Released ATP is an extracellular cytotoxic mediator in salivary histatin 5-induced killing of Candida albicans

Salivary histatins (Hsts) are antifungal peptides with promise as therapeut ic agents against candidiasis. Hst 5 kills the fungal pathogen Candida albi cans via a mechanism that involves release of cellular ATP in the absence o f cytolysis. Here we demonstrate that released ATP has a further role in Hs t 5 killing. Incubation of the cells with ATP analogues induced cell death, and addition of the ATP scavenger apyrase to remove extracellular ATP rele ased during Hst 5 treatment resulted in a reduction in cell killing. Experi ments using anaerobically grown C. albicans with decreased susceptibility t o Hst 5 confirmed that depletion of cellular ATP as a result of ATP efflux was not sufficient to cause cell death. In contrast to Hst-susceptible aero bic cultures, anaerobically grown cells were not killed by exogenously appl ied ATP. These findings established that Hst binding, subsequent entry into the cells, and ATP release precede the signal for cytotoxicity, which is m ediated by extracellular ATP. In a higher-eukaryote paradigm, released ATP acts as a cytotoxic mediator by binding to membrane nucleotide P2X receptor s. Based on a pharmacological profile and detection of a C. albicans 60 kDa membrane protein immunoreactive with antibody to P2X(7) receptor, we propo se that released ATP in response to Hst 5 activates candidal P2X(7)-like re ceptors to cause cell death.