Poster Presentation 25th Lorne Cancer Conference 2013

Mutation of Foxo binding elements in the bim promoter does not abrogate Bim dependent killing (#205)

Marco J Herold 1 , Mathias Lang 1 , Leona Rohrbeck 1 , Lin Tai 1 , Philippe Bouillet 1 , Thomas Kaufmann 2 , Andreas Strasser 1
  1. Walter and Eliza Hall Institute of Medical Research, Melbourne, Vic, Australia
  2. Institute of Pharmacology, University of Bern, Bern, Switzerland

The pro-apoptotic Bcl-2 family member Bim is critical for hematopoietic cell homeostasis, deletion of auto-reactive lymphocytes, the shut-down of  immune responses and tumour suppression. It has been reported that the upregulation of bim in response to certain apoptotic stimuli, particularly cytokine deprivation, is dependent on the forkhead transcription factor family member Foxo3a. To investigate this within a physiological context, we generated mice in which all potential Foxo binding sites in the bim promoter are mutated (BimΔfoxo/Δfoxo). Interestingly, we detected no changes in the composition or frequency of hematopoietic cells in the bone marrow, thymus and spleen between BimΔfoxo/Δfoxo mutant mice and wild-type littermates. Furthermore, we observed no differences in the apoptotic response of thymocytes from wildtype or BimΔfoxo/Δfoxomice when they were either cultured in simple medium (growth factor deprivation) or treated with dexamethasone or PMA. Surprisingly, ConA+IL-2 generated T cell blasts from BimΔfoxo/Δfoxo or wildtype mice died at comparable rates in response to IL-2 deprivation, whereas Bim deficient (Bim-/-)T cell blasts were highly resistant. Contrary to the acceleration in lymphoma development in Eµ-Myc transgenic mice caused by loss of one or both alleles of Bim, we did not observe any change in tumour onset in Eµ-Myc;BimΔfoxo/Δfoxo mice. Taken together these data suggest that transcriptional upregulation of Bim by direct binding of the Foxo family of transcription factors to bim promoter elements is not critical for hematopoietic cell homeostasis, cytokine deprivation induced apoptosis or tumour suppression and therefore the regulation of Bim needs to be further investigated.