Fungal Inositol Pyrophosphate IP 7 Is Crucial for Metabolic Adaptation to the Host Environment and Pathogenicity

Abstract

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.