UGD1 , Encoding the Cryptococcus neoformans UDP-Glucose Dehydrogenase, Is Essential for Growth at 37°C and for Capsule Biosynthesis

Abstract

We report the identification and disruption of the Cryptococcus neoformans var. grubii UGD1 gene encoding the UDP-glucose dehydrogenase, which catalyzes the conversion of UDP-glucose into UDP-glucuronic acid. Deletion of UGD1 led to modifications in the cell wall, as revealed by changes in the sensitivity of ugd1⌬ cells to sodium dodecyl sulfate, NaCl, and sorbitol. Moreover, two of the yeast's major virulence factors-capsule biosynthesis and the ability to grow at 37°C-were impaired in ugd1⌬ strains. These results suggest that the UDP-dehydrogenase represents the major, and maybe only, biosynthetic pathway for UDP-glucuronic acid in C. neoformans. Consequently, deletion of UGD1 blocked not only the synthesis of UDP-glucuronic acid but also that of UDP-xylose. To differentiate the phenotype(s) associated with the UDP-glucuronic acid defect alone from those linked to the UDP-xylose defect, ugd1⌬ mutants were phenotypically compared to strains from which the gene encoding UDP-xylose synthase (i.e., that required for synthesis of UDP-xylose) had been deleted. Finally, studies of strains from which one of the four CAP genes (CAP10, CAP59, CAP60, or CAP64) had been deleted revealed common cell wall phenotypes associated with the acapsular state.

Transcription Factor Nrg1 Mediates Capsule Formation, Stress Response, and Pathogenesis inCryptococcus neoformans

“…These mutant phenotypes may be due to impaired expression of the UGD1 gene, encoding UDP-glucose dehydrogenase. Mutation of this gene results in decreased capsule formation, poor growth at 37°C, and increased susceptibility to cell wall stress (35). In each case, the ugd1 mutant phenotypes are similar but more severe than those of the nrg1 mutant.…”

“…Similarly to the nrg1 strain, the ugd1 mutant also demonstrates cell clustering (35). Additionally, the growth of the ugd1 mutant is inhibited by various cell wall stressors, including high concentrations of NaCl, sorbitol, and SDS (35). Likewise, the nrg1 mutant is more susceptible to 1.5 M NaCl, 2.5 M sorbitol, and SDS than is wild type (Fig.…”

“…Altered expression of the UGD1 gene may therefore explain the mechanism of the delayed capsule formation in the nrg1 strain. Similarly to the nrg1 strain, the ugd1 mutant also demonstrates cell clustering (35). Additionally, the growth of the ugd1 mutant is inhibited by various cell wall stressors, including high concentrations of NaCl, sorbitol, and SDS (35).…”

“…UGD1 encodes a UDP-glucose dehydrogenase that is required for capsule formation and cell wall integrity (35). Altered expression of the UGD1 gene may therefore explain the mechanism of the delayed capsule formation in the nrg1 strain.…”

Cryptococcus neoformans Senses CO 2 through the Carbonic Anhydrase Can2 and the Adenylyl Cyclase Cac1

“…Gene disruptions were carried out as previously described (22,23). The disruption cassette was constructed by PCR fusion, using a strategy similar to that used by Kuwayama and colleagues (15).…”