All Publications

  • The Candida albicans transcription factor Cas5 couples stress responses, drug resistance and cell cycle regulation. Nature communications Xie, J. L., Qin, L., Miao, Z., Grys, B. T., Diaz, J. D., Ting, K., Krieger, J. R., Tong, J., Tan, K., Leach, M. D., Ketela, T., Moran, M. F., Krysan, D. J., Boone, C., Andrews, B. J., Selmecki, A., Ho Wong, K., Robbins, N., Cowen, L. E. 2017; 8 (1): 499


    The capacity to coordinate environmental sensing with initiation of cellular responses underpins microbial survival and is crucial for virulence and stress responses in microbial pathogens. Here we define circuitry that enables the fungal pathogen Candida albicans to couple cell cycle dynamics with responses to cell wall stress induced by echinocandins, a front-line class of antifungal drugs. We discover that the C. albicans transcription factor Cas5 is crucial for proper cell cycle dynamics and responses to echinocandins, which inhibit β-1,3-glucan synthesis. Cas5 has distinct transcriptional targets under basal and stress conditions, is activated by the phosphatase Glc7, and can regulate the expression of target genes in concert with the transcriptional regulators Swi4 and Swi6. Thus, we illuminate a mechanism of transcriptional control that couples cell wall integrity with cell cycle regulation, and uncover circuitry governing antifungal drug resistance.Cas5 is a transcriptional regulator of responses to cell wall stress in the fungal pathogen Candida albicans. Here, Xie et al. show that Cas5 also modulates cell cycle dynamics and responses to antifungal drugs.

    View details for DOI 10.1038/s41467-017-00547-y

    View details for PubMedID 28894103

    View details for PubMedCentralID PMC5593949

  • Staurosporine Induces Filamentation in the Human Fungal Pathogen Candida albicans via Signaling through Cyr1 and Protein Kinase A mSphere Xie, J. L., O'meara, T. R., Polvi, E. J., Robbins, N., Cowen, L. E. 2017; 2 (2)

    View details for DOI 10.1128/mSphere.00056-17

  • Signaling through Lrg1, Rho1 and Pkc1 Governs Candida albicans Morphogenesis in Response to Diverse Cues. PLoS genetics Xie, J. L., Grahl, N., Sless, T., Leach, M. D., Kim, S. H., Hogan, D. A., Robbins, N., Cowen, L. E. 2016; 12 (10)


    The capacity to transition between distinct morphological forms is a key virulence trait for diverse fungal pathogens. A poignant example of a leading opportunistic fungal pathogen of humans for which an environmentally responsive developmental program underpins virulence is Candida albicans. C. albicans mutants that are defective in the transition between yeast and filamentous forms typically have reduced virulence. Although many positive regulators of C. albicans filamentation have been defined, there are fewer negative regulators that have been implicated in repression of filamentation in the absence of inducing cues. To discover novel negative regulators of filamentation, we screened a collection of 1,248 C. albicans homozygous transposon insertion mutants to identify those that were filamentous in the absence of inducing cues. We identified the Rho1 GAP Lrg1, which represses filamentous growth by stimulating Rho1 GTPase activity and converting Rho1 to its inactive, GDP-bound form. Deletion of LRG1 or introduction of a RHO1 mutation that locks Rho1 in constitutively active, GTP-bound state, leads to filamentation in the absence of inducing cues. Deletion of the Rho1 downstream effector PKC1 results in defective filamentation in response to diverse host-relevant inducing cues, including serum. We further established that Pkc1 is not required to sense filament-inducing cues, but its kinase activity is critical for the initiation of filamentous growth. Our genetic analyses revealed that Pkc1 regulates filamentation independent of the canonical MAP kinase cascade. Further, although Ras1 activation is not impaired in a pkc1Δ/pkc1Δ mutant, adenylyl cyclase activity is reduced, consistent with a model in which Pkc1 functions in parallel with Ras1 in regulating Cyr1 activation. Thus, our findings delineate a signaling pathway comprised of Lrg1, Rho1 and Pkc1 with a core role in C. albicans morphogenesis, and illuminate functional relationships that govern activation of a central transducer of signals that control environmental response and virulence programs.

    View details for DOI 10.1371/journal.pgen.1006405

    View details for PubMedID 27788136

  • Functional Genomic Analysis of Candida albicans Adherence Reveals a Key Role for the Arp2/3 Complex in Cell Wall Remodelling and Biofilm Formation PLoS Genet. Lee, J. A., Robbins, N., Xie, J. L., Ketela, T., Cowen, L. E. 2016
  • Elucidating drug resistance in human fungal pathogens FUTURE MICROBIOLOGY Xie, J. L., Polvi, E. J., Shekhar-Guturja, T., Cowen, L. E. 2014; 9 (4): 523-542


    Fungal pathogens cause life-threatening infections in immunocompetent and immunocompromised individuals. Millions of people die each year due to fungal infections, comparable to the mortality attributable to tuberculosis or malaria. The three most prevalent fungal pathogens are Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. Fungi are eukaryotes like their human host, making it challenging to identify fungal-specific therapeutics. There is a limited repertoire of antifungals in clinical use, and drug resistance and host toxicity compromise the clinical utility. The three classes of antifungals for treatment of invasive infections are the polyenes, azoles and echinocandins. Understanding mechanisms of resistance to these antifungals has been accelerated by global and targeted approaches, which have revealed that antifungal drug resistance is a complex phenomenon involving multiple mechanisms. Development of novel strategies to block the emergence of drug resistance and render resistant pathogens responsive to antifungals will be critical to treating life-threatening fungal infections.

    View details for DOI 10.2217/fmb.14.18

    View details for Web of Science ID 000335954700016

    View details for PubMedID 24810351

  • Loss of Elongation Factor P Disrupts Bacterial Outer Membrane Integrity (vol 194, pg 413, 2012) JOURNAL OF BACTERIOLOGY Zou, S. B., Hersch, S. J., Roy, N., Wiggers, J. B., Leung, A. S., Buranyi, S., Xie, J. L., Dare, K., Ibba, M., Navarre, W. W. 2012; 194 (16): 4484-4484
  • Global Analysis of the Evolution and Mechanism of Echinocandin Resistance in Candida glabrata PLOS PATHOGENS Singh-Babak, S. D., Babak, T., Diezmann, S., Hill, J. A., Xie, J. L., Chen, Y., Poutanen, S. M., Rennie, R. P., Heitman, J., Cowen, L. E. 2012; 8 (5)


    The evolution of drug resistance has a profound impact on human health. Candida glabrata is a leading human fungal pathogen that can rapidly evolve resistance to echinocandins, which target cell wall biosynthesis and are front-line therapeutics for Candida infections. Here, we provide the first global analysis of mutations accompanying the evolution of fungal drug resistance in a human host utilizing a series of C. glabrata isolates that evolved echinocandin resistance in a patient treated with the echinocandin caspofungin for recurring bloodstream candidemia. Whole genome sequencing identified a mutation in the drug target, FKS2, accompanying a major resistance increase, and 8 additional non-synonymous mutations. The FKS2-T1987C mutation was sufficient for echinocandin resistance, and associated with a fitness cost that was mitigated with further evolution, observed in vitro and in a murine model of systemic candidemia. A CDC6-A511G(K171E) mutation acquired before FKS2-T1987C(S663P), conferred a small resistance increase. Elevated dosage of CDC55, which acquired a C463T(P155S) mutation after FKS2-T1987C(S663P), ameliorated fitness. To discover strategies to abrogate echinocandin resistance, we focused on the molecular chaperone Hsp90 and downstream effector calcineurin. Genetic or pharmacological compromise of Hsp90 or calcineurin function reduced basal tolerance and resistance. Hsp90 and calcineurin were required for caspofungin-dependent FKS2 induction, providing a mechanism governing echinocandin resistance. A mitochondrial respiration-defective petite mutant in the series revealed that the petite phenotype does not confer echinocandin resistance, but renders strains refractory to synergy between echinocandins and Hsp90 or calcineurin inhibitors. The kidneys of mice infected with the petite mutant were sterile, while those infected with the HSP90-repressible strain had reduced fungal burden. We provide the first global view of mutations accompanying the evolution of fungal drug resistance in a human host, implicate the premier compensatory mutation mitigating the cost of echinocandin resistance, and suggest a new mechanism of echinocandin resistance with broad therapeutic potential.

    View details for DOI 10.1371/journal.ppat.1002718

    View details for Web of Science ID 000305322900051

    View details for PubMedID 22615574

    View details for PubMedCentralID PMC3355103

  • PoxA, YjeK, and Elongation Factor P Coordinately Modulate Virulence and Drug Resistance in Salmonella enterica MOLECULAR CELL Navarre, W. W., Zou, S. B., Roy, H., Xie, J. L., Savchenko, A., Singer, A., Edvokimova, E., Prost, L. R., Kumar, R., Ibba, M., Fang, F. C. 2010; 39 (2): 209-221


    We report an interaction between poxA, encoding a paralog of lysyl tRNA-synthetase, and the closely linked yjeK gene, encoding a putative 2,3-beta-lysine aminomutase, that is critical for virulence and stress resistance in Salmonella enterica. Salmonella poxA and yjeK mutants share extensive phenotypic pleiotropy, including attenuated virulence in mice, an increased ability to respire under nutrient-limiting conditions, hypersusceptibility to a variety of diverse growth inhibitors, and altered expression of multiple proteins, including several encoded on the SPI-1 pathogenicity island. PoxA mediates posttranslational modification of bacterial elongation factor P (EF-P), analogous to the modification of the eukaryotic EF-P homolog, eIF5A, with hypusine. The modification of EF-P is a mechanism of regulation whereby PoxA acts as an aminoacyl-tRNA synthetase that attaches an amino acid to a protein resembling tRNA rather than to a tRNA.

    View details for DOI 10.1016/j.molcel.2010.06.021

    View details for Web of Science ID 000280574800008

    View details for PubMedID 20670890