Role of the inositol polyphosphate kinase Ipk1 in the pathogenesis of <em>Cryptococcus neoformans</em> — ASN Events
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Role of the inositol polyphosphate kinase Ipk1 in the pathogenesis of Cryptococcus neoformans (#136)

Cecilia Li 1 , Sophie Lev 1 , Adolfo Saiardi 2 , Desmarini Desmarini 1 , Tania Sorrell 3 , Julianne Djordjevic 4
  1. Westmead Millennium Institute for Medical Research and University of Sydney, Westmead, NSW, Australia
  2. Medical Research Council Laboratory for Molecular Cell Biology, University College London, Gower Street WC1E 6BT London UK, London, UK
  3. Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney, NSW, Australia
  4. Centre for Infectious Diseases and Microbiology, Westmead Millennium Institute and Sydney Medical School, University of Sydney at Westmead Hospital, Westmead, New South Wales, Australia

Cryptococcus neoformans (Cn)is the leading cause of fungal meningitis worldwide. Cn utilises a number of signalling pathways to aid its survival within a human host and regulate the expression of key virulence-related traits. We have identified a novel signalling pathway in Cn, involving the phosphorylation of inositol trisphosphate (IP3) to more complex inositol polyphosphates (IPs) and inositol pyrophosphates (PP-IPs) by a series of inositol polyphosphate kinases (IPKs).

To determine the role of Ipk1 (a putative IP5 kinase) in IP homeostasis and its contribution to the virulence profile of Cn, an IPK1 gene deletion mutant (CnΔipk1) was created using PCR and biolistic transformation. HPLC revealed that IP5 accumulated in CnΔipk1, consistent with Ipk1 functioning as an IP5 kinase.

Phenotype characterisation of Δipk1 showed an attenuated virulence composite: a cell wall defect, reduced laccase/urease activity, and reduced secretion of the phosphate (Pi)-repressible acid phosphatase (Aph1) activity in phosphate limiting conditions due to reduced induction of APH1 gene expression. Δipk1 was hypersusceptible to antifungals including amphotericin B and the azole drug family. Δipk1 was hypovirulent in a mouse inhalation model of cryptococcosis over a 64 day infection period but established a persistent low-grade asymptomatic lung infection. Δipk1 was not readily phagocytosed by THP-1 cells and failed to activate them to the same extent as the wild-type strain as assessed by flow cytometry and qPCR respectively. For qPCR, an RT2 profiler array designed for analysis of the antifungal immune response was used.  

In conclusion, CnIpk1 is an IP5 kinase required for the expression of virulence-related traits in vitro, thepromotion of drug toleranceand pathogenicity in vivo. These results suggest that IP species produced down-stream of Ipk1 are involved in regulating virulence and phosphate homeostasis, and studies into these mechanisms are ongoing. 

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