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James DeGregori

Publications and source records attributed to James DeGregori.

At least 19 recordsLinked to original sources
PubMed2006

Building a better model of cancer.

The 2006 Cold Spring Harbor Laboratory meeting on the Mechanisms and Models of Cancer was held August 16-20. The meeting featured several hundred presentations of many short talks (mostly selected from the abstracts) and posters, with the airing of a number of exciting new discoveries. We will focus this meeting review on models of cancer (primarily mouse models), highlighting recent advances in new mouse models that better recapitulate sporadic tumorigenesis, demonstrations of tumor addiction to tumor suppressor inactivation, new insight into senescence as a tumor barrier, improved understanding of the evolutionary paths of cancer development, and environmental/immunological influences on cancer.

Journal Article↗
PubMed2006

Recombinant adenoviral vectors can induce expression of p73 via the E4-orf6/7 protein.

Despite the utility of recombinant adenoviral vectors in basic research, their therapeutic promise remains unfulfilled. Most engineered adenoviral vectors use a heterologous promoter to transcribe a foreign gene. We show that adenoviruses containing the cytomegalovirus immediate-early promoter induce the expression of the proapoptotic cellular protein TAp73 via the cyclin-dependent kinase-retinoblastoma protein-E2F pathway in murine embryonic fibroblasts. Cells transduced with these vectors also expressed high levels of the adenoviral E4-orf6/7 and E2A proteins. By contrast, adenoviruses containing the ubiquitin C promoter failed to elicit these effects. E4-orf6/7 is necessary and sufficient for increased TAp73 expression, as shown by using retrovirus-mediated E4-orf6/7 expression and adenovirus with the E4-orf6/7 gene deleted. Activation of TAp73 likely occurs via E4-orf6/7-induced dimerization of E2F and subsequent binding to the inverted E2F-responsive elements within the TAp73 promoter. In addition, adenoviral vectors containing the cytomegalovirus immediate-early promoter, but not the ubiquitin C promoter, cooperated with chemotherapeutic agents to decrease cellularity in vitro. In contrast to murine embryonic fibroblasts, adenoviruses containing the ubiquitin C promoter, but not the cytomegalovirus immediate-early promoter, induced both E4-orf6/7 and TAp73 in human foreskin fibroblasts, emphasizing the importance of cellular context for promoter-dependent effects. Because TAp73 is important for the efficacy of chemotherapy, adenoviruses that increase TAp73 expression may enhance cancer therapies by promoting apoptosis. However, such adenoviruses may impair the long-term survival of transduced cells during gene replacement therapies. Our findings reveal previously unknown effects of foreign promoters in recombinant adenoviral vectors and suggest means to improve the utility of engineered adenoviruses by better controlling their impact on viral and cellular gene expression.

Adenovirus E1A Proteins↗
PubMed2006

Distinct and Overlapping Roles for E2F Family Members in Transcription, Proliferation and Apoptosis.

Since the discovery almost fifteen years ago that E2F transcription factors are key targets of the retinoblastoma protein (RB), studies of the E2F family have uncovered critical roles in the control of transcription, cell cycle and apoptosis. E2F proteins are encoded by at least eight genes, E2F1 through E2F8. While specific roles for individual E2Fs in mediating the effects of RB loss are emerging, it is also becoming clear that there are no simple divisions of labor among the E2F family. Instead, an individual E2F can function to activate or repress transcription, promote or impede cell cycle progression and enhance or inhibit cell death, dependent on the cellular context. While functional redundancy among E2Fs and the striking influences of cellular context on the effects of E2F loss or gain of function have prevented a simple delineation of unique functions within the E2F family, these complexities undoubtedly reflect the extensive regulation and importance of this transcription factor family.

Animals↗
PubMed2005

Impaired DNA replication within progenitor cell pools promotes leukemogenesis.

Impaired cell cycle progression can be paradoxically associated with increased rates of malignancies. Using retroviral transduction of bone marrow progenitors followed by transplantation into mice, we demonstrate that inhibition of hematopoietic progenitor cell proliferation impairs competition, promoting the expansion of progenitors that acquire oncogenic mutations which restore cell cycle progression. Conditions that impair DNA replication dramatically enhance the proliferative advantage provided by the expression of Bcr-Abl or mutant p53, which provide no apparent competitive advantage under conditions of healthy replication. Furthermore, for the Bcr-Abl oncogene the competitive advantage in contexts of impaired DNA replication dramatically increases leukemogenesis. Impaired replication within hematopoietic progenitor cell pools can select for oncogenic events and thereby promote leukemia, demonstrating the importance of replicative competence in the prevention of tumorigenesis. The demonstration that replication-impaired, poorly competitive progenitor cell pools can promote tumorigenesis provides a new rationale for links between tumorigenesis and common human conditions of impaired DNA replication such as dietary folate deficiency, chemotherapeutics targeting dNTP synthesis, and polymorphisms in genes important for DNA metabolism.

Animals↗
PubMed2005

E2F1 and E2F2 are differentially required for homeostasis-driven and antigen-induced T cell proliferation in vivo.

Homeostasis-driven T cell proliferation occurs in response to a lymphopenic environment and is mediated by TCR and IL-7 signaling. In this report, we demonstrate a defect in the proliferation of murine naive and memory T cells lacking both E2F1 and E2F2 in response to lymphopenic conditions, suggesting that E2F1 and E2F2 function redundantly downstream of TCR and/or IL-7 signaling during homeostasis-driven proliferation. In contrast, T cell proliferation in response to antigenic stimulation is either unaffected (in vivo) or potentiated (ex vivo) by loss of E2F1 and E2F2, indicating divergent requirements for these E2F factors in T cell proliferation mediated by distinct stimuli. E2F1/E2F2 double knockout (DKO) T cells enter S phase in response to homeostatic signaling, but fail to divide, suggesting that S phase progression is either incomplete or defective. In addition, E2F1/E2F2 DKO mice do not recover normal T cell numbers following exposure to a sublethal dose of radiation, indicating that this defect in homeostasis-driven proliferation is physiologically relevant. Consistent with their failure in cell cycle progression, the differentiation of DKO T cells into memory T cells in response to homeostatic signals is significantly reduced. These observations support the idea that proliferation is required for memory T cell formation and also have implications for the development of clinical strategies to minimize the occurrence of lymphopenia-induced autoimmunity.

Animals↗
PubMed2005

Human aldehyde dehydrogenase 3A1 inhibits proliferation and promotes survival of human corneal epithelial cells.

Aldehyde dehydrogenase 3A1 (ALDH3A1) is a NAD(P)+-dependent enzyme that is highly expressed in mammalian corneal epithelial cells and has been shown to protect against UV- and 4-hydroxynonenal-induced cellular damage, mainly by metabolizing toxic lipid peroxidation aldehydes. Here we report a novel function of ALDH3A1 as a negative cell cycle regulator. We noticed a reduction in ALDH3A1 gene expression in actively proliferating primary human corneal epithelium explant cultures, indicating that ALDH3A1 expression is inversely correlated with replication. To examine this further, a human corneal epithelial cell line (HCE) lacking endogenous ALDH3A1 was stably transfected to express ALDH3A1 at levels similar to those found in vivo. ALDH3A1-transfected cells exhibited an elongated cell cycle, decreased plating efficiency, and reduced DNA synthesis compared with the mock-transfected cells. These effects were associated with reduced cyclin A- and cyclin B-dependent kinase activities and reduced phosphorylation of the retinoblastoma protein (pRb) as well as decreased protein levels of cyclins A, B, and E, the transcription factor E2F1, and the cyclin-dependent kinase inhibitor p21. These observations were further expanded and confirmed on human keratinocyte cells (NCTC-2544) overexpressing ALDH3A1. Consistent with a protective role of an elongated cell cycle, ALDH3A1-transfected cells exhibited increased resistance to the cytotoxic effects of the DNA-damaging agents mitomycin C and Vp-16. Immunohistochemistry and biochemical fractionation revealed that ALDH3A1 is localized both in the nucleus and cytosol of ALDH3A1-transfected cells, implying a possible association between the nuclear localization of the enzyme and its proliferation-suppressive functions. In conclusion, these results suggest that ALDH3A1 may protect corneal epithelial cells against oxidative damage not only through its metabolic function but also by prolonging the cell cycle.

Aldehyde Dehydrogenase↗
PubMed2005

Prolonged skin allograft survival by IL-10 gene-introduced CD4 T cell administration.

Both CD4 and CD8 T cells play crucial roles in immune responses in transplantation. Immunosuppressive drugs, such as FK506 and cyclosporin A, block the priming of alloreactive CD4 T(h) cells and the subsequent induction of allospecific CD8 cytotoxic effector T cells and inhibit allograft rejection. However, the desire to minimize chronic complications that may arise from the use of immunosuppressive agents drives the search for additional strategies for immunosuppression of allograft rejection. In this study, CD4 or CD8 T cells into which the IL-10 gene is introduced using an adenovirus vector containing human IL-10 (hIL-10) cDNA (Ad-hIL-10) and into mouse T cells transgenic for the Coxsackie virus and adenovirus receptor form a model system to study the effect of administration of IL-10-secreting T cells on the survival of the allogenic skin grafts. Ad-hIL-10-infected CD4 and CD8 T cells secreted a large amount of hIL-10 for 3-4 days in culture in vitro. Ad-hIL-10-infected CD4 T cells administered in vivo could be detected in the spleen for 7 days post-transfer. Significantly prolonged survival of grafts was observed in animals that received either Ad-hIL-10-infected activated CD4 T cells or T(h)2-skewed CD4 T cells as compared with controls. Furthermore, substantial enhancement of the effect was observed in B6.C-H2(bm1)/ByJ transplants. Thus, a direct manipulation of T cells through the introduction of the immunosuppressive cytokine gene IL-10 may be a novel strategy for the control of allograft rejection.

Adenoviridae↗
PubMed2005

E2F and cell survival: context really is key.

Our understanding of roles for the E2F transcription factor in regulating apoptosis has progressed from asking what E2F can do based on overexpression studies to what E2F actually does based on analyses of loss-of-function mutants. A paper in this issue of Developmental Cell implicates Drosophila E2F1 in context-dependent pro- as well as anti-apoptotic roles in the same tissue following genotoxic stress.

Animals↗
PubMed2004

The Rb network.

Explore the source record for details and available documents.

Cell Cycle↗
PubMed2004

Essential role of GATA3 for the maintenance of type 2 helper T (Th2) cytokine production and chromatin remodeling at the Th2 cytokine gene loci.

GATA3 expression is essential for type-2 helper T (Th2) cell differentiation. GATA3-mediated chromatin remodeling at the Th2 cytokine gene loci, including Th2-specific long range histone hyperacetylation of the interleukin (IL)-13/IL-4 gene loci, occurs in developing Th2 cells. However, little is known about the role of GATA3, if any, in the maintenance of established remodeled chromatin at the Th2 cytokine gene loci. Here, we established a Cre/LoxP-based site-specific recombination system in cultured CD4 T cells using a unique adenovirus-mediated gene transfer technique. This system allowed us to investigate the effect of loss of GATA3 expression in in vitro differentiated Th2 cells. After ablation of GATA3, we detected reduced production of all Th2 cytokines, increased DNA methylation at the IL-4 gene locus, and decreased histone hyperacetylation at the IL-5 gene locus but not significantly so at the IL-13/IL-4 gene loci. Thus, GATA3 plays important roles in the maintenance of the Th2 phenotype and continuous chromatin remodeling of the specific Th2 cytokine gene locus through cell division.

Acetylation↗
PubMed2004

Roles for bone-marrow-derived cells in beta-cell maintenance.

With more than 177 million people suffering from diabetes worldwide, and the number expected to double by 2030, finding new ways to treat this disease is a high priority. Intensive effort is being directed towards developing mechanisms for increasing beta-cell expansion as a diabetic therapeutic. Recent studies, in which adult bone marrow has been used to induce beta-cell expansion in mice, have shown both exciting and controversial results. In these reports, marrow-derived cells can contribute towards beta-cell maintenance both by promoting endogenous beta-cell expansion and possibly by transdifferentiation into beta-cells. These studies reveal mechanisms for potential therapeutic intervention.

Animals↗
PubMed2004

Tumor necrosis factor alpha-induced apoptosis requires p73 and c-ABL activation downstream of RB degradation.

The retinoblastoma protein (RB) suppresses cell proliferation and apoptosis. We have previously shown that RB degradation is required for tumor necrosis factor alpha (TNF-alpha) to induce apoptosis. We show here the identification of two apoptotic effectors, i.e., c-ABL tyrosine kinase and p73, which are activated by TNF-alpha following RB degradation. In cells expressing a degradation-resistant RB protein (RB-MI), TNF-alpha does not activate c-ABL. RB-MI also inhibits TNF-alpha-mediated activation of p73. Genetic deletion and pharmacological inhibition of c-ABL or p73 diminish the apoptotic response to TNF-alpha in human cell lines and mouse fibroblasts. Thymocytes isolated from Rb(MI/MI), Abl(-/-), or p73(-/-) mice are resistant to TNF-alpha-induced apoptosis compared to their wild-type counterparts. This is in contrast to p53(-/-) thymocytes, which exhibit a wild-type level of apoptosis in response to TNF-alpha. Thus, c-ABL and p73 contribute to apoptosis induced by TNF-alpha, in addition to their role in promoting DNA damage-associated cell death.

3T3 Cells↗
PubMed2003

The development of diabetes in E2f1/E2f2 mutant mice reveals important roles for bone marrow-derived cells in preventing islet cell loss.

Our studies of mice deficient for the E2F1 and E2F2 transcription factors have revealed essential roles for these proteins in the cell cycle control of pancreatic exocrine cells and the regulation of pancreatic beta cell maintenance. Pancreatic exocrine cells in E2f1-/-E2f2 mutant mice become increasingly polyploid with age, coinciding with severe exocrine atrophy. Furthermore, mice deficient for both E2F1 and E2F2 develop nonautoimmune, insulin-dependent diabetes with high penetrance. Surprisingly, transplantation of wild-type bone marrow can prevent or rescue diabetes in E2f1-/-E2f2-/-mice. We hypothesize that exocrine degeneration results in a destructive environment for beta cells, which can be alleviated by restoration of the hematopoietic system that is also defective in E2f1-/-E2f2-/-mice The demonstration that beta cell maintenance under conditions of stress is influenced by bone marrow-derived cells may provide important insight into the design of therapies to boost islet mass and function in diabetic patients.

Animals↗
PubMed2003

Characterization of transcriptional regulation during negative selection in vivo.

Negative selection is the process whereby immature thymocytes expressing TCRs with high affinity for self-peptide:MHC complexes are induced to undergo apoptosis. The transcriptional events that occur as a result of TCR signaling during negative selection are not well-characterized. Using oligonucleotide arrays, we have identified 33 genes that exhibit changes in RNA levels in CD4(+)CD8(+) thymocytes during negative selection in vivo. Of 18 genes that have been further characterized, 13 are regulated in response to stimulation with Ag or anti-CD3 and anti-CD28 Abs ex vivo, indicating that these genes are regulated independently of activation of the peripheral immune system. These data also support the idea that anti-CD3/CD28-mediated thymocyte apoptosis is a valid model for negative selection in vivo. A detailed examination of the regulation of many of the identified genes in response to treatment with dexamethasone or gamma-radiation or in response to anti-CD3/anti-CD28 stimulation in the presence of pharmacological inhibitors of mitogen-activated protein kinase kinase kinase 1, p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, calcineurin, and cyclin-dependent kinase 2 has facilitated the elucidation of a map of the transcriptional events that occur downstream of the TCR. These studies support a model whereby similar signal transduction pathways are activated by stimuli that induce positive and negative selection and are consistent with the idea that the balance between opposing proapoptotic and antiapoptotic pathways determines cell fate. The data presented in this study also suggest that calcineurin functions to amplify TCR signals by promoting sustained increases in the levels of specific transcripts.

Amino Acid Sequence↗
PubMed2003

The CUSP DeltaNp63alpha isoform of human p63 is downregulated by solar-simulated ultraviolet radiation.

BACKGROUND: In normal human keratinocytes, a p53-like protein, DeltaNp63alpha, also known as CUSP, is constitutively and abundantly expressed. The significant constitutive expression of DeltaNp63alpha in stratified epithelium has been proposed to maintain the proliferative capacity of basal cells, blocking the consequences of inappropriate p53 activation. OBJECTIVE: To determine the response of keratinocyte DeltaNp63alpha to ultraviolet radiation (UVR), a stimulus for p53 activation. METHODS: Cultured normal human keratinocytes were exposed to graded doses of solar-simulated UVR. The expression of DeltaNp63alpha protein and mRNA were measured with Western and Northern blotting. Normal mouse skin was exposed to UVR, and DeltaNp63alpha expression assessed with immunohistochemistry. RESULTS: Increasing doses of UVR virtually shut off DeltaNp63alpha protein and mRNA expression in cultured normal human keratinocytes and in normal mouse skin in vivo. CONCLUSION: This study supports the hypothesis that in situations where p53 activation is desirable, as with DNA-damaging UVR, DeltaNp63alpha downregulation occurs and may possibly allow for better target gene transcription by p53.

Animals↗
PubMed2003

The survival of antigen-stimulated T cells requires NFkappaB-mediated inhibition of p73 expression.

We have explored the interactions between the NFkappaB and Cdk-Rb-E2F pathways in controlling T cell fate following antigen stimulation. The inhibition of NFkappaB in antigen-stimulated T cells results in apoptosis but does not inhibit E2F activation and S phase entry. IkappaB-induced apoptosis coincides with the superinduction of p73 expression and activity. G1 Cdk activity is required for IkappaB-induced apoptosis and the induction of p73. Importantly, p73 deficiency rescues activated T cells from the apoptosis resulting from the inhibition of NFkappaB. Thus, Cdk2 activation sends signals for both cell cycle progression and apoptosis, the latter of which must be blocked by NFkappaB to allow for proliferation.

Adenoviridae↗
PubMed2003

Defective gene expression, S phase progression, and maturation during hematopoiesis in E2F1/E2F2 mutant mice.

E2F plays critical roles in cell cycle progression by regulating the expression of genes involved in nucleotide synthesis, DNA replication, and cell cycle control. We show that the combined loss of E2F1 and E2F2 in mice leads to profound cell-autonomous defects in the hematopoietic development of multiple cell lineages. E2F2 mutant mice show erythroid maturation defects that are comparable with those observed in patients with megaloblastic anemia. Importantly, hematopoietic defects observed in E2F1/E2F2 double-knockout (DKO) mice appear to result from impeded S phase progression in hematopoietic progenitor cells. During DKO B-cell maturation, differentiation beyond the large pre-BII-cell stage is defective, presumably due to failed cell cycle exit, and the cells undergo apoptosis. However, apoptosis appears to be the consequence of failed maturation, not the cause. Despite the accumulation of hematopoietic progenitor cells in S phase, the combined loss of E2F1 and E2F2 results in significantly decreased expression and activities of several E2F target genes including cyclin A2. Our results indicate specific roles for E2F1 and E2F2 in the induction of E2F target genes, which contribute to efficient expansion and maturation of hematopoietic progenitor cells. Thus, E2F1 and E2F2 play essential and redundant roles in the proper coordination of cell cycle progression with differentiation which is necessary for efficient hematopoiesis.

Animals↗