A laboratory model of how leukemia develops – APL as a model disease
Dr. Thomas Sternsdorf
»Acute promyelocytic leukemia serves us as a model to better understand the pathogenesis of leukemias and thus to gain insight into other types of leukemia and into the pathogenesis of cancer in general.«
Acute promyelocytic leukemia (APL) is a cancer of the blood-producing cells in the bone marrow. It is caused by an accidental gene fusion. When broken chromosomes are improperly reassembled, a new gene can be created at the fusion site. We have found that in the case of APL, the protein produced from such a newly created fusion gene disrupts an important mechanism that permanently inactivates cells, which are at risk to become cancerous. This mechanism is called cellular senescence, which can be seen as an “emergency break” for cancerous growth, which is engaged when cells exceed a certain number of divisions. The block of cellular senescence ultimately allows the affected cells to continue dividing infinitely and might also sensitize them to the accumulation of additional cancer-promoting mutations. This puts the cells on a path towards becoming cancer cells. In order to find out how the APL-causing fusion protein, PML-RAR, actually works in detail, we have adapted it to the mouse, so that we can study various aspects of its activity in mouse cells in the petri dish and ultimately also in laboratory mice. By varying the molecular structure of the components RAR-alpha and PML one-by‐one, we can analyze the possible consequences on distinct leukemia-causing activities.
We have found that PML-RAR-alpha influences/disrupts specific structures of the cell nucleus: The so-called “PML nuclear bodies”. Additional proteins, which regulate the packaging of the DNA, bind to these structures. We have named the resulting assembly of proteins “PAX complex”, after the proteins involved in its function and assembly: PML/ATRX/Daxx. How PML-RAR affects the PAX complex is another subject of our current studies. We already know that cellular senescence is connected to multiple large-scale changes in the organization of DNA. The organized or "packaged" form of DNA is also referred to as chromatin. Senescence causes specific chromatin alterations in the cell, ultimately leading to an irreversible growth arrest. We found that the PAX complex plays an important role in this chromatin alteration. It is our hope, that our insights will enable us to treat other forms of cancer by reactivating cellular senescence in cancerous cells through influencing the PAX complex.
Thomas Sternsdorf was born in Vienna and grew up in the Chiemgau region. He studied biology at Ludwig-Maximilians-Universität (LMU) in Munich, majoring in genetics, anthropology and human genetics, biochemistry and immunology.
In his diploma thesis at the LMU Institute of Immunology, he investigated the role of the transcription factor NF kappa B in the regulation of tumor necrosis factor alpha in human monocytes. In 1997 he completed his PhD summa cum laude at the University of Hamburg.
After a brief time as a postdoctoral researcher with Professor Hans Will, his dissertation supervisor at the Heinrich Pette Institute, he went to San Diego for an extended research stay, where he worked at the Salk Institute in La Jolla in the laboratory of Ronald M. Evans on mouse models for acute promyelocytic leukemia.
In 2009, he joined the recently established Research Institute Children’s Cancer Center Hamburg, where he – funded by a Heisenberg grant from the German Research Foundation (DFG) – became leader of the research group ‘Acute Promyelocytic Leukemia and Leukemogenesis’. His main research interests are the effects of the formation of PML-RAR-alpha on the organization of cellular DNA (chromatin) and how cellular senescence can be reactivated for treatment purposes.
Korf, K., H. Wodrich, A. Haschke, C.B. Ocampo, L. Harder, F. Gieseke, A. Bronsema, K. Dierck, S. Prall, H. Staege, M. Horstmann, R.M. Evans, and T. Sternsdorf, PML-RARalpha Blocks Senescence to Promote Leukemia by targeting the Daxx/ATRX-Complex. Proc. Natl. Acad. Sci. USA, 2014 111(33): P.12133-8.
Relevance: Although the future impact of the paper in the field cannot yet be known, I consider it very important in my scientific development, because it marks a shift of my research interests from PML and APL towards epigenetic aspects of cellular senescence and leukemogenesis, there especially the biology of histone variants and their predisposition complexes. I intend develop my future research in direction of this emerging theme of global epigenetic regulators in differentiation and cancer.
Sternsdorf, T., V.T. Phan, M.L. Maunakea, C.B. Ocampo, J. Sohal, A. Silletto, F. Galimi, M.M. Le Beau, R.M. Evans, and S.C. Kogan, Forced retinoic acid receptor alpha homodimers prime mice for APL-like leukemia. Cancer Cell, 2006. 9(2): p. 81-94.
Relevance: The work addresses the oncogenic activation of Retinoic Acid Receptor alpha in an in-vivo study using retroviral and transgenic expression in the mouse. We have generated a rapamycin–regulatable artificial oncoprotein, a forced dimer of RAR alpha which mimics virtually every aspecty of the naturally occurring oncoprotein, PML-RAR, except that it resonds to de-dimerization by the agent Rapamycin. In a follow-up study (unpublished) we found, that the corresponding murine leukemia does indeed responds to de-dimerization by Rapamycin.
Sternsdorf, T., E. Puccetti, K. Jensen, D. Hoelzer, H. Will, O.G. Ottmann, and M. Ruthardt, PIC-1/SUMO-1-modified PML-retinoic acid receptor alpha mediates arsenic trioxide-induced apoptosis in acute promyelocytic leukemia. Mol Cell Biol, 1999. 19(7): p. 5170-8.
Relevance: In this work we investigate the underlying molecular mechanism of action for the to date most effective treatment of APL: arsenic trioxyde. It was awarded with the prestigious “Konietzny Award of the Hamburg Cancer Endowment” Myself performed all immunoblot experiments, all of the immunofluorescence analysis and provided significant conceptual input.
Sternsdorf, T., K. Jensen, B. Reich, and H. Will, The nuclear dot protein Sp100, characterization of domains necessary for dimerization, subcellular localization, and modification by small ubiquitin-like modifiers. J Biol Chem, 1999. 274(18): p. 12555-66.
Relevance: In this work we have analyzed the PML-associated Sp100 protein and have, for the first time, determined its functional domains and suggested the consensus sequence for its SUMO modification.
Sternsdorf, T., K. Jensen, and H. Will, Evidence for covalent modification of the nuclear dot-associated proteins PML and Sp100 by PIC1/SUMO-1. J Cell Biol, 1997. 139(7): p. 1621-34.
Relevance: In my opinion, this is my most important contribution to the field so far: in this work we have co-established SUMO-1 as a covalent modifyer of proteins. PML and Sp100 were the first two substrates for SUMOylation, past RanGAP1, which led to discovery of SUMO. This work was one of the first papers on SUMOylation, and opened up a field that has virtually exploded since then. I wrote the paper. Myself conceived the idea and performed all experiments with technical support of Kirsten E. Jensen.
Fogal, V., M. Gostissa, P. Sandy, P. Zacchi, T. Sternsdorf, K. Jensen, P.P. Pandolfi, H. Will, C. Schneider, and G. Del Sal, Regulation of p53 activity in nuclear bodies by a specific PML isoform. EMBO J, 2000. 19(22): p. 6185-6195.
Relevance: This work gives the first indication for functional differences between PML splice variants and for PML-p53 functional and physical interaction, partially explaining the role of PML in apoptosis. I was involved in the Immunofluorescence analyses and provided several constructs as well as significant conceptual input. This is my most highly cited paper.
Complete List of Publications: PubMed