3B). Therefore, there were no changes in the expression of Bcl2
family members that could provide a simple explanation for the reduced fitness of IL-7R− F5 T cells. Surprisingly, few Bcl2 family members were differentially expressed between IL-7R- and IL-7R+ F5 T cells. However, it was possible that IL-7 signalling in vivo was regulating survival by influencing abundance of these key apoptosis regulators at a post translational level, for instance by influencing protein stability or turnover. We therefore assessed by Western blot the levels of anti- and pro-apoptotic proteins in cell lysates from samples of IL-7R− and IL-7R+ F5 Dabrafenib in vitro T cells. As data in Fig. 6 show, abundance of Bcl2, Bcl-xL, Mcl1, Bad and Puma were similar between IL-7R– and IL-7R+ F5 T cells, consistent with prior transcript analysis (Supporting Information Fig. 3A), and Torin 1 FACS analysis in the case of Bcl2 (Fig. 3). Previous studies of cell lines have shown that IL-7 can promote cell survival by inactivating Bad through its Akt/PKB-dependent phosphorylation 31. However, detailed analysis of F5 transgenic mice that over-express Bad, consequently inducing thymocyte apoptosis 32 (Supporting Information Fig. 4A), revealed no evidence of defects in naïve T-cell survival in vitro (Supporting Information Fig. 4B) or in vivo (Supporting Information
Fig. S4C–S4E) and furthermore phosphorylation of Bad, and thereby its inactivation, is even increased in IL-7R– F5 T cells (Supporting Information Fig. 4F). Examining Bid and Bim-L levels revealed small but significant reductions in protein abundance of both in IL-7R– F5 T cells, which in the case of Bid, mirrored differences observed transcriptionally (Supporting Information Fig. 3B). Furthermore, the active cleaved form of Bid, tBid, was not detected in either IL-7R+ or IL-7R– F5 T cells. Thus, intriguingly, the only detected changes in abundance or activation of anti-apoptotic and BH3-only molecules in IL-7R– F5 T cells would rather be expected to inhibit their apoptosis. Finally, we wished to examine whether there was any evidence
that mitochondrial homeostasis was perturbed in the absence of IL-7 signalling in T cells. We therefore examined mitochondrial integrity of IL-7R– Carbohydrate F5 T cells using the cationic dyes mitotracker red and TMRE that are actively taken up by mitochondria and whose retention is dependent on the integrity of the mitochondrial membrane. While total mitochondrial mass was similar between IL-7R– and IL-7R+ F5 T cells (Fig. 7A), we found that both mitotracker red (Fig. 7B) and TMRE staining (Fig. 7C) of IL-7R– F5 T cells was reduced as compared with control IL-7R+ F5 T cells, suggesting that the integrity of mitochondria in these cells is compromised as compared with control F5 T cells. Such a finding is consistent with the rapid induction of caspase activity and apoptosis observed in IL-7R– F5 T cells (Fig. 2).