Roles of Three Cryptococcus neoformans and Cryptococcus gattii Efflux Pump-Coding Genes in Response to Drug Treatment

Cryptococcus neoformans andCryptococcus gattii species complexes are the etiologic agents of cryptococcosis. We have deciphered the roles of three ABC transporters, Afr1, Afr2, and Mdr1, in the representative strains of the two species,C. neoformans H99 andC. gattii R265. Deletion ofAFR1 in H99 and R265 drastically reduced the levels of resistance to three xenobiotics and three triazoles, suggesting that Afr1 is the major drug efflux pump in both strains. Fluconazole susceptibility was not affected whenAFR2 orMDR1 was deleted in both strains. However, when these genes were deleted in combination withAFR1 , a minor additive effect in susceptibility toward several drugs was observed. Deletion of all three genes in both strains caused further increases in susceptibility toward fluconazole and itraconazole, suggesting that Afr2 and Mdr1 augment Afr1 function in pumping these triazoles. Intracellular accumulation of Nile Red significantly increased inafr1Δ mutants of both strains, but rhodamine 6G accumulation increased only in themdr1Δ mutant of H99. Thus, the three efflux pumps play different roles in the two strains when exposed to different azoles and xenobiotics.AFR1 andAFR2 expression was upregulated in H99 and R265 when treated with fluconazole. However,MDR1 expression was upregulated only in R265 under the same conditions. We screened a library of transcription factor mutants and identified several mutants that manifested either altered fluconazole sensitivity or an increase in the frequency of fluconazole heteroresistance. Gene expression analysis suggests that the three efflux pumps are regulated independently by different transcription factors in response to fluconazole exposure.