Analysis ofPRA1and Its Relationship toCandida albicans- Macrophage Interactions

Phagocytosis ofCandida albicans by either primary bone marrow-derived mouse macrophages or RAW 264.7 cells upregulated transcription ofPRA1 , which encodes a cell wall/membrane-associated antigen previously described as a fibrinogen binding protein. However, apra1 null mutant was still able to bind fibrinogen, showing that Pra1p is not uniquely required for fibrinogen binding. As well, Pra1 tagged with green fluorescent protein did not colocalize with AlexaFluor 546-labeled human fibrinogen, and whilePRA1 expression was inhibited whenCandida was grown in fetal bovine serum-containing medium,Candida binding to fibrinogen was activated by these conditions. Therefore, it appears that Pra1p can play at most a minor role in fibrinogen binding toC. albicans. PRA1 gene expression is induced in vitro by alkaline pH, and therefore its activation in phagosomes suggested that phagosome maturation was suppressed by the presence ofCandida cells. LysoTracker red-labeled organelles failed to fuse with phagosomes containing liveCandida , while phagosomes containing deadCandida underwent a normal phagosome-to-phagolysosome maturation. Immunofluorescence staining with the early/recycling endosomal marker transferrin receptor (CD71) suggested that liveCandida may escape macrophage destruction through the inhibition of phagolysosomal maturation.