Dissecting p56(lck) function in developing thymocytes

Abstract

Previous studies suggest that p56lck activity influences thymocyte development at a stage prior to alpha/beta TCR expression. Dysregulated expression of Lck in transgenic animals revealed Lck's unique and potent effect in thymocyte development and thymic tumorigenicity, as opposed to two other closely related Src-family members p59fyn and p59hck which do not behave analogously when similarly overexpressed. To better understand the relationship between dysregulation of Lck expression, thymic tumorigenesis and Lck's role in thymocyte development, immature thymoblast cell lines derived from thymic lymphomas induced in transgenic animals overexpressing Lck activity are utilized as model systems to study signal transduction pathways activated by Lck in early thymocyte progenitors. The Ras/Raf/MAPK pathway and the PI3K pathway are found to be constitutively activated as a direct result of elevated Lck activity in these lck-immortalized immature thymoblasts. In addition, using strategies to interfere with activities of components of each pathway, our results suggest that activation of both Ras/Raf/MAPK and PI3K pathways is necessary for optimal Lck-dependent cell cycle progression. In an effort to understand the unique role of Lck signaling in developing thymocytes, chimeric kinases between Lck and Fyn are generated and introduced into the germline of animals by transgenic technology. Analyses of animals expressing these chimeric constructs in the Lck null background suggest that the amino-terminal half of Lck, which consists of the unique region, SH3 and SH2 domains, has been specialized to facilitate Lck's role in promoting thymocyte development.