Estradiol-binding proteins from mycelial and yeast-form cultures of Paracoccidioides brasiliensis.

Paracoccidioides brasiliensis, the etiologic agent of paracoccidioidomycosis, causes disease much more frequently in men than it does in women, suggesting that the hormonal milieu of the host might influence P. brasiliensis pathogenicity. We recently demonstrated that cytosol from yeast cultures of P. brasiliensis contains a high-affinity, low-capacity, tritiated 17 beta-estradiol [( 3H]estradiol)-binding protein. Estradiol and, to a lesser degree, diethylstilbestrol (DES), inhibited the transformation of P. brasiliensis cultures from the mycelial to the yeast form, an event critical to the establishment of infection. Our current studies demonstrated a somewhat higher affinity (apparent dissociation constant [Kd], approximately equal to 6 to 12 nM) of the estrogen-binding protein for [3H]estradiol than was previously described for yeast cytosol. The presence of both high- and low-affinity estrogen-binding sites in yeast-form P. brasiliensis cytosol was detected after warming the cytosol to 37 degrees C. The high-affinity protein was labile to further heating (56 degrees C), although the low-affinity protein was stable. Additional experiments demonstrated the presence of an estrogen-binding protein in cytosol prepared from mycelial-form P. brasiliensis. This estrogen-binding protein had a slightly lower affinity for [3H]estradiol (Kd approximately equal to 13 nM), and its cytosol contained somewhat fewer binding sites (approximately equal to 78 fmol/mg of protein) than did yeast-form P. brasiliensis cytosol. Of particular interest was the finding that DES, a weak competitor for [3H]estradiol binding in yeast cytosol, displaced [3H]estradiol from the mycelial-form binding moiety. DES had a 50- to 100-fold-lower affinity for the [3H]estradiol-binding protein than did estradiol, consistent with its lower bioactivity in the mycelial-to-yeast-form transformation studies. The current results lend further support to our hypothesis that endogenous estrogens in the host, acting through the cytosol binding protein in the fungus, inhibit mycelial-to-yeast-form transformation, thus explaining the resistance of women to paracoccidioidomycosis.

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.

Estradiol binds to a receptor-like cytosol binding protein and initiates a biological response in Paracoccidioides brasiliensis.

Paracoccidioidomycosis, a disease caused by Paracoccidioides brasiliensis, which is endemic to Latin America, is much more common in men than women, suggesting a role for hormonal factors. We recently showed that two other yeasts possess steroid binding proteins and postulated that these receptor-like molecules represented a mechanism by which the hormonal milieu of the host might influence an infecting pathogen. Therefore, we examined P. brasiliensis for a sex steroid binding protein. Because tritiated steroids rapidly dissociated from the other fungal binding proteins, we developed a fast binding method with Sephadex G-50 microcolumns speeded by centrifugation. This method detected specific binding of [3H]estradiol in P. brasiliensis cytosol. Other tritiated steroid hormones, including testosterone and corticosterone, failed to exhibit specific binding. Scatchard analysis of [3H]estradiol binding showed an apparent dissociation constant (Kd) of 1.7 X 10(-8) M and a maximal binding capacity (Nmax) of 235 fmol/mg of protein. Susceptibility to trypsin indicated the binding site was protein in nature. The protein had a Stokes radius of approximately equal to 32 A by HPLC exclusion column and a sedimentation coefficient of 4.4 S by sucrose gradient, consistent with an apparent Mr of approximately equal to 60,000. Competition experiments revealed that estrone, estriol, and progesterone had 25% of the affinity of estradiol, whereas diethylstilbestrol, androgens, and corticosteroids had low affinity. Investigation of steroid hormone actions in P. brasiliensis indicated that estradiol inhibited the fungal transformation from mycelial form to yeast form, the initial step of infection. This suppressive effect was dose-dependent and not found with testosterone. We hypothesize that endogenous estrogens in the host, acting through the cytosol binding protein in the fungus, inhibit mycelial-to-yeast transformation, thus explaining the resistance of women to paracoccidioidomycosis.