AML1, the target of chromosomal rearrangements in human leukemia, regulates the expression of human complement receptor type 1 (CR1) gene

IDO2 Drives Autoantibody Production and Joint Inflammation in a Preclinical Model of Arthritis by Repressing Runx1 Function in B Cells

The immunomodulatory enzyme IDO2 is an essential mediator of autoantibody production and joint inflammation in preclinical models of autoimmune arthritis. Although originally identified as a tryptophan-catabolizing enzyme, we recently discovered a previously unknown nonenzymatic pathway is essential for the proarthritic function of IDO2. We subsequently identified Runx1 (Runt-related transcription factor 1) as a potential component of the nonenzymatic pathway IDO2 uses to drive arthritis. In this study, we find that IDO2 directly binds Runx1 and inhibits its localization to the nucleus, implicating Runx1 as a downstream component of IDO2 function. To directly test whether Runx1 mediates the downstream pathway driving B cell activation in arthritis, we bred B cell conditional Runx1-deficient (CD19cre Runx1flox/flox) mice onto the KRN.g7 arthritis model in the presence or absence of IDO2. Runx1 loss did not affect arthritis in the presence of IDO2; however, deleting Runx1 reversed the antiarthritic effect of IDO2 loss in this model. Further studies demonstrated that the IDO2-Runx1 interaction could be blocked with a therapeutic anti-IDO2 mAb in vitro and that Runx1 was required for IDO2 Ig's therapeutic effect in vivo. Taken together, these data demonstrate that IDO2 mediates autoantibody production and joint inflammation by acting as a repressor of Runx1 function in B cells and implicate therapeutic targeting of IDO2-Runx1 binding as a strategy to inhibit autoimmune arthritis and other autoantibody-mediated diseases.

RUNX1: A Regulator of NF-kB Signaling in Pulmonary Diseases

Runt-related transcription factor 1 (RUNX1), a member of the RUNX family, is one of the key regulatory proteins in vertebrates. RUNX1 is involved in embryonic development, hematopoiesis, angiogenesis, tumorigenesis and immune response. In the past few decades, studies mainly focused on the effect of RUNX1 on acute leukemia and cancer. Only few studies about the function of RUNX1 in the pathological process of pulmonary diseases have been reported. Recent studies have demonstrated that RUNX1 is highly expressed in both mesenchymal and epithelial compartments of the developing and postnatal lung and that it plays a critical role in the lipopolysaccharide induced lung inflammation by regulating the NF-kB pathway. RUNX1 participates in the regulation of the NF-kB signaling pathway through interaction with IkB kinase complex in the cytoplasm or interaction with the NF-kB subunit P50. NF-kB is well-known signaling pathway necessary for inflammatory response in the lung. This review is to highlight the RUNX1 structure, isoforms and to present the mechanism that RUNX1 regulates NF-kB. This will illustrate the great potential role of RUNX1 in the inflammation signaling pathway in pulmonary diseases.

TSP-1-1223 A/G Polymorphism as a Potential Predictor of the Recurrence Risk of Bladder Cancer in a Chinese Population

Backgrounds. TSP-1 is a glycoprotein that functions in the biology of bladder cancer. We investigated the relationship between the distribution of TSP-1-1223 A/G polymorphism (rs2169830) and the clinical characteristics of bladder cancer. Materials and Methods. TaqMan assay was performed to determine the genotype of 609 cases and 670 control subjects in a Chinese population. Logistic regression was used to assess the association between the polymorphism and the risk of bladder cancer. Quantitative real-time polymerase chain reaction was performed to determine TSP-1 mRNA expression. Survival curves were generated using the Kaplan-Meier method. Results. No significant differences were detected in the genotype frequencies of healthy control subjects and patients with bladder cancer. By contrast, the time until the first recurrence differed significantly between genotypes (P = 0.017). The expression of TSP-1 mRNA in bladder cancer tissues was lower in patients with an AG genotype than in those with an AA genotype. The lowest expression was observed in patients with a GG genotype. Conclusions. In conclusion, TSP-1-1223 A/G polymorphism may contribute to the recurrence of bladder cancer in Chinese population.

Transcriptional regulation and spatial organisation of the human AML1/RUNX1 gene

The transcription factor RUNX1 is a key regulator of haematopoiesis in vertebrates. In humans, the 260-kb long gene coding for this transcription factor is located on chromosome 21. This gene is transcribed from two alternative promoters that are commonly referred to as the distal and the proximal promoters. In model experiments, these two promoters were found to be active in cells of different lineages, although RUNX1 is preferentially expressed in haematopoietic cells. In the present study, we attempted to identify the regulatory elements that could guide tissue-specific expression of the RUNX1 gene. Two such regulatory elements were found within the RUNX1 gene. One of these elements, located within intron 1, is a haematopoietic-specific enhancer. The second regulatory element, located within intron 5.2, contributes to the formation of an active chromatin hub, which integrates the above-mentioned enhancer and the P1 and P2 promoters.

Erythrocyte complement receptor 1 (CR1) expression level is not associated with polymorphisms in the promoter or 3' untranslated regions of the CR1 gene

Complement receptor 1 (CR1) expression level on erythrocytes is genetically determined and is associated with high (H) and low (L) expression alleles identified by a HindIII restriction fragment-length polymorphism (RFLP) in intron 27 of the CR1 gene. The L allele confers protection against severe malaria in Papua New Guinea, probably because erythrocytes with low CR1 expression, are less able to form pathogenic rosettes with Plasmodium falciparum-infected erythrocytes. Despite the biological importance of erythrocyte CR1, the genetic mutation controlling CR1 expression level remains unknown. We investigated the possibility that mutations in the upstream or 3' untranslated regions of the CR1 gene could control erythrocyte CR1 level. We identified several novel polymorphisms; however, the mutations did not segregate with erythrocyte CR1 expression level or the H and L alleles. Therefore, high and low erythrocyte CR1 levels cannot be explained by polymorphisms in transcriptional control elements in the upstream or 3' untranslated regions of the CR1 gene.

The proto-oncogene ERG in megakaryoblastic leukemias

Aneuploidy is one of the hallmarks of cancer. Acquired additions of chromosome 21 are a common finding in leukemias, suggesting a contributory role to leukemogenesis. About 10% of patients with a germ line trisomy 21 (Down syndrome) are born with transient megakaryoblastic leukemia. We and others have shown acquired mutations in the X chromosome gene GATA1 in all these cases. The gene or genes on chromosome 21 whose overexpression promote the megakaryoblastic phenotype are presently unknown. We propose that ERG, an Ets transcription factor situated on chromosome 21, is one such candidate. We show that ERG is expressed in hematopoietic stem cells, megakaryoblastic cell lines, and in primary leukemic cells from Down syndrome patients. ERG expression is induced upon megakaryocytic differentiation of the erythroleukemia cell lines K562 and UT-7, and forced expression of ERG in K562 cells induces erythroid to megakaryoblastic phenotypic switch. We also show that ERG activates the gpIb megakaryocytic promoter and binds the gpIIb promoter in vivo. Furthermore, both ERG and ETS2 bind in vivo the hematopoietic enhancer of SCL/TAL1, a key regulator of hematopoietic stem cell and megakaryocytic development. We propose that trisomy 21 facilitates the occurrence of megakaryoblastic leukemias through a shift toward the megakaryoblastic lineage caused by the excess expression of ERG, and possibly by other chromosome 21 genes, such as RUNX1 and ETS2, in hematopoietic progenitor cells, coupled with a differentiation arrest caused by the acquisition of mutations in GATA1.

A human CR1-like transcript containing sequence for a binding protein for iC4 is expressed in hematopoietic and fetal lymphoid tissue

Primate immune adherence receptors are erythrocyte complement receptors (E-CR) that favorably influence the clearance of circulating immune complexes (IC). The human E-CR is the type one complement receptor (CR1), most commonly expressed as a 220 kDa protein containing 30 short consensus repeats (SCRs). The chimpanzee E-CR is a 75 kDa protein composed of eight SCRs, and is encoded by an ortholog of human CR1-like (CR1L), a genetic element related to CR1. Human CR1L was previously identified from genomic clones that predict exons for seven SCRs, and there have been no reports of CR1L expression. The purpose of this study was to determine if human CR1L is expressed. Amplification of human bone marrow cDNA using primers specific for CR1/CR1L yielded a product similar to chimp CR1L encoding sequence. The first 6.5 SCRs matched 100% with the predicted human CR1L sequence, while the second half of SCR 7 was homologous to the comparable chimp CR1L sequence but with a stop codon. Expression in COS-7 cells yielded a human CR1L protein of approximately 50 kDa that exhibited binding specificity for iC4 but not for iC3. Neither northern nor western blot analysis of human bone marrow revealed the presence of the CR1L transcript or protein. However, northern blot analysis of various other lymphoid tissue identified a candidate CR1L transcript in human fetal liver. PCR amplification of a cDNA panel of human fetal tissue confirmed the presence of the CR1L transcript in fetal liver, and to a lesser extent in fetal spleen and thymus. Thus, expression of the CR1L transcript appears to be limited to hematopoietic and fetal lymphoid tissue.

AML1 interconnected pathways of leukemogenesis

The AML1 transcription factor, identified by the cloning of the translocation t(8;21) breakpoint, is one of the most frequent targets for chromosomal translocations in leukemia. Furthermore, polysomies and point mutations can also alter AML1 function. AML1, also called CBF alpha 2, PEBP alpha 2 or RUNX1, is thus implicated in a great number of acute leukemias via a variety of pathogenic mechanisms and seems to act either as an oncogene or a tumor suppressor gene. Characterization of AML1 knockout mice has shown that AML1 is necessary for normal development of all hematopoietic lineages and alterations in the overal functional level of AML1 can have a profound effect on hematopoiesis. Numerous studies have shown that AML1 plays a vital role in the regulation of expression of many genes involved in hematopoietic cell development, and the impairment of AML1 function disregulates the pathways leading to cellular proliferation and differentiation. However, heterozygous AML1 mutations alone may not be sufficient for the development of leukemia. A cumulative process of mutagenesis involving additional genetic events in functionally related molecules, may be necessary for the development of leukemia and may determine the leukemic phenotype. We review the known AML1 target genes, AML1 interacting proteins, AML1 gene alterations and their effects on AML1 function, and mutations in AML1-related genes associated with leukemia. We discuss the interconnections between all these genes in cell signaling pathways and their importance for future therapeutic developments.

Correlation between cellular localization of TEL/AML1 fusion protein and repression of AML1-mediated transactivation of CR1 gene

Human chromosome translocation t(12;21)(p12;q22) is the most frequent chromosome rearrangement in childhood B-lineage acute lymphoblastic leukemia (ALL), and produces the TEL/AML1 fusion protein. The chimeric protein, TEL/AML1 contains the first 336 amino acids of TEL that is linked to residues 21-480 of AML1 and the fusion protein is generally known as a transcription repressor to the various target genes. Furthermore, TEL/AML1 has been shown to interfere with AML1-mediated transactivation on the CR1 gene. To understand the mechanism of the TEL/AML1-mediated repression, we used transient-transfection assay and immunofluorescence to monitor subcellular localization of TEL/AML1. Here, we show that TEL/AML1 is localized in the cytoplasm and the transcriptional activities of CR1 promoter are affected by the subcellular localization of TEL/AML1 fusion protein.

Transcription factor fusions in acute leukemia: variations on a theme

The leukemia-associated fusion proteins share several structural or functional similarities, suggesting that they may impart a leukemic phenotype through common modes of transcriptional dysregulation. The fusion proteins generated by these translocations usually contain a DNA-binding domain, domains responsible for homo- or hetero-dimerization, and domains that interact with proteins involved in chromatin remodeling (e.g., co-repressor molecules or co-activator molecules). It is these shared features that constitute the 'variations on the theme' that underling the aberrant growth and differentiation that is the hallmark of acute leukemia cells.