Estrogens inhibit mycelium-to-yeast transformation in the fungus Paracoccidioides brasiliensis: implications for resistance of females to paracoccidioidomycosis.

Evidence that disease due to the thermally dimorphic fungus Paracoccidioides brasiliensis occurs post-puberty predominantly in males led us to hypothesize that hormonal factors critically affect its pathogenesis. We show here that estrogens inhibit mycelial- to yeast-form transformation of P. brasiliensis in vitro. Transformation of three isolates was inhibited to 71, 33, and 19% of the control values in the presence of 10(-10), 10(-8), and 10(-6) M 17 beta-estradiol, respectively. The synthetic estrogen diethylstilbestrol was active but less potent than estradiol, whereas testosterone, 17 alpha-estradiol, tamoxifen, and corticosterone were inactive. This function was specifically inhibited, since yeast-to-mycelium transformation, yeast growth, and yeast reproduction by budding were unaffected by 17 beta-estradiol. Of note is the fact that mycelium-to-yeast transformation occurs as the first step in vivo in the establishment of infection. The cytosol of the three isolates studied possesses a steroid-binding protein which has high affinity for 17 beta-estradiol. We believe that this binding protein represents a P. brasiliensis hormone receptor which can also recognize mammalian estrogens. We hypothesize that the ability of estrogen to decrease or delay mycelium-to-yeast transformation at the initial site of infection contributes to or is responsible for the marked resistance of females, and that the binder described is the molecular site of action.