Intestinal Epithelium - The intestinal epithelium is one of humans major interfaces with the outside world. This interface is very heavily colonized with gram negative bacteria and yet permits absorption of life-sustaining nutrients while protecting the tissues below from microbial onslaught. In addition to serving as a highly selective barrier, the intestinal epithelium regulates immune cells, especially in response to pathogens. Specifically, we have shown that upon detection of ingested pathogens, the intestinal epithelium signals to both innate and adaptive immune cells to provide short and long term protection against the perturbing microbe. My research seeks to understand, at the molecular level, the bacterial-epithelial interactions that regulate such signaling to immune cells. Such bacterial-epithelial interactions are likely germane to both mucosal immunity and inflammatory bowel disease.

TRAIL-induced apoptosis and cancer therapy - The goal of my research is to understand TRAIL physiology for the development of cancer therapeutic agents targeting TRAIL apoptotic pathways. TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) is normally expressed by natural killer cells and plays a role in anti-tumor immunity. TRAIL is therefore a natural cancer killer and recombinant TRAIL and its agonistic antibodies to its death receptors, DR4 and DR5 are currently in clinical trials for cancer therapies. The majority of human cancers, however, develop resistant mechanisms through activation of cell survival pathways. Recently we have identified the receptor-associated proteins complex and demonstrated that the proteins complex determines TRAIL-induced apoptotic and survival signal. Taking a proteomic approach, we have isolated and identified the proteins in the complex. The proteins identified in the complex include E3 ligases and substrate proteins modified by ubiquitin and SUMO (small ubiquitin-like modifier). Our current efforts therefore focus on (i) the characterization of the E3 ligases-mediated ubiquitination and SUMOylation of the substrate proteins in the complex, (ii) the investigation of how the ubiquitin and SUMO modifications modulate the interaction of the substrate proteins with their binding partners and thus control TRAIL-induced apoptotic and survival signaling, (iii) the development of small molecule inhibitors targeting of the ubiquitin/SUMO modification process, and (iv) the identification of the E3 ligases and/or their substrate proteins as biomarkers predicting the cancer resp Read more...

Reactive Oxygen Species (ROS) - Studies focus on reactive oxygen species (ROS) such as superoxide and hydrogen peroxide, and their biological roles, for example, in innate immunity, mitogenic growth, apoptosis, angiogenesis, and biosynthesis/ remodelling of extracellualr matrix. Starting in 1999, we described a new family of ROS-generating enzymes, the Nox/Duox family. This group of enzymes catalyzes the regulated generation of superoxide in response to signals including hormones, growth factors and immune mediators. The enzymology and regulation of ROS generation by the Nox enzymes and their regulatory proteins is an active area of investigation in our group. The biological function of these enzymes is being investigate in various model systems including cell culture, Drosophila melanogaster, C. elegans and mouse. In addition, the function of these enzymes in pathological conditions including cancer and atherosclerosis, and in normal aging is under active investigation. These enzymes now provide novel targets for development of anti-cancer and anti-arteriosclerotic drugs, which are currently under development by our group. These are predicted to be useful in the treatment and prevention of hypertension, atherosclerosis, and certain forms of cancer. The laboratory uses multi-disciplinary approaches ranging from enzymology and biochemistry to cell biology to animal models.

Mitochondrial DNA replication in disease: AIDS, congestive heart failure, hepatitis, renal failure - One classic biological teaching is that mitochondria are the "powerhouses of the cell", particularly in tissues that require significant energy, like heart, liver and muscle. The focus of the Lewis lab is the diverse effects of toxins on mitochondria structure and function. The primary focus is the untoward mitochondrial effects of a class of drugs called nucleoside reverse transcriptase inhibitors (NRTI) used to treat HIV infection, that are known to inhibit mitochondrial (mt-) DNA replication in vitro. These drugs are toxic to various tissues including heart, skeletal muscle, liver and kidney. Our overall goals are to (1) define the molecular mechanisms of how NRTIs change the abundance of precursors for mtDNA replication in vivo (2) define the effects of active NRTI triphosphates on the mitochondrial replicon in vivo (3) define the effects of specific polymerase mutants on the replication of mtDNA in vivo and (4) define the effects of the mtDNA template itself on its replication in vivo. The approach taken employs tissue specific targeting of genes involved in the processes and evaluation of structural and functional defects that result using state of the art biochemical, molecular, physiological, and pathological approaches. Conditional, tissue specific targeting also is addressed. The direct clinical benefits of these studies are twofold (1) the toxicity of important compounds is defined so that better therapeutics can be designed and administered and (2) mechanisms of organ specific changes in HIV disease and related illnesses are elucidated.

Replication and Pathogenesis of influenza A virus and arenaviruses - My lab is interested in studying the replication and pathogenesis of human viral pathogens, mainly influenza A virus and arenaviruses. (1) Influenza virus (flu) is a major global human pathogen that causes annual epidemic infection and the occasional more widespread and deadly pandemics. Influenza viral genomes are composed of eight different viral RNAs, each encoding one or two viral genes in a negative sense orientation. How these viral RNAs are incorporated into a single viral particle is not fully understood. We are currently characterizing the RNA elements required for efficient packaging of each viral RNA molecule, and the potential roles of RNA-RNA and RNA-protein interactions in viral packaging. In addition, we are interested in studying the virus-host interactions and the roles of host factors and signaling pathways in viral replication. (2) Arenaviruses such as Lassa fever virus (LASV) can cause hemorrhagic fevers in humans and can potentially be employed as biological agents. The necessity of high-level containment restriction to work with this virus (in BSL-4 laboratory) and the costly expenses of using non-human primates for LASV studies significantly hinder progress in understanding the disease pathogenesis. Guinea pig infected by a related arenavirus Pichinde (PICV) represents a safe, convenient, and economical small animal model for Lassa fever. A spleen-passaged PICV causes Lassa fever-like symptoms that are limited to guinea pigs. We are currently studying the replication and pathogenesis of PICV in cell culture and in guinea pigs, which will shed l Read more...

Lipocalins: Probing the Mechanisms of Allergy - This project aims to identify molecular properties of allergens responsible for their intrinsic allergenicity by focusing on the set of structurally and functionally homologous proteins of the lipocalin family that comprise the major mammalian respiratory allergens. We hypothesized that conserved molecular motifs in these lipocalins, via non-IgE interactions with the innate immune system, promote IgE-dependent allergy. In support, we recently demonstrated the presence of inducible lipocalin receptors on mast cells. This suggests roles for direct mast cell-lipocalin interactions (a) in the development and maintenance of the hypersensitive phenotype of allergy patients (xenogeneic lipocalins) and (b) in normal mast cell physiology (endogenous lipocalins), to be delineated by our ongoing investigations.