CotH3 mediates fungal invasion of host cells during mucormycosis

Abstract

Angioinvasion is a hallmark of mucormycosis. Previously, we identified endothelial cell glucose-regulated protein 78 (GRP78) as a receptor for Mucorales that mediates host cell invasion. Here we determined that spore coat protein homologs (CotH) of Mucorales act as fungal ligands for GRP78. CotH proteins were widely present in Mucorales and absent from noninvasive pathogens. Heterologous expression of CotH3 and CotH2 in Saccharomyces cerevisiae conferred the ability to invade host cells via binding to GRP78. Homology modeling and computational docking studies indicated structurally compatible interactions between GRP78 and both CotH3 and CotH2. A mutant of Rhizopus oryzae, the most common cause of mucormycosis, with reduced CotH expression was impaired for invading and damaging endothelial cells and CHO cells overexpressing GRP78. This strain also exhibited reduced virulence in a diabetic ketoacidotic (DKA) mouse model of mucormycosis. Treatment with anti-CotH Abs abolished the ability of R. oryzae to invade host cells and protected DKA mice from mucormycosis. The presence of CotH in Mucorales explained the specific susceptibility of DKA patients, who have increased GRP78 levels, to mucormycosis. Together, these data indicate that CotH3 and CotH2 function as invasins that interact with host cell GRP78 to mediate pathogenic host-cell interactions and identify CotH as a promising therapeutic target for mucormycosis.

Bicarbonate correction of ketoacidosis alters host-pathogen interactions and alleviates mucormycosis

“…These results confirm our previous findings that adherence to and invasion of the endothelium are 2 independent processes mediated by different receptors (4,5). Additionally, BHB must upregulate the expression of receptors controlling adhesion of the fungus to the endothelium.…”

“…Therefore, interactions of Mucorales with the endothelial cell lining of the blood vessels represent a critical step in the pathogenesis of mucormycosis. We have shown that Mucorales adhere to and invade endothelial cells (3) by expressing CotH proteins (4). CotH proteins bind to the heat shock host receptor glucose-regulated protein 78 (GRP78) (5), causing host cells to endocytose the organisms.…”

Adaptation to thermotolerance inRhizopuscoincides with virulence as revealed by avian and invertebrate infection models, phylogeny, physiological and metabolic flexibility

“…Recent studies revealed also the iron permease FTR1 and the surface protein cotH as known factors contributing to the virulence of these species. 23,53 However, both factors are present in a variety of mucoralean fungi and are not sufficient to explain the clinical importance of certain species. Comparative analyses of closely related virulent and non-virulent species may improve the understanding of the evolution of the pathogenicity mechanisms.…”

Host Cell Invasion by Medically Important Fungi

“…Knockdown of CotH in R. oryzae by siRNA or treatment with an anti-CotH antiserum inhibits the capacity of this organism to invade human umbilical vein endothelial cells in vitro. Similarly, shRNA knockdown of GRP78 in endothelial cells or treatment with an anti-GRP78 antiserum also significantly reduces fungal invasion of endothelial cells in vitro Gebremariam et al 2014).…”

“…In addition, several different Mucorales members bind to GRP78 in vitro. Finally, mice with diabetic ketoacidosis have increased mRNA levels of grp78 in the lungs and brain, providing a possible explanation for why the presence of diabetic ketoacidosis is a unique risk factor for mucormycosis in patients Gebremariam et al 2014). Therefore, it is likely that the induction of endocytosis via the interaction of CotH with GRP78 is a central mechanism by which Mucorales invade endothelial cells and perhaps other types of host cells.…”