title: Ionophore-resistant mutant of Toxoplasma gondii reveals involvement of a sodium/hydrogen exchanger in calcium regulation.
abstract: Calcium is a critical mediator of many intracellular processes in eukaryotic cells. In the obligate intracellular parasite Toxoplasma gondii, for example, a rise in [Ca2+] is associated with significant morphological changes and rapid egress from host cells. To understand the mechanisms behind such dramatic effects, we isolated a mutant that is altered in its responses to the Ca2+ ionophore A23187 and found the affected gene encodes a homologue of Na+/H+ exchangers (NHEs) located on the parasite's plasma membrane. We show that in the absence of TgNHE1, Toxoplasma is resistant to ionophore-induced egress and extracellular death and amiloride-induced proton efflux inhibition. In addition, the mutant has increased levels of intracellular Ca2+, which explains its decreased sensitivity to A23187. These results provide direct genetic evidence of a role for NHE1 in Ca2+ homeostasis and important insight into how this ubiquitous pathogen senses and responds to changes in its environment.
authors.affiliation: Department of Microbiology and Immunology, Fairchild Building D305, 300 Pasteur Dr., Stanford University School of Medicine, Stanford, CA 94305-5124, USA.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Arrizabalaga
authors.forename: Felix
authors.initials: F
authors.lastname: Ruiz
authors.forename: Silvia
authors.initials: S
authors.lastname: Moreno
authors.forename: John C
authors.initials: JC
authors.lastname: Boothroyd
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics*; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002462:Cell Membrane / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004351:Drug Resistance / Q000235:genetics; D006706:Homeostasis / Q000187:drug effects / Q000235:genetics; D007473:Ion Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D009154:Mutation / Q000235:genetics*; D011522:Protons; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D014122:Toxoplasma / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D007476:Ionophores; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000001:Calcimycin; D000584:Amiloride; D002118:Calcium