The virulence of the opportunistic fungal pathogen Aspergillus fumigatus requires cooperation between the endoplasmic reticulum-associated degradation pathway (ERAD) and the unfolded protein response (UPR)

Department of Pathology & Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, OH, USA.
Virulence (Impact Factor: 4.22). 01/2011; 2(1):12-21. DOI: 10.4161/viru.2.1.13345
Source: PubMed


The filamentous fungal pathogen Aspergillus fumigatus secretes hydrolytic enzymes to acquire nutrients from host tissues. The production of these enzymes exerts stress on the endoplasmic reticulum (ER), which is alleviated by two stress responses: the unfolded protein response (UPR), which adjusts the protein folding capacity of the ER, and ER-associated degradation (ERAD), which disposes of proteins that fail to fold correctly. In this study, we examined the contribution of these integrated pathways to the growth and virulence of A. fumigatus, focusing on the ERAD protein DerA and the master regulator of the UPR, HacA. A ΔderA mutant grew normally and showed no increase in sensitivity to ER stress. However, expression of the UPR target gene bipA was constitutively elevated in this strain, suggesting that the UPR was compensating for the absence of DerA function. To test this, the UPR was disrupted by deleting the hacA gene. The combined loss of derA and hacA caused a more severe reduction in hyphal growth, antifungal drug resistance and protease secretion than the loss of either gene alone, suggesting that DerA and HacA cooperate to support these functions. Moreover, the ΔderA/ΔhacA mutant was avirulent in a mouse model of invasive aspergillosis, which contrasted the wild type virulence of ΔderA and the reduced virulence of the ΔhacA mutant. Taken together, these data demonstrate that DerA cooperates with the UPR to support the expression of virulence-related attributes of A. fumigatus.

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    • "The UPR is responsible for activating a program of gene expression to strengthen ER folding capacity when secretion levels are high, or when environmental conditions are not conducive to protein folding [4]. We have previously demonstrated that A. fumigatus depends on the master transcriptional regulator of this pathway, HacA, for the expression of full virulence [5], [6]. This suggests that the fungus is under ER stress in the mammalian host and needs the UPR to sustain the infection by restoring homeostatic balance to the secretory pathway. "
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