: Schistosomiasis is a parasitic disease caused by trematode flatworms of the genus Schistosoma. The second most prevalent tropical disease, it affects hundreds of millions of people worldwide, killing hundreds of thousands each year. Chemotherapeutic agents are used to treat the disease and control its spread. Praziquantel (PZQ), the drug of choice, has minimal side effects and is effective against all schistosome species. However, reports of PZQ-resistant strains of schistosome have begun to emerge. Furthermore, the mode of PZQ action is unknown, although one of its effects is on calcium (Ca2+) homeostasis in the parasite. Our evidence indicates that PZQ acts on schistosome voltage-gated Ca2+ channels. Ca2+ channels are crucial components of excitable cells and participate in the regulation of several Ca2+-dependent processes. They are membrane protein complexes that consist of multiple subunits, including the pore-forming, voltage-sensing alpha1 subunit. The most thoroughly studied auxiliary subunit is the Beta subunit, which modulates Ca2+ channel properties. We have cloned 3 Ca2+ channel alpha1 subunits and 2 Beta subunit sequences (SmCavBetaA, SmCavBetaB) from S. mansoni. SmCavBetaA has several novel properties. Most strikingly, when schistosome or mammalian alpha1 subunits are co-expressed with this Beta subunit in Xenopus oocytes, they show increases in current amplitude in the presence of PZQ, a response that is consistent with the clinical effects of the drug. In this project we will pursue the mechanism of PZQ action on schistosome Ca2+ channel subunits in greater detail. We will determine whether SmCavBetaA can confer PZQ sensitivity to the two other schistosome alpha1 subunits we have cloned. We will also test whether phosphorylation of a particular Beta subunit domain by protein kinase C (PKC) plays a role in PZQ sensitivity. SmCa43A (and a homolog found in S. japonicum) are the only known Beta subunits lacking two consensus PKC phosphorylation sites in this critical domain. Introduction of either or both of these sites into SmCavBetaA results in a suppression of PZQ sensitivity. We will continue to examine the role of phosphorylation at these sites, using several approaches. Finally, we will examine PZQ-resistant strains of schistosome for single nucleotide polymorphisms at these sites and test whether agents that inhibit or activate PKC can alter sensitivity of these worms to PZQ. These experiments may eventually lead to new chemotherapeutic approaches to treating schistosomiasis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI040522-06
Application #
6640045
Study Section
Tropical Medicine and Parasitology Study Section (TMP)
Program Officer
Coyne, Philip Edward
Project Start
1998-01-01
Project End
2004-04-30
Budget Start
2003-05-01
Budget End
2004-04-30
Support Year
6
Fiscal Year
2003
Total Cost
$217,500
Indirect Cost
Name
University of Florida
Department
Type
Organized Research Units
DUNS #
969663814
City
Gainesville
State
FL
Country
United States
Zip Code
32611
Salvador-Recatalà, Vicenta; Greenberg, Robert M (2012) Calcium channels of schistosomes: unresolved questions and unexpected answers. Wiley Interdiscip Rev Membr Transp Signal 1:85-93
Salvador-Recatalà, Vicenta; Greenberg, Robert M (2010) The N terminus of a schistosome beta subunit regulates inactivation and current density of a Cav2 channel. J Biol Chem 285:35878-88
Kasinathan, Ravi S; Morgan, William M; Greenberg, Robert M (2010) Schistosoma mansoni express higher levels of multidrug resistance-associated protein 1 (SmMRP1) in juvenile worms and in response to praziquantel. Mol Biochem Parasitol 173:25-31
Kasinathan, Ravi S; Goronga, Tinopiwa; Messerli, Shanta M et al. (2010) Modulation of a Schistosoma mansoni multidrug transporter by the antischistosomal drug praziquantel. FASEB J 24:128-35
Messerli, Shanta M; Kasinathan, Ravi S; Morgan, William et al. (2009) Schistosoma mansoni P-glycoprotein levels increase in response to praziquantel exposure and correlate with reduced praziquantel susceptibility. Mol Biochem Parasitol 167:54-9
Salvador-Recatala, Vicenta; Schneider, Toni; Greenberg, Robert M (2008) Atypical properties of a conventional calcium channel beta subunit from the platyhelminth Schistosoma mansoni. BMC Physiol 8:6
Messerli, Shanta M; Morgan, William; Birkeland, Shanda R et al. (2006) Nitric oxide-dependent changes in Schistosoma mansoni gene expression. Mol Biochem Parasitol 150:367-70
Kohn, Andrea B; Lea, Jeanne M; Moroz, Leonid L et al. (2006) Schistosoma mansoni: use of a fluorescent indicator to detect nitric oxide and related species in living parasites. Exp Parasitol 113:130-3
Jeziorski, Michael C; Greenberg, Robert M (2006) Voltage-gated calcium channel subunits from platyhelminths: potential role in praziquantel action. Int J Parasitol 36:625-32
Greenberg, R M (2005) Ca2+ signalling, voltage-gated Ca2+ channels and praziquantel in flatworm neuromusculature. Parasitology 131 Suppl:S97-108

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