The protein Bid is a participant in the pathway that leads to cell death (apoptosis), mediating the release of cytochrome c from mitochondria in response to signals from 'death' receptors known as TNFR1/Fas on the cell surface. It is a member of the proapoptotic Bcd-2 family and is activated as a result of its cleavage by caspase 8, one of a family of proteolytic cell-death proteins. To investigate the role of Bid in vivo, we have generated mice deficient for Bid. We find that when these mice are injected with an antibody directed against Fas, they nearly all survive, whereas wild-type mice die from hepatocellular apoptosis and haemorrhagic necrosis. About half of the Bid-deficient animals had no apparent liver injury and showed no evidence of activation of the effector caspases 3 and 7, although the initiator caspase 8 had been activated. Other Bid-deficient mice survived with only moderate damage: all three caspases (8 and 37) were activated but their cell nuclei were intact and no mitochondrial cytochrome c was released. We also investigated the effects of Bid deficiency in cultured cells treated with anti-Fas antibody (hepatocytes and thymocytes) or with TNFalpha. (fibroblasts). In these Bid-/- cells, mitochondrial dysfunction was delayed, cytochrome c was not released, effector caspase activity was reduced and the cleavage of apoptosis substrates was altered. This loss-of-function model indicates that Bid is a critical substrate in vivo for signalling by death-receptor agonists, which mediates a mitochondrial amplification loop that is essential for the apoptosis of selected cells.

Gasdermin-D (GSDMD) in inflammasome-activated macrophages is cleaved by caspase-1 to generate N-GSDMD fragments. N-GSDMD then oligomerizes in the plasma membrane (PM) to form pores that increase membrane permeability, leading to pyroptosis and IL-1β release. In contrast, we report that although N-GSDMD is required for IL-1β secretion in NLRP3activated human and murine neutrophils, N-GSDMD does not localize to the PM or increase PM permeability or pyroptosis. Instead, biochemical and microscopy studies reveal that N-GSDMD in neutrophils predominantly associates with azurophilic granules and LC3 + autophagosomes. N-GSDMD trafficking to azurophilic granules causes leakage of neutrophil elastase into the cytosol, resulting in secondary cleavage of GSDMD to an alternatively cleaved N-GSDMD product. Genetic analyses using ATG7-deficient cells indicate that neutrophils secrete IL-1β via an autophagy-dependent mechanism. These findings reveal fundamental differences in GSDMD trafficking between neutrophils and macrophages that underlie neutrophil-specific functions during inflammasome activation.

Abnormal mitochondrial fission participates in the pathogenesis of many diseases. Long non-coding RNAs (lncRNAs) are emerging as new players in gene regulation, but how lncRNAs operate in the regulation of mitochondrial network is unclear. Here we report that a lncRNA, named cardiac apoptosis-related lncRNA (CARL), can suppress mitochondrial fission and apoptosis by targeting miR-539 and PHB2. The results show that PHB2 is able to inhibit mitochondrial fission and apoptosis. miR-539 is responsible for the dysfunction of PHB2 and regulates mitochondrial fission and apoptosis by targeting PHB2. Further, we show that CARL can act as an endogenous miR-539 sponge that regulates PHB2 expression, mitochondrial fission and apoptosis. Our present study reveals a model of mitochondrial fission regulation that is composed of CARL, miR-539 and PHB2. Modulation of their levels may provide a new approach for tackling apoptosis and myocardial infarction.

Induction of protein degradation is emerging as a powerful strategy to modulate protein functions and alter cellular signaling pathways. Proteolysis-targeting chimeras (PROTACs) have been used to degrade a range of diverse proteins in vitro and in vivo. Here we present a type of photo-caged PROTACs (pc-PROTACs) to induce degradation activity with light. Photo-removable blocking groups were added to a degrader of Brd4, and the resulting molecule pc-PROTAC1 showed potent degradation activity in live cells only after light irradiation. Furthermore, this molecule efficiently degraded Brd4 and induced expected phenotypic changes in zebrafish. Additionally, this approach was successfully applied to construct pc-PROTAC3 of BTK. Thus, a general strategy to induce protein degradation with light was established to augment the chemists' toolbox to study disease-relevant protein targets. Communication pubs.acs.org/JACS