Host Defense Machinery Research Articles

Mechanistic Approaches To The Prevention Of Mutation And Cancer

AbstractCancer and other mutation-related diseases can be prevented at three levels: primary prevention, which is addressed to healthy individuals in order to prevent occurrence of the disease; secondary prevention, which is addressed to early stage patients in order to prevent progression of the disease; and tertiary prevention, which is addressed to patients after therapy in order to prevent relapses of the disease. Although the most obvious approach to prevention is to minimize exposures to recognized risk factors, a complementary strategy is represented by chemoprevention, using dietary and pharmacological agents that reinforce the host defence machinery. Since 1988, I proposed detailed classifications of mechanisms of inhibitors of mutagenesis and carcinogenesis. They may apply not only to cancer but also to other degenerative diseases that have replaced infectious diseases as the leading causes of death in the population. In fact, certain mechanisms, such as damage to nuclear DNA and mtDNA, oxidative stress, chronic inflammation, signal transduction alterations and epigenetic changes may be involved in the pathogenesis of different diseases. Studies performed in our laboratory have shown that certain genomic alterations that are usually investigated in cancer research may also be detected in other chronic diseases, such as atherosclerosis, degenerative heart diseases, chronic obstructive pulmonary diseases, neurological disorders, eye diseases, skin ageing, and alopecia. Similar alterations were investigated in critical periods of life, such as birth and ageing. The nucleotide alterations occurring at birth in the lung render the newborn particularly vulnerable to the action of environmental agents. In fact, we demonstrated that cigarette smoke becomes a potent carcinogen in mice when exposure starts at birth and continues early in life. We investigated a number of chemopreventive agents by evaluating modulation of intermediate biomarkers and carcinogenicity. An optimal agent should not excessively alter the physiological patterns of gene expression, microRNA and proteome profiles, but at the same time it should be effective in inhibiting alterations induced by mutagens and carcinogens. It should be noted that most chemopreventive agents possess pleiotropic properties. The knowledge of mechanisms can be exploited to combine different agents working with complementary mechanisms. Like the therapy of important diseases, such as cancer, cardiovascular diseases, AIDS, etc., uses combinations of drugs, combined chemoprevention is a quite promising strategy. Although a large number of agents are potentially able to prevent cancer, we are in search of tools to predict, hopefully in the single individual, their efficacy and safety in humans.

Viroids

Viroids are small, circular RNA pathogens, which infect several crop plants and can cause diseases of economic importance. They do not code for proteins but they contain a number of RNA structural elements, which interact with factors of the host. The resulting set of sophisticated and specific interactions enables them to use the host machinery for their replication and transport, circumvent its defence reactions and alter its gene expression. Although found in plants, viroids have a distant relative in the animal world: hepatitis delta virus (HDV), a satellite virus of hepatitis B virus, which has a similar rod-like structure and replicates in the nucleus of infected cells. Viroids have also a cellular relative: the retroviroids, found in some plants as independent (non-infectious) RNA replicons with a DNA copy. In this review, we summarize recent progress in understanding viroid biology. We discuss the possible role of recently identified viroid-binding host proteins as well as the recent data on the interaction of viroids with one part of the host's defence machinery, the RNA-mediated gene silencing and how this might be connected to viroid replication and pathogenicity.

Bcl-2 and Bcl-X L Regulate Proinflammatory Caspase-1 Activation by Interaction with NALP1

Caspases are intracellular proteases that cleave substrates involved in apoptosis or inflammation. In C. elegans, a paradigm for caspase regulation exists in which caspase CED-3 is activated by nucleotide-binding protein CED-4, which is suppressed by Bcl-2-family protein CED-9. We have identified a mammalian analog of this caspase-regulatory system in the NLR-family protein NALP1, a nucleotide-dependent activator of cytokine-processing protease caspase-1, which responds to bacterial ligand muramyl-dipeptide (MDP). Antiapoptotic proteins Bcl-2 and Bcl-X(L) bind and suppress NALP1, reducing caspase-1 activation and interleukin-1beta (IL-1beta) production. When exposed to MDP, Bcl-2-deficient macrophages exhibit more caspase-1 processing and IL-1beta production, whereas Bcl-2-overexpressing macrophages demonstrate less caspase-1 processing and IL-1beta production. The findings reveal an interaction of host defense and apoptosis machinery.

NADPH Oxidase-mediated Generation of Reactive Oxygen Species is Critically Required for Survival of Undifferentiated Human Promyelocytic Leukemia Cell Line HL-60

Nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) mediated generation of reactive oxygen species (ROS) was originally identified as the powerful host defense machinery against microorganism in phagocytes. But recent reports indicated that some non-phagocytic cells also have the NADPH oxidase activity, and the ROS produced by it may act as cell signal molecule. But as far as today, whether the NADPH oxidase also plays similar role in phagocyte has not been paid much attention. Utilizing the undifferentiated HL-60 promyelocytic leukemia cells as a model, the aim of the present study was to determine whether NADPH oxidase plays a role on ROS generation in undifferentiated HL-60, and the ROS mediated by it was essential for cell's survival. For the first time, we verified that the release of ROS in undifferentiated HL-60 was significantly increased by the stimulation with Calcium ionophore or opsonized zymosan, which are known to trigger respiration burst in phagocytes by NADPH oxidase pathway. Diphenylene iodonium (DPI) or apocynin (APO), two inhibitors of NADPH oxidase, significantly suppressed the increasing of ROS caused by opsonized zymosan. Cell survival assay and fluorescence double dyeing with acridine orange and ethidium bromide showed that DPI and APO, as well as superoxide dismutase (SOD) and catalase (CAT) concentration-dependently decreased the viability of undifferentiated HL-60 cells, whereas exogenous H2O2 can rescue the cells from death obviously. Our results suggested that the ROS, generated by NADPH oxidase play an essential role in the survival of undifferentiated HL-60 cells.

Molecular basis of recognition between phytophthora pathogens and their hosts.

Recognition is the earliest step in any direct plant-microbe interaction. Recognition between Phytophthora pathogens, which are oomycetes, phylogenetically distinct from fungi, has been studied at two levels. Recognition of the host by the pathogen has focused on recognition of chemical, electrical, and physical features of plant roots by zoospores. Both host-specific factors such as isoflavones, and host-nonspecific factors such as amino acids, calcium, and electrical fields, influence zoospore taxis, encystment, cyst germination, and hyphal chemotropism in guiding the pathogen to potential infection sites. Recognition of the pathogen by the host defense machinery has been analyzed using biochemical and genetic approaches. Biochemical approaches have identified chemical elicitors of host defense responses, and in some cases, their cognate receptors from the host. Some elicitors, such as glucans and fatty acids, have broad host ranges, whereas others such as elicitins have narrow host ranges. Most elicitors identified appear to contribute primarily to basic or nonhost resistance. Genetic analysis has identified host resistance (R) genes and pathogen avirulence (Avr) genes that interact in a gene-for-gene manner. One Phytophthora Avr gene, Avr1b from P. sojae, has been cloned and characterized. It encodes a secreted elicitor that triggers a system-wide defense response in soybean plants carrying the cognate R gene, Rps1b.

Structure and function of the N-linked glycans of HBP/CAP37/azurocidin: crystal structure determination and biological characterization of nonglycosylated HBP.

The three N-glycosylation sites of human heparin binding protein (HBP) have been mutated to produce a nonglycosylated HBP (ng-HBP) mutant. ng-HBP has been crystallized and tested for biological activity. Complete X-ray data have been collected to 2.1 A resolution, and the structure has been fully refined to an R-factor of 18.4% (R(free) 27.7%). The ng-HBP structure reveals that neither the secondary nor tertiary structure have changed due to the removal of the glycosylation, as compared to the previously determined glycosylated HBP structure. Although the primary events in N-linked glycosylation occurs concomitant with polypeptide synthesis and therefore possesses the ability to influence early events in protein folding, we see no evidence of glycosylation influencing the structure of the protein. The root-mean-square deviation between the superimposed structures was 0.24 A (on C alpha atoms), and only minor local structural differences are observed. Also, the overall stability of the protein seems to be unaffected by glycosylation, as judged by the B-factors derived from the two X-ray structures. The flexibility of a glycan site may be determined by the local polypeptide sequence and structure rather than the glycan itself. The biological in vitro activity assay data show that ng-HBP, contrary to glycosylated HBP, mediates only a very limited stimulation of the lipopolysaccharide induced cytokine release from human monocytes. In animal models of fecal peritonitis, glycosylated HBP treatment rescues mice from and an otherwise lethal injury. It appears that ng-HBP have significant effect on survival, and it can be concluded that ng-HBP can stimulate the host defence machinery albeit to a lesser extent than glycosylated HBP.

EUROSCAN: the European Organization for Research and Treatment of Cancer (EORTC): Chemoprevention study in lung cancer

Cancers of the lung and head and neck arise as a focal transformation by cigarette smoke of chronically injured epithelium as one of its well recognized causes [7]. Cigarette smoke contains several (pro)carcinogens, and free radicals also [29], and it is in fact surprising that not every smoker becomes a victim of malignant disease (Table 1). It is important to realize that clinical cancer represents only the visible top of a huge iceberg. The submerged base symbolizes the interaction between lifestyle, environmental risk factors and the formidable host defense machinery, protecting the organism along all stages of disease development [2]. Two features of the host defense mechanisms are of particular interest: (a) the one governed by interindividual variability factors, which explains the individual susceptibility to carcinogenic agents, and (b) the fact that host defense mechanisms can be modulated by exogenous interventions.