Amro M. Hamdoun, PhD, University of California Davis - US grants

The two main goals of this research are first, to understand the cell biological regulation of multidrug efflux transport and second, to probe the roles of these transporters in protection and regulation of embryonic development. This proposal links between two bodies of knowledge, one on the cellular physiology of multidrug efflux transport, primarily examined in the context of cancer and epithelial transport, and another focusing the structural changes in cell surface and membrane organization of embryo development. In the ROO Phase of this proposal, Hamdoun will continue and expand his investigation ofthe relationship between cell surface changes in early embryo development and changes in the efflux transporter activity focusing on sea urchins as an easily assayed and manipulated model organism. He will also continue efforts, currently ongoing in the K Phase of this award, to translate findings from the sea urchin to the mouse model, in order to characterize the role of these activity changes in protection of the embryo from potential teratogens encountered during assisted reproduction. Research in the K Phase of this award has revealed rapid upregulation of ABCB (pgp) and ABCC (mrp) efflux transporter activity following fertilization of sea urchin eggs and then later down-regualtion of efflux transport In a subset of 4 embryonic germline progenitor cells, known as the small micromeres. In most other systems, cycling of ABC transporters in and out of membranes is continuous, whereas in the sea urchin the two episodes of rapid change in efflux activity and cortical organization provide a powerful model for studying the cell structure and transporter function relationships. In Aims 1 and 2 Hamdoun will characterize the post-fertilization redistribution of Sp-ABCB1a (an ortholog of mammalian p-gp) activity by movement of the transporter to the tips of microvilli. In the third Aim, Hamdoun will extend these findings to the mouse model, specifically following up on his preliminary finding of loss of pgp transporter activity after fertilization of mouse oocytes and again he will focus on how activity changes relate to organization ofthe cortical actin cytoskeleton. In a new fourth Aim, Hamdoun will study the mechansims of transporter regulation in the small micromeres.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The two main goals of this research are first, to understand the cell biological regulation of multidrug efflux transport and second, to probe the roles of these transporters in protection and regulation of embryonic development. This proposal links between two bodies of knowledge, one on the cellular physiology of multidrug efflux transport, primarily examined in the context of cancer and epithelial transport, and another focusing the structural changes in cell surface and membrane organization of embryo development. In this proposal, we will investigate the relationship between cell surface changes in early embryo development and changes in the efflux transporter activity focusing on sea urchins as an easily assayed and manipulated model organism. We will also continue efforts, currently ongoing in the K Phase of this award, to translate findings from the sea urchin to the mouse model, in order to characterize the role of these activity changes in protection of the embryo from potential teratogens encountered during assisted reproduction.

DESCRIPTION (provided by applicant) Marine pollution is of concern for human health through our exposure to contaminated food from the sea. What remains poorly understood is why some chemicals are persistent, accumulating in marine organisms and then in humans, while others are not. Multidrug resistance (MDR) transporters, belonging to the ATP Binding Cassette (ABC) family, are major biological determinants of intracellular chemical accumulation. While they have been implicated as determinants of environmental chemical persistence and used as tools for predicting availability and efficacy of drugs, they have yet to be systematically applied to predicting persistence of pollutants. The investigators' preliminary data indicate striking functional conservation of the major sub-family types (ABCB, ABCC and ABCG) of xenobiotic eliminating transporters between sea urchins and man. This application explores the molecular basis for this conserved substrate selectivity as a first step towards application of transporter biology to prediction of pollutant persistence. In this project, the investigators will over-express, solubilize, and purify sea urchin multidrug efflux transporter proteins, develop assays for their interaction with major marine pollutants and attempt to determine their high-resolution structures. They will measure their interaction with persistent marine pollutants using anisotropy, ATPase and whole cell assays. By comparing structure and functions of sea urchin with those of mammalian transporter proteins, already available through the TransportPDB pipeline, they will identify conserved residues and structural features that are essential for predicting substrate interaction in the poly-specific binding pocket of these ABC transporters

PROJECT SUMMARY Prenatal exposures to environmental chemicals have been shown to cause adverse later life health effects, often involving disorders of reproductive dysfunction. The overall goal of this research is to understand the mechanisms governing accumulation of environmental chemicals in the embryo, so that we can predict and mitigate the negative effects of these exposures. In this proposal, we address two key questions with regard to xenobiotic accumulation in the embryo, with a specific focus on the role of xenobiotic transporters during primordial germ cell (PGC) formation. First, we ask how the program of development leads to changes in xenobiotic transporter expression, and thus generates windows of susceptibility or resistance to xenobiotic accumulation. Second, we ask how real-world chemical mixtures, containing both substrates and inhibitors of transporters, impact the efficacy of this conserved, protective system. Aim 1 uses a powerful in vitro molecular evolution technology to rapidly evolve, validate, and use antibody-like binders called nanobodies to characterize xenobiotic transporter proteins in human PGC-like cells (PGLCs) and in model organism embryos (sea urchin and zebrafish). Aim 2 applies biochemical and cellular approaches to determine relevant environmental ligands of human and model system xenobiotic transporters, and takes advantage of a powerful molecular structure determination pipeline to dissect the molecular mechanisms of these interactions. Aim 3 uses models and molecular targets from Aims 1 and 2 to test the hypothesis that PGCs are vulnerable to the interfering effects of environmental chemicals on the transporter defense system, and that disruption of this system leads to decreased reproductive fitness after xenobiotic challenge. This results will provide new insights into how environmental and developmental factors act in combination to govern the susceptibility of the nascent embryonic germ line to teratogens.

ABSTRACT There is urgent public health need to better understand the relative risks and benefits associated with consumption of seafood. The overall mission of this project is to understand the toxicity of marine organohalogen pollutants. We take a powerful approach to understanding and mitigating this risk by asking two questions, central to future efforts to predict and minimize risk. Aim 1 of this project asks how these compounds bioaccumulate, focusing on xenobiotic transporters, which are a key pathway for limiting accumulation of foreign chemicals. We will determine the interactions of the four major human xenobiotic transporters (XTs) with environmentally relevant natural and man-made marine organohalogens. The results will extend and expand the scope of our previous work indicating that several of these compounds can act as potent inhibitors of transporter function. In parallel, we will take advantage of recent progress with heterologous transporter-expression and CRISPR/CAS9 gene editing in sea urchins, to dissect the functional role of XTs in governing bioaccumulation in marine cells. This will be supported by a structure guided approach to determine how evolutionary changes in transporter structure modify interactions with TICs, following up on recent progress towards purification and crystallization of marine XTs in complex with pollutants. Aim 2 of this project will determine the structure activity relationships governing neurotoxicity of marine pollutants. These studies are motivated by preliminary data indicating that naturally produced organohalogens are highly potent inhibitors of ryanodine sensitive Ca2+ channels (RyRs) and Ca2+ ATPase transporters (SERCAs), which are arguably the most direct targets of environmentally relevant organohalogens in the brain. We will use primary cultures of hippocampal neurons cultured from male and female wild type mice to determine how activity at these molecular targets alter neuronal network Ca2+ dynamics and morphology using real-time fluorescence cell imaging and morphometric approaches. In addition, we will determine how hippocampal neurons that express mutation RyR1-R163C known to confer heat stress intolerance, alter sensitivity to organohalogens, and ask whether these effects are gender-specific. These studies will address the critical need to better understand the molecular mechanisms by which naturally occurring and man-made seafood pollutants accumulate in target cells and perturb the Ca2+ dynamics essential for normal neuronal network development.