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Modulation of the Host Cell Proteome by the Intracellular Apicomplexan Parasite Toxoplasma gondii

Department of Pre-Clinical Veterinary Science and Veterinary Pathology, Faculty of Veterinary Science, University of Liverpool, Liverpool L69 7ZJ, United Kingdom,¹ Division of Infection and Immunity and Sir Henry Wellcome Functional Genomics Facility, University of Glasgow, Glasgow G12 8QQ, United Kingdom,² School of Computer Science, University of Manchester, Manchester M13 9PL, United Kingdom,³ Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine, Lexington, Kentucky 40536⁴

Received 10 August 2007/ Returned for modification 19 September 2007/ Accepted 21 October 2007

To investigate how intracellular parasites manipulate their host cell environment at the molecular level, we undertook a quantitative proteomic study of cells following infection with the apicomplexan parasite Toxoplasma gondii. Using conventional two-dimensional electrophoresis, difference gel electrophoresis (DIGE), and mass spectrometry, we identified host proteins that were consistently modulated in expression following infection. We detected modification of protein expression in key metabolic pathways, including glycolysis, lipid and sterol metabolism, mitosis, apoptosis, and structural-protein expression, suggestive of global reprogramming of cell metabolism by the parasite. Many of the differentially expressed proteins had not been previously implicated in the response to the parasite, while others provide important corroborative protein evidence for previously proposed hypotheses of pathogen-cell interactions. Significantly, over one-third of all modulated proteins were mitochondrial, and this was further investigated by DIGE analysis of a mitochondrion-enriched preparation from infected cells. Comparison of our proteomic data with previous transcriptional studies suggested that a complex relationship exits between transcription and protein expression that may be partly explained by posttranslational modifications of proteins and revealed the importance of investigating protein changes when interpreting transcriptional data. To investigate this further, we used phosphatase treatment and DIGE to demonstrate changes in the phosphorylation states of several key proteins following infection. Overall, our findings indicate that the host cell proteome responds in a dramatic way to T. gondii invasion, in terms of both protein expression changes and protein modifications, and reveal a complex and intimate molecular relationship between host and parasite.

Published ahead of print on 29 October 2007.

Editor: W. A. Petri, Jr.