A Regulator of Aspergillus fumigatus Extracellular Proteolytic Activity Is Dispensable for Virulence

Abstract

Virulence of the fungal pathogen Aspergillus fumigatus is in part based on the saprophytic lifestyle that this mold has evolved. A crucial function for saprophytism resides in secreted proteases that allow assimilation of proteinaceous substrates. The impact of extracellular proteolytic activities on the pathogenesis of aspergillosis, however, remains controversial. In order to address this issue, characterization of a conserved regulatory factor, PrtT, that acts on expression of secreted proteases was pursued. Expression of PrtT appears to be regulated posttranscriptionally, and the existence of an mRNA leader sequence implies translational control via eIF2␣ kinase signaling. Phenotypic classification of a prtT⌬ deletion mutant revealed that expression of several major extracellular proteases is PrtT dependent, resulting in the inability to utilize protein as a nutritional source. Certain genes encoding secreted proteases are not regulated by PrtT. Most strikingly, the deletant strain is not attenuated in virulence when tested in a leukopenic mouse model, which makes a strong case for reconsidering any impact of secreted proteases in pulmonary aspergillosis.

VeA Regulates Conidiation, Gliotoxin Production, and Protease Activity in the Opportunistic Human Pathogen Aspergillus fumigatus

“…The action of some hydrolases facilitates tissue penetration in the infected A549 lung epithelial cell lines (42). Several proteases have been characterized in A. fumigatus with different effects on virulence (9,35,43). Deficiencies of elastolytic serine protease (43) or the protease secretiondeficient hacA mutant (73) presented a reduction in pathogenicity.…”

“…In a separate experiment, the wild-type, veA deletion mutant, complementation, and overexpression strains were incubated on Czapek Dox medium, with 0.4% bovine serum albumin (BSA) or 0.1% peptone substituted for sodium nitrate as the nitrogen source, as described previously (9), and incubated at 37°C for 3 days to observe possible differences in the ability to grow utilizing a nonhydrolyzed nitrogen source.…”

Exploration of Sulfur Assimilation of Aspergillus fumigatus Reveals Biosynthesis of Sulfur-Containing Amino Acids as a Virulence Determinant

“…For instance, biosynthesis of lysine (14,15), aromatic amino acids (16), and folate (17); siderophore-dependent acquisition of iron (18); and transporter-mediated uptake of zinc (19) or calcium (20) are essential for the fungus to grow within the lungs and, therefore, determine its pathogenic effects. On the other hand, any sources of nitrogen in pulmonary tissue have not yet been clearly identified, despite many studies addressing N me-tabolism (21)(22)(23)(24)(25)(26), and there are indications that A. fumigatus endures nitrogen starvation during intrapulmonary growth (27). This is probably due to the complexity of nitrogen metabolism and the high degree of redundancy of proteolytic and transport activities encoded in the A. fumigatus genome.…”

Conserved Regulators of Mating Are Essential for Aspergillus fumigatus Cleistothecium Formation

“…qRT-PCR. Quantitative real-time PCRs (qRT-PCRs) were performed as described recently (6). Sequences of priming oligonucleotides are given in Table S1 of the supplemental material, and gene-specific combinations were as follows: TubFw/TubRev (AFUA_1G10910; encoding ␤-tubulin), ES077/78 (AFUA_6G06360; ␣-like pheromone precursor PpgA), ES079/80 (AFUA_ 5G07880; pheromone receptor PreA), ES081/82 (AFUA_3G14330; pheromone receptor PreB), ES083/84 (AFUA_3G13870; GATA-type transcriptional activator NsdD), and ES085/86 (AFUA_1G12490; sexual development regulator VeA).…”