The catalytic subunit of the first mannosyltransferase in the GPI biosynthetic pathway affects growth, cell wall integrity and hyphal morphogenesis in Candida albicans

Abstract

CaGpi14 is the catalytic subunit of the first mannosyltransferase that is involved in the glycosylphosphatidylinositol (GPI) biosynthetic pathway in Candida albicans. We show that CaGPI14 is able to rescue a conditionally lethal gpi14 mutant of Saccharomyces cerevisiae, unlike its mammalian homologue. The depletion of this enzyme in C. albicans leads to severe growth defects, besides causing deficiencies in GPI anchor levels. In addition, CaGpi14 depletion results in cell wall defects and upregulation of the cell wall integrity response pathway. This in turn appears to trigger the osmoticstress dependent activation of the HOG1 pathway and an upregulation of HOG1 as well as its downstream target, SKO1, a known suppressor of expression of hyphae-specific genes. Consistent with this, mutants of CaGPI14 are unable to undergo hyphal transformations in different hyphae-inducing media, under conditions that produce abundant hyphae in the wild-type cells. Hyphal defects in the CaGPI14 mutants could not be attributed either to reduced protein kinase C activation or to defective Ras signalling in these cells but appeared to be driven by perturbations in the HOG1 pathway.

The ER-resident Ras Inhibitor 1 (Eri1) ofCandida albicansinhibits hyphal morphogenesis via the Ras-independent cAMP-PKA pathway

“…Cell viability assays: Propidium iodide (PI) staining was performed as previously described (25). Briefly, primary cultures of the desired strains were grown as above.…”

Generating anchors only to lose them: The unusual story of glycosylphosphatidylinositol anchor biosynthesis and remodeling in yeast and fungi

“…One possible explanation is that basal levels of CaGpi14 are sufficient for viability. Hyphal growth defects in Cagpi14 could be attributed to upregulation of the HOG1 pathway .…”

“…Thus, Pbn1/PIG‐X seems to be species‐specific and may be critical for substrate recognition or conformational integrity of the catalytic subunit. On the other hand, C. albicans Gpi14 functionally complements S. cerevisiae Gpi14, suggesting that Pbn1 of the two organisms are probably functionally homologous .…”

“…S. cerevisiae and C. albicans gpi14 mutants show CW defects . S. cerevisiae GPI14 is essential and its downregulation triggers unfolded protein response (UPR) and transcriptional upregulation of protein expression .…”

“…S. cerevisiae GPI14 is essential and its downregulation triggers unfolded protein response (UPR) and transcriptional upregulation of protein expression . A conditional null strain of Cagpi14 shows no loss in viability despite exhibiting severe growth defects . One possible explanation is that basal levels of CaGpi14 are sufficient for viability.…”