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Comparative analysis of Protein Kinase A homologues in the growth and virulence of Aspergillus fumigatus

Fuller, Kevin

Abstract Details

2010, PhD, University of Cincinnati, Medicine: Pathobiology and Molecular Medicine.

Invasive infection by the fungus Aspergillus fumigatus has emerged as a leading cause of death among bone marrow and solid organ transplant recipients. The remarkable ability of A. fumigatus to thrive within the physically and nutritionally hostile conditions of its ecological niche, the compost, has likely translated to its capacity to grow rapidly within the mammalian lung. Accordingly, signal transduction pathways that relay environmental cues to the metabolic and stress responsive machinery are undoubtedly important virulence determinants in this organism, and may prove to be effective targets for novel antifungal therapies. Early studies by our laboratory, and others, have demonstrated the importance of the cAMP-dependent Protein Kinase A (PKA) pathway in A. fumigatus pathogenesis. This pathway becomes activated following an environmentally induced spike in intracellular cAMP, which causes the catalytic subunit (kinase) to be released from the inhibition of the regulatory subunit. The overarching goal of this dissertation work was to better understand the contributions of PKA to A. fumigatus growth and virulence. To do so, a combination of cellular and molecular analyses of mutants deficient in either the regulatory (pkaR) or catalytic (pkaC1) subunit genes was employed. Included in these studies is the first functional characterization of a second, divergent PKA catalytic isoform, PkaC2.

The results of these studies have established a central role for PKA in nutrient signaling and utilization in A. fumigatus. For example, the deletion of either the PKA catalytic or regulatory subunit genes resulted in the loss of rapid spore germination in the presence of environmental nutrients. In addition, the PkaC1 and PkaC2 isoforms were shown to act in concert to regulate hyphal proliferation on carbohydrate substrates. More specifically, over-expression of pkaC2 enhanced growth of ΔpkaC1 when glucose or fructose served as the sole carbon source, whereas deletion of pkaC2 abrogated growth of ΔpkaC1 under such conditions.

Given the importance of both rapid germination and the assimilation of host-derived nutrients during infection, we hypothesized that the in vitro phenotypes observed in these strains would translate into defects in virulence. Indeed, the reduced germinative capacity and inability to grow on low glucose observed for the double pkaC1/pkaC2 deletion strain, correlated with an inability of the mutant to establish infection in an immunosuppressed mouse model. Conversely, the over-expression of pkaC2 completely restored the fungal burden and mortality associated with the ΔpkaC1 mutant to that of the wild-type organism. Taken together, the comparison of in vitro and in vivo data across the various mutants has emphasized the importance of carbohydrate utilization during A. fumigatus infection and has established PKA-mediated metabolic control as an important virulence program in this menacing mould.

Judith Rhodes, PhD (Committee Chair)
David Askew, PhD (Committee Member)
Kathryn Wikenheiser-Brokamp, MD, PhD (Committee Member)
Alan Smulian, MD (Committee Member)
William Miller, PhD (Committee Member)
162 p.

Recommended Citations

Citations

  • Fuller, K. (2010). Comparative analysis of Protein Kinase A homologues in the growth and virulence of Aspergillus fumigatus [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379778

    APA Style (7th edition)

  • Fuller, Kevin. Comparative analysis of Protein Kinase A homologues in the growth and virulence of Aspergillus fumigatus. 2010. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379778.

    MLA Style (8th edition)

  • Fuller, Kevin. "Comparative analysis of Protein Kinase A homologues in the growth and virulence of Aspergillus fumigatus." Doctoral dissertation, University of Cincinnati, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379778

    Chicago Manual of Style (17th edition)