de Figueiredo, P. | bioRxiv Science

bioRxiv2020

Interactions between fungal hyaluronic acid and host CD44 promotes internalization by recruiting host autophagy proteins to forming phagosomes

Phagocytosis and autophagy play critical roles in immune defense. Cryptococcus neoformans (Cn), a fungal pathogen that causes fatal infection, subverts the host autophagy initiation complex (AIC) and its upstream regulatory proteins, to promote its phagocytosis and intracellular parasitism of host cells. The mechanisms by which the pathogen engages host AIC proteins remain obscure. Here, we show that the recruitment of host AIC proteins to forming phagosomes is dependent upon the activity of CD44, a host cell surface receptor that engages fungal hyaluronic acid (HA). This interaction elevates intracellular Ca2+ concentrations and activates CaMKK{beta} and its downstream target AMPK, which results in activation of ULK1 and the recruitment of AIC components. Moreover, we demonstrate that HA-coated beads efficiently recruit AIC components to phagosomes. Taken together, these findings show that fungal HA plays a critical role in directing the internalization and productive intracellular membrane trafficking of a fungal pathogen of global importance. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=160 SRC="FIGDIR/small/047621v2_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@72f2b9org.highwire.dtl.DTLVardef@9d5a2corg.highwire.dtl.DTLVardef@8b0218org.highwire.dtl.DTLVardef@3698d0_HPS_FORMAT_FIGEXP M_FIG C_FIG In BriefDing et al. reveal that interactions between fungal hyaluronic acid (HA) and host CD44 activate a Ca2+ - CaMKK{beta}-AMPK-ULK1 signaling pathway that recruits autophagy initiation complex components to forming phagosomes to drive fungal internalization. HighlightsO_LIFungal HA interactions with host cells drive a novel non-canonical, ligand-induced, autophagy pathway in phagocytic cells C_LIO_LICryptococcus neoformans recruits host CD44, together with AIC components and regulatory proteins, to forming phagocytic cups to initiate host cell internalization C_LIO_LIFungal HA interactions with CD44 on host cell surfaces elevate intracellular Ca2+ concentrations, leading to activation of CaMKK{beta} C_LIO_LIA Ca2+-CaMKK{beta}-AMPK-ULK1 signaling axis is involved in HA and CD44 induced autophagy protein recruitment during Cn internalization C_LI

microbiology↗

bioRxiv2020

A tractable Drosophila cell system enables rapid identification of Acinetobacter baumannii host factors

AO_SCPLOWBSTRACTC_SCPLOWAcinetobacter baumannii is an important causative agent of nosocomial infections worldwide. The pathogen also readily acquires resistance to antibiotics, and pan-resistant strains have been reported. A. baumannii is widely regarded as an extracellular bacterial pathogen. However, accumulating evidence demonstrates that the pathogen can invade, survive or persist in infected mammalian cells. Unfortunately, the molecular mechanisms controlling these processes remain poorly understood. Here, we show that Drosophila S2 cells provide several attractive advantages as a model system for investigating the intracellular lifestyle of the pathogen, including susceptibility to bacterial intracellular replication and limited infection-induced host cell death. We also show that the Drosophila system can be used to rapidly identify host factors, including MAP kinase proteins, which confer susceptibility to intracellular parasitism. Finally, analysis of the Drosophila system suggested that host proteins that regulate organelle biogenesis and membrane trafficking contribute to regulating the intracellular lifestyle of the pathogen. Taken together, these findings establish a novel model system for elucidating interactions between A. baumannii and host cells, define new factors that regulate bacterial invasion or intracellular persistence, and identify subcellular compartments in host cells that interact with the pathogen.

microbiology↗