Host insulin stimulates Echinococcus multilocularis insulin signalling pathways and larval development.

BACKGROUND The metacestode of the tapeworm Echinococcus multilocularis is the causative agent of alveolar echinococcosis, a lethal zoonosis. Infections are initiated through establishment of parasite larvae within the intermediate host's liver, where high concentrations of insulin are present, followed by tumour-like growth of the metacestode in host organs. The molecular mechanisms determining the organ tropism of E. multilocularis or the influences of host hormones on parasite proliferation are poorly understood. RESULTS Using in vitro cultivation systems for parasite larvae we show that physiological concentrations (10 nM) of human insulin significantly stimulate the formation of metacestode larvae from parasite stem cells and promote asexual growth of the metacestode. Addition of human insulin to parasite larvae led to increased glucose uptake and enhanced phosphorylation of Echinococcus insulin signalling components, including an insulin receptor-like kinase, EmIR1, for which we demonstrate predominant expression in the parasite's glycogen storage cells. We also characterized a second insulin receptor family member, EmIR2, and demonstrated interaction of its ligand binding domain with human insulin in the yeast two-hybrid system. Addition of an insulin receptor inhibitor resulted in metacestode killing, prevented metacestode development from parasite stem cells, and impaired the activation of insulin signalling pathways through host insulin. CONCLUSIONS Our data indicate that host insulin acts as a stimulant for parasite development within the host liver and that E. multilocularis senses the host hormone through an evolutionarily conserved insulin signalling pathway. Hormonal host-parasite cross-communication, facilitated by the relatively close phylogenetic relationship between E. multilocularis and its mammalian hosts, thus appears to be important in the pathology of alveolar echinococcosis. This contributes to a closer understanding of organ tropism and parasite persistence in larval cestode infections. Furthermore, our data show that Echinococcus insulin signalling pathways are promising targets for the development of novel drugs.

Phorbol-12-myristate-13-acetate induces nociceptin in human Mono Mac 6 cells via multiple transduction signalling pathways.

BACKGROUND Nociceptin in the peripheral circulation has been proposed to have an immunoregulatory role with regards to inflammation and pain. However, the mechanisms involved in its regulation are still not clear. The aim of this study was to investigate signalling pathways contributing to the regulation of the expression of nociceptin under inflammatory conditions. METHODS Mono Mac 6 cells (MM6) were cultured with or without phorbol-12-myristate-13-acetate (PMA). Prepronociceptin (ppNOC) mRNA was detected by RT-qPCR and extracellular nociceptin by fluorescent-enzyme immunoassay. Intracellular nociceptin and phosphorylated kinases were measured using flow cytometry. To evaluate the contribution of various signalling pathways to the regulation of ppNOC mRNA and nociceptin protein, cells were pre-treated with specific kinase inhibitors before co-culturing with PMA. RESULTS ppNOC mRNA was expressed in untreated MM6 at low concentrations. Exposure of cells to PMA upregulated ppNOC after nine h compared with controls without PMA (median normalized ratio with IQR: 0.18 (0.15-0.26) vs. 0 (0-0.02), P<0.01). Inhibition of mitogen-activated protein kinases specific for signal transduction reversed the PMA effects (all P<0.001). Induction of nociceptin protein concentrations in PMA stimulated MM6 was prevented predominantly by identity of ERK inhibitor (P<0.05). CONCLUSIONS Upregulation of nociceptin expression by PMA in MM6 cells involves several pathways. Underlying mechanisms involved in nociceptin expression may lead to new insights in the treatment of pain and inflammatory diseases.

Signalling in malaria parasites. The MALSIG consortium

Depending on their developmental stage in the life cycle, malaria parasites develop within or outside host cells, and in extremely diverse contexts such as the vertebrate liver and blood circulation, or the insect midgut and hemocoel. Cellular and molecular mechanisms enabling the parasite to sense and respond to the intra- and the extra-cellular environments are therefore key elements for the proliferation and transmission of Plasmodium, and therefore are, from a public health perspective, strategic targets in the fight against this deadly disease. The MALSIG consortium, which was initiated in February 2009, was designed with the primary objective to integrate research ongoing in Europe and India on i) the properties of Plasmodium signalling molecules, and ii) developmental processes occurring at various points of the parasite life cycle. On one hand, functional studies of individual genes and their products in Plasmodium falciparum (and in the technically more manageable rodent model Plasmodium berghei) are providing information on parasite protein kinases and phosphatases, and of the molecules governing cyclic nucleotide metabolism and calcium signalling. On the other hand, cellular and molecular studies are elucidating key steps of parasite development such as merozoite invasion and egress in blood and liver parasite stages, control of DNA replication in asexual and sexual development, membrane dynamics and trafficking, production of gametocytes in the vertebrate host and further parasite development in the mosquito. This article, which synthetically reviews such signalling molecules and cellular processes, aims to provide a glimpse of the global frame in which the activities of the MALSIG consortium will develop over the next three years.