arrays. CGH identified significant differences in the presence (76 versus 27%; P = 0.001) and type of DNA copy number aberrations in TCV compared with cPTC. Recurrent gains of 1p34-36, 1q21, 6p21-22, 9q34, 11q13, 17q25, 19, and 22 and losses of 2q21-31, 4, 5p14-q21, 6q11-22, 8q11-22, 9q11-32, and 13q21-31 were unique to TCV. Hierarchical clustering of gene expression profiles revealed significant overlap between TCV and cPTC, but further analysis identified 82 dysregulated genes differentially expressed among the PTC variants. Of these, MUC1 was of particular interest because amplification of 1q by CGH correlated with MUC1 amplification by real-time PCR analysis and protein overexpression by immunohistochemistry in TCV (P = 0.005). Multivariate analysis revealed a significant association between MUC1 overexpression and treatment outcome, independent of histopathological categorization (P = 0.03). Analysis of a validation series containing a matched group of aggressive and indolent cPTCs confirmed the association between MUC1 overexpression and survival (relative risk, 2.3; 95% confidence interval, 1.1-5.5; P = 0.03). Our data suggest that MUC1 dysregulation is associated with aggressive behavior of PTC and may serve as a prognostic marker and potential therapeutic target in this disease.

The 8;21 translocation in leukemogenesis

A common chromosomal translocation in acute myeloid leukemia (AML) involves the AML1 (acute myeloid leukemia 1, also called RUNX1, core binding factor protein (CBF alpha), and PEBP2 alpha B) gene on chromosome 21 and the ETO (eight-twenty one, also called MTG8) gene on chromosome 8. This translocation generates an AML1-ETO fusion protein. t(8;21) is associated with 12% of de novo AML cases and up to 40% in the AML subtype M2 of the French-American-British classification. Furthermore, it is also reported in a small portion of M0, M1, and M4 AML samples. Despite numerous studies on the function of AML1-ETO, the precise mechanism by which the fusion protein is involved in leukemia development is still not fully understood. In this review, we will discuss structural aspects of the fusion protein and the accumulated knowledge from in vitro analyses on AML1-ETO functions, and outline putative mechanisms of its leukemogenic potential.

Relevance of pathologic classifications and diagnosis of acute myeloid leukemia to clinical trials and clinical practice

Many new insights into the diagnosis, pathogenesis, clinical manifestation, treatment and prognosis of patients with AML reflect the heterogeneity of the disease. The initial descriptions of the various subtypes of AML, established by the FAB classification, were based on morphology and cytochemical stains. Although morphology remains the foundation for the diagnosis, additional diagnostic studies including immunophenotyping, cytogenetic evaluation, and molecular genetic studies have become critical, and in some specific cases, mandatory, complementary tools. Several specific subtypes of AML are now treated with directed or targeted therapy. Acute promyelocytic leukemia is currently the only example of a subtype of AML to which specific therapy targeted to a molecular genetic abnormality is available and this subtype now is highly curable. Future studies will address newly identified prognostic factors and gene mutations such as FLT3, Wilm's tumor (WTI), and CEBPA which will enable the further pathologic classification of patients with AML. Finally, microarray analysis will likely identify genes critically involved in the pathogenesis of specific pathologic subtypes.

Characteristics of t(8;21) acute myeloid leukemia (AML) with additional chromosomal abnormality: concomitant trisomy 4 may constitute a distinctive subtype of t(8;21) AML

t(8;21)(q22;q22) is the most frequently observed karyotypic abnormality associated with acute myeloid leukemia (AML), especially in FAB M2. Clinically, this type of AML often shows eosinophilia and has a high complete remission rate with conventional chemotherapy. t(8;21) AML is also frequently associated with additional karyotypic aberrations, such as a loss of the sex chromosome; however, it is unclear whether these aberrations change the biological and clinical characteristics of t(8;21) AML. To investigate this issue, 94 patients with t(8;21) AML were categorized according to their additional karyotypic aberrations, which were detected in more than three cases, and then morphologic features, phenotypes, expression of cytokine receptors, and clinical features were compared to t(8;21) AML without other additional aberrant karyotypes. t(8;21) AML with loss of the sex chromosome and abnormality of chromosome 9 were found in 27 cases (29.3%) and 10 cases (10.6%), respectively; however, no differences were observed from the t(8;21) AML without other additional karyotypes in terms of morphological and phenotypic features. There was also no significant difference in the clinical outcome among these three groups. On the other hand, trisomy 4 was found in three cases (3.2%) and these cells showed low expressions of CD19 (P=0.06) and IL-7 receptor (P=0.05), and high expressions of CD33 (P=0.13), CD18 (P=0.03), and CD56 (P=0.03) when compared to t(8;21) AML without additional karyotypes. Moreover, all three t(8;21) AML cases with trisomy 4 did not show eosinophilia in their bone marrow and died within 2.4 years. These observations suggest that additional karyotypic aberration, t(8;21) with trisomy 4 is rare, but it may constitute a distinctive subtype of t(8;21) AML.