Transcriptional regulation by protein kinase A in Cryptococcus neoformans.
A defect in the PKA1 gene encoding the catalytic subunit of cyclic adenosine 5'-monophosphate (cAMP)-dependent protein kinase A (PKA) is known to reduce capsule size and attenuate virulence in the fungal pathogen Cryptococcus neoformans. Conversely, loss of the PKA regulatory subunit encoded by pkr1 results in overproduction of capsule and hypervirulence. We compared the transcriptomes between the pka1 and pkr1 mutants and a wild-type strain, and found that PKA influences transcript levels for genes involved in cell wall synthesis, transport functions such as iron uptake, the tricarboxylic acid cycle, and glycolysis. Among the myriad of transcriptional changes in the mutants, we also identified differential expression of ribosomal protein genes, genes encoding stress and chaperone functions, and genes for secretory pathway components and phospholipid synthesis. The transcriptional influence of PKA on these functions was reminiscent of the linkage between transcription, endoplasmic reticulum stress, and the unfolded protein response in Saccharomyces cerevisiae. Functional analyses confirmed that the PKA mutants have a differential response to temperature stress, caffeine, and lithium, and that secretion inhibitors block capsule production. Importantly, we also found that lithium treatment limits capsule size, thus reinforcing potential connections between this virulence trait and inositol and phospholipid metabolism. In addition, deletion of a PKA-regulated gene, OVA1, revealed an epistatic relationship with pka1 in the control of capsule size and melanin formation. OVA1 encodes a putative phosphatidylethanolamine-binding protein that appears to negatively influence capsule production and melanin accumulation. Overall, these findings support a role for PKA in regulating the delivery of virulence factors such as the capsular polysaccharide to the cell surface and serve to highlight the importance of secretion and phospholipid metabolism as potential targets for anti-cryptococcal therapy.
Hu
Guanggan
G
The Michael Smith Laboratories, The University of British Columbia, Vancouver, British Columbia, Canada.
Steen
Barbara R
BR
Lian
Tianshun
T
Sham
Anita P
AP
Tam
Nicola
N
Tangen
Kristin L
KL
Kronstad
James W
JW
D001483:Base Sequence; D003455:Cryptococcus neoformans / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005990:Glycerol / Q000494:pharmacology; D006358:Hot Temperature; D018021:Lithium Chloride / Q000494:pharmacology; D008543:Melanins / Q000096:biosynthesis; D008969:Molecular Sequence Data; D049294:Phospholipid Transfer Proteins / Q000502:physiology; D010743:Phospholipids / Q000096:biosynthesis; D013482:Superoxide Dismutase / Q000235:genetics; D014158:Transcription, Genetic; D014774:Virulence
D008543:Melanins; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D000242:Cyclic AMP; D013482:Superoxide Dismutase; D017868:Cyclic AMP-Dependent Protein Kinases; D018021:Lithium Chloride; D005990:Glycerol