An Extensive Circuitry for Cell Wall Regulation in Candida albicans

Abstract

Protein kinases play key roles in signaling and response to changes in the external environment. The ability of Candida albicans to quickly sense and respond to changes in its environment is key to its survival in the human host. Our guiding hypothesis was that creating and screening a set of protein kinase mutant strains would reveal signaling pathways that mediate stress response in C. albicans. A library of protein kinase mutant strains was created and screened for sensitivity to a variety of stresses. For the majority of stresses tested, stress response was largely conserved between C. albicans, Saccharomyces cerevisiae, and Schizosaccharomyces pombe. However, we identified eight protein kinases whose roles in cell wall regulation (CWR) were not expected from functions of their orthologs in the model fungi Saccharomyces cerevisiae and Schizosaccharomyces pombe. Analysis of the conserved roles of these protein kinases indicates that establishment of cell polarity is critical for CWR. In addition, we found that septins, crucial to budding, are both important for surviving and are mislocalized by cell wall stress. Our study shows an expanded role for protein kinase signaling in C. albicans cell wall integrity. Our studies suggest that in some cases, this expansion represents a greater importance for certain pathways in cell wall biogenesis. In other cases, it appears that signaling pathways have been rewired for a cell wall integrity response.

Analysis of the Candida albicans Phosphoproteome

“…To assign protein Table S2). (14), only a single putative tyrosine kinase has been described (62). In addition, some serine/threonine kinases are known to also phosphorylate tyrosine residues, like members of the MEK/Ste7 and Wee1/ Mik1 families (63,64).…”

“…Hyphal growth and the coordinated expression of hypha-specific genes are important virulence traits, since they participate in surface-associated growth and escape after phagocytosis (10,11). Many kinases and phosphatases of biological importance have been described (12)(13)(14)(15). Hyphal morphology in C. albicans is initiated and maintained by the Ras1-Cyr1 (adenylate cyclase)-protein kinase A (PKA) pathway, in which the PKA catalytic subunits Tpk1 and Tpk2 positively regulate hyphal growth (16)(17)(18).…”

Candida albicans Czf1 and Efg1 Coordinate the Response to Farnesol during Quorum Sensing, White-Opaque Thermal Dimorphism, and Cell Death

“…The factors already known to play a role in the response to farnesol, Tup1, Nrg1, Ras1, Cyr1, Efg1, Cek1, and Chk1, are also regulators of morphogenesis. We set out to identify additional regulators of the farnesol response in C. albicans by screening a library of 507 unique homozygous insertion or deletion mutants defective in only their morphological response to farnesol (31,32). C. albicans normally forms yeast at 30°C and hyphae at 37°C.…”

Budding off: bringing functional genomics toCandida albicans

“…This method was used to construct 217 homozygous deletion strains [133], and identified a key regulator of alkaline-dependent filamentation [134]. This technique was subsequently used in targeted gene disruptions [135,136] and additional deletion libraries [137][138][139][140]. A separate approach relied on the generation of heterozygous mutants by insertional mutagenesis with a URA3-marked transposon into the genome [141].…”