Monoclonal anti-neutrophil elastase antibody characterisation: Ability to block function, detect free versus serpin-complexed enzyme and stain intrace

Four commercially available monoclonal antibodies (clones NP57, 256-3K1, 39A and 203) were characterised for their ability to block human neutrophil elastase (HNE) activity; capture free purified HNE or neutralised HNE in complex with alpha-1-antitrypsin (AAT); detect HNE and HNE–AAT by Western blot analysis; and detect intracellular HNE by flow cytometry. The ability to block small substrate cleavage by HNE ranged from 0% (265-3K1) to 15–18% (39A and 203) to 100% (NP57). All antibodies had the ability to capture free HNE with varying degrees of sensitivity, but HNE neutralisation by AAT resulted in complete loss of detection (NP57) to 2–4-fold decreased detection (39A and 203) to a 8-fold increase in detection (265-3K1). None of the monoclonal antibodies could detect 200 ng of free HNE, or HNE in complex with AAT, by Western blot analysis, which was easily detected by polyclonal antibodies. NP57 and 265-3K1 gave 10-fold higher fluorescence when detecting intracellular HNE than 39A and 203, and intracellular fluorescence decreased by 10–28% following maximal stimulation of purified neutrophils with fMLP and cytochalasin B (compared to 40% release determined by functional assay). However, for sub-maximal stimulation of neutrophils intracellular anti-HNE antibody binding increased, likely due to increased accessibility following redistribution of enzyme, indicating that measuring residual intracellular HNE as an index of release is a less reliable method than directly measuring extracellular HNE.


ARTICLE

Terminally misfolded or unassembled proteins in the early secretory pathway are degraded by a ubiquitin- and proteasome-dependent process known as ER-

Terminally misfolded or unassembled proteins in the early secretory pathway are degraded by a ubiquitin- and proteasome-dependent process known as ER-associated degradation (ERAD). How substrates of this pathway are recognized within the ER and delivered to the cytoplasmic ubiquitin-conjugating machinery is unknown. We report here that OS-9 and XTP3-B/Erlectin are ER-resident glycoproteins that bind to ERAD substrates and, through the SEL1L adaptor, to the ER-membrane-embedded ubiquitin ligase Hrd1. Both proteins contain conserved mannose 6-phosphate receptor homology (MRH) domains, which are required for interaction with SEL1L, but not with substrate. OS-9 associates with the ER chaperone GRP94 which, together with Hrd1 and SEL1L, is required for the degradation of an ERAD substrate, mutant 1-antitrypsin. These data suggest that XTP3-B and OS-9 are components of distinct, partially redundant, quality control surveillance pathways that coordinate protein folding with membrane dislocation and ubiquitin conjugation in mammalian cells.