T cell development is regulated by the coordinated function of two Lck promoters (IRM7P.701)

Abstract

Abstract Lck is a T cell lineage-specific tyrosine kinase that is critical for T cell development and activation. Expression of an identical Lck protein can be mediated by two promoters, the proximal and distal lck promoters, but the function of these promoters during T cell development has not been directly assessed. We generated mutant mice by inactivating either one of the two lck promoters. Lck-PROX mice, in which only the proximal promoter is functional, had normal levels of Lck protein and thymic development through the CD4-CD8- double negative (DN) stage of T cell development, but reduced levels of Lck later in development and a dramatic reduction of mature single positive thymic T cells. In contrast, Lck-DIST mice, in which only the distal promoter was functional, were deficient in Lck and severely defective in early T cell development, with a block at the DN3 stage equivalent to the defect seen in complete Lck knockouts. Interestingly, the small number of peripheral T cells that developed in Lck-DIST mice expressed Lck protein and proliferated normally in response to TCR/CD3 cross-linking, while those of Lck-PROX mice were deficient in Lck and defective in response to TCR stimulation. These results define the coordinated requirements for proximal and distal lck promoters during T cell development and represent a unique direct demonstration of the requirement for alternative promoters in allowing developmental stage-specific regulation of a single protein product.