µ-Calpain Conversion of Antiapoptotic Bfl-1 (BCL2A1) into a Prodeath Factor Reveals Two Distinct alpha-Helices Inducing Mitochondria-Mediated Apoptosis

Anti-apoptotic Bfl-1 and pro-apoptotic Bax, two members of the Bcl-2 family sharing a similar structural fold, are classically viewed as antagonist regulators of apoptosis. However, both proteins were reported to be death inducers following cleavage by the cysteine protease µ-calpain. Here we demonstrate that calpain-mediated cleavage of full-length Bfl-1 induces the release of C-terminal membrane active α-helices that are responsible for its conversion into a pro-apoptotic factor. A careful comparison of the different membrane-active regions present in the Bfl-1 truncated fragments with homologous domains of Bax show that helix α5, but not α6, of Bfl-1 induces cell death and cytochrome c release from purified mitochondria through a Bax/Bak-dependent mechanism. In contrast, both helices α5 and α6 of Bax permeabilize mitochondria regardless of the presence of Bax or Bak. Moreover, we provide evidence that the α9 helix of Bfl-1 promotes cytochrome c release and apoptosis through a unique membrane-destabilizing action whereas Bax-α9 does not display such activities. Hence, despite a common 3D-structure, C-terminal toxic domains present on Bfl-1 and Bax function in a dissimilar manner to permeabilize mitochondria and induce apoptosis. These findings provide insights for designing therapeutic approaches that could exploit the cleavage of endogenous Bcl-2 family proteins or the use of Bfl-1/Bax-derived peptides to promote tumor cell clearance

TLR2 engagement on CD8 T cells enables generation of functional memory cells in response to a suboptimal TCR signal.

International audienceTLR are involved in the detection of microbial infection as well as endogenous ligands that signal tissue and cell damage in mammals. This recognition plays an essential role in innate immune response and the initiation of adaptive immune response. We have previously shown that murine CD8 T cells express TLR2, and that costimulation of Ag-activated CD8 T cells with TLR2 ligands enhances their proliferation, survival, and effector functions. We also demonstrated that TLR2 engagement on CD8 T cells significantly reduces their need for costimulatory signals delivered by APC. We show in this study that TLR2 engagement on CD8 T cells lowers the Ag concentration required for optimal activation, and converts a partial activation into a productive process leading to a significant expansion of cells. Using altered peptide ligands, we demonstrate that TLR2 engagement increases CD8 T cell activation and enables the generation of functional memory cells in response to a low TCR signal. This increased activation is associated with an augmented activation of the PI3K. Taken together, our results demonstrate that TLR2 engagement on CD8 T cells lowers their activation threshold for TCR signal strength and enables efficient memory cell generation in response to a weak TCR signal

Tumor necrosis factor-α up-regulates Bcl-2 expression and decreases calcium-dependent apoptosis in human B cell lines

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Synthesis and biological activities of new di- and trimeric quinoline derivatives

International audienceThe synthesis of non-peptidic helix mimetics based on a trimeric quinoline scaffold is described. The ability of these new compounds, as well as their synthetic dimeric intermediates, to bind to various members of the Bcl-2 protein anti-apoptotic group is also evaluated. The most interesting derivative of this new series (compound A) inhibited Bcl-xL/Bak, Bcl-xL/Bax and Bcl-xL/Bid interactions with IC50 values around 25 μM

TLR2 engagement on memory CD8 + T cells improves their cytokine-mediated proliferation and IFN-γ secretion in the absence of Ag

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The Bfl-1-α9 peptide induces mitochondrial permeabilization through a membrane-destabilizing mechanism.

<p>Bfl-1-α9 peptide was incubated for the indicated times with mitochondria at lower concentrations (0.5 µM and 2.5 µM, top panels) and previously used in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038620#pone-0038620-g004" target="_blank">figure 4</a> (10 µM and 25 µM, bottom panels). The release of cytochrome c and the expression of MitoHsp70 were monitored as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038620#pone-0038620-g004" target="_blank">figure 4</a>, combined with the detection of the external membrane associated protein hexokinase 1 (HK1) and the matrix-contained protein MnSOD.</p