Steroid toxicity and detoxification in ascomycetous fungi.

In the last couple of decades fungal infections have become a significant clinical problem. A major interest into fungal steroid action has been provoked since research has proven that steroid hormones are toxic to fungi and affect the host/fungus relationship. Steroid hormones were found to differ in their antifungal activity in ascomycetous fungi Hortaea werneckii, Saccharomyces cerevisiae and Aspergillus oryzae. Dehydroepiandrosterone was shown to be the strongest inhibitor of growth in all three varieties of fungi followed by androstenedione and testosterone. For their protection, fungi use several mechanisms to lower the toxic effects of steroids. The efficiency of biotransformation in detoxification depended on the microorganism and steroid substrate used. Biotransformation was a relatively slow process as it also depended on the growth phase of the fungus. In addition to biotransformation, steroid extrusion out of the cells contributed to the lowering of the active intracellular steroid concentration. Plasma membrane Pdr5 transporter was found to be the most effective, followed by Snq2 transporter and vacuolar transporters Ybt1 and Ycf1. Proteins Aus1 and Dan1 were not found to be involved in steroid import. The research of possible targets of steroid hormone action in fungi suggests that steroid hormones inhibit ergosterol biosynthesis in S. cerevisiae and H. werneckii. Results of this inhibition caused changes in the sterol content of the cellular membrane. The presence of steroid hormones most probably causes the degradation of the Tat2 permease and impairment of tryptophan import.

Aspects of the steroid response in fungi.

The number of fungal infections is increasing due to higher numbers of immunocompromised patients. Unfortunately, drug resistance represents a major additional problem in clinical praxis. Therefore factors contributing to infection by opportunistic pathogens, and to their growth and drug resistance are of major importance. It has been known for some time that mammalian steroid hormones are toxic to fungi. In this paper the response of fungi to the presence of steroid hormones will be discussed at different levels. First, the effect of steroid hormones on fungal growth, morphology and virulence will be considered. Processes affecting steroid intracellular concentration will be discussed; steroid uptake and, even more, steroid extrusion are currently of special interest. The role of biotransformation in the detoxification of active steroids will be taken into consideration and phases of steroid metabolism in fungal cells will be compared to phases of classical xenobiotic metabolism. Steroid signaling in fungi is presently not yet clear. It results in a global response of fungi to steroid hormones. Some of the genes differentially expressed in fungi as the result of exposure to steroid hormones may contribute to fungal drug resistance.

Aspects of the progesterone response in Hortaea werneckii: Steroid detoxification, protein induction and remodelling of the cell wall.

Progesterone in sublethal concentrations temporarily inhibits growth of Hortaea werneckii. This study investigates some of the compensatory mechanisms which are activated in the presence of progesterone and are most probably contributing to escape from growth inhibition. These mechanisms lead on the one hand to progesterone biotransformation/detoxification but, on the other, are suggested to increase the resistance of H. werneckii to the steroid. Biotransformation can detoxify progesterone efficiently in the early logarithmic phase, with mostly inducible steroid transforming enzymes, while progesterone biotransformation/detoxification in the late logarithmic and stationary phases of growth is not very efficient. The relative contribution of constitutive steroid transforming enzymes to progesterone biotransformation is increased in these latter phases of growth. In the presence of progesterone, activation of the cell wall integrity pathway is suggested by the overexpression of Pck2 which was detected in the stationary as well as the logarithmic phase of growth of the yeast. Progesterone treated H. werneckii cells were found to be more resistant to cell lysis than mock treated cells, indicating for the first time changes in the yeast cell wall as a result of treatment with progesterone.

Global Analysis of the Hortaea werneckii proteome: studying steroid response in yeast.

The response of the halophilic black yeast Hortaea werneckii to the steroid hormone progesterone has been studied at the protein level using fluorescent two-dimensional differential gel electrophoresis (2D-DIGE) technology in combination with mass spectrometry. Data on protein identification from this study reveal molecular mechanisms of the response to progesterone. In particular, the overexpression of Pck2 and Pac2 in the stimulated cells indicates the interactions of progesterone with the cell growth and reproduction signaling pathways.

Mass spectrometry and database search in the analysis of proteins from the fungus Pleurotus ostreatus.

Tandem mass spectrometry is a method of choice for rapid analysis in proteomics. Identification and characterization of proteins from organisms with sequenced genomes is today a routine procedure as will be identification of proteins from organisms with unsequenced genomes with new developing tools. Here, we report the use of isotopic labeling with electrospray ionisation (ESI)-tandem mass spectrometry for de novo sequencing in combination with database search taking advantage of different programs for identification of fungal proteins. Using this approach we could identify the proteins of interest. Nevertheless, the identification of a novel protein responsible for the conversion of testosterone into androstenedione was still a difficult task, mostly due to the low homology of steroid transforming enzymes, especially those from microorganisms. Protein p27 was identified as the vanillate O-demethylase oxidoreductase, p33 and p36 as two isoenzymes of malate dehydrogenase, and p45 as citrate synthase. By rechecking the sequences using additional programs it could be shown that the protein p36 has a higher local homology to the steroid-transforming enzyme than to the malate dehydrogenase. Therefore, we assume that p36 is a pluripotent enzyme most probably responsible for the 17beta-hydroxysteroid dehydrogenase activity.