Heterogeneous Expression of the Virulence-Related Adhesin Epa1 between Individual Cells and Strains of the Pathogen Candida glabrata

Abstract

We investigated the relevance of gene expression heterogeneity to virulence properties of a major fungal pathogen, Candida glabrata. The organism's key virulence-associated factors include glycosylphosphatidylinositol-anchored adhesins, encoded subtelomerically by the EPA gene family. Individual-cell analyses of expression revealed very striking heterogeneity for Epa1, an adhesin that mediates ϳ95% of adherence to epithelial cells in vitro. The heterogeneity in Epa1 was markedly greater than that known for other yeast genes. Sorted cells expressing high or low levels of Epa1 exhibited high and low adherence to epithelial cells, indicating a link between gene expression noise and potential virulence. The phenotypes of sorted subpopulations reverted to mixed phenotypes within a few generations. Variation in single-cell Epa1 protein and mRNA levels was correlated, consistent with transcriptional regulation of heterogeneity. Sir-dependent transcriptional silencing was the primary mechanism driving heterogeneous Epa1 expression in C. glabrata BG2, but not in CBS138 (ATCC 2001). Inefficient silencing in the latter strain was not due to a difference in EPA1 sequence or (sub)telomere length and was overcome by ectopic SIR3 expression. Moreover, differences between strains in the silencing dependence of EPA1 expression were evident across a range of clinical isolates, with heterogeneity being the greatest in strains where EPA1 was subject to silencing. The study shows how heterogeneity can impact the virulence-related properties of C. glabrata cell populations, with potential implications for microbial pathogenesis more broadly.

Structural Hot Spots Determine Functional Diversity of the Candida glabrata Epithelial Adhesin Family

“…Importantly, our study permits us to assess the potential host-ligand binding capacity of C. glabrata without knowing the precise EPA gene expression patterns before or during infection. These patterns and underlying regulatory mechanisms are likely to be highly complex and appear to involve both global mechanisms through silencing of subtelomeric regions as well as gene-specific mechanisms (48,49). As such, our study might contribute to the development of novel antimycotics (50), for example the design of anti-adhesive multivalent carbohydrates (51), to effectively combat emerging fungal pathogens of the C. glabrata clade (19,46).…”

Variation in Candida albicans EFG1 Expression Enables Host-Dependent Changes in Colonizing Fungal Populations

“…In the opportunistic fungal pathogen Candida glabrata , individual cells exhibited different levels of Epa1p, an important adhesin, and the different levels were maintained for several cell cycles (23). Switching has also been observed between two states of C. albicans , termed white and opaque, leading to differential mating capabilities (38, 39, 40, 41, 42).…”

Gain-of-Function Mutations in PDR1 , a Regulator of Antifungal Drug Resistance in Candida glabrata, Control Adherence to Host Cells

“…The lectin is the glycosylphosphatidylinositol (GPI)-anchored cell wall adhesin EPA1, which is a member of an extensive family of related EPA genes previously established as a major mediator of adhesion to epithelial cells in vitro (25,31) and a probable contributor to colonization in vivo and virulence (22,25). The regulation of EPA1 is complex (25,(39)(40)(41), and its expression is known to be highly heterogeneous between different C. glabrata strains (apparently due to differences in subtelomeric transcriptional silencing) (42).…”