Functional characterization of the Aspergillus fumigatus calcineurin

Abstract

Aspergillus fumigatus is an aggressive opportunistic pathogen of humans as well as a major allergen. Environmental sensing and retrieving essential nutrients from the environment are general metabolic traits associated with the growth of this saprophytic fungus. Two important mediators of calcium signals in eukaryotic cells are the Ca(2+)-binding protein calmodulin and the Ca(2+)/calmodulin-dependent phosphatase calcineurin. Calcineurin is a heterodimer that consists of a catalytic subunit A and a Ca(2+)/calmodulin binding unit. We deleted the A. fumigatus calA gene, which encodes the calcineurin A catalytic subunit, and demonstrated that this gene is not essential in this fungus. The DeltacalA mutant strain has severe defects in growth extension, branching and conidial architecture. Furthermore, the A. fumigatus DeltacalA mutant strain has decreased fitness in a low dose murine infection and cannot grow in fetal bovine serum (FBS). After potassium phosphate was added to liquid FBS, the DeltacalA mutant strain could grow with the characteristic phenotype of the DeltacalA mutation. When A. fumigatus calcineurin is inhibited by tacrolimus in a phosphate depleted medium, there is a reduction in the inorganic phosphate transport and six putative phosphate transporter genes have altered mRNA levels. However, there is no effect on the acid phosphatase activity. These results suggest that calcineurin is involved in the regulation of the PHO pathway in A. fumigatus. Our work on calcineurin opens new venues for the research on sensing and nutrient acquisition in A. fumigatus.

The putative flavin carrier family FlcA-C is important forAspergillus fumigatusvirulence

“…[46][47][48] For example, similar to the DcnaA (catalytic subunit of the calcineurin) mutant, we found that FlcA was required for A. fumigatus colony extension and influenced hyphal branching. The DflcA mutant was more sensitive to calcium and cyclosporine, excess of metals, and cell wall and oxidative stressing agents.…”

“…15 The signaling by calcium is very important for fungal virulence and drug resistance. 1,2 Calcineurin has been demonstrated to be required for virulence in human fungal pathogens, such as Cryptococcus spp, Candida spp, Paracoccidioides brasiliensis, and Aspergillus fumigatus; [16][17][18][19][20][21][22][23] and fungal plant pathogens, such as Sclerotinia scleotiorum, Botrytis cinerea, Magnaporthe oryza, and Ustilago spp. [24][25][26][27][28] In all these fungal pathogens, calcineurin is important for growth, morphology, state transitions, cation homeostasis, stress responses, and cell membrane and cell wall integrity pathways.…”

Calcineurin as a multifunctional regulator: Unraveling novel functions in fungal stress responses, hyphal growth, drug resistance, and pathogenesis

“…Though calcineurin is not an essential gene in A. fumigatus , it is a key phosphatase involved in regulating the differentiation and fitness of this opportunistic pathogen (Ferreira et al, 2007; Steinbach et al, 2006). A. fumigatus lacking either the calcineurin catalytic subunit or the regulatory subunit exhibited defective hyphal morphology related to apical extension and branching (Juvvadi et al, 2011; Steinbach et al, 2006).…”

Direct effects of non-antifungal agents used in cancer chemotherapy and organ transplantation on the development and virulence ofCandidaandAspergillusspecies

“…62,84 cnaA A. fumigatus mutants defective in the calcineurin A unit also demonstrated aberrant hyphal growth and reduced pathogenicity. 85,86 Direct evidence of the effects of calcineurin and TOR inhibitors on the phenotype of Aspergillus spp. ( Table 2) include reports that rapamycin inhibited the growth of A. fumigatus, A. flavus and A. niger in vitro (MICs, ~50 μg/ml) but that this inhibition was not sustained.…”