of the Max - MDC

Structure of the Group
Group Leader
Dr. Frank Rosenbauer
Scientists
Dr. Andreas Enns*
Saeed Ghani*
Graduate Students
Ann-Marie Bröske
Lena Vockentanz*
Jörg Schönheit*
Chiara Perrod*
Mathias Leddin
Tobias Größl*
Kamran Kaviani*
Technical Assistants
Jann Felix Zinke
Victoria Malchin*
Secretariat
Sonja Giering
Petra Haink
* part of the period reported
transgenic animals in the same cells that express endogenous
PU.1. To further analyze the role of the URE in regulation
of the endogenous PU.1 gene in vivo, we generated URE
deficient mice (URE D/D ) using targeted recombination in ES
cells. Remarkably, URE deletion led to a marked decrease in
PU.1 expression in HSCs, macrophages and B cells, but an
increase in PU.1 expression in early thymocytes. This
demonstrated that the URE has an essential cell context
specific regulator function, and directs PU.1 expression as
an enhancer in myeloid and B-lymphoid cells but functions
as a repressor in T cells. Due to these profound effects of
URE deletion on PU.1 expression, URE ∆/∆ mice regularly
developed aggressive hematopoietic malignancies, such as
acute myeloid leukemia, T cell lymphoma and B1 cell chronic
lymphoid leukemia. Results from the URE ∆/∆ animal model
provided the first demonstration that interference with the
fine-tuned regulation of a single transcription factor,
through disruption of a key cis-regulatory element, can be
sufficient to initiate the formation of cancer stem cells and
subsequent tumor development. We are currently engaged
in studying additional regulatory elements of the PU.1 gene
and the transcription factor pathways that control PU.1
expression through these distal DNA control regions.
DNA methylation level controls hematopoietic
stem cell maintenance and lineage fate programs
Lineage-specific transcription factors are known to form
multiple hetero-complexes among each other or with
numerous other nuclear factors involved in gene regulation.
Recently, we could provide evidence for a collaboration of
PU.1 with an important epigenetic modifying enzyme, the
DNA methyltransferase 1 (DNMT1). This observation sparked
our interest to understand the effect of DNA methylation on
mammalian tissue stem cell function.
DNMT1 is the major enzyme that maintains the DNA methylation
status of the genome. Since knockout of DNMT1 leads
to embryonic lethality prior to the formation of blood cell
production, we used a DNMT1 hypomorphic mouse model to
investigate the effect of reduced DNA methylation on the
hematopoietic system. To assess whether hematopoietic
stem cell (HSC) properties were affected in DNMT1 hypomorphs,
bone marrow transplantation assays were applied.
Phenotypically, DNA hypomethylation led to a decreased
HSC pool size and to the complete lack of Flt3 expressing
stem cells. While the DNMT1 hypomorphic HSCs led to normal
radioprotection in high cell doses, they displayed profound
functional defects in limited dilution, serial and competitive
transplantation assays.
Intriguingly, we could also find a selective B cell differentiation
block prior to the common lymphoid progenitor stage
in DNMT1 hypomorphic mice. In contrast, myeloid differentiation
was not affected. The reduction of B cell potential
was accompanied by a specific loss of a B cell-associated
gene expression program in bone marrow progenitors.
Both, transplantation and OP9 co-culture assays demonstrated
that the defect in the ability of DNMT1 hypomorphic
stem cells to generate B cells was intrinsic. Collectively, we
could show a role for DNMT1 in the maintenance of tissue
stem cell properties as well as in the control of selective differentiation
fates programs. We are currently performing
gene expression profiling of sorted HSCs to identify the
molecular mechanisms involved in the demethylation-based
reduced “stemness” properties and B cell lineage adoption.
Selected Publications
Rosenbauer, F, Wagner, K, Kutok, JL, Iwasaki, H, Le Beau, MM,
Okuno, Y, Akashi, K, Fiering, S, and Tenen DG. (2004) Acute
myeloid leukemia induced by graded reduction of a lineage-specific
transcription factor, PU.1. Nature Genet. 36, 624-630.
Steidl, U, Rosenbauer, F, Verhaak, RGW, Gu X, Out, HH, Bruns, I,
Steidl C, Costa, DB, Klippel, S, Wagner, K, Aivado M, Kobbe, G,
Valk, PJ, Passegué E, Libermann TA, Delwel, R, and Tenen, DG.
(2006) Essential role of Jun family transcription factors in PU.1-
induced leukemic stem cells. Nature Genet 38, 1269-1277.
Scheller M, Huelsken J, Rosenbauer F, Taketo MM, Birchmeier W,
Tenen DG, and Leutz A. (2006) Hematopoietic stem cell and
multi lineage defects by β-catenin activation. Nature Immunol
7, 1037-1047.
Wagner, K, Zhang, P, Rosenbauer, F, Drescher, B, Kobayashi, S,
Radomska, HS, Kutok, JL, Gilliland, DG, Krauter, J, Tenen, DG.
(2006) Absence of the transcription factor CCAAT enhancer binding
protein a results in loss of myeloid identity in bcr/abl-induced
malignancy. Proc Natl Acad Sci U S A 103, 6338-6343.
Rosenbauer, F # , Owens, BM, Yu L, Tumang, JR, Steidl, U, Kuto,k
JL, Clayton, LK, Wagner, K, Scheller, M, Iwasaki, H, Liu, C,
Hackanson, B, Akashi, K, Leutz, A, Rothstein, TL, Plass, C, and
Tenen, DG # . (2006) Lymphoid cell growth and transformation
are suppressed by a key regulatory element of the gene encoding
PU.1. Nature Genet 38, 27-37. # Shared corresponding authors
Rosenbauer, F # and Tenen, DG # . (2007) Transcription factors in
myeloid development: Balancing differentiation with transformation.
Nature Rev Immunol 7,105-117. # Shared corresponding
authors
94 Cancer Research