Tuesday, September 04, 2007

Artemisinin induces calcium-dependent protein secretion in Toxo

Eukaryot Cell. 2007 Aug 31; [Epub ahead of print]

Artemisinin induces calcium-dependent protein secretion in the protozoan parasite Toxoplasma gondii

Nagamune K, Beatty WL, Sibley LD

Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110.

Intracellular calcium controls several crucial cellular events in apicomplexan parasites including protein secretion, motility, invasion into and egress from host cells. The plant compound thapsigargin inhibits the sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA), resulting in elevated calcium and induction of protein secretion in Toxoplasma gondii. Artemisinins are also natural products that show potent and selective activity against parasites, making them useful for the treatment of malaria. While the mechanism of action is uncertain, previous studies have suggested that artemisinin may inhibit SERCA, thus disrupting calcium homeostasis. We cloned the single copy gene encoding SERCA in T. gondii and demonstrate that the protein localizes to the ER in the parasite. In extracellular parasites, TgSERCA partially relocalized to the apical pole, a highly active site for regulated secretion of micronemes. TgSERCA complemented a calcium ATPase-defective yeast mutant and this activity was inhibited by either thapsigargin or artemisinin. Treatment of T. gondii with artemisinin triggered calcium-dependent secretion of microneme proteins, similar to the SERCA inhibitor thapsigargin. Artemisinin treatment also altered intracellular calcium in parasites by increasing the periodicity of calcium oscillations and inducing recurrent, strong calcium spikes, as imaged using fluo-4 labeling. Collectively, these results demonstrate that artemisinin perturbs calcium homeostasis in T. gondii, supporting the idea that Ca(2+)-ATPases are potential drug targets in parasites.

PMID: 17766463 [PubMed - as supplied by publisher]

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