Caspase-1 activity affects AIM2 speck formation/stability through a negative feedback loop.

The inflammasome is an innate immune signaling platform leading to caspase-1 activation, maturation of pro-inflammatory cytokines and cell death. Recognition of DNA within the host cytosol induces the formation of a large complex composed of the AIM2 receptor, the ASC adaptor and the caspase-1 effector. Francisella tularensis, the agent of tularemia, replicates within the host cytosol. The macrophage cytosolic surveillance system detects Francisella through the AIM2 inflammasome. Upon Francisella novicida infection, we observed a faster kinetics of AIM2 speck formation in ASC(KO) and Casp1(KO) as compared to WT macrophages. This observation was validated by a biochemical approach thus demonstrating for the first time the existence of a negative feedback loop controlled by ASC/caspase-1 that regulates AIM2 complex formation/stability. This regulatory mechanism acted before pyroptosis and required caspase-1 catalytic activity. Our data suggest that sublytic caspase-1 activity could delay the formation of stable AIM2 speck, an inflammasome complex associated with cell death.

AIM2/ASC triggers caspase-8-dependent apoptosis in Francisella-infected caspase-1-deficient macrophages.

The inflammasome is a signalling platform leading to caspase-1 activation. Caspase-1 causes pyroptosis, a necrotic-like cell death. AIM2 is an inflammasome sensor for cytosolic DNA. The adaptor molecule ASC mediates AIM2-dependent caspase-1 activation. To date, no function besides caspase-1 activation has been ascribed to the AIM2/ASC complex. Here, by comparing the effect of gene inactivation at different levels of the inflammasome pathway, we uncovered a novel cell death pathway activated in an AIM2/ASC-dependent manner. Francisella tularensis, the agent of tularaemia, triggers AIM2/ASC-dependent caspase-3-mediated apoptosis in caspase-1-deficient macrophages. We further show that AIM2 engagement leads to ASC-dependent, caspase-1-independent activation of caspase-8 and caspase-9 and that caspase-1-independent death is reverted upon caspase-8 inhibition. Caspase-8 interacts with ASC and active caspase-8 specifically colocalizes with the AIM2/ASC speck thus identifying the AIM2/ASC complex as a novel caspase-8 activation platform. Furthermore, we demonstrate that caspase-1-independent apoptosis requires the activation of caspase-9 and of the intrinsic pathway in a typical type II cell manner. Finally, we identify the AIM2/ASC-dependent caspase-1-independent pathway as an innate immune mechanism able to restrict bacterial replication in vitro and control IFN-γ levels in vivo in Casp1(KO) mice. This work underscores the crosstalk between inflammasome components and the apoptotic machinery and highlights the versatility of the pathway, which can switch from pyroptosis to apoptosis.

The procyanidin-mediated induction of apoptosis and cell-cycle arrest in esophageal adenocarcinoma cells is not dependent on p21(Cip1/WAF1).

Previous studies have shown that the proanthocyanidin-mediated induction of apoptosis and arrest of the cell cycle in cancer cells was associated with up-regulation of p21(Cip1/WAF1) (p21), suggesting that p21 may be the molecular mediator of the observed effects. Here we show that procyanidins induce a rapid and sustained arrest of the cell cycle, and increase apoptosis, concomitant with an increase in p21 expression. However, blocking the PA-induced up-regulation of p21 expression with siRNA did not alter PA-mediated changes in apoptosis and cell cycle, demonstrating that p21 is not responsible for the PA-induced effects.

The molecular mechanisms responsible for resistance to ET-743 (Trabectidin; Yondelis) in the Ewing's sarcoma cell line, TC-71.

Identification of new active agents against sarcoma is considered an important challenge in medical oncology. ET-743 (Trabectidin; Yondelis) has recently emerged as the first active drug developed against sarcoma in the last two decades, with promising results especially against soft-tissue sarcoma and Ewing's sarcoma (ES). In this study, we analyzed the molecular mechanisms responsible for resistance to ET-743 in ES cells. Three resistant cell variants (TC/ET 3 nM, TC/ET 6 nM and TC/ET 12 nM) were obtained, showing 28-, 47- and 102-fold increase in ET-743 resistance. Cross-resistance to other drugs was analyzed. Comparative genomic hybridization and cDNA microarray technology were employed to characterize and compare the gene expression profile of two TC/ET variants with the parental cell line. TC/ET cells show a conventional multidrug resistance phenotype and P-glycoprotein overexpression was found to significantly contribute to ET-743 resistance. However, functional studies with the cyclosporine analogue, PSC-833, indicate that other mechanisms are involved in resistance to ET-743. The gene expression profile of TC/ET cells indicated, among up-regulated genes, an increase in expression of insulin-like growth factor receptor-I (IGF-IR) and one of its major intracellular mediators, insulin receptor substrate-1. Functional studies using a neutralizing antibody anti-IGF-IR confirmed involvement of this signaling pathway in resistance to ET-743. Simultaneous blockage of both P-glycoprotein and IGF-IR completely restored sensitivity to ET-743 in ES cells. Overall, these findings provide impetus for future studies testing the therapeutic value of new specific inhibitors of P-glycoprotein and IGF-IR, which could represent a concrete therapeutic option for ES patients refractory to conventional agents.

A mitochondrial ATPase 6 mutation is associated with Leigh syndrome in a family and affects proton flow and adenosine triphosphate output when modeled in Escherichia coli.

A multidisciplinary strategy was used to identify the molecular defect in a family with Leigh syndrome (LS). The propositus presented severe developmental delay, an ataxic-spastic gait and seizures. She died at 3.5 y of age from cardiorespiratory arrest. Postmortem examination disclosed pathological features typical of LS. A 12-y-old sister is affected with the same disease. Respiratory chain enzyme complex activities in skeletal muscle biopsy were normal. Adenosine triphosphate (ATP) synthesis during oxidative phosphorylation in skin fibroblasts mitochondria showed a severely hampered ATP production. Mitochondrial DNA sequencing revealed a new mutation in the ATPase 6 gene (T9176G). Site-directed mutagenesis in Escherichia coli strains was used to measure H+ pumping and ATP synthesis. Results were comparable to findings obtained in human cells. These data corroborate the use of E. coli strains as a feasible "animal" model for functional studies in pathogenic mutations of the ATPase 6 gene.

Two novel mutations of the human delta7-sterol reductase (DHCR7) gene in children with Smith-Lemli-Opitz syndrome.

We analyzed seven unrelated children with the Smith-Lemli-Opitz syndrome (SLOS) for mutations in the delta7-sterol reductase gene by using SSCP and direct sequencing. We identified two novel mutations (V330M and R363C) in the DHCR7 gene. Reported mutations found in this study were T93M (3/14 alleles), E448K (2/14), and W151X, G244R, P329L, and R446Q (each found in one allele). The so-called common IVS8-1 G --> C was found in three alleles, confirming its relative rarity among Italian SLOS families. By using a scoring system, clinical severity did not seem to correlate with 7DHC levels and type of mutation. Expanding the spectrum of mutations in SLOS, our study does not support direct genotype-phenotype correlation.