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Modulation of azole sensitivity and filamentation by GPI15, encoding a subunit of the first GPI biosynthetic enzyme,
Priyanka Jain1, Pramita Garai1, Subhash Chandra Sethi1
1School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.
Abstract:
Glycosylphosphatidylinositol (GPI)-anchored proteins are important for virulence of many pathogenic organisms including the human fungal pathogen, Candida albicans. GPI biosynthesis is initiated by a multi-subunit enzyme, GPI-N-acetylglucosaminyltransferase (GPI-GnT). We showed previously that two GPI-GnT subunits, encoded by CaGPI2 and CaGPI19, are mutually repressive. CaGPI19 also co-regulates CaERG11, the target of azoles while CaGPI2 controls Ras signaling and hyphal morphogenesis. Here, we investigated the role of a third subunit. We show that CaGpi15 is functionally homologous to Saccharomyces cerevisiae Gpi15. CaGPI15 is a master activator of CaGPI2 and CaGPI19. Hence, CaGPI15 mutants are azole-sensitive and hypofilamentous. Altering CaGPI19 or CaGPI2 expression in CaGPI15 mutant can elicit alterations in azole sensitivity via CaERG11 expression or hyphal morphogenesis, respectively. Thus, CaGPI2 and CaGPI19 function downstream of CaGPI15. One mode of regulation is via H3 acetylation of the respective GPI-GnT gene promoters by Rtt109. Azole sensitivity of GPI-GnT mutants is also due to decreased H3 acetylation at the CaERG11 promoter by Rtt109. Using double heterozygous mutants, we also show that CaGPI2 and CaGPI19 can independently activate CaGPI15. CaGPI15 mutant is more susceptible to killing by macrophages and epithelial cells and has reduced ability to damage either of these cell lines relative to the wild type strain, suggesting that it is attenuated in virulence.
Insights
The study identifies CaGpi15 as a master activator of glycosylphosphatidylinositol (GPI)-N-acetylglucosaminyltransferase (GPI-GnT) subunits in Candida albicans. CaGpi15 is crucial for azole sensitivity and virulence, impacting fungal pathogen interactions.
Area of Science:
- Microbiology
- Molecular Biology
- Mycology
Background:
- Glycosylphosphatidylinositol (GPI)-anchored proteins are vital for the virulence of pathogenic organisms like Candida albicans.
- GPI biosynthesis is orchestrated by the multi-subunit enzyme GPI-N-acetylglucosaminyltransferase (GPI-GnT).
- Previous research indicated mutual repression between CaGPI2 and CaGPI19, two GPI-GnT subunits, with CaGPI19 regulating azole target CaERG11 and CaGPI2 controlling Ras signaling and hyphal growth.
Purpose of the Study:
- To investigate the function of a third GPI-GnT subunit, CaGpi15, in Candida albicans.
- To elucidate the regulatory role of CaGpi15 in relation to CaGPI2 and CaGPI19.
- To determine the impact of CaGpi15 on azole sensitivity, hyphal morphogenesis, and virulence.
Main Methods:
- Functional homology analysis of CaGpi15 with Saccharomyces cerevisiae Gpi15.
- Construction and analysis of CaGPI15 mutants, including double heterozygous mutants with CaGPI2 and CaGPI19.
- Assessment of azole sensitivity, hyphal morphogenesis, and virulence factor expression.
- Investigation of H3 acetylation at GPI-GnT and CaERG11 gene promoters by Rtt109.
Main Results:
- CaGpi15 acts as a master activator for CaGPI2 and CaGPI19, with CaGPI15 mutants exhibiting azole sensitivity and reduced filamentation.
- CaGPI15 regulates azole sensitivity and hyphal morphogenesis through CaERG11 expression and Ras signaling, respectively, with CaGPI2 and CaGPI19 functioning downstream.
- H3 acetylation of GPI-GnT gene promoters by Rtt109 is a key regulatory mechanism, and its reduction at the CaERG11 promoter contributes to azole sensitivity.
- CaGPI15 mutants display increased susceptibility to host immune cells and reduced damage to epithelial cells, indicating attenuated virulence.
Conclusions:
- CaGpi15 is a critical regulator of GPI biosynthesis, influencing azole drug efficacy and fungal pathogenicity in Candida albicans.
- The CaGpi15-CaGPI2/CaGPI19 regulatory axis, involving H3 acetylation, is essential for maintaining fungal virulence.
- Targeting CaGpi15 or its regulatory pathways presents a potential strategy for combating Candida albicans infections.
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