The mitochondrial protein Bak is pivotal for gliotoxin-induced apoptosis and a critical host factor of Aspergillus fumigatus virulence in mice

Abstract

Aspergillus fumigatus infections cause high levels of morbidity and mortality in immunocompromised patients. Gliotoxin (GT), a secondary metabolite, is cytotoxic for mammalian cells, but the molecular basis and biological relevance of this toxicity remain speculative. We show that GT induces apoptotic cell death by activating the proapoptotic Bcl-2 family member Bak, but not Bax, to elicit the generation of reactive oxygen species, the mitochondrial release of apoptogenic factors, and caspase-3 activation. Activation of Bak by GT is direct, as GT triggers in vitro a dose-dependent release of cytochrome c from purified mitochondria isolated from wild-type and Bax- but not Bak-deficient cells. Resistance to A. fumigatus of mice lacking Bak compared to wild-type mice demonstrates the in vivo relevance of this GT-induced apoptotic pathway involving Bak and suggests a correlation between GT production and virulence. The elucidation of the molecular basis opens new strategies for the development of therapeutic regimens to combat A. fumigatus and related fungal infections.

A Bim-activating mould

“…11 Geissler et al 4 now show that gliotoxin-induced apoptosis to a substantial degree depends on the presence of Bim. They also confirm their earlier results 12 that gliotoxin requires Bak for full activity, whereas the contribution of Bax is only minor. Importantly, this recent work identifies two additional JNK-phosphorylation sites in Bim and demonstrates that all three sites have to be mutated to prevent gliotoxin-induced apoptosis.…”

Endogenous Bak inhibitors Mcl-1 and Bcl-xL: differential impact on TRAIL resistance in Bax-deficient carcinoma

“…cells, induction of cell death by TRAIL is mediated specifically via an apparently Bak-independent pathway that relies in turn entirely on Bax. Evidence for a differential role of Bak versus Bax in cell death regulation also comes from analyses on BH3-only proteins or bacterial toxins (Cartron et al, 2003b;Gillissen et al, 2003Gillissen et al, , 2007Lindenboim et al, 2005;Pardo et al, 2006). Interestingly, recent studies have shown involvement of Mcl-1, an endogenous Bak inhibitor, in the regulation of TRAIL-induced apoptosis (Henson et al, 2003;Taniai et al, 2004;Wirth et al, 2005;Han et al, 2006;Meng et al, 2007).…”

Granzyme B-induced cell death exerted by ex vivo CTL: discriminating requirements for cell death and some of its signs

“…40 Briefly, MEFs were fixed in 4% PFA, permeabilized with 0.1% saponin in PBS/5% FCS and incubated with polyclonal rabbit a-Bak (NT; Upstate Biotechnology), polyclonal rabbit a-Bax (NT; Upstate Biotechnology) or purified rabbit IgG (control). After washing (2 Â ) with 0.1% saponin in PBS, cells were incubated with a-rabbit-Alexa 488 antibody (Invitrogen) in 0.1% saponin/PBS/5% FCS, washed twice in 0.1% saponin/PBS, resuspended in 1% PFA/PBS and analyzed by FACS.…”