Biomedical subjects

Stefan K Bohlander

Publications and source records attributed to Stefan K Bohlander.

13 recordsLinked to original sources

PubMed2006

Block of C/EBP alpha function by phosphorylation in acute myeloid leukemia with FLT3 activating mutations.

Mutations constitutively activating FLT3 kinase are detected in approximately 30% of acute myelogenous leukemia (AML) patients and affect downstream pathways such as extracellular signal-regulated kinase (ERK)1/2. We found that activation of FLT3 in human AML inhibits CCAAT/enhancer binding protein alpha (C/EBPalpha) function by ERK1/2-mediated phosphorylation, which may explain the differentiation block of leukemic blasts. In MV4;11 cells, pharmacological inhibition of either FLT3 or MEK1 leads to granulocytic differentiation. Differentiation of MV4;11 cells was also observed when C/EBPalpha mutated at serine 21 to alanine (S21A) was stably expressed. In contrast, there was no effect when serine 21 was mutated to aspartate (S21D), which mimics phosphorylation of C/EBPalpha. Thus, our results suggest that therapies targeting the MEK/ERK cascade or development of protein therapies based on transduction of constitutively active C/EBPalpha may prove effective in treatment of FLT3 mutant leukemias resistant to the FLT3 inhibitor therapies.

Aged↗

PubMed2006

Gene expression profiles in acute myeloid leukemia with common translocations using SAGE.

Identification of the specific cytogenetic abnormality is one of the critical steps for classification of acute myeloblastic leukemia (AML) which influences the selection of appropriate therapy and provides information about disease prognosis. However at present, the genetic complexity of AML is only partially understood. To obtain a comprehensive, unbiased, quantitative measure, we performed serial analysis of gene expression (SAGE) on CD15(+) myeloid progenitor cells from 22 AML patients who had four of the most common translocations, namely t(8;21), t(15;17), t(9;11), and inv(16). The quantitative data provide clear evidence that the major change in all these translocation-carrying leukemias is a decrease in expression of the majority of transcripts compared with normal CD15(+) cells. From a total of 1,247,535 SAGE tags, we identified 2,604 transcripts whose expression was significantly altered in these leukemias compared with normal myeloid progenitor cells. The gene ontology of the 1,110 transcripts that matched known genes revealed that each translocation had a uniquely altered profile in various functional categories including regulation of transcription, cell cycle, protein synthesis, and apoptosis. Our global analysis of gene expression of common translocations in AML can focus attention on the function of the genes with altered expression for future biological studies as well as highlight genes/pathways for more specifically targeted therapy.

Apoptosis↗

PubMed2006

Defining the heterochromatin localization and repression domains of SALL1.

SALL1 has been identified as one of four human homologues of the Drosophila region-specific homeotic gene spalt (sal), encoding zinc finger proteins of characteristic structure. Mutations of SALL1 on chromosome 16q12.1 cause Townes-Brocks syndrome (TBS, OMIM 107480). We have shown previously that SALL1 acts as a strong transcriptional repressor in mammalian cells when fused to a heterologous DNA-binding domain. Here, we report that SALL1 contains two repression domains, one located at the extreme N-terminus of the protein and the other in the central region. SALL1 fragments with the central repression domain exhibited a punctate nuclear distribution pattern at pericentromeric heterochromatin foci in murine NIH-3T3 cells, suggesting an association between repression and heterochromatin localization. The implications of these findings for the pathogenesis of Townes-Brocks syndrome are discussed.

Animals↗

PubMed2006

Acute myeloid leukemia is propagated by a leukemic stem cell with lymphoid characteristics in a mouse model of CALM/AF10-positive leukemia.

A challenge for the development of therapies selectively targeting leukemic stem cells in acute myeloid leukemia (AML) is their similarity to normal hematopoietic stem cells (HSCs). Here we demonstrate that the leukemia-propagating cell in murine CALM/AF10-positive AML differs from normal HSCs by B220 surface expression and immunoglobulin heavy chain rearrangement. Furthermore, depletion of B220+ cells in leukemic transplants impaired development of leukemia in recipients. As in the murine model, human CALM/AF10-positive AML was characterized by CD45RA (B220)-positive, IG DH-JH rearranged leukemic cells. These data demonstrate in a murine leukemia model that AML can be propagated by a transformed progenitor with lymphoid characteristics, which can be targeted by antibodies that do not crossreact with normal HSCs.

Animals↗

PubMed2006

Dual-color split signal fluorescence in situ hybridization assays for the detection of CALM/AF10 in t(10;11)(p13;q14-q21)-positive acute leukemia.

We developed dual-color split fluorescence in situ hybridization (FISH) assays to detect AF10 and/or CALM rearrangements. Among nine cases of acute leukemia with translocation breakpoints at 10p13 and 11q14-21, a CALM/AF10 rearrangement was found in seven and was confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) in all. In 2/7 cases, FISH detected CALM/AF10 in extramedullary leukemic infiltrations in the mediastinum and breast. As expected, FISH was less sensitive than RT-PCR for disease monitoring of CALM-AF10 positive cases. This new FISH assay reliably discriminates between MLL/AF10 and CALM/AF10 genomic rearrangements, identifies variant and complex CALM/AF10 translocations and detects the CALM/AF10 rearrangement in extramedullary leukemic infiltrations.

Acute Disease↗

PubMed2005

The AML1-ETO fusion gene and the FLT3 length mutation collaborate in inducing acute leukemia in mice.

The molecular characterization of leukemia has demonstrated that genetic alterations in the leukemic clone frequently fall into 2 classes, those affecting transcription factors (e.g., AML1-ETO) and mutations affecting genes involved in signal transduction (e.g., activating mutations of FLT3 and KIT). This finding has favored a model of leukemogenesis in which the collaboration of these 2 classes of genetic alterations is necessary for the malignant transformation of hematopoietic progenitor cells. The model is supported by experimental data indicating that AML1-ETO and FLT3 length mutation (FLT3-LM), 2 of the most frequent genetic alterations in AML, are both insufficient on their own to cause leukemia in animal models. Here we report that AML1-ETO collaborates with FLT3-LM in inducing acute leukemia in a murine BM transplantation model. Moreover, in a series of 135 patients with AML1-ETO-positive AML, the most frequently identified class of additional mutations affected genes involved in signal transduction pathways including FLT3-LM or mutations of KIT and NRAS. These data support the concept of oncogenic cooperation between AML1-ETO and a class of activating mutations, recurrently found in patients with t(8;21), and provide a rationale for therapies targeting signal transduction pathways in AML1-ETO-positive leukemias.

Animals↗

PubMed2005

A BCR-JAK2 fusion gene as the result of a t(9;22)(p24;q11.2) translocation in a patient with a clinically typical chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is characterized by the presence of a t(9;22)(q34;q11.2), which leads to the well-known BCR-ABL1 fusion protein. We describe a patient who was diagnosed clinically with a typical CML but on cytogenetic analysis was found to have a t(9;22)(p24;q11.2). Chromosomal fluorescence in situ hybridization showed that the BCR gene locus spanned the breakpoint at band 22q11.2 but that the ABL1 gene was not rearranged. By means of a candidate gene approach, the JAK2 gene, at 9p24, was identified as the fusion partner of BCR in this case. The BCR-JAK2 fusion protein contains the coiled-coil dimerization domain of BCR and the protein tyrosine kinase domain (JH1) of JAK2. The patient's disease did not respond to Imatinib, and this unresponsiveness was most likely a result of the BCR-JAK2 fusion protein.

Antineoplastic Agents↗

PubMed2005

ETV6: a versatile player in leukemogenesis.

Alterations of the ets family transcription factor ETV6 (TEL) and the RUNT domain transcription factor RUNX1 (AML1) play pivotal roles in the leukemogenesis of various types of leukemia. While only three fusion partners of RUNX1 namely ETO, ETV6 and MTG16 have been described so far, there is a plethora of ETV6 fusion partners with about 20 partners described so far. Apart from forming fusion genes there are other genetic alterations of ETV6 including deletions, point mutations and possible alterations at the promoter level that might contribute to the malignant phenotype. This review will focus on ETV6 and on the different mechanisms that are used by this gene to cause leukemia.

Animals↗

PubMed2004

A t(1;9)(q23.3 approximately q25;q34) affecting the ABL1 gene in a biphenotypic leukemia.

Recurring chromosome translocations, which are found in leukemia, can result in the inappropriate expression of oncogenes or in the formation of chimeric genes that code for structurally and functionally abnormal proteins. The chromosomal t(1;9)(q23.3 approximately q25;q34) was found in a patient with biphenotypic leukemia. Fluorescence in situ hybridization (FISH) analysis revealed that the break on chromosome 9 occurred in the ABL1 gene. The breakpoint on chromosome 1 occurred distal to the PBX1 gene at 1q23.3, as shown by FISH using BAC RP11-503N16 and RP11-403P14, which flank the PBX1 locus; hence, the ABL1 gene can be fused with another gene distal to PBX1 gene.

Adolescent↗

PubMed2004

Molecular cytogenetic analysis of a de novo balanced X;autosome translocation: Evidence for predominant inactivation of the derivative X chromosome in a girl with multiple malformations.

We report on the characterization of a de novo, apparently balanced translocation t(X;15)(p11.3;q26) detected in a girl with multiple congenital malformations. Replication banding studies on Epstein-Barr virus transformed peripheral blood lymphocytes revealed non-random X chromosome inactivation with predominant inactivation of the derivative X chromosome. Using chromosomal fluorescence in situ hybridization (FISH), we located the breakpoints to a 30 kb region on the short arm of the X chromosome band p11.3 and to a 160 kb region defined by BAC RP11-89K11 on the long arm of chromosome 15. Our data suggest that the disruption/disturbance of plant homeo domain (PHD) zinc finger gene KIAA0215 or of another gene (RGN, RNU12, P17.3, or RBM10) in the breakpoint region on the X chromosome is not well tolerated and leads to the selection of cells with an active non-rearranged X chromosome.

Abnormalities, Multiple↗

PubMed2004

Ectopic expression of the homeobox gene Cdx2 is the transforming event in a mouse model of t(12;13)(p13;q12) acute myeloid leukemia.

Creation of fusion genes by balanced chromosomal translocations is one of the hallmarks of acute myeloid leukemia (AML) and is considered one of the key leukemogenic events in this disease. In t(12;13)(p13;q12) AML, ectopic expression of the homeobox gene CDX2 was detected in addition to expression of the ETV6-CDX2 fusion gene, generated by the chromosomal translocation. Here we show in a murine model of t(12;13)(p13;q12) AML that myeloid leukemogenesis is induced by the ectopic expression of CDX2 and not by the ETV6-CDX2 chimeric gene. Mice transplanted with bone marrow cells retrovirally engineered to express Cdx2 rapidly succumbed to fatal and transplantable AML. The transforming capacity of Cdx2 depended on an intact homeodomain and the N-terminal transactivation domain. Transplantation of bone marrow cells expressing ETV6-CDX2 failed to induce leukemia. Furthermore, coexpression of ETV6-CDX2 and Cdx2 in bone marrow cells did not accelerate the course of disease in transplanted mice compared to Cdx2 alone. These data demonstrate that activation of a protooncogene by a balanced chromosomal translocation can be the pivotal leukemogenic event in AML, characterized by the expression of a leukemia-specific fusion gene. Furthermore, these findings link protooncogene activation to myeloid leukemogenesis, an oncogenic mechanism so far associated mainly with lymphoid leukemias and lymphomas.

Animals↗

PubMed2002

Interaction of the developmental regulator SALL1 with UBE2I and SUMO-1.

Mutations in the SALL1 gene on chromosome 16q12.1 cause Townes-Brocks syndrome (TBS). This autosomal dominantly inherited disorder is characterized by typical malformations of the thumbs, the ears, and the anus, and also commonly affects the kidneys and other organ systems. SALL1 has recently been shown to localize to chromocenters and other heterochromatin foci in murine fibroblasts and to interact with the telomere-repeat-binding factor TRF1/PIN2. Here, we show that the ubiquitin-conjugating enzyme 2I (UBE2I), the human homolog of S. cerevisiae UBC9, and the small ubiquitin-like modifier-1 (SUMO-1) interact with SALL1 in the yeast two-hybrid system. The interaction of SALL1 and UBE2I was confirmed in a glutathione S-transferase (GST) pull-down experiment. In an in vitro assay, it could be demonstrated that SALL1 is covalently modified by at least two SUMO-1 molecules in the presence of UBA2/AOS1 and UBE2I. Mutation of lysine 1086 of SALL1 to arginine abrogates SALL1 sumoylation, suggesting the presence of a polymeric SUMO-1 chain in the wild type state.

Abnormalities, Multiple↗

PubMed2002

Identification of an ETV6-ABL2 fusion transcript in combination with an ETV6 point mutation in a T-cell acute lymphoblastic leukaemia cell line.

ETV6, a member of the Ets family of transcription factors, is frequently rearranged to various translocation partners in human leukaemias. We previously described a CD3+/TCRalpha/beta+ mature T-cell acute lymphoblastic leukaemia (T-ALL) cell line, MT-ALL, carrying a t(1;10;12)(q25; p13;p13) with cytokine-inducible lineage switch into the myeloid lineage. Using reverse transcription polymerase chain reaction with primers complementary to ETV6 and ABL2, two ETV6-ABL2 fusion transcripts were identified in MT-ALL which resulted from alternative splicing of an ABL2 exon. The fusion transcripts code for putative ETV6-ABL2 fusion proteins containing the pointed domain of ETV6 and almost the complete ABL2 protein, including the SH2, SH3 domains and the protein tyrosine kinase domain (PTK). Identical ETV6-ABL2 fusion transcripts have been reported in an acute myeloid leukaemia (AML) M3 cell line, carrying both a t(15;17)(q22;q21) and a t(1;12)(q25;p13) with unusual inducible differentiation to eosinophils, and in a patient with AML-M4eo. Interestingly, the non-rearranged allele of ETV6 in the MT-ALL cell line carries an arginine to histidine (R399H) mutation which affects a conserved amino acid in the ets DNA binding domain.

Amino Acid Sequence↗