Predicting essential genes for identifying potential drug targets in Aspergillus fumigatus.

Background: Aspergillus fumigatus (Af) is a ubiquitous and opportunistic pathogen capable of causing acute, invasive pulmonary disease in susceptible hosts. Despite current therapeutic options, mortality associated with invasive Af infections remains unacceptably high, increasing 357% since 1980. Therefore, there is an urgent need for the development of novel therapeutic strategies, including more efficacious drugs acting on new targets.

Protein kinase A and fungal virulence: a sinister side to a conserved nutrient sensing pathway.

Diverse fungal species are the cause of devastating agricultural and human diseases. As successful pathogenesis is dependent upon the ability of the fungus to adapt to the nutritional and chemical environment of the host, the understanding of signaling pathways required for such adaptation will provide insights into the virulence of these pathogens and the potential identification of novel targets for antifungal intervention. The cAMP-PKA signaling pathway is well conserved across eukaryotes.

HacA-independent functions of the ER stress sensor IreA synergize with the canonical UPR to influence virulence traits in Aspergillus fumigatus.

Endoplasmic reticulum (ER) stress is a condition in which the protein folding capacity of the ER becomes overwhelmed by an increased demand for secretion or by exposure to compounds that disrupt ER homeostasis. In yeast and other fungi, the accumulation of unfolded proteins is detected by the ER-transmembrane sensor IreA/Ire1, which responds by cleaving an intron from the downstream cytoplasmic mRNA HacA/Hac1, allowing for the translation of a transcription factor that coordinates a series of adaptive responses that are collectively known as the unfolded protein response (UPR). Here, we examined the contribution of IreA to growth and virulence in the human fungal pathogen Aspergillus fumigatus.

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).

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.

Divergent Protein Kinase A isoforms co-ordinately regulate conidial germination, carbohydrate metabolism and virulence in Aspergillus fumigatus.

The genome of Aspergillus fumigatus encodes two isoforms of the catalytic subunit of the cAMP-dependent Protein Kinase (PKA). Although deletion of the class I isoform, pkaC1, leads to an attenuation of virulence, the function of the class II subunit, PkaC2, was previously uninvestigated. In this report, we demonstrate that both isoforms act in concert to support various physiologic processes that promote the virulence of this pathogen.

A role for the unfolded protein response (UPR) in virulence and antifungal susceptibility in Aspergillus fumigatus.

Filamentous fungi rely heavily on the secretory pathway, both for the delivery of cell wall components to the hyphal tip and the production and secretion of extracellular hydrolytic enzymes needed to support growth on polymeric substrates. Increased demand on the secretory system exerts stress on the endoplasmic reticulum (ER), which is countered by the activation of a coordinated stress response pathway termed the unfolded protein response (UPR). To determine the contribution of the UPR to the growth and virulence of the filamentous fungal pathogen Aspergillus fumigatus, we disrupted the hacA gene, encoding the major transcriptional regulator of the UPR.

Deletion of the protein kinase A regulatory subunit leads to deregulation of mitochondrial activation and nuclear duplication in Aspergillus fumigatus.

Proper regulation of the cyclic AMP-dependent protein kinase (PKA) pathway is required for normal growth and development in many fungi. We have reported that deletion of the PKA regulatory subunit gene, pkaR, in Aspergillus fumigatus leads to defects in germination and a hypersensitivity of conidia to oxidative stress. In this study, we further analyzed the defects of DeltapkaR conidia and found that a large proportion were abnormally larger than wild type.

Aspergillus fumigatus RasA regulates asexual development and cell wall integrity.

The Ras family of proteins is a large group of monomeric GTPases. Members of the fungal Ras family act as molecular switches that transduce signals from the outside of the cell to signaling cascades inside the cell. A.

Impaired ribosome biogenesis disrupts the integration between morphogenesis and nuclear duplication during the germination of Aspergillus fumigatus.

Aspergillus fumigatus is an important opportunistic fungal pathogen that is responsible for high mortality rates in the immunosuppressed population. CgrA, the A. fumigatus ortholog of a Saccharomyces cerevisiae nucleolar protein involved in ribosome biogenesis, contributes to the virulence of this fungus by supporting rapid growth at 37 degrees C.

Unexpected link between metal ion deficiency and autophagy in Aspergillus fumigatus.

Autophagy is the major cellular pathway for bulk degradation of cytosolic material and is required to maintain viability under starvation conditions. To determine the contribution of autophagy to starvation stress responses in the filamentous fungus Aspergillus fumigatus, we disrupted the A. fumigatus atg1 gene, encoding a serine/threonine kinase required for autophagy.

The Aspergillus fumigatus metacaspases CasA and CasB facilitate growth under conditions of endoplasmic reticulum stress.

We have examined the contribution of metacaspases to the growth and stress response of the opportunistic human mould pathogen, Aspergillus fumigatus, based on increasing evidence implicating the yeast metacaspase Yca1p in apoptotic-like programmed cell death. Single metacaspase-deficient mutants were constructed by targeted disruption of each of the two metacaspase genes in A. fumigatus, casA and casB, and a metacaspase-deficient mutant, DeltacasA/DeltacasB, was constructed by disrupting both genes.

Aspergillus fumigatus: growth and virulence.

Aspergillus fumigatus is a ubiquitous fungus that plays an important role in carbon and nitrogen recycling in nature. Because A. fumigatus is thermotolerant, it is a predominant organism during the high-temperature phase of the compost cycle.

Deletion of the regulatory subunit of protein kinase A in Aspergillus fumigatus alters morphology, sensitivity to oxidative damage, and virulence.

Aspergillus fumigatus is an important opportunistic fungal pathogen. The cAMP-dependent protein kinase (PKA) signaling pathway plays an important role in regulating morphology, growth, and virulence in a number of fungal pathogens of plants and animals. We have constructed a mutant of A.

A fungus-specific ras homolog contributes to the hyphal growth and virulence of Aspergillus fumigatus.

The Ras family of GTPase proteins has been shown to control morphogenesis in many organisms, including several species of pathogenic fungi. In a previous study, we identified a gene encoding a fungus-specific Ras subfamily homolog, rasB, in Aspergillus fumigatus. Here we report that deletion of A.

Nucleolar localization of Aspergillus fumigatus CgrA is temperature-dependent.

Pathogenic fungi must adapt to multiple adverse environmental conditions during the transition from the environment to a mammalian host, one of which is temperature. The ability of Aspergillus fumigatus to grow optimally under conditions of thermal stress requires the nucleolar protein CgrA. In this study, we have determined how temperature affects the intracellular localization of CgrA in A.

Doxycycline-regulated gene expression in the opportunistic fungal pathogen Aspergillus fumigatus.

Background: Although Aspergillus fumigatus is an important human fungal pathogen there are few expression systems available to study the contribution of specific genes to the growth and virulence of this opportunistic mould. Regulatable promoter systems based upon prokaryotic regulatory elements in the E. coli tetracycline-resistance operon have been successfully used to manipulate gene expression in several organisms, including mice, flies, plants, and yeast.

Disruption of the Aspergillus fumigatus gene encoding nucleolar protein CgrA impairs thermotolerant growth and reduces virulence.

Aspergillus fumigatus CgrA is the ortholog of a yeast nucleolar protein that functions in ribosome synthesis. To determine how CgrA contributes to the virulence of A. fumigatus, a Delta cgrA mutant was constructed by targeted gene disruption, and the mutant was reconstituted to wild type by homologous introduction of a functional cgrA gene.

Aspergillus fumigatus rasA and rasB regulate the timing and morphology of asexual development.

Expression of rasA plays an important role in conidial germination in Aspergillus nidulans. Conidial germination is required to initiate both infection and asexual development in the opportunistic pathogen Aspergillus fumigatus. Therefore, we sought to determine the requirements for Ras proteins in conidial germination and asexual development of A.

Deletion of the Aspergillus fumigatus gene encoding the Ras-related protein RhbA reduces virulence in a model of Invasive pulmonary aspergillosis.

Aspergillus fumigatus is the predominant mold pathogen in patients who lack functional innate immunity. The A. fumigatus rhbA gene was first identified as a transcript that was upregulated when the organism was grown in the presence of mammalian cells.

cAMP alteration of growth rate of Aspergillus fumigatus and Aspergillus niger is carbon-source dependent.

cAMP signalling has been shown to be essential for normal growth, morphology and virulence in fungal pathogens of both plants and animals. The effects of exogenous cAMP on the growth of the opportunistic pathogen Aspergillus fumigatus were compared to those of Aspergillus niger, which has previously been demonstrated to respond to extracellular cAMP. Both cAMP and phosphodiesterase inhibitors markedly reduced the radial growth rate of A.

Expression of the Aspergillus fumigatus rheb homologue, rhbA, is induced by nitrogen starvation.

A gene encoding a ras protein with homology to the rheb family was cloned from Aspergillus fumigatus. Although conserved ras domains are present, the predicted RhbA protein sequence deviates from the ras consensus in a manner that is characteristic of rheb proteins. The invariant Gly-Gly in the first GTP-binding domain of ras proteins is replaced by Arg-Ser in RhbA, and a conserved Asp in the effector region of ras proteins is replaced by Asn in RhbA.

Cloning and expression of pkaC and pkaR, the genes encoding the cAMP-dependent protein kinase of Aspergillus fumigatus.

This report describes the cloning and expression of both subunits of PKA in the opportunistic fungal pathogen Aspergillus fumigatus. The predicted translation product of the regulatory subunit, pkaR, is defined as a type II regulatory subunit. The gene encoding the A.

Identification of a role for Saccharomyces cerevisiae Cgr1p in pre-rRNA processing and 60S ribosome subunit synthesis.

Saccharomyces cerevisiae CGR1 encodes a conserved fungal protein that localizes to the nucleolus. To determine if this localization reflects a role for Cgr1p in ribosome biogenesis two yeast cgr1 mutants were examined for defects in ribosome synthesis: a conditional depletion strain in which CGR1 is under the control of a tetracycline-repressible promoter and a mutant strain in which a C-terminal truncated Cgr1p is expressed. Both strains had impaired growth rates and were hypersensitive to the aminoglycosides paromomycin and hygromycin.