Citations

Key Points BCL2 mutations in FL correlate with activation-induced cytidine deaminase expression and frequently alter the amino acid sequence of the protein. Mutations in the BCL2 coding sequence at diagnosis are associated with shortened time to transformation and earlier death due to lymphoma.

Previous studies have shown that human immunodeficiency virus (HIV) protease cleaves procaspase 8 to a fragment, termed Casp8p41, that lacks caspase activity but nonetheless contributes to T cell apoptosis. Herein, we show that Casp8p41 contains a domain that interacts with the BH3-binding groove of pro-apoptotic Bak to cause Bak oligomerization, Bak-mediated membrane permeabilization, and cell death. Levels of active Bak are higher in HIV-infected T cells that express Casp8p41. Conversely, targeted mutations in the Bak-interacting domain diminish Bak binding and Casp8p41-mediated cell death. Similar mutations in procaspase 8 impair the ability of HIV to kill infected T cells. These observations support a novel paradigm in which HIV converts a normal cellular constituent into a direct activator that functions like a BH3-only protein.

Abstract Bcl-2 is phosphorylated on Ser70 after treatment of cells with spindle poisons. On the basis of effects observed in cells overexpressing Bcl-2 S70E or S70A mutants, various studies have concluded that Ser70 phosphorylation either enhances or diminishes Bcl-2 function. In the present study, the ability of phosphorylated Bcl-2, as well as the S70E and S70A mutants, to bind and neutralize proapoptotic Bcl-2 family members under cell-free conditions and in intact cells was examined in an attempt to resolve this controversy. Surface plasmon resonance indicated that phosphorylated Bcl-2, Bcl-2 S70E, and Bcl-2 S70A exhibit enhanced binding to Bim and Bak compared with unmodified Bcl-2. This enhanced binding reflected a readily detectable conformation change in the loop domain of Bcl-2. Furthermore, Bcl-2 S70E and S70A bound more Bak and Bim than wild-type Bcl-2 in pull-downs and afforded greater protection against several chemotherapeutic agents. Importantly, binding of endogenous Bcl-2 to Bim also increased during mitosis, when Bcl-2 is endogenously phosphorylated, and disruption of this mitotic Bcl-2/Bim binding with navitoclax or ABT-199, like Bcl-2 downregulation, enhanced the cytotoxicity of paclitaxel. Collectively, these results provide not only a mechanistic basis for the enhanced antiapoptotic activity of phosphorylated Bcl-2, but also an explanation for the ability of BH3 mimetics to enhance taxane sensitivity. Cancer Res; 73(23); 6998–7008. ©2013 AACR.