Isolation and expression of a gene (CGR1) regulated during the yeast-hyphal transition in Candida albicans

Candida albicans Heat Shock Proteins and Hsps-Associated Signaling Pathways as Potential Antifungal Targets

In recent decades, the incidence of invasive fungal infections has increased notably. Candida albicans (C. albicans), a common opportunistic fungal pathogen that dwells on human mucosal surfaces, can cause fungal infections, especially in immunocompromised and high-risk surgical patients. In addition, the wide use of antifungal agents has likely contributed to resistance of C. albicans to traditional antifungal drugs, increasing the difficulty of treatment. Thus, it is urgent to identify novel antifungal drugs to cope with C. albicans infections. Heat shock proteins (Hsps) exist in most organisms and are expressed in response to thermal stress. In C. albicans, Hsps control basic physiological activities or virulence via interaction with a variety of diverse regulators of cellular signaling pathways. Moreover, it has been demonstrated that Hsps confer drug resistance to C. albicans. Many studies have shown that disrupting the normal functions of C. albicans Hsps inhibits fungal growth or reverses the tolerance of C. albicans to traditional antifungal drugs. Here, we review known functions of the diverse Hsp family, Hsp-associated intracellular signaling pathways and potential antifungal targets based on these pathways in C. albicans. We hope this review will aid in revealing potential new roles of C. albicans Hsps in addition to canonical heat stress adaptions and provide more insight into identifying potential novel antifungal targets.

Candida albicans Msi3p, a homolog of the Saccharomyces cerevisiae Sse1p of the Hsp70 family, is involved in cell growth and fluconazole tolerance

We investigated the cellular function of Msi3p, belonging to the heat shock protein 70 family, in Candida albicans. The mutant strain tetMSI3 was generated, in which MSI3 was controlled by a tetracycline-repressive promoter, because there is evidence to suggest that MSI3 is an essential gene. We controlled the MSI3 expression level by doxycycline (DOX) and compared its phenotype with that of a control strain with the tetracycline-repressive promoter and a wild-type copy MSI3. The results indicated that MSI3 was essential for cell growth. In addition, all the tetMSI3-infected mice survived after DOX administration. Drug susceptibility tests indicated that repression of MSI3 expression resulted in hypersensitivity to fluconazole and conferred fungicidal activity to fluconazole. The expression levels of MSI3 and calcineurin-dependent genes were upregulated in response to fluconazole in the control strain. In tetMSI3, the upregulation of MSI3 was lost, and the expression level of the calcineurin-dependent genes was no longer elevated in response to fluconazole and was not affected by DOX, indicating that the upregulation of MSI3 expression was required for the induction of the calcineurin-dependent gene expression. These data suggest that Msi3p confers fluconazole tolerance by partially influencing the calcineurin signaling pathway and also other tolerance mechanisms.

Transcriptional profiling of the early stages of germination in by real-time RT-PCR

By using real-time RT-PCR, we profiled the expression of CGR1, CaMSI3, EFG1, NRG1, and TUP1 in Candida albicans strains JCM9061 and CAI4 under several conditions, including induction of morphological transition, heat shock, and treatment with calcium inhibitors. Expression of CaMSI3 changed under these growth conditions except during heat shock. CGR1 expression increased during the early stages of hyphal growth in JCM9061, while expression was strain-dependent during heat shock. Both EFG1 and NRG1 were similarly expressed under hypha-inducing conditions and heat shock. Expression of TUP1 was slightly different from the expression of EFG1 or NRG1.

Strategies for the identification of virulence determinants in human pathogenic fungi

The incidence of fungal infections is increasing in different countries. The current available therapy of these infections does not satisfy all requirements in terms of specificity and therapeutic index, a fact that has stimulated the scientific community to identify fungal virulence determinants. Several pathogenic fungi are opportunistic and, therefore, identification of virulence genes is difficult, given their close relationship with host cells. In recent years, the development of genetic tools in several pathogenic fungi has enabled the development of genetic strategies for their identification. These include several strategies based on the phenotypic analysis of strains or environmental conditions in which the expression of the putative gene(s) is either altered or deleted; and this is accomplished through the development of in vitro or in vivo systems. In the near future, this research will produce a better picture of fungal pathogenesis and therefore define novel promising targets in antifungal therapy.

Isolation and sequencing of the Candida albicans MSI3, a putative novel member of the HSP70 family

We have reported previously that the expression of CGR1 increased at an early stage of the yeast-mycelial transition (morphogenesis) in Candida albicans. We now show that Cgr1p interacts in a yeast two-hybrid system with the C. albicans Msi3p (CaMsi3p), a putative novel member of the heat shock protein 70 (HSP70) family. The DNA sequence of CaMSI3 encodes a predicted protein of 702 amino acids with a molecular mass of 78.6 kDa. The amino acid sequence of CaMsi3p is 63% identical to Msi3p/Sse1p of the HSP70 family of Saccharomyces cerevisiae. Further, CaMSI3 complemented the temperature-sensitive phenotype of the msi3(-) mutant of S. cerevisiae. Other heat shock proteins of C. albicans are required for morphogenesis and are highly antigenic. These observations suggest that CaMSI3 may well provide functions for this organism unrelated to a heat shock function. The DDBJ Accession No. for the sequence reported in this paper is AB061274.

Molecular cloning and expression of the cDNAs encoding luciferin-regenerating enzyme from Luciola cruciata and Luciola lateralis

In the firefly light organ, oxyluciferin, a product of the light-emitting reaction of firefly luciferase, is thought to be converted into luciferin. Previously, we isolated the luciferin-regenerating enzyme (LRE) from Photinus pyralis. LRE plays an important role in the recycling of oxyluciferin into luciferin. We have cloned two cDNAs encoding LRE, G-LRE and H-LRE, from poly(A)+ RNA of the lanterns of Luciola cruciata and Luciola lateralis, using reverse transcription-polymerase chain reaction, 5'-RACE (5'-rapid amplification of cDNA ends) and 3'-RACE. The putative translation products have molecular masses of 33,804 and 34,285 Da, corresponding to 309 and 307 amino acids, respectively. The deduced amino acid sequence of G-LRE shows 57 and 56% identity with H-LRE and A-LRE (P. pyralis), respectively. LRE (G-LRE, H-LRE, A-LRE) shows at most 39% amino acid sequence identity with insect anterior fat protein (AFP) and mammalian senescence marker protein-30 (SMP30). G-LRE and H-LRE were successfully expressed under the control of the lac promoter in Escherichia coli.