Molecular Biology of Gastrointestinal Viruses

The gastrointestinal (GI) tract represents the largest and most heterogeneous organ in the body. However, information on the molecular biology of most cell types in the GI tract remains limited. We are using viruses that infect distinct types of cells (enterocytes, crypt cells, M cells) in the GI tract as probes to learn about the biology, host response and gene expression of these cells. We are using multidisciplinary approaches to probe the structure and molecular biology of GI viruses to understand the basic mechanisms that control virus replication, morphogenesis, virus-host interactions, and pathogenesis.

Our work uses two viruses, rotaviruses, the major cause of diarrhea in children and animals worldwide, and human caliciviruses, the major cause of epidemic gastroenteritis. Studies on the molecular biology of the rotaviruses seek to dissect the biologic, biochemical and structural role(s) inducing disease. Current studies are focusing on the rotavirus spike protein and the viral enterotoxin and how these proteins induce signaling pathways in cells that are important in immunity and pathogenesis. We are studying proteins expressed from inducible cDNAs in mammalian cells and virus-like particles (VLPs) produced using the baculovirus expression system. We aim to determine how specific domains of the viral proteins interact with intestinal cell receptors, affect cell signaling mechan-isms, and induce diarrhea. We also are evaluating how to effectively orally deliver virus-like particlesubunit vaccines to induce a mucosal immune response and protection from virus infection.

Studies on the human caliciviruses are using molecular approaches to characterize Norwalk virus and related viruses. Sequence analysis and expression of genes from a cloned DNA library of Norwalk virus nucleic acid have classified this virus, determined its genome organization and relatedness to other Norwalk-like viruses and other gastroenteritis viruses such as astroviruses and enteroviruses, and produced new diagnostic assays. Use of these new assays is changing our understanding of the natural history and epidemiology of infections with these viruses. Notably, these viruses are being increasingly recognized as important causes of disease in children and in immunocompromised individuals. Expression of the capsid protein using mammalian and plant VLPs allowed the first crystallographic structure of a calicivirus to be solved and they are being tested directly as mucosal vaccines or as delivery systems for vaccines containing epitopes from other pathogens. Finally, the molecular basis of the restricted replication of Norwalk viruses to the gastrointestinal tract of humans is being probed by expression of Norwalk virus genes with different vectors and testing the interactions of virus with different cell lines and tissues derived from the gastrointestinal tract.