A novel gene, FGA7, is fused to RUNX1/AML1 in a t(4;21)(q28;q22) in a patient with T-cell acute lymphoblastic leukemia

Neoplasia-associated Chromosome Translocations Resulting in Gene Truncation

Chromosomal translocations in cancer as well as benign neoplasias typically lead to the formation of fusion genes. Such genes may encode chimeric proteins when two protein-coding regions fuse in-frame, or they may result in deregulation of genes via promoter swapping or translocation of the gene into the vicinity of a highly active regulatory element. A less studied consequence of chromosomal translocations is the fusion of two breakpoint genes resulting in an out-of-frame chimera. The breaks then occur in one or both protein-coding regions forming a stop codon in the chimeric transcript shortly after the fusion point. Though the latter genetic events and mechanisms at first awoke little research interest, careful investigations have established them as neither rare nor inconsequential. In the present work, we review and discuss the truncation of genes in neoplastic cells resulting from chromosomal rearrangements, especially from seemingly balanced translocations.

FAM53B truncation caused by t(10;19)(q26;q13) chromosome translocation in acute lymphoblastic leukemia

RNA-sequencing of the patient's bone marrow detected fusion transcripts in which the coding sequence of the FAM53B gene (from 10q26) was fused to a genomic sequence (from 19q13) that mapped upstream of the SLC7A10 locus. Reverse transcription-polymerase chain reaction together with Sanger sequencing verified the presence of this fusion transcript. The FAM53B fusion transcript is not expected to produce any chimeric protein. However, it may code for a truncated FAM53B protein consisting of the first 302 amino acids of FAM53B together with amino acids from the 19q13 sequence. Functionally, the truncated FAM53B would be similar to the protein encoded by the FAM53B sequence with accession no. BC031654.1 (FAM53B protein accession no. AAH31654.1). Furthermore, the truncated protein contains the entire conserved domain of the FAM53 protein family. The chromosome aberration t(10;19)(q26;q13) detected in this study was previously reported in a single case of ALL, in which it was also the sole karyotypic change. Both patients entered complete hematological and cytogenetic remission following treatment.

Pediatric T-cell acute lymphoblastic leukemia

The most common pediatric malignancy is acute lymphoblastic leukemia (ALL), of which T-cell ALL (T-ALL) comprises 10-15% of cases. T-ALL arises in the thymus from an immature thymocyte as a consequence of a stepwise accumulation of genetic and epigenetic aberrations. Crucial biological processes, such as differentiation, self-renewal capacity, proliferation, and apoptosis, are targeted and deranged by several types of neoplasia-associated genetic alteration, for example, translocations, deletions, and mutations of genes that code for proteins involved in signaling transduction, epigenetic regulation, and transcription. Epigenetically, T-ALL is characterized by gene expression changes caused by hypermethylation of tumor suppressor genes, histone modifications, and miRNA and lncRNA abnormalities. Although some genetic and gene expression patterns have been associated with certain clinical features, such as immunophenotypic subtype and outcome, none has of yet generally been implemented in clinical routine for treatment decisions. The recent advent of massive parallel sequencing technologies has dramatically increased our knowledge of the genetic blueprint of T-ALL, revealing numerous fusion genes as well as novel gene mutations. The challenges now are to integrate all genetic and epigenetic data into a coherent understanding of the pathogenesis of T-ALL and to translate the wealth of information gained in the last few years into clinical use in the form of improved risk stratification and targeted therapies. Here, we provide an overview of pediatric T-ALL with an emphasis on the acquired genetic alterations that result in this disease. © 2016 Wiley Periodicals, Inc.

RUNX1 truncation resulting from a cryptic and novel t(6;21)(q25;q22) chromosome translocation in acute myeloid leukemia: A case report

Fluorescence in situ hybridization examination of a pediatric AML patient whose bone marrow cells carried trisomy 4 and FLT3-ITD mutation, demonstrated that part of the RUNX1 probe had unexpectedly moved to chromosome band 6q25 indicating a cryptic t(6;21)(q25;q22) translocation. RNA sequencing showed fusion of exon 7 of RUNX1 with an intergenic sequence of 6q25 close to the MIR1202 locus, something that was verified by RT-PCR together with Sanger sequencing. The RUNX1 fusion transcript encodes a truncated protein containing the Runt homology domain responsible for both heterodimerization with CBFB and DNA binding, but lacking the proline-, serine-, and threonine-rich (PST) region which is the transcription activation domain at the C terminal end. Which genetic event (+4, FLT3-ITD, t(6;21)-RUNX1 truncation or other, undetected acquired changes) was more pathogenetically important in the present case of AML, remains unknown. The case illustrates that submicroscopic chromosomal rearrangements may accompany visible numerical changes and perhaps should be actively looked for whenever a single trisomy is found. An active search for them may provide both pathogenetic and prognostic novel information.

Acute myeloid leukemia with t(7;21)(p22;q22) and 5q deletion: a case report and literature review

The gene RUNX1 at chromosome 21q22 encodes the alpha subunit of Core binding factor (CBF), a heterodimeric transcription factor involved in the development of normal hematopoiesis. Translocations of RUNX1 are seen in several types of leukemia with at least 21 identified partner genes. The cryptic t(7;21)(p22;q22) rearrangement involving the USP42 gene appears to be a specific and recurrent cytogenetic abnormality. Eight of the 9 cases identified in the literature with this translocation were associated with acute myeloid leukemia (AML), with the remaining case showing refractory anemia with excess blasts, type 2. Herein, we present a patient with two preceding years of leukopenia and one year of anemia prior to the diagnosis of AML, NOS with monocytic differentiation (myelomonocytic leukemia) whose conventional cytogenetics showed an abnormal clone with 5q deletion. Interphase FISH using LSI RUNX1/RUNXT1 showed three signals for RUNX1. FISH studies on previously G-banded metaphases showed the extra RUNX1 signal on the short arm of chromosome 7. Further characterization using the subtelomeric 7p probe showed a cryptic 7;21 translocation. Our case and eight previously reported leukemic cases with the t(7;21)(p22;q22) appear to share similar features including monocytic differentiation, immunophenotypic aberrancies (often with CD56 and/or CD7), and a generally poor response to standard induction chemotherapy. About 80% of these cases had loss of 5q material as an additional abnormality at initial diagnosis or relapse. These findings suggest that t(7;21) may represent a distinct recurrent cytogenetic abnormality associated with AML. The association between the t(7;21) and 5q aberrancies appears to be non-random, however the pathogenetic connection remains unclear. Additional studies to evaluate for RUNX1 partner genes may be considered for AML patients with RUNX1 rearrangement and 5q abnormalities; however knowledge of the prognostic implications of this rearrangement is still limited.

A novel RUNX1-C11orf41 fusion gene in a case of acute myeloid leukemia with a t(11;21)(p14;q22)

The RUNX1 locus, which encodes a transcription factor that is essential for normal hematopoiesis, is a frequent location of chromosomal rearrangements in human hematological malignancies. We report the case of a 78-year-old man with acute myeloid leukemia (AML), M1 subtype (French-American-British classification), with a t(11;21)(p14;q22). Fluorescence in situ hybridization showed a split signal for RUNX1, which indicated that RUNX1 was involved in this translocation. Using 3'-rapid amplification of cDNA ends and reverse transcription-polymerase chain reaction analyses, we found that RUNX1 was fused to C11orf41 on 11p14 and detected two in-frame C11orf41-RUNX1 fusion transcripts. One was a fusion between exon 5 of RUNX1 and exon 13 of C11orf41, and the other was between exon 6 of RUNX1 and exon 13 of C11orf41. This suggested that the RUNX1 breakpoint was in intron 6 and had generated alternative fusion splice variants. A reciprocal C11orf41-RUNX1 fusion was not detected. Thus, we identified C11orf41 as a novel fusion partner of RUNX1 in AML.

Control of alternative splicing by forskolin through hnRNP K during neuronal differentiation

The molecular basis of cell signal-regulated alternative splicing at the 3′ splice site remains largely unknown. We isolated a protein kinase A-responsive ribonucleic acid (RNA) element from a 3′ splice site of the synaptosomal-associated protein 25 (Snap25) gene for forskolin-inhibited splicing during neuronal differentiation of rat pheochromocytoma PC12 cells. The element binds specifically to heterogeneous nuclear ribonucleo protein (hnRNP) K in a phosphatase-sensitive way, which directly competes with the U2 auxiliary factor U2AF65, an essential component of early spliceosomes. Transcripts with similarly localized hnRNP K target motifs upstream of alternative exons are enriched in genes often associated with neurological diseases. We show that such motifs upstream of the Runx1 exon 6 also bind hnRNP K, and importantly, hnRNP K is required for forskolin-induced repression of the exon. Interestingly, this exon encodes the peptide domain that determines the switch of the transcriptional repressor/activator activity of Runx1, a change known to be critical in specifying neuron lineages. Consistent with an important role of the target genes in neurons, knocking down hnRNP K severely disrupts forskolin-induced neurite growth. Thus, through hnRNP K, the neuronal differentiation stimulus forskolin targets a critical 3′ splice site component of the splicing machinery to control alternative splicing of crucial genes. This also provides a regulated direct competitor of U2AF65 for cell signal control of 3′ splice site usage.

RUNX1 translocations and fusion genes in malignant hemopathies

The RUNX1 gene, located in chromosome 21q22, is crucial for the establishment of definitive hematopoiesis and the generation of hematopoietic stem cells in the embryo. It contains a 'Runt homology domain' as well as transcription activation and inhibition domains. RUNX1 can act as activator or repressor of target gene expression depending upon the large number of transcription factors, coactivators and corepressors that interact with it. Translocations involving chromosomal band 21q22 are regularly identified in leukemia patients. Most of them are associated with a rearrangement of RUNX1. Indeed, at present, 55 partner chromosomal bands have been described but the partner gene has solely been identified in 21 translocations at the molecular level. All the translocations that retain Runt homology domains but remove the transcription activation domain have a leukemogenic effect by acting as dominant negative inhibitors of wild-type RUNX1 in transcription activation.

CLCA2, a novel RUNX1 partner gene in a therapy-related leukemia with t(1;21)(p22;q22)

The RUNX1 gene is frequently rearranged in de novo and therapy-related leukemia. In the present study, we identified the CLCA2 gene as a novel fusion partner of RUNX1 in a case of therapy-related acute myeloid leukemia associated with t(1;21)(p22;q22). Reverse transcriptase-polymerase chain reaction analysis and sequencing revealed that the t(1;21) results in out-of-frame RUNX1-CLCA2 fusions. Alternative splicing generates at least six fusion transcripts, including a major transcript fusing RUNX1 exon 6 with CLCA2 exon 2. These out-of-frame fusions produce putative truncated RUNX1 isoforms retaining the DNA binding Runt domain but not the transcriptional regulatory domain of RUNX1. No mutations were found in the exons encoding the Runt and C-terminal domains of the nonrearranged RUNX1 gene. Similar to truncated RUNX1 isoforms previously described, these shortened products could act as dominant negative inhibitors of RUNX1-dependent transactivation. CLCA2 is a breast tumor suppressor gene that encodes a member of the calcium-activated chloride channel family and is involved for the first time in a chromosomal translocation. The RUNX1-CLCA2 fusion is another example of out-of-frame fusion generating truncated RUNX1 isoforms that represent a recurrent molecular mechanism in RUNX1-related leukemias.

LPXN, a member of the paxillin superfamily, is fused to RUNX1 in an acute myeloid leukemia patient with a t(11;21)(q12;q22) translocation

RUNX1 (previously AML1) is involved in multiple recurrent chromosomal rearrangements in hematological malignances. Recently, we identified a novel fusion between RUNX1 and LPXN from an acute myeloid leukemia (AML) patient with t(11;21)(q12;q22). This translocation generated four RUNX1/LPXN and one LPXN/RUNX1 chimeric transcripts. Two representative RUNX1/LPXN fusion proteins, RL and RLs, were both found to localize in the nucleus and could bring the CBFB protein into the nucleus like the wild-type RUNX1. Both fusion proteins inhibit the ability of RUNX1 to transactivate the CSF1R promoter, probably through competition for its target sequences. Unlike RL and RLs, the LPXN/RUNX1 fusion protein LR was found to localize in the cytoplasm. Thus, we believe it has little impact on the transcriptional activity of RUNX1. We also found that fusion proteins RL, RLs, LR, and wild-type LPXN could confer NIH3T3 cells with malignant transformation characteristics such as more rapid growth, the ability to form colonies in soft agar, and the ability to form solid tumors in the subcutaneous tissue of the BALB/c nude mice. Taken together, our data indicated that the RUNX1/LPXN and LPXN/RUNX1 fusion proteins may play important roles in leukemogenesis and that deregulation of cell adhesion pathways may be pathogenetically important in AML. Our study also suggests that LPXN may play an important role in carcinogenesis.

Identification of the novel AML1 fusion partner gene, LAF4, a fusion partner of MLL, in childhood T-cell acute lymphoblastic leukemia with t(2;21)(q11;q22) by bubble PCR method for cDNA

The AML1 gene is frequently rearranged by chromosomal translocations in acute leukemia. We identified that the LAF4 gene on 2q11.2-12 was fused to the AML1 gene on 21q22 in a pediatric patient having T-cell acute lymphoblastic leukemia (T-ALL) with t(2;21)(q11;q22) using the bubble PCR method for cDNA. The genomic break points were within intron 7 of AML1 and of LAF4, resulting in the in-frame fusion of exon 7 of AML1 and exon 8 of LAF4. The LAF4 gene is a member of the AF4/FMR2 family and was previously identified as a fusion partner of MLL in B-precursor ALL with t(2;11)(q11;q23), although AML1-LAF4 was in T-ALL. LAF4 is the first gene fused with both AML1 and MLL in acute leukemia. Almost all AML1 translocations except for TEL-AML1 are associated with myeloid leukemia; however, AML1-LAF4 was associated with T-ALL as well as AML1-FGA7 in t(4;21)(q28;q22). These findings provide new insight into the common mechanism of AML1 and MLL fusion proteins in the pathogenesis of ALL. Furthermore, we successfully applied bubble PCR to clone the novel AML1-LAF4 fusion transcript. Bubble PCR is a powerful tool for detecting unknown fusion transcripts as well as genomic fusion points.

Two novel translocations disrupt the RUNX1 gene in acute myeloid leukemia

Translocations involving 21q22 are commonly observed in both de novo and therapy-related acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). They often result in the disruption of RUNX1 and give rise to fusion genes consisting of RUNX1 and different partner genes, which contribute to leukemogenesis. To date, at least 21 such translocations are known from the literature. Here we report two novel translocations involving the RUNX1 gene: t(1;21)(q12;q22) in a 53-year-old woman with AML-M5b and t(11;21)(q13;q22) in a 65-year-old man with AML-M2. The abnormalities revealed by R-banding karyotypic analysis were confirmed with interphase and metaphase fluorescence in situ hybridization (FISH), chromosome painting, and M-FISH.

LRP16 is fused to RUNX1 in monocytic leukemia cell line with t(11;21)(q13;q22)

OBJECTIVE

The RUNX1 (also known as AML1) gene is observed frequently as the target of chromosomal rearrangements in human acute leukemia. We describe here a previously unreported rearrangement, t(11;21)(q13;q22), that disrupts the RUNX1 gene in a patient with acute leukemia and the molecular analysis of the fusion gene.

METHODS

We have established a monocytic leukemia cell line, ELAM-1, from a patient with acute leukemia evolving from myelodysplastic syndrome (MDS). Translocation (11;21) (q13;q22) was observed in both patient leukemia cells and ELAM-1.

RESULTS

The split signal of RUNX1 was detected by fluorescence in situ hybridization and indicated the involvement of RUNX1 in ELAM-1. Using 3'- Rapid amplification of cDNA ends and reverse transcription-Polymerase chain reaction analysis, we detected both RUNX1 (exon 5)-LRP16 and RUNX1 (exon 6)-LRP16 transcripts, suggesting that the RUNX1 breakpoint lies in intron 6 and that alternative fusion splice variants are generated. Reciprocal LRP16-RUNX1 fusion was also detected.

CONCLUSIONS

We identified a novel RUNX1 fusion partner, LRP16 on 11q13 involving t(11;21)(q13;q22). Although it was reported that overexpression of LRP16 promotes human breast cancer cell proliferation, the function of LRP16 in leukemia remains to be studied. This fusion gene and cell line may provide a new research tool to investigate the mechanism of leukemogenesis generated by the RUNX1 fusion gene.

Identification of novel Runx1 (AML1) translocation partner genes SH3D19, YTHDf2, and ZNF687 in acute myeloid leukemia

Three patients diagnosed with acute myeloid leukemia (AML) with reciprocal 21q22/RUNX1(AML1) translocations involving chromosomes 1 and 4 were studied. Three novel RUNX1 translocation partner genes on 1q21.2 (ZNF687), 1p35 (YTHDF2), and 4q31.3 (SH3D19) were identified using a panhandle polymerase chain reaction and the 3' rapid amplification of cDNA ends method. The translocation events occurred between exons 3 and 7 of the RUNX1 gene. The partner gene breakpoints localized to the region in the partner gene with the highest Alu density, suggesting that Alus may contribute to the recombination events. Two out of three of the cases retained RUNX1's entire RUNT domain in the translocation, and RUNX1 mutations were absent in the fusion transcripts, confirmed by reverse transcription-polymerase chain reaction and sequencing analysis. SH3D19 encodes a cytoplasmic protein EBP known to suppress RAS-induced cellular transformation, which can be inhibited by nuclear recruitment. The t(4;21) created a hybrid RUNX1-EBP protein retaining RUNX1's DNA binding domain, which may result in nuclear localization of the chimeric protein and inhibition of EBP's RAS-suppressive functions. Future studies would be useful to further characterize these novel fusion protein products.

Normal and transforming functions of RUNX1: a perspective

Converging studies from many investigators indicate that RUNX1 has a critical role in the correct maintenance of essential cellular functions during embryonic development and after birth. The discovery that this gene is also frequently mutated in human leukemia has increased the interest in the role that RUNX1 plays in both normal and transforming pathways. Here, we provide an overview of the many roles of RUNX1 in hematopoietic self-renewal and differentiation and summarize the information that is currently available on the many mechanisms of RUNX1 deregulation in human leukemia.

A novel and cytogenetically cryptic t(7;21)(p22;q22) in acute myeloid leukemia results in fusion of RUNX1 with the ubiquitin-specific protease gene USP42

Although many of the chromosomal abnormalities in hematologic malignancies are identifiable cytogenetically, some are only detectable using molecular methods. We describe a novel cryptic t(7;21)(p22;q22) in acute myeloid leukemia (AML). FISH, 3'RACE, and RT-PCR revealed a fusion involving RUNX1 and the ubiquitin-specific protease (USP) gene USP42. The genomic breakpoint was in intron 7 of RUNX1 and intron 1 of USP42. The reciprocal chimera was not detected - neither on the transcriptional nor on the genomic level - and FISH showed that the 5' part of USP42 was deleted. USP42 maps to a 7p22 region characterized by segmental duplications. Notably, 17 kb duplicons are present 1 Mb proximal to USP42 and 3 Mb proximal to RUNX1; these may be important in the genesis of t(7;21). This is the second cryptic RUNX1 translocation in hematologic malignancies and the first in AML. The USPs have not previously been reported to be rearranged in leukemias. The cellular context in which USP42 is active is unknown, but we here show that it is expressed in normal bone marrow, in primary AMLs, and in cancer cell lines. Its involvement in the t(7;21) suggests that deregulation of ubiquitin-associated pathways may be pathogenetically important in AML.

Novel RUNX1-PRDM16 fusion transcripts in a patient with acute myeloid leukemia showing t(1;21)(p36;q22)

The t(1;21)(p36;q22) is a recurrent chromosome abnormality associated with therapy-related acute myeloid leukemia (AML). Although involvement of RUNX1 has been detected by fluorescence in situ hybridization analysis, the partner gene has not been reported previously. We identified a novel RUNX1 partner gene, MDS1/EVI1-like-gene 1 (PRDM16), in an AML patient with t(1;21). Alternative splicing of the fusion gene generates five different fusion transcripts. In two of them, the PRDM16 reading frame is maintained in the fusion with RUNX1, suggesting that the RUNX1-PRDM16 gene fusion results in the production of a protein that is highly homologous to the RUNX1-MDS1/EVI1 chimeric protein. It is suggested that PRDM16 and MDS1/EVI1 share a common molecular mechanism for the leukemogenesis of RUNX1-associated leukemia. Characterization of the RUNX1-PRDM16 fusion protein and comparison with the RUNX1-MDS1/EVI1 protein will facilitate the understanding of the mechanisms underlying RUNX1-associated leukemia.

The Distal Zinc Finger Domain of AML1/MDS1/EVI1 Is an Oligomerization Domain Involved in Induction of Hematopoietic Differentiation Defects in Primary Cells In vitro

AML1/MDS1/EVI1 (AME) is a chimeric transcription factor produced by the (3;21)(q26;q22) translocation. This chromosomal translocation is associated with de novo and therapy-related acute myeloid leukemia and with the blast crisis of chronic myelogenous leukemia. AME is obtained by in-frame fusion of the AML1 and MDS1/EVI1 (ME) genes. The mechanisms by which AME induces a neoplastic transformation in bone marrow cells are unknown. AME interacts with the corepressors CtBP and HDAC1, and it was shown that AME is a repressor in contrast to the parent transcription factors AML1 and ME, which are transcription activators. Studies with murine bone marrow progenitors indicated that the introduction of a point mutation that destroys the CtBP-binding consensus impairs but does not abolish the disruption of cell differentiation and replication associated with AME expression, suggesting that additional events are required. Several chimeric proteins, such as AML1/ETO, BCR/ABL, and PML/RARa, are characterized by the presence of a self-interaction domain critical for transformation. We report that AME is also able to oligomerize and displays a complex pattern of self-interaction that involves at least three oligomerization regions, one of which is the distal zinc finger domain. Although the deletion of this short domain does not preclude the self-interaction of AME, it significantly reduces the differentiation defects caused in vitro by AME in primary murine bone marrow progenitors. The addition of a point mutation that inhibits CtBP binding completely abrogates the effects of AME on differentiation, suggesting that AME induces hematopoietic differentiation defects through at least two separate but cooperating pathways.

Functional domains of Runx1 are differentially required for CD4 repression, TCRbeta expression, and CD4/8 double-negative to CD4/8 double-positive transition in thymocyte development

Runx1 (AML1) has multiple functions in thymocyte development, including CD4 repression in immature thymocytes, expression of TCRbeta, and efficient beta-selection. To determine the functional domains of Runx1 important for thymocyte development, we cultured Runx1-deficient murine fetal liver (FL) cells on OP9-Delta-like 1 murine stromal cells, which express Delta-like 1 and support thymocyte development in vitro, and introduced Runx1 or C-terminal-deletion mutants of Runx1 into the FL cells by retrovirus infection. In this system, Runx1-deficient FL cells failed to follow normal thymocyte development, whereas the introduction of Runx1 into the cells was sufficient to produce thymocyte development that was indistinguishable from that in wild-type FL cells. In contrast, Runx1 mutants that lacked the activation domain necessary for initiating gene transcription did not fully restore thymocyte differentiation, in that it neither repressed CD4 expression nor promoted the CD4/8 double-negative to CD4/8 double-positive transition. Although the C-terminal VWRPY motif-deficient mutant of Runx1, which cannot interact with the transcriptional corepressor Transducin-like enhancer of split (TLE), promoted the double-negative to double-positive transition, it did not efficiently repress CD4 expression. These results suggest that the activation domain is essential for Runx1 to establish thymocyte development and that Runx1 has both TLE-dependent and TLE-independent functions in thymocyte development.

PRDX4, a member of the peroxiredoxin family, is fused to AML1 (RUNX1) in an acute myeloid leukemia patient with a t(X;21)(p22;q22)

The AML1 gene (also known as RUNX1) at 21q22 codes for core binding factor (CBF) alpha, which forms a heterodimer with CBF beta that acts as a transcriptional activating factor. CBF is a critical regulator in the generation and differentiation of definitive hematopoietic stem cells and is frequently disrupted in leukemia through chromosome translocations. We cloned a novel AML1 partner gene, PRDX4, in an X;21 translocation in a 74-year-old male patient diagnosed with acute myeloid leukemia-M2. Chromosome analysis detected a t(X;21)(p22;q22) as the sole abnormality in bone marrow samples. The involvement of AML1 was confirmed by fluorescence in situ hybridization studies. Using 3' RACE-PCR, we cloned a fusion between exon 5 of AML1 and exon 2 of PRDX4. RT-PCR confirmed the fusion and detected another fusion between exon 6 of AML1 and exon 2 of PRDX4, indicating alternative splicing of exon 6 of AML1 in the fusion transcripts. PRDX4 is one of six peroxiredoxin-family genes that are highly conserved in eukaryotes and prokaryotes and are ubiquitously expressed. Peroxiredoxin genes exhibit thioredoxin-dependent peroxidase activity and have been implicated in a number of other cellular functions such as cell proliferation and differentiation. PRDX4 plays a regulatory role in the activation of the transcription factor NF-kappaB and is significantly down-regulated in acute promyelocytic leukemia. This is the first example of antioxidant enzyme involvement in a chromosome translocation in leukemia.