My lab primarily works with mouse models, and we frequently use gene knock-out mice. Studies to better understand the conditions that foster the initiation of leukemias and lymphomas are currently a major thrust of the lab. In particular, we are investigating how conditions of stress (particularly those that impair DNA replication) promote the competitive expansion of cells expressing particular oncogenes, and the mechanism whereby these oncogenes can improve cell cycle progression and survival under conditions of stress. In addition, our studies of E2F transcription factors range from the organismal level, such as the development of disease in E2F knock-out mice, to the molecular level, such as our mechanistic studies of E2F control of transcription.
Some current projects in the DeGregori lab:
Poor cell cycling in progenitor pools predisposes to tumor development. Contexts of impaired DNA replication, including those resulting from certain vitamin deficiencies and chemotherapeutics, can be paradoxically associated with increased tumor development. Using retroviral transduction of bone marrow stem cells followed by transplantation into mice, we have demonstrated that genetic and pharmacologic impairment of DNA replication promotes the development of leukemias caused by Bcr-Abl as a result of poor competition among hematopoietic stem and progenitor cells. In contrast, competent replication among hematopoietic progenitors is inherently tumor suppressive, preventing the expansion of Bcr-Abl expressing progenitors. We are currently determining the signaling pathways controlled by Bcr-Abl that contribute to this oncogene's ability to overcome genetic and chemotherapeutic contexts of replicative stress. Further understanding of the role of competitive interactions among blood progenitor cells in leukemogenesis and influences of chemotherapeutic treatments should help develop strategies to prevent and treat leukemias.
p53 mutation prevents replicative stress induced proliferation arrest and senescence. Cells have an intricate network of checkpoints that ensure the proper duplication and segregation of genetic material. Inhibitors of deoxynucleotide synthesis, such as the ribonucleotide reductase inhibitor hydroxyurea (HU), impair DNA synthesis and activate checkpoint pathways that prevent further cell cycle progression. HU and other inhibitors of DNA replication are commonly used anti-cancer chemotherapeutics. While dNTP depletion and cell cycle arrest imposed by HU treatment does not require the p53 tumor suppressor, chronic treatment of cells with low HU concentrations, which approximate those experienced by cells in HU treated patients, results in permanent growth arrest and senescence that can be overcome by the expression of dominant negative p53 mutants. Downregulation of p21Cip1 levels indicates that cyclin dependent kinase inhibition dependent on p53 is critical for replicative stress induced senescence. The chronic limitation of DNA replication that we study may serve as a general paradigm for contexts of chronic replication stress experienced by people treated with chemotherapeutics like HU or under other conditions (genetic, dietary or environmental) that cause genotoxic stress.
The regulation of the lymphocyte cell cycle and hematopoiesis by E2F. We have shown that the combined loss of E2F1 and E2F2 profoundly impedes S phase progression and hematopoiesis. We are currently characterizing E2F1/2 dependent target genes and linking the E2F1/2 dependent regulation of these target genes with roles for these E2Fs in cell cycle progression, with the eventual goal of connecting these transcriptional and cellular roles with organismal phenotypes observed in E2F1/2 mutant mice. Related experiments in the lab are using tandem tag affinity purification to isolate E2F1 and E2F4 containing complexes from cells in order to identify proteins that associate with these E2Fs, which should provide insight into transcriptional control by these E2Fs.
The development of insulin dependent diabetes in E2F1/E2F2 mutant mice reveals important roles for bone marrow (BM) derived cells in preventing exocrine pancreatic degeneration induced b islet destruction. We have discovered that mice mutant for E2F1 and E2F2 develop non-autoimmune insulin dependent diabetes with high penetrance, and we have shown that diabetes in part results from hematopoietic deficiencies in these mice. We are currently trying to understand roles for hematopoietic cells in the maintenance of b islet cells in the face of stress. These studies indicate a normal role for macrophages in supporting the survival and maintenance of b islet cells, and may indicate therapeutic approaches to augment macrophage function in diabetic patients.
Representative Publications:
Zhu, J.W., S. J.
Field, L. Gore, M. Thompson, H. Yang, Y. Fujiwara, R. D.
Cardiff, M. Greenberg, S. H. Orkin, and J. DeGregori.
(2001). E2F1 and E2F2 Determine Thresholds for
Antigen-Induced T-Cell Proliferation and Suppress
Tumorigenesis. Mol. Cell. Biol. 21 8547-8564.
DeGregori, J.
(2002). The genetics of the E2F transcription factor family:
shared roles and unique functions. Biochemica et
Biophysica Acta 1602, 131-150.
Wan, Y.Y. and
J. DeGregori (2003). The survival of antigen
stimulated T cells requires NFkappaB mediated inhibition of
p73 expression. Immunity 18, 331-342.
Li, F.X., J.Z.
Zhu, C. Hogan and J. DeGregori (2003). Defective gene
expression, S phase progression and maturation during
hematopoiesis in E2F1/E2F2 mutant mice. Mol. Cell.
Biol., 23, 3607-3622.
Li, F.X., J.W.
Zhu, J. Tessem, J. Beilke, M. Varella-Garcia, J.
Jensen, C. J. Hogan and J. DeGregori (2003). The
development of diabetes in E2f1/E2f2 mutant
mice reveals important roles for bone marrow derived cells
in preventing islet cell loss. Proc. Natl. Acad. Sci.
USA 100, 12935-12940.
DeRyckere, D.
and J. DeGregori (2005). E2F1 and E2F2 are
differentially required for homeostasis-driven and
antigen-induced T cell proliferation in vivo.
J Immunology, 175:647-55.
Bilousova G., A. Marusyk, C. Porter, R. Cardiff and J.
DeGregori (2005). Impaired DNA replication in progenitor
cell pools promotes leukemogenesis. PLoS Biology,
3(12):e401.
DeGregori, J. (2006). A Surprising Dependency for the Retinoblastoma Protein in Ras mediated Tumorigenesis. Mol. Cell. Biol., 9:442-4.
Shapiro, G., C. Van Peursem, D. Ornelles, J. Schaack, and J. DeGregori (2006) Recombinant adenoviral vectors can induce the expression of p73 via the E4-orf6/7 protein. J. Virology, 80:5349-60.
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