H. Nakayama et al., Depletion of the squalene synthase (ERG9) gene does not impair growth of Candida glabrata in mice, ANTIM AG CH, 44(9), 2000, pp. 2411-2418
Squalene synthase (farnesyl-diphosphate farnesyltransferase, EC 2.5.1.21) i
s the first committed enzyme of the sterol biosynthesis pathway. Inhibitors
of this enzyme have been intensively studied as potential antifungal agent
s. To assess the effect of deactivating squalene synthase on the growth of
fungi in mice, we isolated the squalene synthase (ERG9) gene from the patho
genic fungus Candida glabrata and generated strains in which the CgERG9 gen
e was under the control of the tetracycline-regulatable promoter. Depletion
of the ERG9 gene by doxycycline (DOX), a derivative of tetracycline, decre
ased the cell viability in laboratory media, whereas it did not affect cell
growth in mice at all. The growth defect caused by DOX in laboratory media
was suppressed by the addition of serum. Analyses of the sterol compositio
n of the restored cells in serum-containing media suggest that the defect o
f ergosterol biosynthesis can be complemented by the incorporation of exoge
nous cholesterol into the cells. Thus, deactivation of squalene synthase di
d not affect fungal growth in mice, presumably because the cells were able
to incorporate cholesterol from the serum, These results showed that squale
ne synthase could not be a suitable target of antifungals for the treatment
of C. glabrata infection.