How most apoptotic stimuli trigger mitochondrial dysfunction remains to be resolved. We screened the entire Bcl-2 network for its involvement in DNA damage-induced apoptosis in HeLa cells. Although the anti-apoptotic member Bcl-xL served as a major suppressor, apoptosis initiated only when both Mcl-1 and Bcl-xL were eliminated. The pro-apoptotic members Bak, Bad, Bim, and Noxa were required for apoptosis induced by DNA damaging agents camptothecin and UV. We, therefore, used a His-tagged Bcl-xL expression system to capture the relevant BH3-only proteins that bind to Bcl-xL in response to DNA damage. Surprisingly, unlike Bad and Bim, which bound Bcl-xL constitutively, Noxa became "Mcl-1-free" and interacted with Bcl-xL after DNA damage but not after death receptor engagement. Similar observations were also made in A431 cells. Importantly, this induced interaction caused cytochrome c release and apoptosis and was directly inhibited by Mcl-1, a protein eliminated or inactivated after DNA damage. These results suggest that the loss/ inactivation of Mcl-1 in conjunction with an induced Noxa/ Bcl-xL interaction may serve as a trigger for mitochondrial dysfunction during DNA damage-induced apoptosis.

No abstract

The mechanism of Bax/Bak-dependent mitochondrial outer membrane permeabilization (MOMP), a central apoptotic event primarily controlled by the Bcl-2 family proteins, remains not well understood. Here, we express active Bax/Bak in bacteria, the putative origin of mitochondria, and examine their functional similarities to the l bacteriophage (l) holin. As critical effectors for bacterial lysis, holin oligomers form membrane lesions, through which endolysin, a muralytic enzyme, escapes the cytoplasm to attack the cell wall at the end of the infection cycle. We found that active Bax/Bak, but not any other Bcl-2 family protein, displays holin behavior, causing bacterial lysis by releasing endolysin in an oligomerization-dependent manner. Strikingly, replacing the holin gene with active alleles of Bax/Bak results in plaque-forming phages. Furthermore, we provide evidence that active Bax produces large membrane holes, the size of which is controlled by structural elements of Bax. Notably, lysis by active Bax is inhibited by Bcl-xL, and the lysis activity of the wild-type Bax is stimulated by a BH3-only protein.Together, these results mechanistically link MOMP to holin-mediated hole formation in the bacterial plasma membrane.

In an effort to expand human islets and enhance allogeneic islet transplant for the treatment of type 1 diabetes, identifying signaling pathways that stimulate human β-cell proliferation is paramount. TGF-β superfamily members, in particular activin-A, are likely involved in islet development and may contribute to β-cell proliferation. Nodal, another TGF-β member, is present in both embryonic and adult rodent islets. Nodal, along with its coreceptor, Cripto, are pro-proliferative factors in certain cell types. Although Nodal stimulates apoptosis of rat insulinoma cells (INS-1), Nodal and Cripto signaling have not been studied in the context of human islets. The current study investigated the effects of Nodal and Cripto on human β-cell proliferation, differentiation, and viability. In the human pancreas and isolated human islets, we observed Nodal mRNA and protein expression, with protein expression observed in β and α-cells. Cripto expression was absent from human islets. Furthermore, in cultured human islets, exogenous Nodal stimulated modest β-cell proliferation and inhibited α-cell proliferation with no effect on cellular viability, apoptosis, or differentiation. Nodal stimulated the phosphorylation of mothers against decapentaplegic (SMAD)-2, with no effect on AKT or MAPK signaling, suggesting phosphorylated SMAD signaling was involved in β-cell proliferation. Cripto had no effect on human islet cell proliferation, differentiation, or viability. In conclusion, Nodal stimulates human β-cell proliferation while maintaining cellular viability. Nodal signaling warrants further exploration to better understand and enhance human β-cell proliferative capacity.

Type II diabetes is an inflammatory disease marked by chronic immune activation. Our goal is to describe the fundamental distinctions in the immune system of the db/db mouse. Serum was collected for a 58-factor immunoassay. Splenic leukocytes were isolated for six panels of flow cytometry to examine immune subsets and activation states. Db/db mice exhibit higher levels of proinflammatory factors such as C-reactive protein, granulocyte chemotactic protein-2, monocyte chemotactic protein-1, macrophage inflammatory protein-2, IL1α, and T-RANTES and lower levels in regulatory IL10. Flow cytometry data revealed upregulation of the adhesion molecule CD11b on neutrophils, monocytes and macrophages. Macrophages also expressed increased levels of costimulatory molecule CD80. Inflammatory DC were increased while regulatory DC were decreased. Pre-germinal center B cells were decreased. Plasma and memory B cells were increased with an increase in CD22 maturity marker. FoxP3+ T regs were decreased with a reciprocal increase in CD127. Total CD8 T cells were increased with greater naive populations. Unactivated NK cells were increased, and all NK populations had decreased Ly49H and KLRG1. Above results were significant with p<0.05. Baseline immune activation in db/db mice is marked by increased circulating proinflammatory factors, decreased circulating regulatory factors, increased activation of innate and humoral immunity, and suppressed regulatory and cellular immunity.