Epithelial cell polarity: what flies can teach us about cancer.

Epithelial cells are polarized along their apical-basal axis. Much of the cellular machinery that goes into establishing and maintaining epithelial cell polarity is evolutionarily conserved. Model organisms, including the fruit fly, Drosophila melanogaster, are thus particularly useful for the study of cell polarity. Work in Drosophila has identified several important components of the polarity machinery and has also established the surprising existence of a secondary cell polarity pathway required only under conditions of energetic stress. This work has important implications for the understanding of human cancer. Most cancers are epithelial in origin, and the loss of cell polarity is a critical step towards malignancy. Thus a better understanding of how polarity is established and maintained in epithelial cells will help us to understand the process of malignant transformation and may lead to improved therapies. In the present chapter we discuss the current understanding of how epithelial cell polarity is regulated and the known associations between polarity factors and cancer.

The NLR adaptor ASC/PYCARD regulates DUSP10, mitogen-activated protein kinase (MAPK), and chemokine induction independent of the inflammasome.

ASC/PYCARD is a common adaptor for a diverse set of inflammasomes that activate caspase-1, most prominently the NLR-based inflammasome. Mounting evidence indicates that ASC and these NLRs also elicit non-overlapping functions, but the molecular basis for this difference is unclear. To address this, we performed microarray and network analysis of ASC shRNA knockdown cells. In pathogen-infected cells, an ASC-dependent interactome is centered on the mitogen-activated protein kinase (MAPK) ERK and on multiple chemokines. ASC did not affect the expression of MAPK but affected its phosphorylation by pathogens and Toll-like receptor agonists via suppression of the dual-specificity phosphatase, DUSP10/MKP5. Chemokine induction, DUSP function, and MAPK phosphorylation were independent of caspase-1 and IL-1ß. MAPK activation by pathogen was abrogated in Asc(-/-) but not Nlrp3(-/-), Nlrc4(-/-), or Casp1(-/-) macrophages. These results demonstrate a function for ASC that is distinct from the inflammasome in modulating MAPK activity and chemokine expression and further identify DUSP10 as a novel ASC target.

NLRP3 (NALP3, Cryopyrin) facilitates in vivo caspase-1 activation, necrosis, and HMGB1 release via inflammasome-dependent and -independent pathways.

Bacterial infection elicits a range of beneficial as well as detrimental host inflammatory responses. Key among these responses are macrophage/monocyte necrosis, release of the proinflammatory factor high-mobility group box 1 protein (HMGB1), and induction of the cytokine IL-1. Although the control of IL-1beta has been well studied, processes that control macrophage cell death and HMGB1 release in animals are poorly understood. This study uses Klebsiella pneumonia as a model organism because it elicits all three responses in vivo. The regulation of these responses is studied in the context of the inflammasome components NLRP3 and ASC, which are important for caspase-1 activation and IL-1beta release. Using a pulmonary infection model that reflects human infection, we show that K. pneumonia-induced mouse macrophage necrosis, HMGB1, and IL-1beta release are dependent on NLRP3 and ASC. K. pneumoniae infection of mice lacking Nlrp3 results in decreased lung inflammation and reduced survival relative to control, indicating the overall protective role of this gene. Macrophage/monocyte necrosis and HMGB1 release are controlled independently of caspase-1, suggesting that the former two responses are separable from inflammasome-associated functions. These results provide critical in vivo validation that the physiologic role of NLRP3 and ASC is not limited to inflammasome formation.

Drosophila MUS312 and the vertebrate ortholog BTBD12 interact with DNA structure-specific endonucleases in DNA repair and recombination.

DNA recombination and repair pathways require structure-specific endonucleases to process DNA structures that include forks, flaps, and Holliday junctions. Previously, we determined that the Drosophila MEI-9-ERCC1 endonuclease interacts with the MUS312 protein to produce meiotic crossovers, and that MUS312 has a MEI-9-independent role in interstrand crosslink (ICL) repair. The importance of MUS312 to pathways crucial for maintaining genomic stability in Drosophila prompted us to search for orthologs in other organisms. Based on sequence, expression pattern, conserved protein-protein interactions, and ICL repair function, we determined that the mammalian ortholog of MUS312 is BTBD12. Orthology between these proteins and S. cerevisiae Slx4 helped identify a conserved interaction with a second structure-specific endonuclease, SLX1. Genetic and biochemical evidence described here and in related papers suggest that MUS312 and BTBD12 direct Holliday junction resolution by at least two distinct endonucleases in different recombination and repair contexts.

MAVS-mediated apoptosis and its inhibition by viral proteins.

BACKGROUND: Host responses to viral infection include both immune activation and programmed cell death. The mitochondrial antiviral signaling adaptor, MAVS (IPS-1, VISA or Cardif) is critical for host defenses to viral infection by inducing type-1 interferons (IFN-I), however its role in virus-induced apoptotic responses has not been elucidated. PRINCIPAL FINDINGS: We show that MAVS causes apoptosis independent of its function in initiating IFN-I production. MAVS-induced cell death requires mitochondrial localization, is caspase dependent, and displays hallmarks of apoptosis. Furthermore, MAVS(-/-) fibroblasts are resistant to Sendai virus-induced apoptosis. A functional screen identifies the hepatitis C virus NS3/4A and the Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) nonstructural protein (NSP15) as inhibitors of MAVS-induced apoptosis, possibly as a method of immune evasion. SIGNIFICANCE: This study describes a novel role for MAVS in controlling viral infections through the induction of apoptosis, and identifies viral proteins which inhibit this host response.

Neisseria gonorrhoeae activates the proteinase cathepsin B to mediate the signaling activities of the NLRP3 and ASC-containing inflammasome.

Neisseria gonorrhoeae is a common sexually transmitted pathogen that significantly impacts female fertility, neonatal health, and transmission of HIV worldwide. N. gonorrhoeae usually causes localized inflammation of the urethra and cervix by inducing production of IL-1beta and other inflammatory cytokines. Several NLR (nucleotide-binding domain, leucine-rich repeat) proteins are implicated in the formation of pro-IL-1beta-processing complexes called inflammasomes in response to pathogens. We demonstrate that NLRP3 (cryopyrin, NALP3) is the primary NLR required for IL-1beta/IL-18 secretion in response to N. gonorrhoeae in monocytes. We also show that N. gonorrhoeae infection promotes NLRP3-dependent monocytic cell death via pyronecrosis, a recently described pathway with morphological features of necrosis, including release of the strong inflammatory mediator HMBG1. Additionally, N. gonorrhoeae activates the cysteine protease cathepsin B as measured by the breakdown of a cathepsin B substrate. Inhibition of cathepsin B shows that this protease is an apical controlling step in the downstream activities of NLRP3 including IL-1beta production, pyronecrosis, and HMGB1 release. Nonpathogenic Neisseria strains (Neisseria cinerea and Neisseria flavescens) do not activate NLRP3 as robustly as N. gonorrhoeae. Conditioned medium from N. gonorrhoeae contains factors capable of initiating the NLRP3-mediated signaling events. Isolated N. gonorrhoeae lipooligosaccharide, a known virulence factor from this bacterium that is elaborated from the bacterium in the form of outer membrane blebs, activates both NLRP3-induced IL-1beta secretion and pyronecrosis. Our findings indicate that activation of NLRP3-mediated inflammatory response pathways is an important venue associated with host response and pathogenesis of N. gonorrhoeae.

C-C chemokine receptor 5 on pulmonary fibrocytes facilitates migration and promotes metastasis via matrix metalloproteinase 9.

Previously, our group has used a B16-F10 melanoma model to show that C-C chemokine receptor 5 (CCR5) knockout (CCR5(-/-)) mice form fewer pulmonary metastases than wild-type mice. This advantage can be eliminated by injecting CCR5(-/-) mice with wild-type pulmonary mesenchymal cells before tumor injection. In this article, we present the mechanisms underlying this finding. First, we demonstrate that wild-type mesenchymal cells migrate to CCL4 more efficiently in vitro than CCR5(-/-) cells. Wild-type mesenchymal cells were also 3.6 (1.85 to 5.85) times more efficient than CCR5(-/-) cells at migrating into the lung after intravenous injection (P < 0.01). The injection of wild-type but not CCR5(-/-) mesenchymal cells led to a 7.0 +/- 1.6 (P < 0.05)-fold induction of matrix metalloproteinase 9 (MMP9) in the host lung. Neither wild-type nor CCR5(-/-) cells caused significant increases in MMP2, MMP3, or MMP8. Inhibition of the gelatinase activity of MMP9 decreased the number of metastases and restored the advantage that CCR5(-/-) mice have over wild-type mice. Further analysis showed that the CCR5(+) mesenchymal cells expressed CD45(+) and CD13(+) but did not express alpha-smooth muscle actin. This phenotype is characteristic of a subset of mesenchymal cells called fibrocytes. Together, these data suggest a novel role for CCR5 in the migration of pulmonary fibrocytes and the promotion of metastasis.

NLRs at the intersection of cell death and immunity.

Inflammation is a crucial element of the host response to cellular insult. Pathogen-induced inflammation includes a molecular pathway which proceeds through activation of the protease caspase-1 to the release of the inflammatory cytokines interleukin-1 (IL-1) and IL-18. Importantly, pathogens may also induce forms of cell death that have inherently pro-inflammatory features. Here, we review recent evidence demonstrating that NLR (nucleotide-binding domain, leucine-rich repeat containing) family proteins serve as a common component of both caspase-1-activated apoptotic pathways and caspase-independent necrotic pathways. Parallels are drawn between NLR protein function and the activity of structurally similar proteins involved in cell death: the apoptotic mediator APAF1 (apoptotic-protease-activating factor 1) and the plant disease resistance NBS-LRR (nucleotide-binding site leucine-rich repeats) proteins.

Interstrand crosslink repair: can XPF-ERCC1 be let off the hook?

The interstrand crosslink (ICL) presents a challenge to both the cell and the scientist. From a clinical standpoint, these lesions are particularly intriguing: ICL-inducing agents are powerful tools in cancer chemotherapy, and spontaneous ICLs have recently been linked with accelerated aging phenotypes. Nevertheless, the ICL repair process has proven difficult to elucidate. Here we discuss recent additions to the current model and argue that the endonuclease xeroderma pigmentosum complementation group F-excision repair cross-complementing rodent repair deficiency complementation group 1 (XPF-ERCC1) has been heretofore misplaced. During nucleotide excision repair, XPF-ERCC1 makes a single-strand nick adjacent to the lesion. XPF-ERCC1 has been thought to play an analogous role in ICL repair. However, recent data has implicated XPF-ERCC1 in homologous recombination. We suggest that this role, rather than its function in nucleotide excision repair, defines its importance to ICL repair.

NLRX1 is a regulator of mitochondrial antiviral immunity.

The RIG-like helicase (RLH) family of intracellular receptors detect viral nucleic acid and signal through the mitochondrial antiviral signalling adaptor MAVS (also known as Cardif, VISA and IPS-1) during a viral infection. MAVS activation leads to the rapid production of antiviral cytokines, including type 1 interferons. Although MAVS is vital to antiviral immunity, its regulation from within the mitochondria remains unknown. Here we describe human NLRX1, a highly conserved nucleotide-binding domain (NBD)- and leucine-rich-repeat (LRR)-containing family member (known as NLR) that localizes to the mitochondrial outer membrane and interacts with MAVS. Expression of NLRX1 results in the potent inhibition of RLH- and MAVS-mediated interferon-beta promoter activity and in the disruption of virus-induced RLH-MAVS interactions. Depletion of NLRX1 with small interference RNA promotes virus-induced type I interferon production and decreases viral replication. This work identifies NLRX1 as a check against mitochondrial antiviral responses and represents an intersection of three ancient cellular processes: NLR signalling, intracellular virus detection and the use of mitochondria as a platform for anti-pathogen signalling. This represents a conceptual advance, in that NLRX1 is a modulator of pathogen-associated molecular pattern receptors rather than a receptor, and identifies a key therapeutic target for enhancing antiviral responses.

Microbial pathogen-induced necrotic cell death mediated by the inflammasome components CIAS1/cryopyrin/NLRP3 and ASC.

Cryopyrin (CIAS1, NLRP3) and ASC are components of the inflammasome, a multiprotein complex required for caspase-1 activation and cytokine IL-1beta production. CIAS1 mutations underlie autoinflammation characterized by excessive IL-1beta secretion. Disease-associated cryopyrin also causes a program of necrosis-like cell death in macrophages, the mechanistic details of which are unknown. We find that patient monocytes carrying disease-associated CIAS1 mutations exhibit excessive necrosis-like death by a process dependent on ASC and cathepsin B, resulting in spillage of the proinflammatory mediator HMGB1. Shigella flexneri infection also causes cryopyrin-dependent macrophage necrosis with features similar to the death caused by mutant CIAS1. This necrotic death is independent of caspase-1 and IL-1beta, and thus independent of the inflammasome. Furthermore, necrosis of primary macrophages requires the presence of Shigella virulence genes. While similar proteins mediate pathogen-induced cell death in plants, this report identifies cryopyrin as an important host regulator of programmed pathogen-induced necrosis in animals, a process we term pyronecrosis.

Cryopyrin/NALP3 binds ATP/dATP, is an ATPase, and requires ATP binding to mediate inflammatory signaling.

The CATERPILLER (CLR/NLR) gene family encodes a family of putative nucleotide-binding proteins important for host defense. Although nucleotide binding is thought to be central to this family, this aspect is largely unstudied. The CATERPILLER protein cryopyrin/NALP3 regulates IL-1beta processing by assembling the multimeric inflammasome complex. Mutations within the exon encoding the nucleotide-binding domain are associated with hereditary periodic fevers characterized by constitutive IL-1beta production. We demonstrate that purified cryopyrin binds ATP, dATP, and ATP-agarose, but not CTP, GTP, or UTP, and exhibits ATPase activity. Mutation of the nucleotide-binding domain reduces ATP binding, caspase-1 activation, IL-1beta production, cell death, macromolecular complex formation, self-association, and association with the inflammasome component ASC. Disruption of nucleotide binding abolishes the constitutive activation of disease-associated mutants, identifying nucleotide binding by cryopyrin as a potential target for antiinflammatory pharmacologic intervention.

Global functional analysis of nucleophosmin in Taxol response, cancer, chromatin regulation, and ribosomal DNA transcription.

Analysis of lung cancer response to chemotherapeutic agents showed the accumulation of a Taxol-induced protein that reacted with an anti-phospho-MEK1/2 antibody. Mass spectroscopy identified the protein as nucleophosmin/B23 (NPM), a multifunctional protein with diverse roles: ribosome biosynthesis, p53 regulation, nuclear-cytoplasmic shuttling, and centrosome duplication. Our work demonstrates that following cellular exposure to mitosis-arresting agents, NPM is phosphorylated and its chromatographic property is altered, suggesting changes in function during mitosis. To determine the functional relevance of NPM, its expression in tumor cells was reduced by siRNA. Cells with reduced NPM were treated with Taxol followed by microarray profiling accompanied by gene/protein pathway analyses. These studies demonstrate several expected and unexpected consequences of NPM depletion. The predominant downstream effectors of NPM are genes involved in cell proliferation, cancer, and the cell cycle. In congruence with its role in cancer, NPM is over-expressed in primary malignant lung cancer tissues. We also demonstrate a role for NPM in the expression of genes encoding SET (TAF1beta) and the histone methylase SET8. Additionally, we show that NPM is required for a previously unobserved G2/M upregulation of TAF1A, which encodes the rDNA transcription factor TAF(I)48. These results demonstrate multi-faceted functions of NPM that can affect cancer cells.

Cutting edge: ASC mediates the induction of multiple cytokines by Porphyromonas gingivalis via caspase-1-dependent and -independent pathways.

Porphyromonas gingivalis (Pg) is a major etiologic agent for chronic periodontitis. Tissue destruction by Pg results partly from induction of host inflammatory responses through TLR2 signaling. This work examines the role of apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), an adaptor molecule important for TLR-mediated caspase-1 activation. Results demonstrate that ASC levels are stable upon infection of human THP1 monocytic cells with Pg but decrease after cytokine induction. Using short hairpin RNA, we demonstrate an essential role for ASC in induction of IL-1beta by TLR2, 4, and 5 agonists, live Escherichia coli, and Pg. Induction of IL-6, IL-8, IL-10, and TNF also requires ASC, but this induction is not inhibited by IL-1 receptor antagonist or caspase-1 inhibitor. Similar results in U937 indicate broad applicability of these findings. Pg-infected ASC knockdown THP1 cells exhibit reduced transcript levels and NF-kappaB activation. These results suggest a role for ASC in cytokine induction by Pg involving both caspase-1-dependent and -independent mechanisms.

Microtubule stabilizing agents: their molecular signaling consequences and the potential for enhancement by drug combination.

Microtubule stabilization by chemotherapy is a powerful weapon in the war against cancer. Disruption of the mitotic spindle activates a number of signaling pathways, with consequences that may protect the cell or lead to its death via apoptosis. Taxol, the first microtubule stabilizing drug to be identified, has been utilized successfully in the treatment of solid tumors for two decades. Several features, however, make this drug less than ideal, and the search for next generation stabilizing drugs with increased efficacy has been intense and fruitful. Microtubule stabilizing agents (MSAs), including the taxanes, the epothilones, discodermolide, laulimalide, and eleutherobin, form an important and expanding family of chemotherapeutic agents. A strong understanding of their molecular signaling consequences is essential to their value, particularly in regard to their potential for combinatorial chemotherapy - the use of multiple agents to enhance the efficacy of cancer treatment. Here we present a critical review of research on the signaling mechanisms induced by MSAs, their relevance to apoptosis, and their potential for exploitation by combinatorial therapy.

Upregulation of the stress-associated gene p8 in mouse models of demyelination and in multiple sclerosis tissues.

Cuprizone-induced demyelination is a mouse model of multiple sclerosis (MS) as cuprizone-fed mice exhibit neuroinflammation and demyelination in the brain. Upon removal of cuprizone from the diet, inflammation is resolved and reparative remyelination occurs. In an Affymetrix GeneChip analysis, the stress-associated gene p8 was strongly upregulated (>10x) during cuprizone-induced demyelination but not remyelination. We verified this upregulation (>15x) of p8 in the CNS during demyelination by real-time polymerase chain reaction (PCR). This upregulation is brain-specific, as p8 is not elevated in the liver, lung, kidney, spleen, and heart of cuprizone-treated mice. We also localized the cellular source of p8 during cuprizone treatment, and further found elevated expression during embryogenesis but not in normal adult brain. Compared with wild-type controls, the death of oligodendrocytes in p8-/- mice is delayed, as is microglial recruitment to areas of demyelination. The corpus callosum of p8-/- mice demyelinates at a slower rate than wild-type mice, suggesting that p8 exacerbates CNS inflammation and demyelination. Enhanced expression of p8 is also observed in the spinal cords of mice with acute experimental autoimmune encephalomyelitis (EAE) induced by PLP139-151 peptide (10x). Increased expression is detected during disease onset and expression wanes during the remission phase. Finally, p8 is found upregulated (8x) in post-mortem tissue from MS patients and is higher in the plaque tissue compared with adjacent normal-appearing white and gray matter. Thus, p8 is an excellent candidate as a novel biomarker of demyelination.

Transcriptional profiling of targets for combination therapy of lung carcinoma with paclitaxel and mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor.

A combination of paclitaxel (Taxol) and mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK/Erk) inhibitor represents a rational new approach to chemotherapy. We performed Affymetrix microarray analysis to understand the global effects of this combination in lung carcinoma. Genes involved in cell cycle control, apoptosis, adhesion, proliferation, invasion, and metastasis were modulated. We observed similar patterns of gene modulation in ovarian and melanoma cell lines, indicating the general applicability of these findings. Functional genomic analysis identified two genes as new targets of drug-induced tumor apoptosis. The MGSA/Gro1 gene, important in melanoma growth, was induced by paclitaxel and reduced by MEK inhibition. Blockage of paclitaxel-induced melanoma growth stimulatory activity significantly reduced melanoma growth. Additionally, the expression of topoisomerase III beta, which exhibited a clear pattern of gene reduction by a combination of the two drugs, was significantly increased (5.7-fold) in primary lung cancers but not adjacent tissues. These findings provide potential new biomarkers and gene targets for the development of improved cancer treatment.