Role of Glucose in the Expression of Cryptococcus neoformans Antiphagocytic Protein 1, App1

Abstract

The cryptococcus-specific protein antiphagocytic protein 1 (App1) regulates Cryptococcus neoformans virulence by controlling macrophage-driven fungal phagocytosis. This is accomplished through complement receptors (CR), specifically CR3. When inhaled, C. neoformans can cause a life-threatening meningoencephalitis in immunocompromised patients. Because glucose starvation can significantly change the gene expression and virulence of C. neoformans and because App1 is critical for phagocytosis in the lung-a low-glucose environment-we investigated the role of glucose in App1 expression. We found that App1 was upregulated dramatically under low-glucose conditions, and it was upregulated when C. neoformans cells were incubated in bronchoalveolar lavage (BAL) fluid, serum, and cerebrospinal fluid, which are low-glucose environments. Characterization of App1's regulation based on mammalian lung physiology revealed that App1 is upregulated via both increases in transcription and increases in mRNA stability. Our data provide new insights regarding C. neoformans adaptations to low-glucose environments.

Opposing PKA and Hog1 signals control the post‐transcriptional response to glucose availability in Cryptococcus neoformans

“…These data confirm that carbon starvation induces an accelerated deadenylation-dependent decay of RP transcripts mediated by Ccr4. We also performed a reciprocal stability experiment where mid-log wild type cells were shifted from glucose-rich YPD medium to YNB supplemented with glucose (0.002%), at a concentration that models host nutrient deficient environment of lungs and macrophages (Lorenz et al , 2004, Williams & Del Poeta, 2011, Hu et al , 2008, Kronstad et al , 2012). Our result from Fig.…”

Expression and Characterization of Cryptococcus neoformans Recombinant App1

“…Finally, since we have previously shown that App1 expression is regulated by environmental glucose levels [2], we were interested in examining its expression under conditions of glucose starvation and in the absence of capsule. As shown in Fig.…”

“…Recombinant App1 (rApp1) was obtained as previously described [1] and stored at −80°C in 50 mM Tris–HCl, 150 mM NaCl, 5% glycerol, 2 mM β-mercaptoethanol, pH 7.9. Total protein from WT was extracted as described previously [2]. High Five™ insect cells were a kind gift from Dr Sergey Krupenko (Medical University of South Carolina).…”

“…App1 regulates Cryptococcus neoformans virulence by inhibiting phagocytosis of the fungus by alveolar macrophages via a complement- mediated mechanism [1, 2]. C. neoformans var.…”

The Glucose Sensor-Like Protein Hxs1 Is a High-Affinity Glucose Transporter and Required for Virulence in Cryptococcus neoformans

“…The antiphagocytic protein App1 is a fungal virulence factor and inhibits macrophage-mediated phagocytosis via complement receptor 3 (CR3) [7]. Expression of App1 is highly induced during lung infection due to the low glucose concentration (∼ 0.002%) environment in the lung and macrophages [8]. These results demonstrate the importance of glucose as a host signal in regulation of Cryptococcus -macrophage interactions [8].…”