Identification of progesterone binding sites in the plasma membrane of the filamentous fungus Cochliobolus lunatus

[Dehydroepiandrosterone metabolism by Epidermophyton floccosum]

Steroid hormones may be relevant for the fungus-host relation in dermatophytoses. In contrast to most other hosts of dermatophytes, humans are characterized by a high cutaneous concentration of the adrenal androgen dehydroepiandrosterone (DHEA) and its sulphate (DHEAS). To investigate whether the strictly anthropophilic dermatophyte Epidermophyton floccosum can metabolize this steroid hormone, cultures of E. floccosum were supplemented with DHEA. After 5 days of incubation the steroids in the culture supernatants were extracted and differentiated by gaschromatography and massspectrometry (GC-MS). The results show that a nearly complete metabolization of DHEA by E. floccosum leads to the formation of multiple new steroids/metabolites some of which have not been reported before. Therefore, this fungus could possibly mediate the hormone regulated cutaneous defense mechanisms of the host by an intraepidermal metabolization of DHEA.

Membrane-bound progesterone receptors coupled to G proteins in the fungus Rhizopus nigricans

Steroid binding sites with high affinity for progesterone (Kd=40+/-14 nM determined by binding, and Kd=71+/-22 nM determined by displacement studies) and lower affinity for 21-hydroxyprogesterone and for testosterone, but no affinity for estradiol-17beta, onapristone and alpha-naphthoflavone were detected in the enriched plasma membrane fraction of the fungus Rhizopus nigricans. The amount of steroid binding sites is in accordance with the value of B(max)=744+/-151 fmol (mg protein)(-1). In the membrane fraction, progesterone induced about 30% activation of G proteins over basal level, as determined by GTPase activity (EC50=32+/-8 nM) and by the guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding rate (EC50=61+/-21 nM). The affinity of receptors for progesterone was substantially decreased in the presence of GTPgammaS and of cholera toxin. Our results suggest the existence of progesterone receptors in the membrane of Rhizopus nigricans and their coupling to G proteins.

[Hormones, fungi and skin]

It is indicated by some epidemiological and clinical observations, that steroidal hormones may belong to those factors that are capable to influence the clinical courses of mycotic infections in man. Several fungal species, including pathogenic ones, are able to produce or metabolize steroidal hormones, or their growth can be affected by such hormones. Since, on the other hand, the steroid-responsive human skin is also capable to synthesize and convert steroidal hormones, the relationship between pathogenic fungi and host may be influenced by hormonal mediators in dermatomycoses.

Steroid hormone signalling system and fungi

Three components of the steroid hormone signalling system, 17 beta-hydroxysteroid dehydrogenase, androgen binding proteins and steroid hormone signalling molecule testosterone were determined in the filamentous fungus Cochliobolus lunatus for the first time in a fungus. Their possible role in C. lunatus is discussed in comparison with their role in mammalian steroid hormone signalling system. The results are in accordance with the hypothesis, that the elements of primordial signal transduction system should exist in present day eukaryotic microorganisms.

The role of cytochrome P450(11 alpha) in detoxification of steroids in the filamentous fungus Rhizopus nigricans

The evidence was presented that steroid hydroxylating enzyme complex induced by substrate in the filamentous fungus Rhizopus nigricans (R. nigricans) alleviated toxic effect(s) of the steroid on fungal growth. The growth inhibition of fungal mycelium observed in steroid-containing culture(s) became much more obvious when fungal mycelia were grown in the simultaneous presence of inducing steroid and the P450(11 alpha) inhibitor metyrapone. On the other hand, in experiments where we followed the fate of radioactively labelled progesterone added to the mycelial suspension, we noticed that steroid, after being initially accumulated in the microorganism, was, after some time, released from it; the latter phenomenon was not observed if induction of 11 alpha-hydroxylase was prevented by cycloheximide. Results of experiments presented in this communication can be regarded as the first strong indication that the biological role of P450(11 alpha) induction in R. nigricans is in removal of steroids which are toxic for the mycelium.