Rab14 regulates the maturation of macrophage phagosomes containing the fungal pathogen Candida albicans and the outcome of the host-pathogen interaction

Avoidance of innate immune defence is an important mechanism contributing to the pathogenicity of microorganisms. The fungal pathogen Candida albicans undergoes morphogenetic switching from yeast to filamentous hyphal forms following phagocytosis by macrophages, facilitating their escape from the phagosome which can result in host cell lysis. We show that the intracellular host trafficking GTPase Rab14 has an important role in protecting macrophages against hyphal mediated lysis by C. albicans. Live cell imaging of macrophages expressing GFP-tagged Rab14, dominant negative Rab14 or siRNA-mediated knockdown of Rab14 revealed the temporal dynamics of this protein and its influence upon maturation of macrophage phagosomes following engulfment of C. albicans. Phagosomes containing live C. albicans became transiently Rab14-positive within 2 min following engulfment. The duration of Rab14 retention on phagosomes was prolonged for hyphal cargo and directly proportional to hyphal length. Interference with endogenous Rab14 did not affect macrophage migration towards C. albicans, rate of engulfment, overall uptake of fungal cells, or early phagosome processing. However, Rab14 depletion delayed the acquisition of late phagosome maturation markers LAMP1 and lysosomal cathepsin indicating delayed formation of a fully bioactive lysosome. This was associated with a significant increase in macrophage killing by C. albicans. Therefore, Rab14 activity promotes phagosome maturation during C. albicans infection but is dysregulated on the phagosome in the presence of the invasive hyphal morphology, which favours fungal survival and escape.