Sac1 links phosphoinositide turnover to cryptococcal virulence

Area of Science:

• Mycology and Infectious Diseases
• Cell Biology and Pathogenesis

Background:

• Cryptococcus neoformans is a major cause of fungal meningitis, responsible for over 140,000 deaths annually.
• Host cell phagocytosis and the fungal capsule are critical determinants of cryptococcal infection outcomes.
• Understanding the molecular mechanisms governing C. neoformans-host cell interactions is vital for developing new therapies.

Purpose of the Study:

• To identify Cryptococcus neoformans genes involved in host cell uptake using genome-wide screening.
• To investigate the role of identified genes in capsule production and virulence.
• To characterize the function of the phosphatidylinositol-4-phosphate phosphatase Sac1 in cryptococcal pathogenesis.

Main Methods:

• Genome-wide screening of approximately 4,700 C. neoformans gene deletion mutants for altered uptake by primary mouse and human phagocytic cells.
• Secondary screening of identified mutants for changes in capsule thickness.
• Characterization of sac1 mutants, including analysis of lipid trafficking, secretory system function, and capsule composition.

Main Results:

• 93 mutants showed altered uptake in both human and mouse phagocytic cells, with 45 exhibiting changes in both uptake and capsule.
• The sac1 mutant displayed defects in lipid trafficking and secretory system function, leading to altered capsule size and composition.
• Sac1's role in host cell uptake and capsule production is particularly evident under host-like tissue culture conditions.

Conclusions:

• Genome-scale screening is effective for identifying novel factors in cryptococcal biology.
• Sac1 is a key regulator of C. neoformans host cell uptake and capsule production.
• Sac1 activity is important for cryptococcal virulence, especially in response to host-associated stresses.