Fungal Inositol Pyrophosphate IP
7
Is Crucial for Metabolic Adaptation to the Host Environment and Pathogenicity
Authors: Lev Sophie , Li Cecilia , Desmarini Desmarini , Saiardi Adolfo , Fewings Nicole L. , Schibeci Stephen D. , Sharma Raghwa , Sorrell Tania C. , Djordjevic Julianne T. 
Published: June 2015

ABSTRACT

Inositol pyrophosphates (PP-IPs) comprising inositol, phosphate, and pyrophosphate (PP) are essential for multiple functions in eukaryotes. Their role in fungal pathogens has never been addressed.
Cryptococcus neoformans
is a model pathogenic fungus causing life-threatening meningoencephalitis. We investigate the cryptococcal kinases responsible for the production of PP-IPs (IP
7
/IP
8
) and the hierarchy of PP-IP importance in pathogenicity. Using gene deletion and inositol polyphosphate profiling, we identified Kcs1 as the major IP
6
kinase (producing IP
7
) and Asp1 as an IP
7
kinase (producing IP
8
). We show that Kcs1-derived IP
7
is the most crucial PP-IP for cryptococcal drug susceptibility and the production of virulence determinants. In particular, Kcs1 kinase activity is essential for cryptococcal infection of mouse lungs, as reduced fungal burdens were observed in the absence of Kcs1 or when Kcs1 was catalytically inactive. Transcriptome and carbon source utilization analysis suggested that compromised growth of the
KCS1
deletion strain (Δ
kcs1
mutant) in the low-glucose environment of the host lung is due to its inability to utilize alternative carbon sources. Despite this metabolic defect, the Δ
kcs1
mutant established persistent, low-level asymptomatic pulmonary infection but failed to elicit a strong immune response
in vivo
and
in vitro
and was not readily phagocytosed by primary or immortalized monocytes. Reduced recognition of the Δ
kcs1
cells by monocytes correlated with reduced exposure of mannoproteins on the Δ
kcs1
mutant cell surface. We conclude that IP
7
is essential for fungal metabolic adaptation to the host environment, immune recognition, and pathogenicity.

IMPORTANCE
Cryptococcus neoformans
is responsible for 1 million cases of AIDS-associated meningitis and ~600,000 deaths annually. Understanding cellular pathways responsible for pathogenicity might have an impact on new drug development. We characterized the inositol polyphosphate kinases Kcs1 and Asp1, which are predicted to catalyze the production of inositol pyrophosphates containing one or two diphosphate moieties (PP-IPs). Using gene deletion analysis and inositol polyphosphate profiling, we confirmed that Kcs1 and Asp1 are major IP
6
and IP
7
kinases, respectively
.
Kcs1-derived IP
7
, but not Asp1-derived IP
8
, is crucial for pathogenicity
.
Global expression profiling and carbon source utilization testing suggest that IP
7
-deficient cryptococci cannot adapt their metabolism to allow growth in the glucose-poor environment of the host lung, and consequently, fungal burdens are significantly reduced. Persistent asymptomatic Δ
kcs1
mutant infection correlated with decreased mannoprotein exposure on the Δ
kcs1
mutant surface and reduced phagocytosis. We conclude that IP
7
is crucial for the metabolic adaptation of
C. neoformans
to the host environment and for pathogenicity.