Regulation of Hoxb2 by APL-associated PLZF protein.

The PLZF gene is translocated in a subset of all-trans-retinoic acid resistant acute promyelocytic leukaemia (APL) cases, encodes a DNA binding transcription factor and is expressed highly in haematopoietic progenitor cells as well-developing central nervous system (CNS). The spatially restricted and temporally dynamic pattern of PLZF expression in the developing CNS suggested that it might play a role in the circuitry regulating hindbrain segmentation. We have now identified a PLZF binding site (PLZF-RE) in an enhancer region of Hoxb2 that itself is required for directing high-level expression in rhombomers 3 and 5 of the developing hindbrain.

Recruitment of the nuclear receptor corepressor N-CoR by the TEL moiety of the childhood leukemia-associated TEL-AML1 oncoprotein.

The t(12;21)(p13;q22) chromosomal translocation is the most frequent illegitimate gene recombination in a pediatric cancer and occurs in approximately 25% of common acute lymphoblastic leukemia (cALL) cases. This rearrangement results in the in frame fusion of the 5'-region of the ETS-related gene, TEL (ETV6), to almost the entire acute myeloid leukemia 1 (AML1) (also called CBFA2 or PEBP2AB1) locus and expression of the TEL-AML1 chimeric protein. Although AML1 stimulates transcription, TEL-AML1 functions as a repressor of some AML1 target genes.

Analysis of the region of the 5' end of the MLL gene involved in genomic duplication events.

Rearrangements of the MLL gene are associated with both myeloid and lymphoid acute leukaemia. The gene is commonly involved in reciprocal translocations leading to the creation of chimaeric genes encoding novel protein products. An alternative mechanism of MLL gene rearrangement is due to intragenic duplication, leading to partial duplication of the amino-terminal portion of the protein.

Regulation of the apoptotic response to radiation damage in B cell development.

B lymphocyte precursor cells are ultrasensitive to DNA damage induced by irradiation and drugs and die by apoptosis at very low levels of exposure. Previous studies have shown that this high level sensitivity is p53-dependent, associated with very low level expression of Bcl-2 protein and can be reversed by expression of a bcl-2 transgene. We show here that transition from the pro-B to pre-B and then mature B cell stages of murine lymphopoiesis is accompanied by changes in proliferating cells in sensitivity to X-irradiation induced apoptosis and that this is paralleled by variation in the ratio of anti-(Bcl-2/Bcl-chiL) to pro-(Bax) apoptotic proteins.

Novel BTB/POZ domain zinc-finger protein, LRF, is a potential target of the LAZ-3/BCL-6 oncogene.

BTB/POZ-domain C2H2 zinc(Zn)-finger proteins are encoded by a subfamily of genes related to the Drosophila gap gene krüppel. To date, two such proteins, PLZF and LAZ-3/BCL-6, have been implicated in oncogenesis. We have now identified a new member of this gene subfamily which encodes a 62 kDa Zn-finger protein, termed LRF, with a BTB/POZ domain highly similar to that of PLZF.

Lymphopain, a cytotoxic T and natural killer cell-associated cysteine proteinase.

Through differential screening of established human leukaemia cell lines, we have identified and molecularly cloned lymphopain, a novel cysteine proteinase of the papain family. Lymphopain exhibits a remarkably restricted cellular pattern of expression, being predominantly expressed in cytotoxic T-lymphocytes and natural killer cells. The human lymphopain locus maps to chromosome 11q13, encodes a polypeptide of 376 amino acids and is conserved in the mouse.

Haemopoietic transformation by the TEL/ABL oncogene.

Rare, novel forms of activated ABL kinase, the result of a fusion between TEL (or ETV6, a member of the ETS transcription factor family), and the non-receptor tyrosine kinase ABL, have been identified. We have analysed the TEL/ABL fusion protein (type A) cloned from an acute lymphoblastic leukaemia patient. In contrast to a second TEL/ABL fusion (type B) identified in two cases of myeloid leukaemia, the portion of TEL contained in the type A TEL/ABL fusion was smaller and did not contain a potential Grb2 binding site.

Isolation and characterization of a pufferfish MLL (mixed lineage leukemia)-like gene (fMll) reveals evolutionary conservation in vertebrate genes related to Drosophila trithorax.

The MLL gene is interrupted and fused to a number of partner genes as a result of chromosomal translocations in human leukemias. MLL is a very large protein with a unique domain structure and large regions of homology to Drosophila trx. To define the key structural and functional domains of the MLL protein in vertebrates, we have cloned the genomic region encoding an MLL-like gene in the compact model vertebrate genome of Fugu rubripes.

Successful treatment of aplastic anemia with G-CSF and high dose erythropoietin.

We report the successful treatment of pancytopenia with G-CSF and high dose erythropoietin (Epo) in an elderly patient diagnosed with aplastic anemia (AA). Furthermore this effect is dose dependent for Epo in vivo. Detection of apoptosis by gel electrophoresis shows that high dose Epo protects bone marrow mononuclear cells from spontaneous apoptosis in vitro.

Reduced retinoic acid-sensitivities of nuclear receptor corepressor binding to PML- and PLZF-RARalpha underlie molecular pathogenesis and treatment of acute promyelocytic leukemia.

Typical acute promyelocytic leukemia (APL) is associated with expression of the PML-RARalpha fusion protein and responsiveness to treatment with all-trans retinoic acid (ATRA). A rare, but recurrent, APL has been described that does not respond to ATRA treatment and is associated with a variant chromosomal translocation and expression of the PLZF-RARalpha fusion protein. Both PML- and PLZF-RARalpha possess identical RAR sequences and inhibit ATRA-induced gene transcription as well as cell differentiation.

Exon scrambling of MLL transcripts occur commonly and mimic partial genomic duplication of the gene.

The MLL gene is frequently rearranged in acute human leukemia of both the myeloid and lymphoid lineages. Using a sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) assay, we identified several abnormally spliced transcripts in which MLL exons were joined in an order different from the genomic orientation (scrambled exons). Mis-splicing of MLL was present in both normal and malignant tissues.

Backtracking leukemia to birth: identification of clonotypic gene fusion sequences in neonatal blood spots.

Epidemiological evidence has suggested that some pediatric leukemias may be initiated in utero and, for some pairs of identical twins with concordant leukemia, this possibility has been strongly endorsed by molecular studies of clonality. Direct evidence for a prenatal origin can only be derived by prospective or retrospective detection of leukemia-specific molecular abnormalities in fetal or newborn samples. We report a PCR-based method that has been developed to scrutinize neonatal blood spots (Guthrie cards) for the presence of numerically infrequent leukemic cells at birth in individuals who subsequently developed leukemia.

Multilineage gene expression precedes commitment in the hemopoietic system.

We have tested the hypothesis that multipotential hemopoietic stem and progenitor cells prime several different lineage-affiliated programs of gene activity prior to unilineage commitment and differentiation. Using single cell RT-PCR we show that erythroid (beta-globin) and myeloid (myeloperoxidase) gene expression programs can be initiated by the same cell prior to exclusive commitment to the erythroid or granulocytic lineages. Furthermore, the multipotential state is characterized by the coexpression of several lineage-affiliated cytokine receptors.

Leukemia translocation gene, PLZF, is expressed with a speckled nuclear pattern in early hematopoietic progenitors.

The PLZF gene was discovered by studying a rearrangement of the RAR alpha locus in a patient with acute promyelocytic leukemia and a t(11;17) chromosomal translocation. To understand further the potential role(s) of the PLZF gene product in hematopoiesis, we have examined its expression levels in a variety of murine tissues and in established cell lines that are representative of various stages of myeloid and lymphoid development. We show that murine PLZF(mPLZF) is expressed at the highest levels in undifferentiated, multipotential hematopoietic progenitor cells and that its expression declines as cells become more mature and committed to various hematopoietic lineages.

Analysis of the developmental and transcriptional potentiation functions of 5'HS2 of the murine beta-globin locus control region in transgenic mice.

We analyze the role of 5'HS2 of the mouse beta-globin LCR in the transcriptional and developmental regulation of beta-globin gene expression. Previous studies have shown that the human beta-globin gene behaves as an adult gene in transgenic mice, being expressed in fetal liver and bone marrow-derived erythroblasts but not in yolk sac-derived embryonic erythroid cells. We show that linkage of mLCR5'HS2 to a human beta-globin gene alters this pattern of expression during ontogeny, resulting in expression of the linked beta-globin gene at all stages of murine erythroid development.