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Krüppel-Like Transcription Factor 13 Regulates T Lymphocyte Survival In Vivo1

Krüppel-like transcription factor (KLF)13, previously shown to regulate RANTES expression in vitro, is a member of the Krüppel- like family of transcription factors that controls many growth and developmental processes. To ascertain the function of KLF13 in vivo, Klf13-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 Klf13−/− thymocytes was due to decreased apoptosis. Microarray analysis suggests that protection from apoptosis-inducing stimuli in Klf13−/− thymocytes is due in part to increased expression of BCL-XL, 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-XL promoter and results in decreased Bcl-XL promoter activity, making KLF13 a negative regulator of BCL-XL.