Characterization of a carbohydrate epitope defined by the monoclonal antibody H185: sialic acid O-acetylation on epithelial cell-surface mucins

Abstract

Sialic acids comprise a large family of derivatives of neuraminic acid containing methyl, acetyl, sulfate, and phosphate among other groups, which confer specific physicochemical properties (e.g., hydrophobicity and resistance to hydrolases) to the molecules carrying them. Several years ago, a monoclonal antibody, designated H185, was developed, which binds to cell membranes of human corneal, conjunctival, laryngeal, and vaginal epithelia and whose distribution is altered on the ocular surface of patients with keratinizing disease. Recent findings using immunoprecipitation and immunodepletion techniques have demonstrated that, in human corneal epithelial cells, the H185 antigen is carried by the membrane-associated mucin MUC16. In this study, we show that the H185 epitope on human corneal cells and in tear fluid is an O-acetylated sialic acid epitope that can be selectively hydrolyzed in an enzyme-concentration-dependent manner by sialidase from Arthrobacter ureafaciens and to a lesser extent by sialidases from Newcastle disease virus, Clostridium perfringens, and Streptococcus pneumoniae. Binding of the H185 antibody was impaired by treatment of tear fluid with a recombinant 9-O-acetylesterase from influenza C virus. Two O-acetyl derivatives, Neu5,7Ac(2) and Neu5,9Ac(2), were identified in human tear fluid by fluorometric high-performance liquid chromatography (HPLC) and electrospray mass spectrometry (MS). Immunoprecipitation of the H185 epitope from human corneal epithelial cells revealed that Neu5,9Ac(2) was the major derivative on the mucin isolate. These results indicate that exposed wet-surfaced epithelia are decorated with O-acetyl sialic acid derivatives on membrane-associated mucins and suggest that O-acetylation on cell surfaces may protect against pathogen infection by preventing degradation of membrane-associated mucins.

Glycan structures of ocular surface mucins in man, rabbit and dog display species differences

“…9-O-acetylated esters of Nacetylneuraminic acid are known to represent a significant proportion of the total sialic acid found in healthy canine ocular mucin, but are depleted in Keratoconjunctivitus sicca [57]. They are also present in human ocular mucins [58]. Neuraminic acid O-acetylation may therefore be a common cross-species modification for ocular mucins.…”

Cell Surface O-Glycans LimitStaphylococcus aureusAdherence to Corneal Epithelial Cells

“…The apical surface of the human corneal epithelium is heavily coated by MUC16-associated Oacetylated sialic acid, as shown by H185 antibody binding (3,4,47). O-acetyl sialic acid can decrease the rate of mucin oligosaccharide degradation and has been hypothesized to regulate bacterial access to mucosal surfaces (12).…”

Characterisation of psoriasis susceptibility locus 6 (PSORS6) in patients with early onset psoriasis and evidence for interaction with PSORS1

“…Interestingly, we showed that one of the neighbouring genes, mucin 16 ( MUC16 ), of unknown function is expressed in several tissues that are relevant for psoriasis and/or other autoimmune diseases such as skin, thymus, and thyroid. Expression in other epithelia such as ocular surfaces (cornea, conjunctiva), respiratory tract and vagina has been described 45 46. The highly glycosylated MUC16 has long been known as a tumour marker indicating recurrence of ovarian cancer and preceding cancer genesis47 and is often referred to as antigen CA125 48.…”