ABSTRACT
Chitin, a major component of fungal cell walls, has been associated with allergic disorders such as asthma. However, it is unclear how mammals recognize chitin and the principal receptor(s) on epithelial cells that sense chitin remain to be determined. In this study, we show that LYSMD3 is expressed on the surface of human airway epithelial cells and demonstrate that LYSMD3 is able to bind chitin, as well as ß-glucan, on the cell walls of fungi. Knockdown or knockout of LYSMD3 also sharply blunts the production of inflammatory cytokines by epithelial cells in response to chitin and fungal spores. Competitive inhibition of the LYSMD3 ectodomain by soluble LYSMD3 protein, multiple ligands, or antibody against LYSMD3 also blocks chitin signaling. Our study reveals LYSMD3 as a mammalian pattern recognition receptor (PRR) for chitin and establishes its role in epithelial cell inflammatory responses to chitin and fungi.
Subject(s)
Chitin , Mammals , Membrane Proteins , Receptors, Pattern Recognition , Animals , Humans , Mice , beta-Glucans/metabolism , Candida albicans/physiology , Cell Membrane/metabolism , Chitin/metabolism , Epithelial Cells/metabolism , HeLa Cells , Immunity, Innate , Inflammation/pathology , Mammals/metabolism , Membrane Proteins/metabolism , RAW 264.7 Cells , Receptors, Pattern Recognition/metabolism , Respiratory Mucosa/metabolism , Respiratory Mucosa/microbiology , Signal TransductionABSTRACT
Flavanone 3beta-hydroxylase (F3H; EC 1.14.11.9) is a 2-oxoglutarate dependent dioxygenase that catalyzes the synthesis of dihydrokaempferol, the common precursor for three major classes of 3-hydroxy flavonoids, the flavonols, anthocyanins, and proanthocyanidins. This enzyme also competes for flux into the 3-deoxy flavonoid branch pathway in some species. F3H genes are increasingly being used, often together with genes encoding other enzymes, to engineer flavonoid synthesis in microbes and plants. Although putative F3H genes have been cloned in a large number of plant species, only a handful have been functionally characterized. Here we describe the biochemical properties of the Arabidopsis thaliana F3H (AtF3H) enzyme and confirm the activities of gene products from four other plant species previously identified as having high homology to F3H. We have also investigated the surprising "leaky" phenotype of AtF3H mutant alleles, uncovering evidence that two related flavonoid enzymes, flavonol synthase (EC 1.14.11.23) and anthocyanidin synthase (EC 1.14.11.19), can partially compensate for F3H in vivo. These experiments further indicate that the absence of F3H in these lines enables the synthesis of uncommon 3-deoxy flavonoids in the Arabidopsis seed coat.
