Browsing by Author "Chen, Chia-Geun"

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Rep1p negatively regulating MDR1 efflux pump involved in drug resistance in Candida albicans
(2009-09-01)
Chen, Chia-Geun
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Yang, Yun-Liang
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Tseng, Kuo-Yun
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Shih, Hsin-I
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Liou, Ci-Hong
Overexpression of MDR1 efflux pump is a major mechanism contributing to drug resistance in Candida albicans, the most common human fungal pathogen. To elucidate the regulatory pathway of drug resistance, we have identified a negative regulator of MDR1 and named it Regulator of Efflux Pump 1 (REP1). Overexpression of REPI in Saccharomyces cerevisiae increased susceptibility to fluconazole. Furthermore, null mutations on REP1 decreased the susceptibility to antifungal drugs in C albicans resulting from increased expression of MDR1 mRNA. Hence, Rep1p is involved in drug resistance by negatively regulating MDR1 in C albicans. (c) 2009 Elsevier Inc. All rights reserved.
Serum repressing efflux pump CDR1 in Candida albicans
(2006-07-13)
Yang, Yun-Liang
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Lin, Yi-Hsuan
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Tsao, Ming-Yang
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Chen, Chia-Geun
;
Shih, Hsin-I
Background: In the past decades, the prevalence of candidemia has increased significantly and drug resistance has also become a pressing problem. Overexpression of CDR1, an efflux pump, has been proposed as a major mechanism contributing to the drug resistance in Candida albicans. It has been demonstrated that biological fluids such as human serum can have profound effects on antifungal pharmacodynamics. The aim of this study is to understand the effects of serum in drug susceptibility via monitoring the activity of CDR1 promoter of C. albicans. Results: The wild-type C. albicans cells ( SC5314) but not the cdr1/cdr1 mutant cells became more susceptible to the antifungal drug when the medium contained serum. To understand the regulation of CDR1 in the presence of serum, we have constructed CDR1 promoter-Renilla luciferase ( CDR1p-RLUC) reporter to monitor the activity of the CDR1 promoter in C. albicans. As expected, the expression of CDR1p-RLUC was induced by miconazole. Surprisingly, it was repressed by serum. Consistently, the level of CDR1 mRNA was also reduced in the presence of serum but not N-acetyl-D-glucosamine, a known inducer for germ tube formation. Conclusion: Our finding that the expression of CDR1 is repressed by serum raises the question as to how does CDR1 contribute to the drug resistance in C. albicans causing candidemia. This also suggests that it is important to re-assess the prediction of in vivo therapeutic outcome of candidemia based on the results of standard in vitro antifungal susceptibility testing, conducted in the absence of serum.
The DNA-binding domain of CaNdt80p is required to activate CDR1 involved in drug resistance in Candida albicans
(2006-10-01)
Wang, Jang-Shiun
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Yang, Yun-Liang
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Wu, Chin-Jung
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Ouyang, Karen J.
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Tseng, Kuo-Yun
CaNdt80p, the Candida albicans homologue of the Saccharomyces cerevisiae transcription factor ScNdt80p, has been identified as a positive regulator of CDR1, which encodes an eff lux pump involved in drug resistance in C. albicans. To investigate the involvement of the putative DNA-binding domain of CaNdt80p in drug resistance, chimeras of CaNdt80p and ScNdt80p were constructed. Interestingly, the DNA-binding domain of ScNdt80p could functionally complement that of CaNdt80p to activate CDR1p-lacZ in S. cerevisiae. Consistently, CaNdt80p containing a mutation in the DNA-binding domain failed to activate CDR1p-lacZ in S. cerevisiae. Furthermore, a copy of CaNDT80 with the same mutation also failed to complement the drug-sensitive phenotype caused by a null mutation in C. albicans. Thus, the DNA-binding domain of CaNdt80p is critical for its function in drug resistance in C. albicans.