Helicobacter pylori targets mitochondrial import and components of mitochondrial DNA replication machinery through an alternative VacA-dependent and a VacA-independent mechanisms.

in Scientific reports (2017), 7(1), 15901

Targeting mitochondria is a powerful strategy for pathogens to subvert cell physiology and establish infection. Helicobacter pylori is a bacterial pathogen associated with gastric cancer development that ... [more ▼]

Targeting mitochondria is a powerful strategy for pathogens to subvert cell physiology and establish infection. Helicobacter pylori is a bacterial pathogen associated with gastric cancer development that is known to target mitochondria directly and exclusively through its pro-apoptotic and vacuolating cytotoxin VacA. By in vitro infection of gastric epithelial cells with wild-type and VacA-deficient H. pylori strains, treatment of cells with purified VacA proteins and infection of a mouse model, we show that H. pylori deregulates mitochondria by two novel mechanisms, both rather associated with host cell survival. First, early upon infection VacA induces transient increase of mitochondrial translocases and a dramatic accumulation of the mitochondrial DNA replication and maintenance factors POLG and TFAM. These events occur when VacA is not detected intracellularly, therefore do not require the direct interaction of the cytotoxin with the organelle, and are independent of the toxin vacuolating activity. In vivo, these alterations coincide with the evolution of gastric lesions towards severity. Second, H. pylori also induces VacA-independent alteration of mitochondrial replication and import components, suggesting the involvement of additional H. pylori activities in mitochondria-mediated effects. These data unveil two novel mitochondrial effectors in H. pylori-host interaction with links on gastric pathogenesis. [less ▲]

PINK1 and BECN1 relocalize at mitochondria-associated membranes during mitophagy and promote ER-mitochondria tethering and autophagosome formation.

in Autophagy (2017), 13(4), 654-669

Mitophagy is a highly specialized process to remove dysfunctional or superfluous mitochondria through the macroautophagy/autophagy pathway, aimed at protecting cells from the damage of disordered ... [more ▼]

Mitophagy is a highly specialized process to remove dysfunctional or superfluous mitochondria through the macroautophagy/autophagy pathway, aimed at protecting cells from the damage of disordered mitochondrial metabolism and apoptosis induction. PINK1, a neuroprotective protein mutated in autosomal recessive Parkinson disease, has been implicated in the activation of mitophagy by selectively accumulating on depolarized mitochondria, and promoting PARK2/Parkin translocation to them. While these steps have been characterized in depth, less is known about the process and site of autophagosome formation upon mitophagic stimuli. A previous study reported that, in starvation-induced autophagy, the proautophagic protein BECN1/Beclin1 (which we previously showed to interact with PINK1) relocalizes at specific regions of contact between the endoplasmic reticulum (ER) and mitochondria called mitochondria-associated membranes (MAM), from which the autophagosome originates. Here we show that, following mitophagic stimuli, autophagosomes also form at MAM; moreover, endogenous PINK1 and BECN1 were both found to relocalize at MAM, where they promoted the enhancement of ER-mitochondria contact sites and the formation of omegasomes, that represent autophagosome precursors. PARK2 was also enhanced at MAM following mitophagy induction. However, PINK1 silencing impaired BECN1 enrichment at MAM independently of PARK2, suggesting a novel role for PINK1 in regulating mitophagy. MAM have been recently implicated in many key cellular events. In this light, the observed prevalent localization of PINK1 at MAM may well explain other neuroprotective activities of this protein, such as modulation of mitochondrial calcium levels, mitochondrial dynamics, and apoptosis. [less ▲]

PINK1 protects against cell death induced by mitochondrial depolarization, by phosphorylating Bcl-xL and impairing its pro-apoptotic cleavage.

in Cell death and differentiation (2013), 20(7), 920-30

Mutations in the PINK1 gene are a frequent cause of autosomal recessive Parkinson's disease (PD). PINK1 encodes a mitochondrial kinase with neuroprotective activity, implicated in maintaining ... [more ▼]

Mutations in the PINK1 gene are a frequent cause of autosomal recessive Parkinson's disease (PD). PINK1 encodes a mitochondrial kinase with neuroprotective activity, implicated in maintaining mitochondrial homeostasis and function. In concurrence with Parkin, PINK1 regulates mitochondrial trafficking and degradation of damaged mitochondria through mitophagy. Moreover, PINK1 can activate autophagy by interacting with the pro-autophagic protein Beclin-1. Here, we report that, upon mitochondrial depolarization, PINK1 interacts with and phosphorylates Bcl-xL, an anti-apoptotic protein also known to inhibit autophagy through its binding to Beclin-1. PINK1-Bcl-xL interaction does not interfere either with Beclin-1 release from Bcl-xL or the mitophagy pathway; rather it protects against cell death by hindering the pro-apoptotic cleavage of Bcl-xL. Our data provide a functional link between PINK1, Bcl-xL and apoptosis, suggesting a novel mechanism through which PINK1 regulates cell survival. This pathway could be relevant for the pathogenesis of PD as well as other diseases including cancer. [less ▲]

Molecular pathways in sporadic PD.

in Parkinsonism & related disorders (2012), 18 Suppl 1

Over the last decade, several autosomal dominant and recessive genes causative of Parkinson's disease (PD) have been identified. The functional studies on their protein products and the pathogenetic ... [more ▼]

Over the last decade, several autosomal dominant and recessive genes causative of Parkinson's disease (PD) have been identified. The functional studies on their protein products and the pathogenetic effect related to their mutations have greatly contributed to understand the many cellular pathways leading to neurodegeneration, that include oxidative stress damage, mitochondrial dysfunction, misfolded protein stress and impairment of cellular clearance systems, namely the ubiquitin-proteasome system (UPS) and the autophagy pathway. Although mendelian genes are responsible only for a small subset of PD patients, it is expected that the same pathogenetic mechanisms could play a relevant role also in the more frequent sporadic PD, that is currently recognized as a multifactorial disorder. In this model, different genetic and environmental factors, either playing a protective or a susceptibility role, variably interact to reach a threshold of disease over which PD will become clinically manifest. As an example, mutations or multiplication of the alpha-synuclein gene cause autosomal dominant PD, while common genetic variants at the same locus have been consistently associated to the risk of developing PD by genome-wide association studies. These findings are opening novel interesting perspectives to identify critical molecular pathways leading to neurodegeneration. [less ▲]

Epstein-Barr virus lytic cycle activation alters proteasome subunit expression in Burkitt's lymphoma cells.

in Biological chemistry (2010), 391(9), 1041-6

We have shown that Epstein-Barr virus (EBV) lytic cycle activation in Burkitt's lymphoma (BL) cells down-regulates chymotrypsin- and caspase-like activities of the proteasome. The aim of the present study ... [more ▼]

We have shown that Epstein-Barr virus (EBV) lytic cycle activation in Burkitt's lymphoma (BL) cells down-regulates chymotrypsin- and caspase-like activities of the proteasome. The aim of the present study was to evaluate whether EBV activation might also affect proteasome subunit composition. Our results indicate that, independently of the latency program established in the host cells, induction of the EBV lytic cycle reduces the expression of the proteasomal components β5, β1 and β2i, whereas it increases that of β2, β1i, PA28α and PA28β. The modulation of the composition and enzymatic activities of the proteolytic complex are indicative of a less efficient generation of viral immunoepitopes. [less ▲]

Inhibition of p38 MAP kinase pathway induces apoptosis and prevents Epstein Barr virus reactivation in Raji cells exposed to lytic cycle inducing compounds.

in Molecular cancer (2009), 8

BACKGROUND: EBV lytic cycle activators, such as phorbol esters, anti-immunoglobulin, transforming growth factor beta (TGFbeta), sodium butyrate, induce apoptosis in EBV-negative but not in EBV-positive ... [more ▼]

BACKGROUND: EBV lytic cycle activators, such as phorbol esters, anti-immunoglobulin, transforming growth factor beta (TGFbeta), sodium butyrate, induce apoptosis in EBV-negative but not in EBV-positive Burkitt's lymphoma (BL) cells. To investigate the molecular mechanisms allowing EBV-infected cells to be protected, we examined the expression of viral and cellular antiapoptotic proteins as well as the activation of signal transduction pathways in BL-derived Raji cells exposed to lytic cycle inducing agents. RESULTS: Our data show that, following EBV activation, the latent membrane protein 1 (LMP1) and the cellular anti-apoptotic proteins MCL-1 and BCL-2 were quickly up-regulated and that Raji cells remained viable even when exposed simultaneously to P(BU)(2), sodium butyrate and TGFbeta. We report here that inhibition of p38 pathway, during EBV activation, led to a three fold increment of apoptosis and largely prevented lytic gene expression. CONCLUSION: These findings indicate that, during the switch from the latent to the lytic phase of EBV infection, p38 MAPK phosphorylation plays a key role both for protecting the host cells from apoptosis as well as for inducing viral reactivation. Because Raji cells are defective for late antigens expression, we hypothesize that the increment of LMP1 gene expression in the early phases of EBV lytic cycle might contribute to the survival of the EBV-positive cells. [less ▲]