Rac1, RhoA, and Cdc42 participate in HeLa cell invasion by group B streptococcus

The group B streptococcus (GBS) is an important human pathogen with the ability to cause invasive disease. To do so, the bacteria must invade host cells. It has been well documented that GBS are able to invade a variety of nonphagocytic host cell types, and this process is thought to involve a number of pathogen-host cell interactions. While some of the molecular aspects of the GBS-host cell invasion process have been characterized, many events still remain unclear. The objective of this investigation was to evaluate the role of the Rho-family GTPases Rac, Rho, and Cdc42 in GBS invasion into epithelial cells. The epithelial cell invasion process was modeled using HeLa 229 cell culture. Treatment of HeLa cells with 10 microM compactin, a pan-GTPase inhibitor, abolished GBS internalization, suggesting that GTPases are involved in the GBS invasion process. The addition of Toxin B or exoenzyme C3 to HeLa cells before GBS infection reduced invasion by 50%, further suggesting that the Rho-family GTPases are involved in GBS entry. Examining invasion of GBS into HeLa cells with altered genetic backgrounds was used to confirm these findings; GBS invasion into HeLa cells transiently transfected with dominant negative Rac1, Cdc42, or RhoA reduced invasion by 75%, 51%, and 42%, respectively. Results of this study suggest that the Rho-family GTPases are required for efficient invasion of HeLa cells by GBS.     

Human U87 astrocytoma cell invasion induced by interaction of βig-h3 with integrin α5β1 involves calpain-2

It is known that βig-h3 is involved in the invasive process of many types of tumors, but its mechanism in glioma cells has not been fully clarified. Using immunofluorescent double-staining and confocal imaging analysis, and co-immunoprecipitation assays, we found that βig-h3 co-localized with integrin α5β1 in U87 cells. We sought to elucidate the function of this interaction by performing cell invasion assays and gelatin zymography experiments. We found that siRNA knockdowns of βig-h3 and calpain-2 impaired cell invasion and MMP secretion. Moreover, βig-h3, integrins and calpain-2 are known to be regulated by Ca(2+), and they are also involved in tumor cell invasion. Therefore, we further investigated if calpain-2 was relevant to βig-h3-integrin α5β1 interaction to affect U87 cell invasion. Our data showed that βig-h3 co-localized with integrin α5β1 to enhance the invasion of U87 cells, and that calpain-2, is involved in this process, acting as a downstream molecule.     

Evolution and invasion dynamics of multiple infections with Wolbachia investigated using matrix based models

Endosymbiotic bacteria are often transmitted vertically from one host generation to the next via oocytes cytoplasm. The generally small number of colonizing bacteria in the oocytes leads to a bottleneck at each generation, resulting in genetic homogenization of the symbiotic population. Nevertheless, in many of the species infected by Wolbachia (maternally transmitted bacteria), individuals do sometimes simultaneously harbor several bacterial strains, owing to the fact that Wolbachia induces cytoplasmic incompatibility (CI) that maintains multiple infections. CI occurs in crosses in which the male is infected by at least one Wolbachia strain that the female lacks, and consequently it favors individuals with the greatest symbiotic diversity. CI results in death of offspring in diploid species. In haplodiploid individuals, unfertilized eggs hatch normally into males and fertilized ones, which would lead to females, either die (female mortality type: FM) or develop into males (male development type: MD). Until now, only one theoretical study, restricted to diploid species, has investigated the associations where multiple CI-inducing Wolbachia co-exist, and explored the conditions under which multiple infections can spread. The consequences of double infections on Wolbachia maintenance in host populations, and the selective pressures to which it is subjected have not yet been analysed. Here, we have re-written a model previously developed for single infection in matrix form, which allows easy extension to multiple infections and introduction of mutant strains. We show that (i) the CI type has a strong influence on invasiveness and maintenance of multiple infections; (ii) double infection lowers the invasion threshold of less competitive strains that hitch-hike with their companion strain; (iii) when multiple infections occur, as in single infections, the strains selected are those which maximize the production of infected offspring; and (iv) for the MD CI type, invasion of mutant strains can carry the whole infection to extinction.     

Dose-dependent infection rates of parasites produce the Allee effect in epidemiology

In many epidemiological models of microparasitic infections it is assumed that the infection process is governed by the mass-action principle, i.e. that the infection rate per host and per parasite is a constant. Furthermore, the parasite-induced host mortality (parasite virulence) and the reproduction rate of the parasite are often assumed to be independent of the infecting parasite dose. However, there is empirical evidence against those three assumptions: the infection rate per host is often found to be a sigmoidal rather than a linear function of the parasite dose to which it is exposed; and the lifespan of infected hosts as well as the reproduction rate of the parasite are often negatively correlated with the parasite dose. Here, we incorporate dose dependences into the standard modelling framework for microparasitic infections, and draw conclusions on the resulting dynamics. Our model displays an Allee effect that is characterized by an invasion threshold for the parasite. Furthermore, in contrast to standard epidemiological models a parasite strain needs to have a basic reproductive rate that is substantially greater than 1 to establish an infection. Thus, the conditions for successful invasion of the parasite are more restrictive than in mass-action infection models. The analysis further suggests that negative correlations of the parasite dose with host lifespan and the parasite reproduction rate helps the parasite to overcome the invasion constraints of the Allee-type dynamics.     

Switching Plasmodium falciparum genes on and off for erythrocyte invasion

Culture-adapted lines of the malaria parasite Plasmodium falciparum use alternative pathways for the invasion of erythrocytes. The expression of parasite ligands that are involved in the different pathways varies among parasite lines. Recently, several studies have attempted to characterize the use of different invasion pathways and the expression of specific invasion ligands in field isolates, opening the way to understand how invasion occurs in natural infections. In this review, these findings are discussed in the context of the most recent data on invasion by culture-adapted parasites to describe the current understanding of how wild parasites invade, how the variant expression of invasion ligands relates to switching between alternative invasion pathways and why so many different pathways are needed.     

中国近海入侵贝类及其影响

海洋贝类种类繁多,是近海底栖生态系统的优势种,在生态系统物质循环和能量流动中起着极其重要的作用;但因频繁的人类活动导致的贝类入侵问题,往往使该过程不能正常运转。大量研究表明,入侵贝类会抑制原著贝类或其他生物的生长及拓殖,形成单一优势群落,破坏当地生态系统的平衡,也会对海洋渔业生产和近海工程及作业等造成不可预测的危害。目前,欧美等国家针对该问题已开展了大量工作,十分重视入侵贝类的生物学、生态学与行为学特征及特性的研究,并根据其入侵途径与方式的不同开展了检测、监测、防控及管理工作。但在我国,入侵贝类还未引起相关部门及研究机构的足够重视。本文主要简述了我国近海的3种入侵贝类沙筛贝、指甲履螺和地中海贻贝的生物学、生态学及行为学等特征及其对当地生态系统的影响;同时,根据其特性及入侵过程控制的难易,建议在完善我国入侵贝类数据库的基础上加强早期预警与检测,以及安全防控和管理等工作。     

Membrane and membrane-associated proteins involved in the aggressive phenotype displayed by highly invasive cancer cells

Invasion, the penetration of tumour cells into adjacent tissues, is a fundamental characteristic of malignant carcinomas and a first step in the metastatic process. The molecular mechanisms involved in tumour cell invasion are complex, but over the last couple of decades the knowledge base has grown quite considerably and many proteins with important roles in invasion have been identified and characterised. Benign tumours typically are encapsulated, which inhibits their ability to behave in a malignant manner, meaning these tumours do not grow in a location-limited less aggressive manner, do not invade surrounding tissues and do not metastasise. The ability of malignant tumours to invade and metastasise is the major cause of death for cancer patients. A greater insight into the molecular basis of cancer invasion and metastasis will lead to the development of novel therapies and specific panels of biomarkers for use in the treatment and diagnosis/monitoring in many types of metastatic cancer.     

The development of vaccines: how the past led to the future

The history of vaccine development has seen many accomplishments, but there are still many diseases that are difficult to target, and new technologies are being brought to bear on them. Past successes have been largely due to elicitation of protective antibodies based on predictions made from the study of animal models, natural infections and seroepidemiology. Those predictions have often been correct, as indicated by the decline of many infections for which vaccines have been made over the past 200 years.     

From the laboratory to the patient and back--an interview with Marc Mareel. Interview by Marc E. Bracke

The career of Marc Mareel is a synthesis of scientific research and clinical activity. During his medical studies, he already made his first enthusiastic steps in research via experimental work on avian developmental biology. Later, during his training as a radiotherapist, he founded his own laboratory for experimental cancer research. There he built up his international reputation as a pioneer in invasion research. Although invasion is the hallmark of tumor malignancy, he also kept an open mind about invasion in non-cancer conditions, such as in placental behavior, developmental biology, immunology and parasitology. His contribution to our understanding of invasion mechanisms has been both technical and conceptual. A number of assays have been developed in his lab, such as the embryonic chick heart and collagen gel invasion models, that have been (and still are) useful for many other research teams. He also contributed to the discovery of a number of key elements in the process of invasion, such as the stromal influence (including its extracellular matrix) and the cadherin family of cell-cell adhesion molecules. Concerning metastasis formation, he developed the original concept that a number of interacting eco-systems are implicated, such as the primary tumor, regional lymph nodes, the bone marrow and the (pre)metastatic niches in distant organs. Since his retirement, Marc Mareel has continued to integrate clinical practice with research creativity. He favours the idea of translational research bringing the results of laboratory findings to medical applications, and exploiting the feedback to the laboratory. The team in the Laboratory of Experimental Cancer Research at Ghent University currently consists of about 25 collaborators, who continue to appreciate his inspiring ideas and suggestions.     

The ins and outs of host‐microsporidia interactions during invasion,proliferation and exit

Microsporidia are a large group of fungal‐related obligate intracellular parasites. They are responsible for infections in humans as well as in agriculturally and environmentally important animals. Although microsporidia are abundant in nature, many of the molecular mechanisms employed during infection have remained enigmatic. In this review, we highlight recent work showing how microsporidia invade, proliferate and exit from host cells. During invasion, microsporidia use spore wall and polar tube proteins to interact with host receptors and adhere to the host cell surface. In turn, the host has multiple defence mechanisms to prevent and eliminate these infections. Microsporidia encode numerous transporters and steal host nutrients to facilitate proliferation within host cells. They also encode many secreted proteins which may modulate host metabolism and inhibit host cell defence mechanisms. Spores exit the host in a non‐lytic manner that is dependent on host actin and endocytic recycling proteins. Together, this work provides a fuller picture of the mechanisms that these fascinating organisms use to infect their hosts.     

Foodborne Salmonella ecology in the avian gastrointestinal tract

Foodborne Salmonella continues to be a major cause of salmonellosis with Salmonella Enteritidis and S. Typhimurium considered to be responsible for most of the infections. Investigation of outbreaks and sporadic cases has indicated that food vehicles such as poultry and poultry by-products including raw and uncooked eggs are among the most common sources of Salmonella infections. The dissemination and infection of the avian intestinal tract remain somewhat unclear. In vitro incubation of Salmonella with mammalian tissue culture cells has shown that invasion into epithelial cells is complex and involves several genetic loci and host factors. Several genes are required for the intestinal phase of Salmonella invasion and are located on Salmonella pathogenicity island 1 (SPI 1). Salmonella pathogenesis in the gastrointestinal (GI) tract and the effects of environmental stimuli on gene expression influence bacterial colonization and invasion. Furthermore, significant parameters of Salmonella including growth physiology, nutrient availability, pH, and energy status are considered contributing factors in the GI tract ecology. Approaches for limiting Salmonella colonization have been primarily based on the microbial ecology of the intestinal tract. In vitro studies have shown that the toxic effects of short chain fatty acids (SCFA) to some Enterobacteriaceae, including Salmonella, have resulted in a reduction in population. In addition, it has been established that native intestinal microorganisms such as Lactobacilli provide protective mechanisms against Salmonella in the ceca. A clear understanding of the key factors involved in Salmonella colonization in the avian GI tract has the potential to lead to better approach for more effective control of this foodborne pathogen.     

Under siege: virus control in plant meristems and progeny

In the arms race between plants and viruses, two frontiers have been utilized for decades to combat viral infections in agriculture. First, many pathogenic viruses are excluded from plant meristems, which allows the regeneration of virus-free plant material by tissue culture. Second, vertical transmission of viruses to the host progeny is often inefficient, thereby reducing the danger of viral transmission through seeds. Numerous reports point to the existence of tightly linked meristematic and transgenerational antiviral barriers that remain poorly understood. In this review, we summarize the current understanding of the molecular mechanisms that exclude viruses from plant stem cells and progeny. We also discuss the evidence connecting viral invasion of meristematic cells and the ability of plants to recover from acute infections. Research spanning decades performed on a variety of virus/host combinations has made clear that, beside morphological barriers, RNA interference (RNAi) plays a crucial role in preventing—or allowing—meristem invasion and vertical transmission. How a virus interacts with plant RNAi pathways in the meristem has profound effects on its symptomatology, persistence, replication rates, and, ultimately, entry into the host progeny.

We review what is known about the biological mechanisms regulating virus exclusion from—or invasion of—plant host meristems and progeny, including possible consequences and implications of these phenomena.     

Yeast flocculation and its biotechnological relevance

Adhesion properties of microorganisms are crucial for many essential biological processes such as sexual reproduction, tissue or substrate invasion, biofilm formation and others. Most, if not all microbial adhesion phenotypes are controlled by factors such as nutrient availability or the presence of pheromones. One particular form of controlled cellular adhesion that occurs in liquid environments is a process of asexual aggregation of cells which is also referred to as flocculation. This process has been the subject of significant scientific and biotechnological interest because of its relevance for many industrial fermentation processes. Specifically adjusted flocculation properties of industrial microorganisms could indeed lead to significant improvements in the processing of biotechnological fermentation products such as foods, biofuels and industrially produced peptides. This review briefly summarises our current scientific knowledge on the regulation of flocculation-related phenotypes, their importance for different biotechnological industries, and possible future applications for microorganisms with improved flocculation properties.     

The Plasmodium vivax rhoptry-associated protein 1

Rhoptries are cellular organelles localized at the apical pole of apicomplexan parasites. Their content is rich in lipids and proteins that are released during target cell invasion. Plasmodium falciparum rhoptry-associated protein 1 (RAP1) has been the most widely studied among this parasite species' rhoptry proteins and is considered to be a good anti-malarial vaccine candidate since it displays little polymorphism and induces antibodies in infected humans. Monoclonal antibodies directed against RAP1 are also able to inhibit target cell invasion in vitro and protection against P. falciparum experimental challenge is induced when non-human primates are immunized with this protein expressed in its recombinant form. This study describes identifying and characterizing RAP1 in Plasmodium vivax, the most widespread parasite species causing malaria in humans, producing more than 80 million infections yearly, mainly in Asia and Latin America. This new protein is encoded by a two-exon gene, is proteolytically processed in a similar manner to its falciparum homologue and, as observed by microscopy, the immunofluorescence pattern displayed is suggestive of its rhoptry localization. Further studies evaluating P. vivax RAP1 protective efficacy in non-human primates should be carried out taking into account the relevance that its P. falciparum homologue has as an anti-malarial vaccine candidate.     

Specific and nonspecific T-cell recruitment in viral meningitis: Possible implications for autoimmunity

Specific and nonspecific T-cell invasion into cerebrospinal fluid has been investigated in the nonfatal viral meningoencephalitis induced by intracerebral inoculation of mice with vaccinia virus. At the peak of the inflammatory process on Day 7 approximately 5 to 10% of the Lyt 2⁺ T cells present are apparently specific for vaccinia virus. Concurrently, in mice primed previously with influenza virus, 0.5 to 1.0% of the appropriate T-cell set located in cerebrospinal fluid is reactive to influenza-infected target cells. This vaccinia virus-induced inflammatory exudate may thus contain as many as 500 influenza-immune memory T cells. These findings are discussed from the aspect that such nonspecific T-cell invasion into the central nervous system during aseptic viral meningitis could result in exposure of potentially brain-reactive T cells to central nervous system components.     

Revisiting the use of the invasive species concept: An empirical approach

Invasion science has not been developed without controversies. Two questions that are still unsolved are: what is an invasive species?, and are invasive species an inherent conservation problem? These questions have led to discussions about effects versus origins. In contrast to the definitional problems, a unified framework describing invasion as a step‐by‐step process has been widely accepted. I conducted a bibliographic search with two separate databases searching for (i) evidence of less use of controversial terms over time; (ii) how many articles defined ‘invasive species’; (iii) the criteria used to define a species as invasive; and (iv) in which stage of the invasion continuum were species labelled as invasive located. My results show that controversial terms are widely used, that authors rarely define ‘invasive species’ and, often, it is very complicated to determine which criterion they used. In addition, only a fraction of the species labelled as invasive could be classified as such according to the unified framework of invasion stages. This is not a merely semantic issue, because invasive is a strong and value‐laden term that is used to guide environmental agendas. The uncritical use of a key concept could hamper research, complicate communication among peers and produce mixed results.     

Incorporation of carbon from decomposing litter of two pioneer plant species into microbial communities of the detritusphere

For several Staphylococci, such as Staphylococcus aureus, Staphylococcus saprophyticus, and Staphylococcus epidermidis, invasion of eukaryotic cells has been described and this mechanism has been considered an important part of the infection process. The fibrinogen-binding protein (Fbl) of Staphylococcus lugdunensis, a homolog of the clumping factor A of S. aureus, has been described as fibrinogen-binding adhesin and might promote invasion of cells. We therefore characterized several clinical strains of S. lugdunensis in terms of whole cell fibrinogen and fibronectin binding and correlated these results with the invasion of epithelial and endothelial cells by S. lugdunensis. We described for the first time invasion of cells by S. lugdunensis. As invasion of cells by S. lugdunensis was only partly inhibited by cytochalasin D in contrast to a complete inhibition of invasion of cells by S. aureus, further invasion mechanisms are likely to be present in S. lugdunensis. In addition, the Fbl of S. lugdunensis is not involved in the invasion of cells as ruled out by an isogenic fbl mutant.     

细菌生物薄膜相关感染的靶向治疗

细菌依其生存的环境不同能够在生物薄膜和浮游细菌两种生存形式之间转换。细菌生物薄膜的形成导致对抗生素治疗的低敏感性,是慢性感染过程中的重要因素。细菌生物薄膜形成过程涉及多种因素,相当部分已被证实为抑制生物薄膜形成的潜在靶点。本文主要就近几年抑制生物薄膜形成的靶点筛选作一介绍。