Chung Shan Medical University, Taiwan
Jia-Ching Shieh’s research interests are on genetic, epigenetic, and environmental factors involved in a variety of human diseases, which are in concert with the subjects of his teaching. His main research focus presently addresses the mechanism underlying morphological plasticity of the opportunistic human fungal pathogen Candida albicans, which is significant in both biology and medicine. His studies revealed the cross-talk between morphogenesis and stress and nutrient responses, and the role of epigenetic regulation in morphological plasticity and are under further investigation using classical approaches of genetics, molecular biology, cell biology and biochemistry incorporated with cutting edge technologies of functional genomics, proteomics, and epigenomics. To overcome C. albicans having a non-canonical codon usage and being a diploid without a complete sexual cycle, novel and non-genetic platforms have been established to reinforce revealing unique genes involved in morphogenesis and other virulence-related factors.
We have previously identified Candida albicans GPH1 (orf19.7021) as one of the C. albicans Cdc4 associated proteins by affinity purification. Significantly, we showed that constitutively expression CaGPH1 partially suppresses the filamentation where the expression of CaCDC4 is repressed. CaGPH1 gene is a putative glycogen phosphorylase as its Saccharomyces cerevisiaehomolog is known to participate in carbohydrate metabolism, particularly in glycogen catabolism that is associated with synthesis of b-glucan of the fungal cell wall. Hence, we establishedCaGPH1 null mutant strain and used to perform the in vitro virulence assays that are attributed to the affection of cell wall function. The in vitro virulence assay is centered on biofilm formation in which analytic procedures to evaluate the ability in germ tube formation, cell surface hydrophobicity, calcium-dependent flocculation, association with fibronectin, stress resistance, and XTT-based adhesion and biofilm formation are performed. Compared with the wild-type strain, the Cagph1D/Cagph1D mutant showed a decrease in the ability to form germ tube and the cell surface hydrophobicity but an increase in the capacity to associate with fibronectin. Ca2+-dependent flocculation did not appear to be different between the wild-type and the null mutant strains. In comparison with the wild-type strain, the Cagph1D/Cagph1D mutant exhibited an increase in adhesion, the early phase of biofilm formation, but showed the same ability to form a mature biofilm. No significant effect on Cagph1D/Cagph1D mutant in regarding to the conditions of cell wall damaging and TOR pathway-associated nutrient depletion. We conclude that the loss of CaGPH1 affects only some of the specific features related to cell wall structure, and the sum of these alterations are insufficient to reflect the ability of C. albicans to form a mature biofilm, hence the overall virulence.