Role of Endothelial Cell Septin 7 in the Endocytosis of Candida albicans

Abstract

Candida albicans invades endothelial cells by binding to N-cadherin and other cell surface receptors. This binding induces rearrangement of endothelial cell actin microfilaments, which results in the formation of pseudopods that surround the organism and pull it into the endothelial cell. Here, we investigated the role of endothelial cell septin 7 (SEPT7) in the endocytosis of C. albicans hyphae. Using confocal microscopy, we determined that SEPT7 accumulated with N-cadherin and actin microfilaments around C. albicans as it was endocytosed by endothelial cells. Affinity purification studies indicated that a complex containing N-cadherin and SEPT7 was recruited by C. albicans and that formation of this complex around C. albicans was mediated by the fungal Als3 and Ssa1 invasins. Knockdown of N-cadherin by small interfering RNA (siRNA) reduced recruitment of SEPT7 to C. albicans, suggesting that N-cadherin functions as a link between SEPT7 and the fungus. Also, depolymerization of actin microfilaments with cytochalasin D decreased the association between SEPT7 and N-cadherin and inhibited recruitment of both SEPT7 and N-cadherin to C. albicans, indicating the necessity of an intact cytoskeleton in the functional interaction between SEPT7 and N-cadherin. Importantly, knockdown of SEPT7 decreased accumulation of N-cadherin around C. albicans in intact endothelial cells and reduced binding of N-cadherin to this organism, as revealed by the affinity purification assay. Furthermore, SEPT7 knockdown significantly inhibited the endocytosis of C. albicans. Therefore, in response to C. albicans infection, SEPT7 forms a complex with endothelial cell N-cadherin, is required for normal accumulation of N-cadherin around C. albicans hyphae, and is necessary for maximal endocytosis of the organism.

Functional regions of Candida albicans hyphal cell wall protein Als3 that determine interaction with the oral bacterium Streptococcus gordonii

“…Als3 is able to bind extracellular matrix (ECM) proteins, epithelial and endothelial cells (Fu et al, 1998;Sheppard et al, 2004;Zhao et al, 2004;Liu & Filler, 2011), induce endocytosis via adherence to E-or Ncadherins (Phan et al, 2013), and mediate trafficking to the brain (Fu et al, 2013). The ability of C. albicans to form biofilms on a variety of substrata including the salivary pellicle, polystyrene and silicone elastomer is also influenced by expression of Als3 (Nobile et al, 2006(Nobile et al, , 2008Nobbs et al, 2010).…”

Sep(t)arate or not – how some cells take septin-independent routes through cytokinesis

“…The endocytic machinery is often utilized by pathogenic microbes to gain entry into host cells. Although it has been known for some time that local actin polymerization and clathrin recruitment are needed to create membrane pits for pathogen entry, recent evidence suggests that septins also have a role in bacterial and yeast invasion of epithelial and endothelial cells Phan et al, 2013). More interestingly, intracytosolic Shigella is entrapped by cage-like septin structures and delivered to autophagosomes for degradation (Mostowy et al, 2010).…”

Use of <em>Shigella flexneri</em> to Study Autophagy-Cytoskeleton Interactions

“…A wide open field of investigation now lies in 'septin biology and infection'. Septin assembly, induced by a variety of pathogens (e.g., Listeria monocytogenes 7,9,10 , Mycobacterium marinum 7,8 , Candida albicans 11 ), may emerge as a key issue in host defense 5,12 .…”