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Research Description:
The general goal of the neurodegeneration project is to understand the cellular changes that occur in nerve cells that are exposed to oxidative stress. In response to acute injury such as stroke or in many chronic neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, nerve cells are subjected to oxidative stress. Through a better understanding of the biochemical changes that occur in response to oxidative stress in nerve cells Dr. DeFranco hopes to identify molecules and pathways that could be targets for therapeutic intervention. The DeFranco laboratory is also interested in prostate cancer and focuses on important components of the tumor microenvironment, (i.e. stromal cells) that provde the support necessary for cancer cells to survive and expand. The group has identified one molecular target in stromal cells that plays an important role in the communication between stromal cells and developing cancer cells in the prostate. The hope is to devise new strategies for limiting the contribution of the tumor microenvironment through detailed molecular studies of prostate stromal factors essential for cancer development and progression. Finally, Dr. DeFranco examines the cell biology and clinical relevance of glucocorticoid signaling in various models. The basic mechanism of trafficking of the receptor for glucocorticoids (i.e. the glucocorticoid receptor) is examined using state-of-the-art fluorescence microscopy technology coupled with biochemical approaches. In addition, the impact of glucocorticoids on various tissues during development focusing on the brain in model studies in fetal mice and on white blood cells in critically ill children. Since glucocorticoids are a standard course of therapy for premature infants and critically ill children, we hope to provide insights into appropriate treatment strategies when glucocorticoids therapy is indicated. Extracellular signal-regulated kinases-1/2 (ERK1/2), members of the mitogen-activated protein kinase (MAPK) family, are well-established regulators of cell proliferation and survival particularly in the brain. However, the DeFranco laboratory was one of the first to demonstrate a role for ERK1/2 in promoting toxicity in neurons using in vitro models of oxidative stress (i.e. neuronal cell line and primary neurons). Many examples have since been documented establishing a role for ERK1/2 in promoting cell death in neurons both in vitro and in vivo. Ongoing analysis of the mechanistic basis for ERK1/2 activation in oxidatively stress neurons has also implicated the oxidative inhibition of select protein phosphatases in persistent activation of ERK1/2 and neurotoxicity. Importantly, one of the secondary consequences of oxidative stress in neurons (i.e. increased accumulation of intracellular Zn2+) also contributes significantly to ERK1/2 activation through selective inhibition of protein phosphatases. The regulation of promoter activity by nuclear receptors requires the assembly of large multi-subunit complexes that either directly impact the basal transcriptional machinery or modify core histones to affect chromatin structure and remodeling. The mechanisms responsible for maintaining the highly ordered dynamics of protein binding to hormonally responsive promoters have not been definitively established. Dr. DeFranco’s laboratory recently developed a novel in situ fluorescence recovery after photobleaching assay that led to the identification of molecular chaperones and their associated cochaperones as nuclear mobility factors for the glucocorticoid receptor. They plan to further exploit this assay to provide additional mechanistic insights into the role of chaperones in nuclear dynamics of glucocorticoid receptor and perhaps reveal how stress response proteins could impact epigenetic events that regulate chromatin remodeling. Communication between the epithelial and stromal compartments of the prostate that is mediated by growth factors and cytokines is crucial for the maintenance of prostate growth and function. However, alterations in the expression and response to these factors can occur during prostate cancer progression and alter signaling between these compartments. The DeFranco laboratory has identified a prostate stromal cell specific transcriptional coactivator, the Hic-5 protein, that functions in both basal and androgen regulated expression of keratinocyte growth factor, a paracrine factor that impacts prostate cancer cell proliferation. Furthermore, Hic-5 expression in prostate stromal cells is induced by an epithelial cell derived factor transforming growth factor–beta 1, which promotes the transdifferentiation of normal stromal fibroblasts to activated “myofibroblasts". Thus, Hic-5 is integral to stromal/epithelial cell communication in the prostate through its impact on endocrine, paracrine and perhaps autocrine signaling networks. In their role as essential modulators of basal and stress-related homeostasis, glucocorticoids modulate host immune response, intermediary metabolism, and the cardiovascular system. Due to its anti-inflammatory actions, cortisol has been administered to adults and children with septic shock. Cortisol therapy is clearly beneficial in the Waterhouse-Friedrichsen syndrome characterized by adrenal hemorrhage and infarction, which was first described in children with meningococcal meningitis. However, both beneficial and deleterious outcomes of glucocorticoid therapy among critically ill patients have been reported. Despite the lack of objective data, high dose cortisol therapy has been used in the pediatric intensive care setting. Outcome measures to assess efficacy of cortisol therapy such as cortisol concentrations, adrenocorticotrophic hormone (ACTH)-stimulated cortisol concentrations, and blood pressure are indirect. Furthermore, these measurements do not assess the cellular actions of glucocorticoids, which are mediated by the glucocorticoid receptor (GR), a ligand dependent transcription factor. Many GR target genes participate in the immune response. We will examine the cellular actions of GR in peripheral blood mononuclear cells (PMBCs) of critically ill children using assays that will provide insights into the anti-inflammatory actions of glucocorticoids.
Education:
B.A. (Biology), Temple University, 1976.
Ph.D. (Biochemistry), Yale University, 1981.
Postdoctoral Fellow, University of California, 1985.
Important Publications:
- Ho Y, M Knoch, R Samarasinghe, E Aizenman and DB DeFranco. Selective inhibition of MAPK phosphatases by zinc accounts for ERK1/2-dependent oxidative neuronal cell death. Molecular Pharmacology 74:1141-1151, 2008
- Wolf IM, MD Heitzer, M Grubisha and DB DeFranco. Coactivators and nuclear receptor transactivation. J Cell Biochem 104:1580-1586, 2008
- Heitzer MD and DB DeFranco. Hic-5/ARA55 a LIM domain-containing nuclear receptor coactivator expressed in prostate stromal cells. Cancer Research 66: 7326-7333, 2006
- Witchell S and DB DeFranco. Mechanisms of disease: Regulation of glucocorticoid hormone and receptor levels-impact on the metabolic syndrome. Nature Clinical Practice: Endocrinology and Metabolism 2:621-631, 2006
- Levinthal DJ and DB DeFranco. Reversible oxidation of ERK-directed protein phosphatases drives oxidative toxicity in neurons. J Biol Chem 280:5875-5883, 2005
- Wang X and DB DeFranco. Alternative effects of the ubiquitin-proteasome pathway on glucocorticoid receptor downregulation and transactivation are mediated by the CHIP E3 ligase. Mol Endocrinol 19:1474-1482, 2005
- Elbi C, G Romero, D Walker, W Sullivan, DO Toft, GL Hager and DB DeFranco. Molecular chaperones function as nuclear mobility factors for steroid receptors. Proc Natl Acad Sci USA 101:2876-2881, 2004
- Jiang H, F Nucifora, CA Ross and DB DeFranco. Cell death triggered by polyglutamine-expanded huntinigtin in a neuronal cell line is associated with degradation of CREB-binding protein. Human Mol Genet 12:1-12, 2003
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