PubMed Health⌕ Search

Biomedical subjects

Achim Leutz

Publications and source records attributed to Achim Leutz.

15 recordsLinked to original sources
PubMed2006

Hematopoietic stem cell and multilineage defects generated by constitutive beta-catenin activation.

Gain of Wnt signaling through beta-catenin has been ascribed a critical function in the stimulation of hematopoietic stem cell self-renewal, whereas loss of beta-catenin is reportedly dispensable for hematopoiesis. Here we have used conditional mouse genetics and transplantation assays to demonstrate that constitutive activation of beta-catenin blocked multilineage differentiation, leading to the death of mice. Blood cell depletion was accompanied by failure of hematopoietic stem cells to repopulate irradiated hosts and to differentiate into mature cells. Activation of beta-catenin enforced cell cycle entry of hematopoietic stem cells, thus leading to exhaustion of the long-term stem cell pool. Our data suggest that fine-tuned Wnt stimulation is essential for hematopoiesis and is thus critical for therapeutic hematopoietic stem cell population expansion.

Animals↗
PubMed2006

A translation control reporter system (TCRS) for the analysis of translationally controlled processes in the vertebrate cell.

Regulation of translation is critical for the accurate expression of a broad variety of genes that function in cell cycle progression and cell differentiation, as well as in the adaptation to cellular stress. The aetiologies of a number of human diseases, including cancer, have been linked to mutations in genes that control mRNA translation, or in cis-regulatory mRNA-sequences. Therefore, research on translational control and its therapeutic appliance has become most important. However, to date only a limited number of therapeutic drugs are known to affect translational control. Here we describe a novel, straightforward approach for the detection of cellular translational activity. We developed a Translational Control Reporter System (TCRS), which utilizes the cis-regulatory upstream open reading frame (uORF) from the c/ebpalpha locus to direct the translation of a dual reporter gene into two unique reporter peptides. The peptides contain a pre-pro-trypsin (PPT) signal for secretion into the medium and distinct immunogenic epitopes for detection and quantification purposes. TCRS-peptide expression levels reflect changes of translation initiation induced by serum growth factors, drugs or translation factor mutants. TCRS can be tailored to various research settings and the system may accomplish a broad application to uncover links between translational control and drugs.

Animals↗
PubMed2005

Lymphoid cell growth and transformation are suppressed by a key regulatory element of the gene encoding PU.1.

Tight regulation of transcription factors, such as PU.1, is crucial for generation of all hematopoietic lineages. We previously reported that mice with a deletion of an upstream regulatory element (URE) of the gene encoding PU.1 (Sfpi1) developed acute myeloid leukemia. Here we show that the URE has an essential role in orchestrating the dynamic PU.1 expression pattern required for lymphoid development and tumor suppression. URE deletion ablated B2 cells but stimulated growth of B1 cells in mice. The URE was a PU.1 enhancer in B cells but a repressor in T cell precursors. TCF transcription factors coordinated this repressor function and linked PU.1 to Wnt signaling. Failure of appropriate PU.1 repression in T cell progenitors with URE deletion disrupted differentiation and induced thymic transformation. Genome-wide DNA methylation assessment showed that epigenetic silencing of selective tumor suppressor genes completed PU.1-initiated transformation of lymphoid progenitors with URE deletion. These results elucidate how a single transcription factor, PU.1, through the cell context-specific activity of a key cis-regulatory element, affects the development of multiple cell lineages and can induce cancer.

Animals↗
PubMed2005

Histone H3 tail positioning and acetylation by the c-Myb but not the v-Myb DNA-binding SANT domain.

The c-Myb transcription factor coordinates proliferation and differentiation of hematopoietic precursor cells. Myb has three consecutive N-terminal SANT-type repeat domains (R1, R2, R3), two of which (R2, R3) form the DNA-binding domain (DBD). Three amino acid substitutions in R2 alter the way Myb regulates genes and determine the leukemogenicity of the retrovirally transduced v-Myb oncogene. The molecular mechanism of how these mutations unleash the leukemogenic potential of Myb is unknown. Here we demonstrate that the c-Myb-DBD binds to the N-terminal histone tails of H3 and H3.3. C-Myb binding facilitates histone tail acetylation, which is mandatory during activation of prevalent differentiation genes in conjunction with CCAAT enhancer-binding proteins (C/EBP). Leukemogenic mutations in v-Myb eliminate the interaction with H3 and acetylation of H3 tails and abolish activation of endogenous differentiation genes. In primary v-myb-transformed myeloblasts, pharmacologic enhancement of H3 acetylation restored activation of differentiation genes and induced cell differentiation. Our data link a novel chromatin function of c-Myb with lineage-specific expression of differentiation genes and relate the loss of this function with the leukemic conversion of Myb.

Acetylation↗
PubMed2005

A rapamycin derivative (everolimus) controls proliferation through down-regulation of truncated CCAAT enhancer binding protein {beta} and NF-{kappa}B activity in Hodgkin and anaplastic large cell lymphomas.

The immunosuppressive macrolide rapamycin and its derivative everolimus (SDZ RAD, RAD) inhibit the mammalian target of rapamycin (mTOR) signaling pathway. In this study, we provide evidence that RAD has profound antiproliferative activity in vitro and in NOD/SCID mice in vivo against Hodgkin lymphoma (HL) and anaplastic large cell lymphoma (ALCL) cells. Moreover, we identified 2 molecular mechanisms that showed how RAD exerts antiproliferative effects in HL and ALCL cells. RAD down-regulated the truncated isoform of the transcription factor CCAAT enhancer binding protein beta (C/EBPbeta), which is known to disrupt terminal differentiation and induce a transformed phenotype. Furthermore, RAD inhibited constitutive nuclear factor kappaB (NF-kappaB) activity, which is a critical survival factor of HL cells. Pharmacologic inhibition of the mTOR pathway by RAD therefore interferes with essential proliferation and survival pathways in HL and ALCL cells and might serve as a novel treatment option.

Animals↗
PubMed2004

Ras induces mediator complex exchange on C/EBP beta.

C/EBPbeta is an intrinsically repressed transcription factor that regulates genes involved in differentiation, proliferation, tumorigenesis, and apoptosis. C/EBPbeta acts as a repressor that is turned into an activator by the Ras oncoprotein through phosphorylation of a MAPK site. C/EBPbeta activation is accompanied by a conformational change. Active and repressive C/EBPbeta interacts with multisubunit Mediator complexes through the CRSP130/Sur2 subunit. The CRSP130/Sur2 subunit is common to two distinct types of Mediator complexes, characterized by CRSP70 and CDK8 proteins as transcriptionally active and inactive Mediator, respectively. Knockdown of CRSP130/Sur2 prevents Mediator binding and transactivation through C/EBPbeta. Oncogenic Ras signaling or activating mutations in C/EBPbeta selects the transcriptionally active Mediator complex that also associates with RNA polymerase II. These results show that a Ras-induced structural alteration of C/EBPbeta determines differential gene activation through selective interaction with distinct Mediator complexes.

Apoptosis↗
PubMed2004

Essential requirement of CCAAT/enhancer binding proteins in embryogenesis.

The CCAAT/enhancer binding proteins C/EBPalpha and C/EBPbeta are related transcription factors that are important for the function of various organs in the postnatal mouse. Gene replacement and tissue culture experiments have suggested partial redundancy of both transcription factors. Here we show that mouse embryos deficient of both C/EBPalpha and C/EBPbeta (C/EBPalphabeta(-/-)) die between embryonic day 10 (E10) and E11 and display defective placentas. In situ hybridization revealed that C/EBPalpha and C/EBPbeta are coexpressed in the chorionic plate at E9.5 and later in the trophoblasts of the labyrinthine layer. In C/EBPalphabeta(-/-) placentas, allantoic blood vessels invaded the chorion; however, vessel expansion and development of the labyrinthine layer was impaired. Furthermore, a single copy of either C/EBPalpha in the absence of C/EBPbeta or C/EBPbeta in the absence of C/EBPalpha is sufficient to complete development, suggesting complementation of these C/EBPs during embryogenesis. A single copy of C/EBPalpha in the absence of C/EBPbeta, however, fails to rescue survival after birth, suggesting haploinsufficiency of C/EBPalpha in newborns. Our data thus reveal novel essential, redundant, and dosage dependent functions of C/EBPs.

Animals↗
PubMed2003

The CCAAT enhancer-binding protein alpha (C/EBPalpha) requires a SWI/SNF complex for proliferation arrest.

The transcription factor CCAAT enhancer-binding protein alpha (C/EBPalpha) is a tumor suppressor in myeloid cells and inhibits proliferation in all cell types examined. C/EBPalpha interacts with the SWI/SNF chromatin-remodeling complex during the regulation of differentiation-specific genes. Here we show that C/EBPalpha fails to suppress proliferation in SWI/SNF defective cell lines after knock-down of SWI/SNF core components or after deletion of the SWI/SNF interaction domain in C/EBPalpha, respectively. Reconstitution of SWI/SNF function restores C/EBPalpha-dependent proliferation arrest. Our results show that the anti-proliferation activity of C/EBPalpha critically depends on components of the SWI/SNF core complex and suggest that the functional interaction between SWI/SNF and C/EBPalpha is a prerequisite for proliferation arrest.

Animals↗
PubMed2003

Translational control of SCL-isoform expression in hematopoietic lineage choice.

We investigated the translational regulation of SCL protein expression and its role in hematopoietic lineage choice. We show that the expression of different SCL protein isoforms is regulated by signal transduction pathways that modulate translation initiation factor (eIF) function. A conserved small upstream open reading frame (uORF) in SCL transcripts acts as a cis-regulatory element for isoform expression. At the onset of erythroid differentiation, truncated SCL protein isoforms arise by alternative translation initiation and favor the erythroid lineage. In comparison, full-length SCL proteins are more efficient at enhancing the megakaryocyte lineage. Together, our studies unravel translational control as a novel mechanism regulating hematopoietic outcome.

Animals↗
PubMed2003

Distinct changes in gene expression induced by A-Myb, B-Myb and c-Myb proteins.

The c-Myb, A-Myb and B-Myb transcription factors have nearly identical DNA-binding domains, activate the same reporter gene constructs in animal cells, but have different biological roles. The Myb proteins are often coexpressed in the same cells, raising questions about whether they activate similar or distinct gene expression profiles, and whether they cooperate or compete in regulating the same promoters. Here, recombinant adenoviruses were used to express each protein in human mammary cells, and then microarray assays were used to assess global changes in gene expression. Each Myb protein induced a unique and specific set of changes, displaying activities far more complex than revealed by standard reporter gene assays. These results have important implications for the roles of various Myb proteins in normal and transformed human cells, for regulatory pathways that might modify their activities and for the importance of acquired mutations that may qualitatively alter their functions in tumors.

Adenoviridae↗
PubMed2002

Phosphorylation-dependent down-regulation of c-Myb DNA binding is abrogated by a point mutation in the v-myb oncogene.

The viral Myb (v-Myb) oncoprotein of the avian myeloblastosis virus (AMV) is an activated form of the cellular transcription factor c-Myb causing acute monoblastic leukemia in chicken. Oncogenic v-Myb alterations include N- and C-terminal deletions as well as point mutations. Whereas truncations in Myb cause loss of various protein modifications, none of the point mutations in v-Myb has been directly linked to protein modifications. Here we show that the DNA-binding domain of c-Myb can be phosphorylated on serine 116 by the catalytic subunit of protein kinase A. Phosphorylation of Ser(116) differentially destabilizes a subtype of c-Myb-DNA complexes. The V117D mutation of the AMV v-Myb oncoprotein abolishes phosphorylation of the adjacent Ser(116) residue. Modification of Ser(116) was also detected in live cells in c-Myb, but not in AMV v-Myb. Phosphorylation-mimicking mutants of c-Myb failed to activate the resident mim-1 gene. Our data imply that protein kinase A or a kinase with similar specificity negatively regulates c-Myb function, including collaboration with C/EBP, and that the leukemogenic AMV v-Myb version evades inactivation by a point mutation that abolishes a phosphoacceptor consensus site. This suggests a novel link between Myb, a signal transduction pathway, cooperativity with C/EBP, and a point mutation in the myb oncogene.

Amino Acid Sequence↗
PubMed2002

The LIM domain protein Lmo2 binds to AF6, a translocation partner of the MLL oncogene.

The LIM only protein Lmo2 plays an important role in hematopoiesis and leukemogenesis. Lmo2 acts as a bridging molecule between components of hematopoietic gene regulatory protein complexes. We used the yeast two-hybrid system to identify novel Lmo2 interacting proteins and found that the AF6 protein binds to Lmo2. AF6 is a recurrent fusion partner of MLL, the human homolog of Drosophila trithorax chromatin remodeling protein that is involved in childhood leukemia and mixed lineage leukemia. Our data support the notion that recurrent fusion partners of chimeric MLL proteins recruit hematopoietic gene regulatory complexes.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Translational control of gene expression and disease.

In the past decade, translational control has been shown to be crucial in the regulation of gene expression. Research in this field has progressed rapidly, revealing new control mechanisms and adding constantly to the list of translationally regulated genes. There is accumulating evidence that translational control plays a primary role in cell-cycle progression and cell differentiation, as well as in the induction of specific cellular functions. Recently, the aetiologies of several human diseases have been linked with mutations in genes of the translational control machinery, highlighting the significance of this regulatory mechanism. In addition, deregulation of translation is associated with a wide range of cancers. Current research focuses on novel therapeutic strategies that target translational control, a promising concept in the treatment of human diseases.

Eukaryotic Initiation Factors↗
PubMed2001

The conserved Mynd domain of BS69 binds cellular and oncoviral proteins through a common PXLXP motif.

BS69 is a transcriptional co-repressor protein and a potential tumor suppressor that binds to the adenoviral oncoprotein E1A. We show that the C-terminal Mynd domain of BS69 (amino acids 516-561) or the closely related Mynd domains of the Caenorhabditis elegans proteins Bra-1 and Bra-2 bind not only to E1A but also to the Epstein-Barr virus EBNA2 oncoprotein and the Myc-related cellular protein MGA. Interaction depends on intact PXLXP motifs present in all three proteins. Moreover, viral proteins compete for binding of BS69 to MGA in a PXLXP-dependent fashion. Because deletions in E1A or EBNA2 that cover the PXLXP motifs are non-transforming, our observations suggest a role for BS69 in cell growth control that is reminiscent of abrogation of the Rb function by various oncoproteins.

Adenoviridae↗