Kruppel-like transcription factor 13 regulates T lymphocyte survival in vivo

Kruppel-like transcription factor (KLF)13, previously shown to regulate RANTES expression in vitro, is a member of the Kruppel-like family of transcription factors that controls many growth and developmental processes. To ascertain the function of KLF13 in vivo, Klf3-deficient mice were generated by gene targeting. As expected, activated T lymphocytes from Klf13(-/-) mice show decreased RANTES expression. However, these mice also exhibit enlarged thymi and spleens. TUNEL, as well as spontaneous and activation-induced death assays, demonstrated that prolonged survival of Klf3(-/-) thymocytes was due to decreased apoptosis. Microarray analysis suggests that protection from apoptosis-inducing stimuli in Ktf13(-/-) thymocytes is due in part to increased expression of BCL-X-L, a potent antiapoptotic factor. This finding was confirmed in splenocytes and total thymocytes by real-time quantitative PCR and Western blot as well as in CD4(+)CD8(-) single-positive thymocytes by real-time quantitative PCR. Furthermore, EMSA and luciferase reporter assays demonstrated that KLF13 binds to multiple sites within the Bcl-X-L promoter and results in decreased Bcl-X-L promoter activity, making KLF13 a negative regulator of BCL-X-L.