A Sch9 protein kinase homologue controlling virulence independently of the cAMP pathway in Cryptococcus neoformans
The polysaccharide capsule is one of the established virulence factors in Cryptococcus neoformans that provides a barrier against the host-mediated immune response. Mutation of the gene encoding the Saccharomyces cerevisiae Sch9 protein kinase homologue resulted in cells with enlarged capsules in C. neoformans. Capsule production was abrogated in sch9 pka1 double mutants, indicating that protein kinase A (PKA) signaling is still necessary for capsule formation in sch9 mutants. The sch9 mutant also exhibited increased thermal tolerance, a phenotype similar to sch9 mutant strains of S. cerevisiae. In addition, the sch9 mutant was attenuated in mating and the highly encapsulated cells were attenuated in virulence, in contrast to the pkr1 mutant, lacking the regulatory subunit of protein kinase A, that produced similarly enlarged capsules yet was increased in virulence. Interestingly, the virulence for the sch9 mutant strain could be restored by introduction of a pkr1 mutation; and the sch9 pkr1 mutant strain was dramatically increased in size and capsule thickness, suggesting that Sch9 and PKA function via different targets involved in virulence. Our findings support a model in which Sch9 modulates capsule formation and contributes to the virulence of C. neoformans both independently of and in conjunction with the cAMP–PKA pathway.
KeywordsCryptococcus neoformans Sch9 kinase PKA pathway Capsule Virulence
We thank C. Arndt, J. King, and D. Palmer for technical assistance and thank Y.-S. Bahn, D. Fox, J. Hicks, J. Perfect and C. D’Souza for comments. This work was supported in part by the National Institutes of Health grants AI54958 (P.W.), AI39115, and AI42159 (J.H.). G.C. is the recipient of a Burroughs Wellcome Fund New Investigator Award. J.H. is an associate investigator of the Howard Hughes Medical Institute and a Burroughs Wellcome Scholar in Molecular Pathogenic Mycology.
- Crauwels M, Donaton MCV, Pernambuco MB, Winderickx J, Winde JH de, Thevelein JM (1997) The Sch9 protein kinase in the yeast Saccharomyces cerevisiae controls cAPK activity and is required for nitrogen activation of the fermentable-growth-medium-induced (FGM) pathway. Microbiology 143:2627–2637Google Scholar
- Jin M, Fujita M, Culley BM, Apolinario E, Yamamoto M, Maundrell K, Hoffman CS (1995) sck1, a high copy number suppressor of defects in the cAMP-dependent protein kinase pathway in fission yeast, encodes a protein homologous to the Saccharomyces cerevisiae SCH9 kinase. Genetics 140:457–467PubMedGoogle Scholar
- Kwon-Chung KJ, Bennett JE (1992) Cryptococcosis. In: Medical mycology. Lea & Febiger, Malvern, pp 397–446Google Scholar
- Sambrook J, Fritsch EF, Maniatis T (1989) Molecular cloning: a laboratory manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.Google Scholar
- Wang P, Cardenas ME, Cox GM, Perfect J, Heitman J (2001) Two cyclophilin A homologs with shared and distinct functions important for growth and virulence of Cryptococcus neoformans. EMBO J 2:511–518Google Scholar