Volume 396, Issue 12

Resistance to both cytotoxic and targeted therapies is a major problem facing cancer treatment. The mechanisms of resistance to unrelated drugs share many common features, including up-regulation of detoxifying pathways, activation of pro-survival mechanisms, and ineffective induction of cell death. Oncolytic viruses (OVs) are promising biotherapeutics for cancer treatment that specifically replicate in and lyse cancer cells. In addition to direct viral lysis, the anti-tumor effects of OVs are mediated via innate and adaptive immune responses, and several adaptation mechanisms such as autophagy appear to contribute to their anti-tumor properties. Autophagy is a versatile pathway that plays a key role in cancer survival during stressful conditions such as starvation or cytotoxic drug challenges. Autophagy also plays a role in mediating innate and adaptive immune responses by contributing to antigen presentation and cytokine secretion. This role of autophagy in regulation of immune responses can be utilized to design therapeutic combinations using approaches that either stimulate or block autophagy to potentiate therapeutic efficacy of OVs. Additional studies are needed to determine optimal multimodal combination approaches that will facilitate future successful clinical implementation of OV-based therapies.

Lipids serve many distinct functions in cellular homeostasis such as membrane organization, as a platform for membrane function and protein/protein or protein/lipid interaction, energy storage, as well as secondary messengers in signal transduction. Perturbations in lipid homeostasis may result in abnormal cellular function. Alzheimer’s disease (AD) is a neurodegenerative disorder in which the brain represents the primary site of pathology. While there is a plethora of previous work pertaining to AD pathogenesis, the precise mechanism of the disease is still not well-understood. Recent waves of technological advances in the realm of lipidomics have enabled scientists to look at AD pathogenesis from a previously unexplored perspective, and studies have revealed extensive lipid aberrations are implicated in the disease pathology. Herein, we review the critical lipids alternations, which affect amyloid plaque and neurofibrillary tangles formation and accumulation, as well as lipid aberrations related to neuronal and synaptic dysfunction in cells and animal models. We also summarize lipid abnormalities observed in the human cerebrospinal fluid (CSF), as well as other circulating fluids including plasma and serum in association with AD, which could serve as candidate biomarkers to diagnose and monitor the disease.

Mutations of the inositol-5-phosphatase OCRL cause Lowe syndrome and Dent-II disease. Both are rare genetic disorders characterized by renal defects. Lowe syndrome is furthermore characterized by defects of the eye (congenital cataracts) and nervous system (mental disabilities, hypotonia). OCRL has been localised to various endocytic compartments suggesting impairments in the endocytic pathway as possible disease mechanism. Recent evidence strongly supports this view and shows essential roles of OCRL at clathrin coated pits, transport of cargo from endosomes to the trans-Golgi network as well as recycling of receptors from endosomes to the plasma membrane. In particular in vitro and in vivo evidence demonstrates an important role of OCRL in recycling of megalin, a multi-ligand receptor crucial for reabsorption of nutrients in the proximal tubulus, a process severely impaired in Lowe syndrome patients. Thus defects in the endocytic pathway are likely to significantly contribute to the kidney phenotype in Lowe syndrome and Dent-II disease.

Fine tuning of c-MYC expression is critical for its action and is achieved by several regulatory mechanisms. The contribution of c- myc mRNA regulatory sequences on its translational control has been investigated individually. However, putative interactions have not been addressed so far. The effect of these interactions upon the translatability of monocistronic and bicistronic chimaeric mRNAs, carrying combinations of the c- myc mRNA 5′-untranlated region (UTR), 3′-UTR, and coding region instability element (CRD) was investigated on this study. The presence of the 5′-UTR induced an increase in translatability of 50%. The presence of the CRD element, when in frame, reduced translatability by approximately 50%, regardless of the expression levels of the wild type CRD- binding protein (CRD-BP/IMP1). Conversely, overexpression of a mutated CRD-BP/IMP1 (Y396F) further impeded translation of the chimaeric mRNAs carrying its cognate sequences. The presence of the c- myc 3′-UTR increased translatability by approximately 300% affecting both cap and c- myc internal ribosome entry site (IRES) mediated translation. In addition, 3′-UTR rescued the cap mediated translation in the presence of the polyadenylation inhibitor cordycepin. Furthermore, the 3′-UTR rescued cap mediated translation under metabolic stress conditions and this was enhanced in the absence of a long poly (A) tail.

Changes of Leu109 and Arg448 of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) have as yet not been associated with altered fitness. However, in a recent study, we described that the simultaneous substitution of L109 and R448 by methionine leads to an error-producing polymerase phenotype that is not observed for the isolated substitutions. The double mutant increased the error rate of DNA-dependent DNA synthesis 3.1-fold as compared to the wildtype enzyme and showed a mutational spectrum with a fraction of 28% frameshift mutations and 48% transitions. We show here that weaker binding of DNA:DNA primer-templates as indicated by an increased dissociation rate constant ( k off ) could account for the higher frameshift error rate. Furthermore, we were able to explain the prevalence of transition mutations with the finding that HIV-1 RT variant L109M/R448M preferred misincorporation of C opposite A and elongation of C:A mismatches.

Septins are a family of conserved cytoskeletal proteins playing an essential role in cytokinesis and in many other cellular processes in fungi and animals. In budding yeast Saccharomyces cerevisiae , septins form filaments and higher-order structures at the mother-bud neck depending on the particular stage of the cell cycle. Septin structures at the division plane serve as a scaffold to recruit the proteins required for particular cellular processes. The formation and localization of septin structures at particular stages of the cell cycle also determine functionality of these proteins. Many different proteins participate in regulating septin assembly. Despite recent developments, we are only beginning to understand how specific protein-protein interactions lead to changes in the polymerization of septin filaments or assembly of higher-order structures. Here, using fluorescence and electron microscopy, we found that Bni5 crosslinks septin filaments into networks by bridging pairs or multiple filaments, forming structures that resemble railways. Furthermore, Bni5 appears to be a substrate of the Elm1 protein kinase in vitro. Moreover, Elm1 induces in the presence of Bni5 disassembly of long septin filaments, suggesting that these proteins may participate in the hourglass to double ring transition. This work gives new insight into the regulatory role of Bni5 in the structural changes of septins.

Oncogenic transformation is dependent on activated membrane-associated NADPH oxidase (NOX). However, the resultant extracellular superoxide anions are also driving the NO/peroxynitrite and the HOCl pathway, which eliminates NOX-expressing transformed cells through selective apoptosis induction. Tumor progression is dependent on dominant interference with intercellular apoptosis-inducing ROS signaling through membrane-associated catalase, which decomposes H 2 O 2 and peroxynitrite and oxidizes NO. Particularly, the decomposition of extracellular peroxynitrite strictly requires membrane-associated catalase. We utilized small interfering RNA (siRNA)-mediated knockdown of catalase and neutralizing antibodies directed against the enzyme in combination with challenging H 2 O 2 or peroxynitrite to determine activity and localization of catalase in cells from three distinct steps of multistage oncogenesis. Nontransformed cells did not generate extracellular superoxide anions and only showed intracellular catalase activity. Transformed cells showed superoxide anion-dependent intercellular apoptosis-inducing ROS signaling in the presence of suboptimal catalase activity in their membrane. Tumor cells exhibited tight control of intercellular apoptosis-inducing ROS signaling through a high local concentration of membrane-associated catalase. These data demonstrate that translocation of catalase to the outside of the cell membrane is already associated with the transformation step. A strong local increase in the concentration of membrane-associated catalase is achieved during tumor progression and is controlled by tumor cell-derived H 2 O 2 and by transglutaminase.

Hypoxia-inducible transcription factors (HIFs) regulate hundreds of genes involved in cellular adaptation to reduced oxygen availability. HIFs consist of an O 2 -labile α-subunit (primarily HIF-1α and HIF-2α) and a constitutive HIF-1β subunit. In normoxia the HIF-α subunit is hydroxylated by members of a family of prolyl-4-hydroxylase domain (PHD) proteins, PHD1-3, resulting in recognition by von Hippel-Lindau protein, ubiquitination and proteasomal degradation. In contrast, reduced oxygen availability inhibits PHD activity resulting in HIF-1α stabilisation and nuclear accumulation. Nuclear import of HIF-1α mainly depends on classical nuclear localisation signals (NLS) and involves importin α/β heterodimers. Recently, a specific inhibitor of nuclear import has been identified that inhibits importin α/β-dependent import with no effects on a range of other nuclear transport pathways involving members of the importin protein family. In this study we evaluated the physiological activity of this importin α/β-inhibitor (Ivermectin) in the hypoxia response pathway. Treatment with Ivermectin decreases binding activity of HIF-1α to the importin α/β-heterodimer. Moreover, HIF-1α nuclear localisation, nuclear HIF-1α protein levels, HIF-target gene expression, as well as HIF-transcriptional activity are reduced upon Ivermectin treatment. For the first time, we demonstrate the effect of specific importin α/β-inhibition on the hypoxic response on the molecular level.

Ten secreted aspartic proteases (Saps) of Candida albicans cleave numerous peptides and proteins in the host organism and deregulate its homeostasis. Human kininogens contain two internal antimicrobial peptide sequences, designated NAT26 and HKH20. In our current study, we characterized a Sap-catalyzed cleavage of kininogen-derived antimicrobial peptides that results in the loss of the anticandidal activity of these peptides. The NAT26 peptide was effectively inactivated by all Saps, except Sap10, whereas HKH20 was completely degraded only by Sap9. Proteolytic deactivation of the antifungal potential of human kininogens can help the pathogens to modulate or evade the innate immunity of the host.