Functional control of the Candida albicans cell wall by catalytic protein kinase A subunit Tpk1

Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, 15213, USA.
Molecular Microbiology (Impact Factor: 4.42). 08/2012; 86(2):284-302. DOI: 10.1111/j.1365-2958.2012.08193.x
Source: PubMed


The cyclic AMP protein kinase A pathway governs numerous biological features of the fungal pathogen Candida albicans. The catalytic protein kinase A subunits, Tpk1 (orf19.4892) and Tpk2 (orf19.2277), have divergent roles, and most studies indicate a more pronounced role for Tpk2. Here we dissect two Tpk1-responsive properties: adherence and cell wall integrity. Homozygous tpk1/tpk1 mutants are hyperadherent, and a Tpk1 defect enables biofilm formation in the absence of Bcr1, a transcriptional regulator of biofilm adhesins. A quantitative gene expression-based assay reveals that tpk1/tpk1 and bcr1/bcr1 genotypes show mixed epistasis, as expected if Tpk1 and Bcr1 act mainly in distinct pathways. Overexpression of individual Tpk1-repressed genes indicates that cell surface proteins Als1, Als2, Als4, Csh1 and Csp37 contribute to Tpk1-regulated adherence. Tpk1 is also required for cell wall integrity, but has no role in the gene expression response to cell wall inhibition by caspofungin. Interestingly, increased expression of the adhesin gene ALS2 confers a cell wall defect, as manifested in hypersensitivity to the cell wall inhibitor caspofungin and a shallow cell wall structure. Our findings indicate that Tpk1 governs C. albicans cell wall properties through repression of select cell surface protein genes.

11 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Upon entrance into the host, fungi encounter a myriad of host effector products and microenvironments that they sense and adapt to for survival. Alterations of the structure and composition of the cell wall is a major fungal adaptation mechanism to evade these environments. Here we discuss recent findings of host-microenvironmental induced fungal cell wall changes, including structure, composition, and protein content, and their effects on host immune responses. A take home message from these recent studies is an emerging understanding of how integration of multiple signals, of both fungal and host responses to dynamic infection site microenvironments, determines outcomes of infection. A challenge moving forward is to further understand these mechanisms and harness them for therapeutic benefit.
    Current opinion in microbiology 04/2013; 16(4). DOI:10.1016/j.mib.2013.03.003 · 5.90 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Rim101 protein is a conserved pH-responsive transcription factor that that mediates important interactions between several fungal pathogens and the infected host. In the human fungal pathogen Cryptococcus neoformans, the Rim101 protein retains conserved functions to allow this microorganism to respond to changes in pH and other host stresses. This coordinated cellular response enables this fungus to effectively evade the host immune response. Preliminary studies suggest that this conserved transcription factor is uniquely regulated in C. neoformans by both the canonical pH-sensing pathway and the cAMP/Protein Kinase A (PKA) pathway. Here, we present comparative transcriptional data that demonstrate a strong concordance between the downstream effectors of PKA and Rim101. To define Rim101-dependent gene expression during a murine lung infection, we used nanoString profiling of lung tissue infected with wild type versus rim101Δ mutant strains. In this setting, we demonstrated that Rim101 controls the expression of multiple cell wall biosynthetic genes, likely explaining the enhanced immunogenicity of the rim101Δ mutant. Despite its divergent upstream regulation, the C. neoformans Rim101 protein recognizes a conserved DNA binding motif. Using this data, we identified direct targets of this transcription factor, including genes involved in cell wall regulation. Therefore, the Rim101 protein directly controls cell wall changes required for the adaptation of this pathogen to its host environment. Moreover, we propose that integration of the cAMP/PKA and pH-sensing pathways allows C. neoformans to respond to a broad range of host-specific signals.
    Molecular and Cellular Biology 12/2013; 34(4). DOI:10.1128/MCB.01359-13 · 4.78 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Septin proteins are conserved structural proteins that often demarcate regions of cell division. The essential nature of the septin ring, composed of several septin proteins, complicates investigation of the functions of the ring, although careful analysis in the model yeast Saccharomyces cerevisiae has elucidated the role that septins play in the cell cycle. Mutation analysis of nonessential septins in the pathogenic fungus Candida albicans has shown that septins also have vital roles in cell wall regulation (CWR), hyphal formation, and pathogenesis. While mutations in nonessential septins have been useful in establishing phenotypes, the septin defect is so slight that identifying causative associations between septins and downstream effectors has been difficult. In this work, we describe decreased abundance by mRNA perturbation (DAmP) alleles of essential septins, which display a septin defect more severe than the defect observed in deletions of nonessential septins. The septin DAmP alleles have allowed us to genetically separate the roles of septins in hyphal growth and CWR and to identify the cyclic AMP pathway as a pathway that likely acts in a parallel manner with septins in hyphal morphogenesis.
    Eukaryotic Cell 09/2014; 13(11). DOI:10.1128/EC.00127-14 · 3.18 Impact Factor
Show more