SIGMAL - Targeting malaria transmission through interference with signalling in Plasmodium falciparum gametocytogenesis

EC contribution: : € 969.000
Duration: : 27 months
Starting date: : 01/03/2005
Funding scheme: : Specific Targeted Research Project
Keywords: : Malaria; transmission; gametocyte; cell signalling; protein phosphorylation; antimalarial
Contract/Grant agreement number: : LSHP- CT-2004 -012174
Project web-site:: http://ec.europa.eu/research/health/poverty-diseases/projects/101_en.htm

Background:

Inhibiting transmission of the malaria parasite from infected humans to the mosquito vector would be of considerable interest in the context of malaria control, especially in order to prevent the dissemination of drug-resistant genotypes. Since only sexual forms of the parasite (the gametocytes) are infective to the mosquito, blocking gametocytogenesis would prevent transmission. The molecular control of gametocytogenesis is not understood. Our laboratories have independently brought significant contributions to the characterisation of (i) components of signalling pathways, some of which are likely to be involved in parasite sexual differentiation, and (ii) proteins expressed at the onset of gametocytogenesis, such as Pfg27 and Pfs16. The SIGMAL project merges these lines of investigation to generate an integrated picture of the early events of sexual development at the molecular level. In particular, we use a reverse genetics approach to identify the function of specific genes in gametocytogenesis and gametogenesis. Furthermore, we conduct in silico structure-based and in vitro screening assays for enzymes suspected to be involved in these processes, in order to identify compounds able to interfere with malaria transmission.

Problem:

Malaria is a major public health problem in most of the developing world, and the morbidity and mortality burden inflicted by this disease on many developing countries significantly contributes to hinder their socio-economic development. The emergence and spread of malaria parasites that are resistant to existing anti-malarials exacerbates this problem. A way to control the spread of drug-resistant parasites would be to prevent transmission of the parasite from infected humans to the mosquito vector. To infect a mosquito, the parasite must first develop into specialised sexual forms, the male and female gametocytes, while in the bloodstream of the human host. Although proteins that are specifically expressed at the onset of gametocyte formation have been characterised, the molecular mechanisms controlling this phenomenon remain to be elucidated. It is likely that intracellular signalling, and particularly the phosphorylation of proteins, is involved in gametocyte differentiation and further stages of the sexual cycle. Indeed, reverse genetics data generated within the SIGMAL consortium have already identified protein kinases (the enzymes responsible for protein phosphorylation) and other signalling molecules as essential for Plasmodium sexual development. Interference with these enzymes may provide lead compounds for the development of transmission-blocking drugs.

Aim:

The aims of the project were (i) to further our understanding of gametocyte formation, in particular by characterizing the signalling pathways involved, and (ii) to identify inhibitors of protein kinases that may inhibit sexual development of the parasite, and thus interfere with malaria transmission.
Specific objectives were:

to establish a map of protein-protein interactions for molecules expressed at the onset of gametocytogenesis, identified within the consortium by conventional and genome-wide approaches;
to define the role of phosphorylation of Pfg27, an RNA-binding phosphoprotein essential to sexual development whose structure is solved, integrating biochemical, functional and structural approaches;
to establish the role that protein kinases and proteins expressed specifically in early gametocytes play in differentiation, using a reverse genetics approach;
to elucidate the organization of signalling pathways thought to be involved in gametocytogenesis, such as the cyclic nucleotide and MAPK pathways, central components of which have been characterised in our laboratories.
to establish biochemical assays for signalling protein kinases, and optimize such assays to medium throughput screening.

Expected and obtained results:

improved knowledge of the basic biology of malaria parasites, particularly with respect to cell differentiation. This includes the characterisation of early gametocyte antigens (function, subcellular localisation, interaction with other proteins) and the identification of signalling pathways regulating sexual development.
validation by reverse genetics of novel molecular targets for transmission-blocking intervention. We have produced evidence that some enzymes involved in signal transduction, such as protein kinases, nucleotide cyclases and phosphodiesterases, are dispensable for asexual growth but required for sexual development of the parasite.
identification of protein kinase inhibitors to interfere with the sexual cycle of malaria parasites. Inhibition assays have been developed for several enzymes expressed during gametocytogenesis/gametogenesis, and screening in ongoing.

Potential applications:

List of validated targets for transmission-blocking drugs in the context of anti-malarial chemotherapy.

Coordinator:

Prof. Christian Doerig
INSERM U609
Wellcome Centre for Molecular Parasitology
University of Glasgow Biomedical Research Centre
120 University Place
Glasgow, G12 8TA, Scotland, UK
Tel. +44 1413306201
Fax +44 1413305422
E-mail: cdoer001@udcf.gla.ac.uk

European Commission