An environmentally regulated receptor for diamine oxidase modulates human endothelial cell/fibroblast histamine...

Human vascular endothelial cells and fibroblasts express a cell-surface degradative pathway for the multifunctional mediator histamine, which employs a receptor for the metabolic enzyme diamine oxidase (DAO) and results in cellular accumulation of the final metabolite methylimidazoleacetic acid. We demonstrate recognition and regulatory properties of DAO receptors as a function of cellular environmental conditions. Fast and slow ligand binding receptor populations bind DAO at 4 degrees C maximally in 1 and 7 h, respectively; upon warming cells to 37 degrees C both populations participate in degradative uptake of histamine accumulated as methylimidazoleacetic acid. Bound DAO is displaced by heparin with 24-fold greater potency than dextran sulfate, implicating structural specificity of heparin-like glycosaminoglycan moieties as a critical factor in initial receptor/enzyme interaction at fast and slow sites. Receptor-bound DAO is retained under mildly acidic conditions characteristic of early to mid endocytic intracellular compartments and thus could recycle to the plasma membrane intact after internalization. DAO initially bound to receptors in whole cells is retained through cell disruption/membrane fractionation procedures, but DAO binds poorly to isolated membrane fractions or presolubilized receptors, suggesting that the geometry of DAO binding components is not readily maintained upon cell disruption unless DAO is already bound. Cells down-regulate their complement of DAO receptors upon prolonged exposure to DAO. In cells plated at high density, half of the bound DAO becomes nondisplaceable by heparin within 15 min at 37 degrees C, a time consistent with receptor internalization, whereas cells plated at low density retain all bound DAO in a heparin-sensitive state. The protein kinase C activator phorbol 12-myristate 13-acetate modulates DAO receptor number by 35% and total histamine degradative uptake by > 2-fold. Thus this pathway is subject to regulation at the levels of DAO receptor numbers, their state of cell-surface display, and additional cellular elements of the degradative pathway with which the DAO receptors interface.