Rebecca Jo van Beneden
Professor
Ph.D., Johns Hopkins University

The University of Maine Department of Biochemistry, Microbiology, and Molecular Biology 5751 Murray Hall Orono, Maine 04469 Phone: 207-581-2602 Fax: 207-581-2537 Email: rebeccav@maine.edu

Research Interests:

My laboratory is interested in the response of aquatic organisms to environmental stress, the molecular basis of the response and how it compares to higher animals, including humans. By understanding the differences and similarities in the responses of phylogenetically diverse organisms to environmental exposures, we may be better able to better assess the risks to both environmental and human health. Our research projects are directed along several related lines: (1) the analysis of tumors of the reproductive system in the soft-shell clam, Mya arenaria; (2) the role of the aryl hydrocarbon receptor (AHR) in the presence and absence of dioxin-like compounds; (3) the biological effects of pesticide exposure to early life stages of finfish and shellfish. In all of these studies, we are using aquatic models to study molecular mechanisms of the complex interactions of the genetic and environmental factors involved in disease as models for both humans and environmental health.

Clam Studies - Epidemiological investigations of germ cell tumors in Maine soft- shell clams (Mya arenaria) demonstrate a 20-40% prevalence of gonadal cancers in specific sites in eastern Maine. Although the etiology of the neoplasm is unknown, contamination of the watersheds by herbicides from silviculture, agriculture and roadside maintenance appears to be a common factor. When the tumors were first observed, the predominant herbicides used were the phenoxyacetic acid derivatives, dichlorophenoxyacetic acid (2,4-D) and trichlorophenoxyacetic acid (2,4,5-T). These herbicides alone exhibit relatively low toxicity in rodent assays. However, a common byproduct of 2,4,5-T synthesis - 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) - is a very potent carcinogen in laboratory animals.

Dioxins belong to the halogenated aromatic hydrocarbons (HAHs), which include polychlorinated dibenzodioxins (PCDDs), dibenzofurans (PCDFs), and coplanar and mono- ortho-substituted polychlorinated biphenyls (PCBs). Sources of environmental dioxins include high temperature combustion, contaminated herbicides and chlorine bleaching of wood products. The molecular mechanism of toxicity has been extensively investigated. Dioxins are broadly dispersed, persistent environmental contaminants causing numerous toxicities in rodent models and posing a significant risk to human health. Gonads of clams exposed to TCDD in the laboratory exhibit a dramatic alteration in tissue structure and gamete development (Butler et al., in press). The primary mode of HAH toxicity is through aryl hydrocarbon receptor (AHR) a ligand-activated transcription factor. AHR with its dimerization partner ARNT ( AH R nuclear translocator) bind to xenobiotic responsive elements (DRE) to regulate expression of a suite of genes involved in cellular detoxification pathways and cell cycle regulation.

Recent evidence suggests that not all toxic effects of dioxin are AHR-dependent. Characterization of the clam AHR revealed a lack of dioxin binding, a general property of the known invertebrate AHR homologues (Butler et al., 2001) . This supports the hypothesis that AHR has a role in normal cellular function in the absence of exogenous ligand. The clam model provides the opportunity to study the role of the AHR in normal development as well as AHR-independent mechanisms of dioxin toxicity.

We have also undertaken a broad search for the differential expression of genes in normal vs tumor bearing (or dioxin/herbicide-exposed) animals. We have shown that the clam E3 gene (a ubiquitinating protein ligase) is up-regulated in tumor-bearing clams as well as clams exposed to dioxin in the laboratory. Furthermore, expression of the p53 tumor suppressor gene (a known E3 target in vertebrates) is down regulated in the same animals, suggesting a loss of the anti-proliferative effect of p53. Since recent studies in the laboratory (Olberding et al., 2004) suggest that these two proteins do not interact directly, the roles of p53 and E3 in clam tumorigenesis remain open areas of investigation.

Environmental Contaminants Projects - Numerous toxicants of natural and anthropogenic origin have been released into the environment in quantities sufficient to disrupt developing endocrine and nervous systems in wildlife and humans. Many such toxicants have been identified as acute problems in Maine, including organophosphates and other pesticides, herbicides, organo-arsenic, organo-mercury, dioxins and polychlorinated biphenyls (PCBs). These chemicals are especially harmful during embryonic, fetal and early post-natal periods because they may mimic or interfere with hormones, neurotransmitters, growth factors and other signaling molecules that normally control developmental processes.

Agrochemicals currently registered for use in maintaining blueberry fields in downeast Maine include hexizanone (Velpar) , guthion, benomyl, phosmet, glyphosate, propiconazole, sethoxidim, clethodim and fluazifop-p-butyl). Fish and shellfish resident in rivers of eastern Maine are potentially exposed to these chemicals through runoff into the watershed. Very little is known about the effects of these agrochemicals on aquatic populations. The degree of estragenicity of these chemicals relative to 17 β-estradiol was determined using E-SCREEN, an in vitro bioassay. Preliminary data suggest that some of the pesticides have marginal proliferative effects on estrogen-responsive cells in culture. These studies are in progress and will be expanded to include early-life stages of fish and shellfish.

Selected Publications:

Kelley, M.L. and Van Beneden, R.J. Identification of an E3 Ubiquitin-Protein Ligase in the Softshell Clam (Mya arenaria) . Marine Environmental Research 50: 289-293, 2000.

Kelley, M.L., Winge, P., Heaney, J.D., Stephens, Farrell, J.H., Van Beneden, R.J., Reinsich, C.L., Lesser, M.P. and Walker , C.W. Expression of homologues for p53 and p73 in the softshell clam (Mya arenaria) , a Naturally-Occurring Model for Human Cancer. Oncogene 20: 748-758, 2001.

Rotchell, J.M., Ungal, E., Van Beneden, R.J. and Ostrander, G.K. Retinoblastoma gene mutations in chemically-induced liver tumors from the Japanese medaka (Oryzias latipes) . Marine Biotechnology 3 : S44-49, 2001.

Butler , R.A., Kelley, M.L., Powell, W., Hahn , M.E. and Van Beneden, R.J. An aryl hydrocarbon receptor (AHR) homologue from the soft-shell clam, Mya arenaria : evidence that invertebrate homologues lack 2,3,7,8-tetrachlorodibenzo-p- dioxin and ß-naphthoflavone binding. Gene 278: 223-234, 2001.

Olberding, K.E., Kelley, M.L., Butler , R.A. and Van Beneden, R.J. A HECT E3 ubiquitin-protein ligase with sequence similarity to E6AP does not target p53 for degradation in the softshell clam (Mya arenaria) . Mutation Research 552: 61-71, 2004.

Butler, R.A., Kelley, M.L., Olberding, K.E., Gardner, G.R., and Van Beneden, R.J. The Aryl Hydrocarbon Receptor (AHR)-Independent effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on Softshell Clam (Mya arenaria) Reproductive Tissue. Comp. Biochem. Physiol, in press.

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