FUNCTION OF A MURINE POLIOVIRUS RECEPTOR HOMOLOG

All viruses initiate infection of cells by binding to a host cell component known as a receptor. Viral receptors serve a particular cell function, and do not exist solely for the benefit of viruses. The cell function of most of the viral receptors that have been identified is either known or suspected. the poliovirus receptor (PVR) is one viral receptor whose cell function is unknown. The protein encoded by PVR cDNA is a transmembrane glycoprotein that is a new member of the immunoglobulin (Ig) superfamily of proteins. While we are pursuing several approaches to determining the function of PVR, this problem might be best approached in an easily manipulable animal model. While only primate cells express poliovirus-binding receptors, our results indicate that the mouse genome contains a murine sequence homolog, which we have celled MPH (Murine PVR Homolog). The protein encoded by the MPH gene is structurally similar to PVR, with three extracellular Ig-like domains, a transmembrane domain and a cytoplasmic tail. We have planed three experimental approaches to obtain information on the cell function of MPH. These approaches take advantage of the flexibility afforded by studies in the mouse: the ease of studying gene expression in tissues of different developmental stages, and the ability to determine the effect on mouse development of targeting mutations to specific genes. (1) Characterization of MPH RNA and protein expression in mouse cells and tissues. In situ hybridization and immunohistochemistry will be used to determine which mouse tissues and cells express the MPH gene, during embryonic development and in adult mice. Anti-MPH antisera will be generated and used to determine whether the MPH protein associates with other cell proteins, and if it is modified post-translationally. (2) Identification f a ligand for MPH. A soluble form of MPH protein will be expressed in cultured cells, purified, and used to probe mouse tissues in situ, to determine the location of a putative ligand for MPH. The chemical nature of the ligand will be identified. If a MPH ligand is identified, cDNA clones encoding th ligand will be isolated. (3) Targeted disruption of the MPH gene in mice. To determine the consequences of the lack of the MPH gene product in the mouse, the MPH gene will be disrupted by homologous recombination in embryonic stem (ES) cells. ES cells containing the MPH mutation will be used to generate chimeric mice containing the disrupted allele. Chimeric mice will be bred to generate mice homozygous for the disrupted allele, and the resulting phenotype will be studied to determine the role of MPH in the mouse. Members of the Ig superfamily all have important roles in immunity, development, and cell growth mediated by their recognition/adhesion activities. MPH is likely to have a role in one of these activities, and the study of its function may therefore clarify one of these cell processes. In addition, knowledge of the cell function of MPH may also provide information on the interaction of poliovirus with host cells.