Three undergraduate Biology majors participated with Dr. Wes Rose, associate professor of biology, in the American Society for Cell Biology meeting in Philadelphia in December. Catherine Brown ’15, Lauren Jolley ’16, and David Klein ’15 work in Rose’s research lab. The group presented a poster of their work titled “Distinct Patterns of Phosphatase Activation and Subcellular Localization Impact the Kinetics of Interferon-Gamma Signaling in CNS Neurons.” The work was co-authored by two recent graduates of the Biology Department, Colby Stotesbury ’13 and Katelyn Sweeney ’13, as well as by Rose’s collaborator Glenn Rall, of the Immune Cell Development and Host Defense program at the Fox Chase Cancer Center in Philadelphia. The presentation included data from the students’ capstone projects. The abstract of the poster follows:
The immune cytokine interferon-gamma (IFN-g) plays an essential role in the elimination of numerous central nervous system (CNS) viral infections. The cellular response to IFN-g, mediated by JAK/STAT signal transduction, involves the upregulation of genes that result in the establishment of the antiviral state, and is controlled by multiple negative feedback mechanisms. However, whether these control mechanisms, previously characterized in non-neuronal cells, operate similarly in CNS neurons has not been well-characterized. Our lab previously demonstrated that the control of the neuronal IFN-g pathway is distinct from that in non-neuronal cells, as the duration of STAT1 phosphorylation and IFN-g responsive gene expression in IFN-g treated neurons was markedly extended as compared to mouse embryonic fibroblasts (MEF). We also showed that compared to MEF, STAT1 dephosphorylation was delayed in IFN-g treated neurons, providing a mechanism for the extended kinetics of neuronal STAT1 phosphorylation. The current study investigated the expression and subcellular localization of two STAT1 phosphatases, TC45 and SHP-2, to address the hypothesis that mislocalization of these phosphatases could result in the observed delay in neuronal STAT1 dephosphorylation. Although no differences in overall expression levels of TC45 were observed between neurons and MEF, neurons demonstrated an approximately 3-fold lower level of SHP-2 activation as compared to MEF, regardless of IFN-g exposure. To examine the subcellular localization of these phosphatases, neurons and MEF were exposed to IFN-g, and nuclear and cytoplasmic fractions were purified at 1, 24, and 48h post-IFN-g treatment. Our results showed that while SHP-2 was found strictly in the cytoplasmic fraction of both cell types, TC45 was found only in the cytoplasmic fraction of the neurons, whereas it was equally distributed between nuclear and cytoplasmic fractions in MEF. These results indicate that neurons (but not MEF) lack TC45 in the nucleus, which provides a likely explanation for the observation that neuronal STAT1 is not dephosphorylated as rapidly as it is in MEF. Understanding the control of the IFN-g response in CNS neurons will ultimately aid in the characterization of antiviral immune mechanisms of the CNS.