Reduced expression of the hyphal-independent Candida albicans proteinase genes SAP1 and SAP3 in the efg1 mutant is associated with attenuated virulence during infection of oral epithelium

Abstract

The transition of Candida albicans from a yeast to a hyphal form is controlled by several transcriptional factors, including the key regulators Cph1 and Efg1, and is considered an important virulence attribute. These factors, especially Efg1, regulate the expression of hyphal-associated genes e.g. SAP4-SAP6. In order to investigate the relevance of these transcriptional regulators for hyphal-independent SAP genes, recently constructed cph1 and efg1 single mutants and a cph1/ efg1 double mutant lacking these factors were tested during interaction with oral epithelium and polymorphonuclear neutrophils. In contrast to the parental wild-type strain and the cph1 mutant, the efg1 and the cph1/efg1 mutants did not produce hyphal forms in all experiments and were less capable of damaging epithelial cells and neutrophil granulocytes. The attenuated epithelial lesions of these mutants were correlated not only with reduced expression of the hyphal-associated gene SAP4, but also with the lack of SAP1 and SAP3 expression previously shown to be important for oral infections. An efg1 mutant strain carrying a plasmid-borne copy of the EFG1 gene regained hyphal growth, damage of keratinocytes, granulocytes and the expression of SAP1 and SAP3. Although efg1 and cph1/efg1 mutants did not produce germ tubes during infection, expression of the hyphalassociated genes SAP5 and SAP6 was not completely abolished. A reduced capacity to stimulate an epithelial immune response manifested by a delayed onset of IL-1â, IL-8 and TNF expression was only observed in the cph1/efg1-infected tissue. These results provide further evidence for a combined regulation of different virulence factors, such as dimorphism and expression of SAP genes. Furthermore, it could be demonstrated that the lack of Efg1 also caused reduced expression of hyphal-independent SAP genes. Both the EFG1 and the CPH1 gene products are necessary for adequate induction of an immune response.

Genetic and phenotypic intra-species variation in Candida albicans

“…Each of these attributes was shown to be the result, at least in part, of a premature stop codon in the EFG1 transcription factor gene. It is striking that a clinical strain lacks this key transcriptional regulator given its established role in C. albicans filamentation and virulence (Lo et al 1997;Stoldt et al 1997;Braun and Johnson 2000;Korting et al 2003;Noffz et al 2008). However, loss of EFG1 in P94015 provides a fitness advantage in commensal growth.…”

“…None of the other clinical isolates contained a premature stop mutation in EFG1. In addition to controlling white-opaque switching (Sonneborn et al 1999;Srikantha et al 2000;Zordan et al 2007), EFG1 is a key regulator of filamentous growth and virulence (Lo et al 1997;Stoldt et al 1997;Braun and Johnson 2000;Korting et al 2003;Noffz et al 2008). To test whether the truncated EFG1 gene product in P94015 is functional, we introduced the nonsense mutation into the full-length SC5314 EFG1 allele, generating efg1 STOP .…”

Environmental Sensing and Signal Transduction Pathways Regulating Morphopathogenic Determinants of Candida albicans

“…Concomitant with the up-regulation of hyphal wall proteins, the expression of yeast-specific genes such as YWP1 is down-regulated during the yeast-to-hypha transition. Thus, the reduced virulence of the efg1 mutant likely reflects both a lack of expression of hypha-specific genes and a change in the overall organization of the cell wall (155,182). Microarray analysis has further demonstrated that apart from yeast-or hypha-specific genes, Efg1 is also important for the expression of metabolism genes, inducing glycolytic genes and repressing genes essential for oxidative metabolism (81).…”

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

“…It was shown that the yeast-to-hypha morphogenetic transition promotes escape from macrophages and neutrophils (284,342). Furthermore, dendritic cells are able to differentiate between yeast and hyphal morphotypes, and while both are phagocytosed, this occurs via different receptors and stimulates different immune responses (156).…”