Full virulence of the dermatophyte Trichophyton rubrum is dependent on transcription factor PacC

SILVEIRA HC; FERREIRA-NOZAWA MS; ONO CJ; GRAS DE; ROSSI A; MARTINEZ-ROSSI NM

Viena

Conferencia; 8th European Conference on Fungal Genetics; 2006

Federation of European Microbiological Societies

Dermatophytosis is commonly caused by fungi that parasite the human skin and nails. Although several factors contribute to their virulence, adaptive responses to environmental pH signaling have also been evidenced. The functionality of gene pacC, which encodes a protein that is homologous to the PacC/Rim101p family of pH signaling transcription regulators, was examined in T. rubrum for the ability of the H6 and pacC-1 mutant strains to grow on nails in vitro. The disruption of gene pacC was checked by Southern analysis for the predicted disruption restriction fragments and by Western blot analysis, where the proteolytic processing of the PacC protein at pH 5.0 was shown. Moreover, disruption of gene pacC was correlated with a decreased ability of the mutant pacC-1 to grow on human nail fragments as the only nutrition source. This result is consistent with thefact that keratinolytic proteases are under the regulation of gene pacC. Also, T. rubrum failed to grow on nail ragments in the presence of the protease inhibitor PMSF, in a clear indication that proteases with keratinolytic activity are indispensable for the utilization of nails as nutrition source. Furthermore, the growth of T. rubrum is dependent on the initial pH, with an apparent optimum at pH 4.0, although the pH of the medium changed during cultivation, reaching values that ranged from 8.3 to 8.9. The derepression of keratinolytic and nonspecific proteolytic enzymes with optimum activity at acid pH occurs during the initial stages of infection probably because human skin has an acidic pH. In addition, the metabolization by fungi of some amino acids, such as glycine, for example, causes the alkalinization of the growth medium, raising the pH to values as high as 9.0, an ambient in which most of the known keratinolytic proteases of dermatophytes have optimal enzymatic activity. This suggests that the secretion of keratinases with optimal activity at alkaline pH is required for the dermatophyte to complete its installation and to remain in the host. We therefore suggest that full virulence of T. rubrum depends on the action of protein PacC.