Dynein mediates the localization and activation of mTOR in normal and human cytomegalovirus-infected cells

Genomic Markers Associated with Cytomegalovirus DNAemia in Kidney Transplant Recipients

Human cytomegalovirus (CMV) is a major pathogen after solid organ transplantation, leading to high morbidity and mortality. Transplantation from a CMV-seropositive donor to a CMV-seronegative recipient (D+/R-) is associated with high risk of CMV disease. However, that risk is not uniform, suggesting a role for host factors in immune control of CMV. To identify host genetic factors that control CMV DNAemia post transplantation, we performed a whole-exome association study in two cohorts of D+/R- kidney transplant recipients. Quantitative CMV DNA was measured for at least one year following transplantation. Several CMV-protective single-nucleotide polymorphisms (SNPs) were identified in the first cohort (72 patients) but were not reproducible in the second cohort (126 patients). A meta-analysis of both cohorts revealed several SNPs that were significantly associated with protection from CMV DNAemia. The copy number variation of several genes was significantly different between recipients with and without CMV DNAemia. Amongst patients with CMV DNAemia in the second cohort, several variants of interest (p < 5 × 10-5), the most common of which was NLRC5, were associated with peak viral load. We provide new predictive genetic markers for protection of CMV DNAemia. These markers should be validated in larger cohorts.

An allosteric inhibitor of sirtuin 2 deacetylase activity exhibits broad-spectrum antiviral activity

Most drugs used to treat viral disease target a virus-coded product. They inhibit a single virus or virus family, and the pathogen can readily evolve resistance. Host-targeted antivirals can overcome these limitations. The broad-spectrum activity achieved by host targeting can be especially useful in combating emerging viruses and for treatment of diseases caused by multiple viral pathogens, such as opportunistic agents in immunosuppressed patients. We have developed a family of compounds that modulate sirtuin 2, an NAD+-dependent deacylase, and now report the properties of a member of that family, FLS-359. Biochemical and x-ray structural studies show that the drug binds to sirtuin 2 and allosterically inhibits its deacetylase activity. FLS-359 inhibits the growth of RNA and DNA viruses, including members of the coronavirus, orthomyxovirus, flavivirus, hepadnavirus, and herpesvirus families. FLS-359 acts at multiple levels to antagonize cytomegalovirus replication in fibroblasts, causing modest reductions in viral RNAs and DNA, together with a much greater reduction in infectious progeny, and it exhibits antiviral activity in humanized mouse models of infection. Our results highlight the potential of sirtuin 2 inhibitors as broad-spectrum antivirals and set the stage for further understanding of how host epigenetic mechanisms impact the growth and spread of viral pathogens.

Targeting the lysosome: Mechanisms and treatments for nonalcoholic fatty liver disease

The multiple functions of the lysosome, including degradation, nutrient sensing, signaling, and gene regulation, enable the lysosome to regulate lipid metabolism at different levels. In this review, I summarize the recent studies on lysosomal regulation of lipid metabolism and the alterations of the lysosome functions in the livers affected by nonalcoholic fatty liver disease (NAFLD). NAFLD is a highly prevalent lipid metabolic disorder. The progression of NAFLD leads to nonalcoholic steatohepatitis (NASH) and other severe liver diseases, and thus the prevention and treatments of NAFLD progression are critically needed. Targeting the lysosome is a promising strategy. I also discuss the current manipulations of the lysosome functions in the preclinical studies of NAFLD and propose my perspectives on potential future directions.

Virus-induced FoxO factor facilitates replication of human cytomegalovirus

Recently, it was reported that the forkhead box O (FoxO) transcription factor promotes human cytomegalovirus (HCMV) replication via direct binding to the promoters of the major immediate-early (MIE) genes, but how the FoxO factor impacts HCMV replication remains unknown. Here, it is reported that FoxO1 expression is strongly induced by HCMV infection in cells of fibroblast origin. Suppression of the FoxO1 gene by specific RNA interference significantly inhibited HCMV growth and replication, but viral DNA synthesis was not affected considerably. Interestingly, depletion or overexpression of FoxO1 had a significant effect on the expression of viral early/late transcripts. FoxO1 was found to colocalize with the pUL44 protein subunit of viral replication compartments without direct association with DNA. This study highlights how FoxO enhances HCMV gene transcription and viral replication to promote infection.

Human Cytomegalovirus Exploits TACC3 To Control Microtubule Dynamics and Late Stages of Infection

While it is well established that microtubules (MTs) facilitate various stages of virus replication, how viruses actively control MT dynamics and functions remains less well understood. Recent work has begun to reveal how several viruses exploit End-Binding (EB) proteins and their associated microtubule plus-end tracking proteins (+TIPs), in particular to enable loading of viral particles onto MTs for retrograde transport during early stages of infection. Distinct from other viruses studied to date, at mid- to late stages of its unusually protracted replication cycle, human cytomegalovirus (HCMV) increases the expression of all three EB family members. This occurs coincident with the formation of a unique structure, termed the assembly compartment (AC), which serves as a Golgi-derived MT organizing center. Together, the AC and distinct EB proteins enable HCMV to increase the formation of dynamic and acetylated microtubule subsets to regulate distinct aspects of the viral replication cycle. Here, we reveal that HCMV also exploits EB-independent +TIP pathways by specifically increasing the expression of transforming acidic coiled coil protein 3 (TACC3) to recruit the MT polymerase, chTOG, from initial sites of MT nucleation in the AC out into the cytosol, thereby increasing dynamic MT growth. Preventing TACC3 increases or depleting chTOG impaired MT polymerization, resulting in defects in early versus late endosome organization in and around the AC as well as defects in viral trafficking and spread. Our findings provide the first example of a virus that actively exploits EB-independent +TIP pathways to regulate MT dynamics and control late stages of virus replication. IMPORTANCE Diverse viruses rely on host cell microtubule networks to transport viral particles within the dense cytoplasmic environment and to control the broader architecture of the cell to facilitate their replication. However, precisely how viruses regulate the dynamic behavior and function of microtubule filaments remains poorly defined. We recently showed that the assembly compartment (AC) formed by human cytomegalovirus (HCMV) acts as a Golgi-derived microtubule organizing center. Here, we show that at mid- to late stages of infection, HCMV increases the expression of transforming acidic coiled coil protein 3 (TACC3) to control the localization of the microtubule polymerase, chTOG. This, in turn, enables HCMV to generate dynamic microtubule subsets that organize endocytic vesicles in and around the AC and facilitate the transport of new viral particles released into the cytosol. Our findings reveal the first instance of viral targeting of TACC3 to control microtubule dynamics and virus spread.

The Autophagy-Initiating Protein Kinase ULK1 Phosphorylates Human Cytomegalovirus Tegument Protein pp28 and Regulates Efficient Virus Release

Autophagy is a catabolic process contributing to intrinsic cellular defense by degrading viral particles or proteins; however, several viruses hijack this pathway for their own benefit. The role of autophagy during human cytomegalovirus (HCMV) replication has not been definitely clarified yet. Utilizing small interfering RNA (siRNA)-based screening, we observed that depletion of many autophagy-related proteins resulted in reduced virus release, suggesting a requirement of autophagy-related factors for efficient HCMV replication. Additionally, we could show that the autophagy-initiating serine/threonine protein kinase ULK1 as well as other constituents of the ULK1 complex were upregulated at early times of infection and stayed upregulated throughout the replication cycle. We demonstrate that indirect interference with ULK1 through inhibition of the upstream regulator AMP-activated protein kinase (AMPK) impaired virus release. Furthermore, this result was verified by direct abrogation of ULK1 kinase activity utilizing the ULK1-specific kinase inhibitors SBI-0206965 and ULK-101. Analysis of viral protein expression in the presence of ULK-101 revealed a connection between the cellular kinase ULK1 and the viral tegument protein pp28 (pUL99), and we identified pp28 as a novel viral substrate of ULK1 by in vitro kinase assays. In the absence of ULK1 kinase activity, large pp28- and pp65-positive structures could be detected in the cytoplasm at late time points of infection. Transmission electron microscopy demonstrated that these structures represent large perinuclear protein accumulations presumably representing aggresomes. Our results indicate that HCMV manipulates ULK1 and further components of the autophagic machinery to ensure the efficient release of viral particles.IMPORTANCE The catabolic program of autophagy represents a powerful immune defense against viruses that is, however, counteracted by antagonizing viral factors. Understanding the exact interplay between autophagy and HCMV infection is of major importance since autophagy-related proteins emerged as promising targets for pharmacologic intervention. Our study provides evidence for a proviral role of several autophagy-related proteins suggesting that HCMV has developed strategies to usurp components of the autophagic machinery for its own benefit. In particular, we observed strong upregulation of the autophagy-initiating protein kinase ULK1 and further components of the ULK1 complex during HCMV replication. In addition, both siRNA-mediated depletion of ULK1 and interference with ULK1 protein kinase activity by two chemically different inhibitors resulted in impaired viral particle release. Thus, we propose that ULK1 kinase activity is required for efficient HCMV replication and thus represents a promising novel target for future antiviral drug development.

Molecular Mechanisms of Lysosome and Nucleus Communication

Lysosomes transcend the role of degradation stations, acting as key nodes for interorganelle crosstalk and signal transduction. Lysosomes communicate with the nucleus through physical proximity and functional interaction. In response to external and internal stimuli, lysosomes actively adjust their distribution between peripheral and perinuclear regions and modulate lysosome-nucleus signaling pathways; in turn, the nucleus fine-tunes lysosomal biogenesis and functions through transcriptional controls. Changes in coordination between these two essential organelles are associated with metabolic disorders, neurodegenerative diseases, and aging. In this review, we address recent advances in lysosome-nucleus communication by multi-tiered regulatory mechanisms and discuss how these regulations couple metabolic inputs with organellar motility, cellular signaling, and transcriptional network.

TRANSPIRE: A Computational Pipeline to Elucidate Intracellular Protein Movements from Spatial Proteomics Data Sets

Protein localization is paramount to protein function, and the intracellular movement of proteins underlies the regulation of numerous cellular processes. Given advances in spatial proteomics, the investigation of protein localization at a global scale has become attainable. Also becoming apparent is the need for dedicated analytical frameworks that allow the discovery of global intracellular protein movement events. Here, we describe TRANSPIRE, a computational pipeline that facilitates TRanslocation ANalysis of SPatIal pRotEomics data sets. TRANSPIRE leverages synthetic translocation profiles generated from organelle marker proteins to train a probabilistic Gaussian process classifier that predicts changes in protein distribution. This output is then integrated with information regarding co-translocating proteins and complexes and enriched gene ontology associations to discern the putative regulation and function of movement. We validate TRANSPIRE performance for predicting nuclear-cytoplasmic shuttling events. Analyzing an existing data set of nuclear and cytoplasmic proteomes during Kaposi Sarcoma-associated herpesvirus (KSHV)-induced cellular mRNA decay, we confirm that TRANSPIRE readily discerns expected translocations of RNA binding proteins. We next investigate protein translocations during infection with human cytomegalovirus (HCMV), a β-herpesvirus known to induce global organelle remodeling. We find that HCMV infection induces broad changes in protein localization, with over 800 proteins predicted to translocate during virus replication. Evident are protein movements related to HCMV modulation of host defense, metabolism, cellular trafficking, and Wnt signaling. For example, the low-density lipoprotein receptor (LDLR) translocates to the lysosome early in infection in conjunction with its degradation, which we validate by targeted mass spectrometry. Using microscopy, we also validate the translocation of the multifunctional kinase DAPK3, a movement that may contribute to HCMV activation of Wnt signaling.

Novel anti-EGFR scFv human antibody-conjugated immunoliposomes enhance chemotherapeutic efficacy in squamous cell carcinoma of head and neck

BACKGROUND AND OBJECTIVES

Squamous cell carcinoma of head and neck (SCCHN) is the fifth most prevalent cancer worldwide. Because the anatomical complexity of this region, complete surgical resection is often not achievable and conventional chemotherapy would aid locoregional control and mitigate distant metastasis. Nonetheless, the nonspecific cytotoxicity and short in vivo half-life of conventional chemotherapeutic drugs limit their effects. Given the high frequency of overexpression of wild type epidermal growth factor receptor (EGFR), we exploit EGFR as a homing beacon for drug delivery system with cytotoxic payloads.

MATERIALS AND METHODS

We generated fully human anti-EGFR single chain variable fragment (scFv)-conjugated immunoliposomes (IL) containing doxorubicin and vinorelbine and tested their anti-neoplastic efficacy in vitro and in vivo.

RESULT

Our IL enhanced endocytosis and significantly reduced the half maximal inhibitory concentrations of the therapeutic payloads when compared to non-targeting liposomal counterparts in various cell lines of SCCHN. Furthermore, median survival time was significantly prolonged in subcutaneous and orthotopic SCCHN xenograft murine models treated with our IL formulations than those treated with non-targeting counterparts (94 days versus 60 days and 72 days versus 56 days, respectively) without evident increased systemic toxicity.

CONCLUSION

The therapeutic index of the chemotherapeutic payloads was augmented by our EFGR-targeting IL formulation and they are warranted for further development and preclinical trial.

Pathogens MenTORing Macrophages and Dendritic Cells: Manipulation of mTOR and Cellular Metabolism to Promote Immune Escape

Myeloid cells, including macrophages and dendritic cells, represent an important first line of defense against infections. Upon recognition of pathogens, these cells undergo a metabolic reprogramming that supports their activation and ability to respond to the invading pathogens. An important metabolic regulator of these cells is mammalian target of rapamycin (mTOR). During infection, pathogens use host metabolic pathways to scavenge host nutrients, as well as target metabolic pathways for subversion of the host immune response that together facilitate pathogen survival. Given the pivotal role of mTOR in controlling metabolism and DC and macrophage function, pathogens have evolved strategies to target this pathway to manipulate these cells. This review seeks to discuss the most recent insights into how pathogens target DC and macrophage metabolism to subvert potential deleterious immune responses against them, by focusing on the metabolic pathways that are known to regulate and to be regulated by mTOR signaling including amino acid, lipid and carbohydrate metabolism, and autophagy.

Ciliogenesis-coupled accumulation of IFT-B proteins in a novel cytoplasmic compartment

Cluap1/IFT38 is a ciliary protein that belongs to the IFT-B complex and is required for ciliogenesis. In this study, we have examined the behaviors of Cluap1 protein in nonciliated and ciliated cells. In proliferating cells, Cluap1 is located at the distal appendage of the mother centriole. When cells are induced to form cilia, Cluap1 is found in a novel noncentriolar compartment, the cytoplasmic IFT spot, which mainly exists once in a cell. Other IFT-B proteins such as IFT46 and IFT88 are colocalized in this spot. The cytoplasmic IFT spot is present in mouse embryonic fibroblasts (MEFs) but is absent in ciliogenesis-defective MEFs lacking Cluap1, Kif3a or Odf2. The cytoplasmic IFT spot is also found in mouse embryos but is absent in the Cluap1 mutant embryo. When MEFs are induced to form cilia, the cytoplasmic IFT spot appears at an early step of ciliogenesis but starts to disappear when ciliogenesis is mostly completed. These results suggest that IFT-B proteins such as Cluap1 accumulate in a previously undescribed cytoplasmic compartment during ciliogenesis.

mTOR Senses Intracellular pH through Lysosome Dispersion from RHEB

Acidity, generated in hypoxia or hypermetabolic states, perturbs homeostasis and is a feature of solid tumors. That acid peripherally disperses lysosomes is a three-decade-old observation, yet one little understood or appreciated. However, recent work has recognized the inhibitory impact this spatial redistribution has on mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of metabolism. This finding argues for a paradigm shift in localization of mTORC1 activator Ras homolog enriched in brain (RHEB), a conclusion several others have now independently reached. Thus, mTORC1, known to sense amino acids, mitogens, and energy to restrict biosynthesis to times of adequate resources, also senses pH and, via dampened mTOR-governed synthesis of clock proteins, regulates the circadian clock to achieve concerted responses to metabolic stress. While this may allow cancer to endure metabolic deprivation, immune cell mTOR signaling likewise exhibits pH sensitivity, suggesting that suppression of antitumor immune function by solid tumor acidity may additionally fuel cancers, an obstacle potentially reversible through therapeutic pH manipulation.

Lysosome Positioning Influences mTORC2 and AKT Signaling

Growth factor signaling is initiated at the plasma membrane and propagated through the cytoplasm for eventual relay to intracellular organelles such as lysosomes. The serine/threonine kinase mTOR participates in growth factor signaling as a component of two multi-subunit complexes, mTORC1 and mTORC2. mTORC1 associates with lysosomes, and its activity depends on the positioning of lysosomes within the cytoplasm, although there is no consensus regarding the exact effect of perinuclear versus peripheral distribution. mTORC2 and its substrate kinase AKT have a widespread distribution, but they are thought to act mainly at the plasma membrane. Using cell lines with knockout of components of the lysosome-positioning machinery, we show that perinuclear clustering of lysosomes delays reactivation of not only mTORC1, but also mTORC2 and AKT upon serum replenishment. These experiments demonstrate the existence of pools of mTORC2 and AKT that are sensitive to lysosome positioning.

Cell size sensing-a one-dimensional solution for a three-dimensional problem?

Individual cell types have characteristic sizes, suggesting that size sensing mechanisms may coordinate transcription, translation, and metabolism with cell growth rates. Two types of size-sensing mechanisms have been proposed: spatial sensing of the location or dimensions of a signal, subcellular structure or organelle; or titration-based sensing of the intracellular concentrations of key regulators. Here we propose that size sensing in animal cells combines both titration and spatial sensing elements in a dynamic mechanism whereby microtubule motor-dependent localization of RNA encoding importin β1 and mTOR, coupled with regulated local protein synthesis, enable cytoskeleton length sensing for cell growth regulation.

Chewing the Fat: The Conserved Ability of DNA Viruses to Hijack Cellular Lipid Metabolism

Viruses manipulate numerous host factors and cellular pathways to facilitate the replication of viral genomes and the production of infectious progeny. One way in which viruses interact with cells is through the utilization and exploitation of the host lipid metabolism. While it is likely that most-if not all-viruses require lipids or intermediates of lipid synthesis to replicate, many viruses also actively induce lipid metabolic pathways to sustain a favorable replication environment. From the formation of membranous replication compartments, to the generation of ATP or protein modifications, viruses exhibit differing requirements for host lipids. Thus, while the exploitation of lipid metabolism is a common replication strategy, diverse viruses employ a plethora of mechanisms to co-opt these critical cellular pathways. Here, we review recent literature regarding the exploitation of host lipids and lipid metabolism specifically by DNA viruses. Importantly, furthering the understanding of the viral requirements for host lipids may offer new targets for antiviral therapeutics and provide opportunities to repurpose the numerous FDA-approved compounds targeting lipid metabolic pathways as antiviral agents.

Everolimus delayed and suppressed cytomegalovirus DNA synthesis, spread of the infection, and alleviated cytomegalovirus infection

Everolimus is an inhibitor of mammalian target of rapamycin (mTOR) and reduces the risk of cytomegalovirus (CMV) infection in transplant recipients. Everolimus inhibits mTOR complex 1, which regulates factors involved in several crucial cellular functions and is required for CMV replication. However, it is not clear how everolimus regulates CMV replication and prevents and alleviates CMV infection. Effects of everolimus on CMV infection, spread, and DNA synthesis and release from infected cells were assessed by plaque formation, infectious centre assay, real-time PCR of infected cells, and culture supernatant in CMV-infected cultures with and without everolimus. Everolimus enhanced plaque formation by 3.6 times, but the size of the plaques was reduced to 36.4% of untreated cultures in the absence of a pretreatment period. Everolimus reduced viral adsorption but enhanced the replication efficiency of inoculated virus, resulting in an increase in plaque number in the early phase of infection. Preinfection treatment of cells with everolimus efficiently exhibited its antiviral efficacy, and everolimus delayed and suppressed viral DNA synthesis and release from infected cells. Everolimus had suppressed the spread of infection and reduced the number of total infected cells to 40% of untreated cells on day 9, indicating reduction of the size of CMV lesions to one-sixth in 2-3 replication cycles. Preinfection treatment of the cells with everolimus augmented its suppressive effect on CMV infection and replication. Everolimus reduced the total number of infected cells and limited the CMV lesions, and this reduction in the spread of CMV infection would alleviate CMV infection in transplant recipients.

Remodeling mTORC1 Responsiveness to Amino Acids by the Herpes Simplex Virus UL46 and Us3 Gene Products Supports Replication during Nutrient Insufficiency

By sensing fundamental parameters, including nutrient availability, activated mechanistic target of rapamycin complex 1 (mTORC1) suppresses catabolic outcomes and promotes anabolic processes needed for herpes simplex virus 1 (HSV-1) productive growth. While the virus-encoded Us3 Ser/Thr kinase is required to activate mTORC1, whether stress associated with amino acid insufficiency impacts mTORC1 activation in infected cells and virus reproduction was unknown. In contrast to uninfected cells, where amino acid withdrawal inhibits mTORC1 activation, we demonstrate that mTORC1 activity is sustained in HSV-1-infected cells during amino acid insufficiency. We show that in the absence of Us3, the insensitivity of mTORC1 to amino acid withdrawal in infected cells was dependent on the host kinase Akt and establish a role for the HSV-1 UL46 gene product, which stimulates phosphatidylinositol (PI) 3-kinase signaling. Significantly, virus reproduction during amino acid insufficiency was stimulated by the viral UL46 gene product. By synergizing with Us3, UL46 reprograms mTORC1 such that it is insensitive to amino acid withdrawal and supports sustained mTORC1 activation and virus reproduction during amino acid insufficiency. This identifies an unexpected function for UL46 in supporting virus reproduction during physiological stress and identifies a new class of virus-encoded mTORC1 regulators that selectively uncouple mTORC1 activation from amino acid sufficiency.IMPORTANCE Mechanistic target of rapamycin complex 1 (mTORC1) is a multisubunit cellular kinase that coordinates protein synthesis with changing amino acid levels. During amino acid insufficiency, mTORC1 is repressed in uninfected cells, dampening protein synthesis and potentially restricting virus reproduction. Here, we establish that HSV-1 alters the responsiveness of mTORC1 to metabolic stress resulting from amino acid insufficiency. Unlike in uninfected cells, mTORC1 remains activated in HSV-1-infected cells deprived of amino acids. Synergistic action of the HSV-1 UL46 gene product, which stimulates PI 3-kinase, and the Us3 kinase supports virus reproduction during amino acid withdrawal. These results define how HSV-1, a medically important human pathogen associated with a range of diseases, uncouples mTORC1 activation from amino acid availability. Furthermore, they help explain how the virus reproduces during physiological stress. Reproduction triggered by physiological stress is characteristic of herpesvirus infections, where lifelong latency is punctuated by episodic reactivation events.

Virus Control of Trafficking from Sorting Endosomes

The maintenance of cell surface proteins is critical to the ability of a cell to sense and respond to information in its environment. As such, modulation of cell surface composition and receptor trafficking is a potentially important target of control in virus infection. Sorting endosomes (SEs) are control stations regulating the recycling or degradation of internalized plasma membrane proteins. Here we report that human cytomegalovirus (HCMV), a ubiquitous betaherpesvirus, alters the fate of internalized clathrin-independent endocytosis (CIE) cargo proteins, retaining them in virally reprogrammed SEs. We show that the small G protein ARF6 (ADP ribosylation factor 6), a regulator of CIE trafficking, is highly associated with SE membranes relative to uninfected cells. Combined with the observation of accumulated CIE cargo at the SE, these results suggest that infection diminishes the egress of ARF6 and its cargo from the SE. Expression of ubiquitin-specific protease 6 (USP6), also known as TRE17, was sufficient to restore ARF6 and some ARF6 cargo trafficking to the cell surface in infected cells. The USP activity of TRE17 was required to rescue both ARF6 and associated cargo from SE retention in infection. The finding that TRE17 expression does not rescue the trafficking of all CIE cargos retained at SEs in infection suggests that HCMV hijacks the normal sorting machinery and selectively sorts specific cargos into endocytic microdomains that are subject to alternative sorting fates.

Cells maintain their surface composition, take up nutrients, and respond to their environment through the internalization and recycling of cargo at the cell surface through endocytic trafficking pathways. During infection with human cytomegalovirus (HCMV), host endocytic membranes are reorganized into a juxtanuclear structure associated with viral assembly and egress. Less appreciated is the effect of this reorganization on the trafficking of host proteins through the endocytic pathway. We show that HCMV retains internalized cargo and the effector of clathrin-independent endocytosis at sorting endosomes. The retention of some cargo, but not all, was reversed by overexpression of a ubiquitin-specific protease, TRE17. Our results demonstrate that HCMV induces profound reprogramming of endocytic trafficking and influences cargo sorting decisions. Further, our work suggests the presence of a novel ubiquitin-regulated checkpoint for the recycling of cargo from sorting endosome. These findings have important implications for host signaling and immune pathways in the context of HCMV infection.

Acid Suspends the Circadian Clock in Hypoxia through Inhibition of mTOR

Recent reports indicate that hypoxia influences the circadian clock through the transcriptional activities of hypoxia-inducible factors (HIFs) at clock genes. Unexpectedly, we uncover a profound disruption of the circadian clock and diurnal transcriptome when hypoxic cells are permitted to acidify to recapitulate the tumor microenvironment. Buffering against acidification or inhibiting lactic acid production fully rescues circadian oscillation. Acidification of several human and murine cell lines, as well as primary murine T cells, suppresses mechanistic target of rapamycin complex 1 (mTORC1) signaling, a key regulator of translation in response to metabolic status. We find that acid drives peripheral redistribution of normally perinuclear lysosomes away from perinuclear RHEB, thereby inhibiting the activity of lysosome-bound mTOR. Restoring mTORC1 signaling and the translation it governs rescues clock oscillation. Our findings thus reveal a model in which acid produced during the cellular metabolic response to hypoxia suppresses the circadian clock through diminished translation of clock constituents.

Arginase 2 Suppresses Renal Carcinoma Progression via Biosynthetic Cofactor Pyridoxal Phosphate Depletion and Increased Polyamine Toxicity

Kidney cancer, one of the ten most prevalent malignancies in the world, has exhibited increased incidence over the last decade. The most common subtype is "clear cell" renal cell carcinoma (ccRCC), which features consistent metabolic abnormalities, such as highly elevated glycogen and lipid deposition. By integrating metabolomics, genomic, and transcriptomic data, we determined that enzymes in multiple metabolic pathways are universally depleted in human ccRCC tumors, which are otherwise genetically heterogeneous. Notably, the expression of key urea cycle enzymes, including arginase 2 (ARG2) and argininosuccinate synthase 1 (ASS1), is strongly repressed in ccRCC. Reduced ARG2 activity promotes ccRCC tumor growth through at least two distinct mechanisms: conserving the critical biosynthetic cofactor pyridoxal phosphate and avoiding toxic polyamine accumulation. Pharmacological approaches to restore urea cycle enzyme expression would greatly expand treatment strategies for ccRCC patients, where current therapies only benefit a subset of those afflicted with renal cancer.

The HCMV Assembly Compartment Is a Dynamic Golgi-Derived MTOC that Controls Nuclear Rotation and Virus Spread

Human cytomegalovirus (HCMV), a leading cause of congenital birth defects, forms an unusual cytoplasmic virion maturation site termed the "assembly compartment" (AC). Here, we show that the AC also acts as a microtubule-organizing center (MTOC) wherein centrosome activity is suppressed and Golgi-based microtubule (MT) nucleation is enhanced. This involved viral manipulation of discrete functions of MT plus-end-binding (EB) proteins. In particular, EB3, but not EB1 or EB2, was recruited to the AC and was required to nucleate MTs that were rapidly acetylated. EB3-regulated acetylated MTs were necessary for nuclear rotation prior to cell migration, maintenance of AC structure, and optimal virus replication. Independently, a myristoylated peptide that blocked EB3-mediated enrichment of MT regulatory proteins at Golgi regions of the AC also suppressed acetylated MT formation, nuclear rotation, and infection. Thus, HCMV offers new insights into the regulation and functions of Golgi-derived MTs and the therapeutic potential of targeting EB3.

TUFT1 interacts with RABGAP1 and regulates mTORC1 signaling

The mammalian target of rapamycin (mTOR) pathway is commonly activated in human cancers. The activity of mTOR complex 1 (mTORC1) signaling is supported by the intracellular positioning of cellular compartments and vesicle trafficking, regulated by Rab GTPases. Here we showed that tuftelin 1 (TUFT1) was involved in the activation of mTORC1 through modulating the Rab GTPase-regulated process. TUFT1 promoted tumor growth and metastasis. Consistently, the expression of TUFT1 correlated with poor prognosis in lung, breast and gastric cancers. Mechanistically, TUFT1 physically interacted with RABGAP1, thereby modulating intracellular lysosomal positioning and vesicular trafficking, and promoted mTORC1 signaling. In addition, expression of TUFT1 predicted sensitivity to perifosine, an alkylphospholipid that alters the composition of lipid rafts. Perifosine treatment altered the positioning and trafficking of cellular compartments to inhibit mTORC1. Our observations indicate that TUFT1 is a key regulator of the mTORC1 pathway and suggest that it is a promising therapeutic target or a biomarker for tumor progression.

Cytomegalovirus Late Protein pUL31 Alters Pre-rRNA Expression and Nuclear Organization during Infection

The replication cycle of human cytomegalovirus (CMV) leads to drastic reorganization of domains in the host cell nucleus. However, the mechanisms involved and how these domains contribute to infection are not well understood. Our recent studies defining the CMV-induced nuclear proteome identified several viral proteins of unknown functions, including a protein encoded by the UL31 gene. We set out to define the role of UL31 in CMV replication. UL31 is predicted to encode a 74-kDa protein, referred to as pUL31, containing a bipartite nuclear localization signal, an intrinsically disordered region overlapping arginine-rich motifs, and a C-terminal dUTPase-like structure. We observed that pUL31 is expressed with true late kinetics and is localized to nucleolin-containing nuclear domains. However, pUL31 is excluded from the viral nuclear replication center. Nucleolin is a marker of nucleoli, which are membrane-less regions involved in regulating ribosome biosynthesis and cellular stress responses. Other CMV proteins associate with nucleoli, and we demonstrate that pUL31 specifically interacts with the viral protein, pUL76. Coexpression of both proteins altered pUL31 localization and nucleolar organization. During infection, pUL31 colocalizes with nucleolin but not the transcriptional activator, UBF. In the absence of pUL31, CMV fails to reorganize nucleolin and UBF and exhibits a replication defect at a low multiplicity of infection. Finally, we observed that pUL31 is necessary and sufficient to reduce pre-rRNA levels, and this was dependent on the dUTPase-like motif in pUL31. Our studies demonstrate that CMV pUL31 functions in regulating nucleolar biology and contributes to the reorganization of nucleoli during infection.IMPORTANCE Nucleolar biology is important during CMV infection with the nucleolar protein, with nucleolin playing a role in maintaining the architecture of the viral nuclear replication center. However, the extent of CMV-mediated regulation of nucleolar biology is not well established. Proteins within nucleoli regulate ribosome biosynthesis and p53-dependent cellular stress responses that are capable of inducing cell cycle arrest and/or apoptosis, and they are proposed targets for cancer therapies. This study establishes that CMV protein pUL31 is necessary and sufficient to regulate nucleolar biology involving the reorganization of nucleolar proteins. Understanding these processes will help define approaches to stimulate cellular intrinsic stress responses that are capable of inhibiting CMV infection.

A Cap-to-Tail Guide to mRNA Translation Strategies in Virus-Infected Cells

Although viruses require cellular functions to replicate, their absolute dependence upon the host translation machinery to produce polypeptides indispensable for their reproduction is most conspicuous. Despite their incredible diversity, the mRNAs produced by all viruses must engage cellular ribosomes. This has proven to be anything but a passive process and has revealed a remarkable array of tactics for rapidly subverting control over and dominating cellular regulatory pathways that influence translation initiation, elongation, and termination. Besides enforcing viral mRNA translation, these processes profoundly impact host cell-intrinsic immune defenses at the ready to deny foreign mRNA access to ribosomes and block protein synthesis. Finally, genome size constraints have driven the evolution of resourceful strategies for maximizing viral coding capacity. Here, we review the amazing strategies that work to regulate translation in virus-infected cells, highlighting both virus-specific tactics and the tremendous insight they provide into fundamental translational control mechanisms in health and disease.

MCRS1 associates with cytoplasmic dynein and mediates pericentrosomal material recruitment

MCRS1 is involved in multiple cellular activities, including mitotic spindle assembly, mTOR signaling and tumorigenesis. Although MCRS1 has been reported to bind to the dynein regulator NDE1, a functional interaction between MCRS1 and cytoplasmic dynein remains unaddressed. Here, we demonstrate that MCRS1 is required for dynein-dependent cargo transport to the centrosome and also plays a role in primary cilium formation. MCRS1 localized to centriolar satellites. Knockdown of MCRS1 resulted in a dispersion of centriolar satellites whose establishment depends on cytoplasmic dynein. By contrast, NDE1 was not necessary for the proper distribution of centriolar satellites, indicating a functional distinction between MCRS1 and NDE1. Unlike NDE1, MCRS1 played a positive role for the initiation of ciliogenesis, possibly through its interaction with TTBK2. Zebrafish with homozygous mcrs1 mutants exhibited a reduction in the size of the brain and the eye due to excessive apoptosis. In addition, mcrs1 mutants failed to develop distinct layers in the retina, and showed a defect in melatonin-induced aggregation of melanosomes in melanophores. These phenotypes are reminiscent of zebrafish dynein mutants. Reduced ciliogenesis was also apparent in the olfactory placode of mcrs1 mutants. Collectively, our findings identify MCRS1 as a dynein-interacting protein critical for centriolar satellite formation and ciliogenesis.

Adapting the Stress Response: Viral Subversion of the mTOR Signaling Pathway

The mammalian target of rapamycin (mTOR) is a central regulator of gene expression, translation and various metabolic processes. Multiple extracellular (growth factors) and intracellular (energy status) molecular signals as well as a variety of stressors are integrated into the mTOR pathway. Viral infection is a significant stress that can activate, reduce or even suppress the mTOR signaling pathway. Consequently, viruses have evolved a plethora of different mechanisms to attack and co-opt the mTOR pathway in order to make the host cell a hospitable environment for replication. A more comprehensive knowledge of different viral interactions may provide fruitful targets for new antiviral drugs.

Human Cytomegalovirus: Coordinating Cellular Stress, Signaling, and Metabolic Pathways

Viruses face a multitude of challenges when they infect a host cell. Cells have evolved innate defenses to protect against pathogens, and an infecting virus may induce a stress response that antagonizes viral replication. Further, the metabolic, oxidative, and cell cycle state may not be conducive to the viral infection. But viruses are fabulous manipulators, inducing host cells to use their own characteristic mechanisms and pathways to provide what the virus needs. This article centers on the manipulation of host cell metabolism by human cytomegalovirus (HCMV). We review the features of the metabolic program instituted by the virus, discuss the mechanisms underlying these dramatic metabolic changes, and consider how the altered program creates a synthetic milieu that favors efficient HCMV replication and spread.

Trehalose, an mTOR-Independent Inducer of Autophagy, Inhibits Human Cytomegalovirus Infection in Multiple Cell Types

Human cytomegalovirus (HCMV) is the major viral cause of birth defects and a serious problem in immunocompromised individuals and has been associated with atherosclerosis. Previous studies have shown that the induction of autophagy can inhibit the replication of several different types of DNA and RNA viruses. The goal of the work presented here was to determine whether constitutive activation of autophagy would also block replication of HCMV. Most prior studies have used agents that induce autophagy via inhibition of the mTOR pathway. However, since HCMV infection alters the sensitivity of mTOR kinase-containing complexes to inhibitors, we sought an alternative method of inducing autophagy. We chose to use trehalose, a nontoxic naturally occurring disaccharide that is found in plants, insects, microorganisms, and invertebrates but not in mammals and that induces autophagy by an mTOR-independent mechanism. Given the many different cell targets of HCMV, we proceeded to determine whether trehalose would inhibit HCMV infection in human fibroblasts, aortic artery endothelial cells, and neural cells derived from human embryonic stem cells. We found that in all of these cell types, trehalose induces autophagy and inhibits HCMV gene expression and production of cell-free virus. Treatment of HCMV-infected neural cells with trehalose also inhibited production of cell-associated virus and partially blocked the reduction in neurite growth and cytomegaly. These results suggest that activation of autophagy by the natural sugar trehalose or other safe mTOR-independent agents might provide a novel therapeutic approach for treating HCMV disease.

IMPORTANCE

HCMV infects multiple cell types in vivo, establishes lifelong persistence in the host, and can cause serious health problems for fetuses and immunocompromised individuals. HCMV, like all other persistent pathogens, has to finely tune its interplay with the host cellular machinery to replicate efficiently and evade detection by the immune system. In this study, we investigated whether modulation of autophagy, a host pathway necessary for the recycling of nutrients and removal of protein aggregates, misfolded proteins, and pathogens, could be used to target HCMV. We found that autophagy could be significantly increased by treatment with the nontoxic, natural disaccharide trehalose. Importantly, trehalose had a profound inhibitory effect on viral gene expression and strongly impaired viral spread. These data constitute a proof-of-concept for the use of natural products targeting host pathways rather than the virus itself, thus reducing the risk of the development of resistance to treatment.

Antagonistic Relationship between Human Cytomegalovirus pUL27 and pUL97 Activities during Infection

Human cytomegalovirus (HCMV) is a member of the betaherpesvirus family. During infection, an array of viral proteins manipulates the host cell cycle. We have previously shown that expression of HCMV pUL27 results in increased levels of the cyclin-dependent kinase (CDK) inhibitor p21(Cip1). In addition, pUL27 is necessary for the full antiviral activity of the pUL97 kinase inhibitor maribavir (MBV). The purpose of this study was to define the relationship between pUL27 and pUL97 and its role in MBV antiviral activity. We observed that expression of wild-type but not kinase-inactive pUL97 disrupted pUL27-dependent induction of p21(Cip1). Furthermore, pUL97 associated with and promoted the phosphorylation of pUL27. During infection, inhibition of the kinase resulted in elevated levels of p21(Cip1) in wild-type virus but not a pUL27-deficient virus. We manipulated the p21(Cip1) levels to evaluate the functional consequence to MBV. Overexpression of p21(Cip1) restored MBV activity against a pUL27-deficient virus, while disruption reduced activity against wild-type virus. We provide evidence that the functional target of p21(Cip1) in the context of MBV activity is CDK1. One CDK-like activity of pUL97 is to phosphorylate nuclear lamin A/C, resulting in altered nuclear morphology and increased viral egress. In the presence of MBV, we observed that infection using a pUL27-deficient virus still altered the nuclear morphology. This was prevented by the addition of a CDK inhibitor. Overall, our results demonstrate an antagonistic relationship between pUL27 and pUL97 activities centering on p21(Cip1) and support the idea that CDKs can complement some activities of pUL97.

IMPORTANCE

HCMV infection results in severe disease upon immunosuppression and is a leading cause of congenital birth defects. Effective antiviral compounds exist, yet they exhibit high levels of toxicity, are not approved for use during pregnancy, and can result in antiviral resistance. Our studies have uncovered new information regarding the antiviral efficacy of the HCMV pUL97 kinase inhibitor MBV as it relates to the complex interplay between pUL97 and a second HCMV protein, pUL27. We demonstrate that pUL97 functions antagonistically against pUL27 by phosphorylation-dependent inactivation of pUL27-mediated induction of p21(Cip1). In contrast, we provide evidence that p21(Cip1) functions to antagonize overlapping activities between pUL97 and cellular CDKs. In addition, these studies further support the notion that CDK inhibitors or p21(Cip1) activators might be useful in combination with MBV to effectively inhibit HCMV infections.

Ciliobrevins as tools for studying dynein motor function

Dyneins are a small class of molecular motors that bind to microtubules and walk toward their minus ends. They are essential for the transport and distribution of organelles, signaling complexes and cytoskeletal elements. In addition dyneins generate forces on microtubule arrays that power the beating of cilia and flagella, cell division, migration and growth cone motility. Classical approaches to the study of dynein function in axons involve the depletion of dynein, expression of mutant/truncated forms of the motor, or interference with accessory subunits. By necessity, these approaches require prolonged time periods for the expression or manipulation of cellular dynein levels. With the discovery of the ciliobrevins, a class of cell permeable small molecule inhibitors of dynein, it is now possible to acutely disrupt dynein both globally and locally. In this review, we briefly summarize recent work using ciliobrevins to inhibit dynein and discuss the insights ciliobrevins have provided about dynein function in various cell types with a focus on neurons. We temper this with a discussion of the need for studies that will elucidate the mechanism of action of ciliobrevin and as well as the need for experiments to further analyze the specificity of ciliobreviens for dynein. Although much remains to be learned about ciliobrevins, these small molecules are proving themselves to be valuable novel tools to assess the cellular functions of dynein.

Tuberous Sclerosis Complex Protein 2-Independent Activation of mTORC1 by Human Cytomegalovirus pUL38

The mammalian target of rapamycin complex 1 (mTORC1) controls cell growth and anabolic metabolism and is a critical host factor activated by human cytomegalovirus (HCMV) for successful infection. The multifunctional HCMV protein pUL38 previously has been reported to activate mTORC1 by binding to and antagonizing tuberous sclerosis complex protein 2 (TSC2) (J. N. Moorman et al., Cell Host Microbe 3:253-262, 2008, http://dx.doi.org/10.1016/j.chom.2008.03.002). pUL38 also plays a role in blocking endoplasmic reticulum stress-induced cell death during HCMV infection. In this study, we showed that a mutant pUL38 lacking the N-terminal 24 amino acids (pHA-UL3825-331) was fully functional in suppressing cell death during infection. Interestingly, pHA-UL3825-331 lost the ability to interact with TSC2 but retained the ability to activate mTORC1, although to a lesser extent than full-length pHA-UL38. Recombinant virus expressing pHA-UL3825-331 replicated with ∼10-fold less efficiency than the wild-type virus at a low multiplicity of infection (MOI), but it grew similarly well at a high MOI, suggesting an MOI-dependent importance of pUL38-TSC2 interaction in supporting virus propagation. Site-directed mutational analysis identified a TQ motif at amino acid residues 23 and 24 as critical for pUL38 interaction with TSC2. Importantly, when expressed in isolation, the TQ/AA substitution mutant pHA-UL38 TQ/AA was capable of activating mTORC1 just like pHA-UL3825-331. We also created TSC2-null U373-MG cell lines by CRISPR genome editing and showed that pUL38 was capable of further increasing mTORC1 activity in TSC2-null cells. Therefore, this study identified the residues important for pUL38-TSC2 interaction and demonstrated that pUL38 can activate mTORC1 in both TSC2-dependent and -independent manners.

IMPORTANCE

HCMV, like other viruses, depends exclusively on its host cell to propagate. Therefore, it has developed methods to protect against host stress responses and to usurp cellular processes to complete its life cycle. mTORC1 is believed to be important for virus replication, and HCMV maintains high mTORC1 activity despite the stressful cellular environment associated with infection. mTORC1 inhibitors suppressed HCMV replication in vitro and reduced the incidence of HCMV reactivation in transplant recipients. We demonstrated that mTORC1 was activated by HCMV protein pUL38 in both TSC2-dependent and TSC2-independent manners. The pUL38-independent mode of mTORC1 activation also has been reported. These novel findings suggest the evolution of sophisticated approaches whereby HCMV activates mTORC1, indicating its importance in the biology and pathogenesis of HCMV.

Release of human cytomegalovirus from latency by a KAP1/TRIM28 phosphorylation switch

Human cytomegalovirus (HCMV) is a highly prevalent pathogen that induces life-long infections notably through the establishment of latency in hematopoietic stem cells (HSC). Bouts of reactivation are normally controlled by the immune system, but can be fatal in immuno-compromised individuals such as organ transplant recipients. Here, we reveal that HCMV latency in human CD34⁺ HSC reflects the recruitment on the viral genome of KAP1, a master co-repressor, together with HP1 and the SETDB1 histone methyltransferase, which results in transcriptional silencing. During lytic infection, KAP1 is still associated with the viral genome, but its heterochromatin-inducing activity is suppressed by mTOR-mediated phosphorylation. Correspondingly, HCMV can be forced out of latency by KAP1 knockdown or pharmacological induction of KAP1 phosphorylation, and this process can be potentiated by activating NFkB with TNF-α. These results suggest new approaches both to curtail CMV infection and to purge the virus from organ transplants.

DOI:http://dx.doi.org/10.7554/eLife.06068.001

Human cytomegalovirus (HCMV) is an extremely common virus that causes life-long infections in humans. Most individuals are exposed to HCMV during childhood, and the infection rarely causes any symptoms of disease in healthy individuals. However, in people with weaker immune systems—for example, newborn babies, people with AIDS, or individuals who have received an organ transplant—HCMV can cause life-threatening illnesses.

It is difficult for the immune system to fight the infection because HCMV is able to hide in cells within the bone marrow called hematopoietic stem cells. Inside these cells, the virus can survive in a ‘dormant’ state for many years, before being reactivated and starting to multiply again. In most people, the immune system manages to control this new outbreak of HCMV, and the virus becomes dormant again, but reactivation of the virus in individuals with weakened immune systems is much more likely to cause serious illness.

The results of previous studies suggest that when HCMV infects the hematopoietic stem cells, human proteins switch off the expression of many virus genes, which makes the virus inactive. The virus can be reactivated when infected stem cells change into a type of immune cell called dendritic cells, but it is not clear how this is controlled.

Here, Rauwel et al. reveal that a human protein called KAP1 is responsible for switching off the virus genes in the stem cells. It does so by interacting with two other proteins to alter the structure of the DNA in these genes. However, if the stem cells are stimulated to change into dendritic cells, KAP1 becomes inactive, which allows the virus genes to be switched on.

Rauwel et al. also show that it is possible to force HCMV out of its dormant state by using drugs to block the activity of KAP1. This may aid the development of treatments that prevent the virus from causing serious illness in patients with weakened immune systems. For example, it could be used to remove dormant HCMV infections from bone marrow before it is transplanted into a new individual.

DOI:http://dx.doi.org/10.7554/eLife.06068.002

Fatty acid elongase 7 catalyzes lipidome remodeling essential for human cytomegalovirus replication

Human cytomegalovirus (HCMV) infection rewires host cell metabolism, up-regulating flux from glucose into acetyl-CoA to feed fatty acid metabolism, with saturated very long-chain fatty acids (VLFCA) required for production of infectious virion progeny. The human genome encodes seven elongase enzymes (ELOVL) that extend long chain fatty acids into VLCFA. Here we identify ELOVL7 as pivotal for HCMV infection. HCMV induces ELOVL7 by more than 150-fold. This induction is dependent on mTOR and SREBP-1. ELOVL7 knockdown or mTOR inhibition impairs HCMV-induced fatty acid elongation, HCMV particle release, and infectivity per particle. ELOVL7 overexpression enhances HCMV replication. During HCMV infection, mTOR activity is maintained by the viral protein pUL38. Expression of pUL38 is sufficient to induce ELOVL7, and pUL38-deficient virus is partially defective in ELOVL7 induction and fatty acid elongation. Thus, through its ability to modulate mTOR and SREBP-1, HCMV induces ELOVL7 to synthesize the saturated VLCFA required for efficient virus replication.

Scaffold protein JLP is critical for CD40 signaling in B lymphocytes

CD40 expression on the surface of B lymphocytes is essential for their biological function and fate decision. The engagement of CD40 with its cognate ligand, CD154, leads to a sequence of cellular events in B lymphocytes, including CD40 cytoplasmic translocation, a temporal and spatial organization of effector molecules, and a cascade of CD40-induced signal transduction. The JLP scaffold protein was expressed in murine B lymphocytes. Using B lymphocytes from jlp-deficient mice, we observed that JLP deficiency resulted in defective CD40 internalization upon CD154/CD40 engagement. Examination of interactions and co-localization among CD40, JLP, dynein, and Rab5 in B lymphocytes suggested that CD40 internalization is a process of JLP-mediated vesicle transportation that depends on Rab5 and dynein. JLP deficiency also diminished CD40-dependent activation of MAPK and JNK, but not NF-κB. Inhibiting vesicle transportation from the direction of cell periphery to the cell center by a dynein inhibitor (ciliobrevin D) impaired both CD154-induced CD40 internalization and CD40-dependent MAPK activities in B lymphocytes. Collectively, our data demonstrate a novel role of the JLP scaffold protein in the bridging of CD154-triggered CD40 internalization and CD40-dependent signaling in splenic B lymphocytes.

Dynein function and protein clearance changes in tumor cells induced by a Kunitz-type molecule, Amblyomin-X

Amblyomin-X is a Kunitz-type recombinant protein identified from the transcriptome of the salivary glands of the tick Amblyomma cajennense and has anti-coagulant and antitumoral activity. The supposed primary target of this molecule is the proteasome system. Herein, we elucidated intracellular events that are triggered by Amblyomin-X treatment in an attempt to provide new insight into how this serine protease inhibitor, acting on the proteasome, could be comparable with known proteasome inhibitors. The collective results showed aggresome formation after proteasome inhibition that appeared to occur via the non-exclusive ubiquitin pathway. Additionally, Amblyomin-X increased the expression of various chains of the molecular motor dynein in tumor cells, modulated specific ubiquitin linkage signaling and inhibited autophagy activation by modulating mTOR, LC3 and AMBRA1 with probable dynein involvement. Interestingly, one possible role for dynein in the mechanism of action of Amblyomin-X was in the apoptotic response and its crosstalk with autophagy, which involved the factor Bim; however, we observed no changes in the apoptotic response related to dynein in the experiments performed. The characteristics shared among Amblyomin-X and known proteasome inhibitors included NF-κB blockage and nascent polypeptide-dependent aggresome formation. Therefore, our study describes a Kunitz-type protein that acts on the proteasome to trigger distinct intracellular events compared to classic known proteasome inhibitors that are small-cell-permeable molecules. In investigating the experiments and literature on Amblyomin-X and the known proteasome inhibitors, we also found differences in the structures of the molecules, intracellular events, dynein involvement and tumor cell type effects. These findings also reveal a possible new target for Amblyomin-X, i.e., dynein, and may serve as a tool for investigating tumor cell death associated with proteasome inhibition.

Targeting microtubules by natural agents for cancer therapy

Natural compounds that target microtubules and disrupt the normal function of the mitotic spindle have proven to be one of the best classes of cancer chemotherapeutic drugs available in clinics to date. There is increasing evidence showing that even minor alteration of microtubule dynamics can engage the spindle checkpoint, arresting cell-cycle progression at mitosis and subsequently leading to cell death. Our improved understanding of tumor biology and our continued appreciation for what the microtubule targeting agents (MTAs) can do have helped pave the way for a new era in the treatment of cancer. The effectiveness of these agents for cancer therapy has been impaired, however, by various side effects and drug resistance. Several new MTAs have shown potent activity against the proliferation of various cancer cells, including resistance to the existing MTAs. Sustained investigation of the mechanisms of action of MTAs, development and discovery of new drugs, and exploring new treatment strategies that reduce side effects and circumvent drug resistance could provide more effective therapeutic options for patients with cancer. This review focuses on the successful cancer chemotherapy from natural compounds in clinical settings and the challenges that may abort their usefulness.

Host translation at the nexus of infection and immunity

By controlling gene expression at the level of mRNA translation, organisms temporally and spatially respond swiftly to an ever-changing array of environmental conditions. This capacity for rapid response is ideally suited for mobilizing host defenses and coordinating innate responses to infection. Not surprisingly, a growing list of pathogenic microbes target host mRNA translation for inhibition. Infection with bacteria, protozoa, viruses, and fungi has the capacity to interfere with ongoing host protein synthesis and thereby trigger and/or suppress powerful innate responses. This review discusses how diverse pathogens manipulate the host translation machinery and the impact of these interactions on infection biology and the immune response.