Three Candida albicans strains were tested in the presence of 17-beta-estradiol (10-6 M and 10-9 M) for increased growth and for enhanced survival during incubation at nonpermissive temperatures. All 3 test organisms showed increased growth in the presence of estradiol compared with estrogen-free controls. Likewise, all 3 strains, when treated with estradiol, survived incubation at 48 degrees C better than did controls. Cytoplasmic extracts were probed with an anti-hsp90 antibody, and results suggested that intracellular hsp90 was up-regulated in the presence of 10-9 M 17-beta-estradiol. The results were confirmed by reverse-transcriptase polymerase chain reaction with primers specific for C. albicans hsp90. A kinetic study revealed that peak hsp90 expression occurred within 2 h of exposure to 17-beta-estradiol. In addition, estrogen increased the amount of cdr1 (Candida multidrug resistance) mRNA compared with cells not treated with estrogen. Coumarin and phenol also up-regulated hsp90 and cdr1 mRNAs, indicating that the estrogen-sensing and -response systems in C. albicans may lack specificity.

It was previously shown that the presence of estrogen enhances survival of Candida albicans under heat and oxidative stresses. A 92-kDa protein is inducible by heat shock and estrogen in C. albicans. Previous studies have described this protein as hsp90 because of its molecular size and heat inducibility as seen on electrophoretic gels and Western blots. In this study, ion exchange, hydroxyapatite and size exclusion chromatography were used to isolate a 92-kDa-protein band. The N-terminal sequence of isolated protein blotted onto a PVDF membrane was determined to be V-Q-S-?-V-L-G-F-P-R. This sequence is homologous to the N-terminal sequence of the MET6 gene product, cobalamin-independent methionine synthase, from Saccharomyces cerevisiae. The results of this study suggest that a cobalamin-independent methionine synthase homolog is inducible by heat and estrogen in C. albicans. This study also suggests that Candida hsp90 is more likely to exist as an 82-kDa protein as predicted by a previously described cDNA and not as a 92-kDa protein as reported in the literature.

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