title: Fibroblast receptor for lysosomal enzymes mediates pinocytosis of multivalent phosphomannan fragment.
abstract: Mild acid hydrolysis of phosphomannan secreted by the yeast hansenula holstii (NRRL Y- 2448) produces two phosphomannyl fragments which differ strikingly in their potency as inhibitors of pinocytosis of human beta-glucuronidase by human fibroblasts. The larger molecular weight polyphosphomonoester fragment is 100,000-fold more potent an inhibitor of enzyme uptake than the smaller penta-mannosyl-monophosphate fragment. Binding to attached fibroblasts at 3 degrees C was much greater with the polyphosphomonoester fragment than with the pentamannosyl-monophosphate. The larger molecular weight fragment was also subject to adsorptive pinocytosis and was taken up by fibroblasts at a rate 30- fold greater than the rate of uptake of pentamannosyl-monophosphate. Evidence that the polyphosphomonoester fragment is taken up by the phosphomannosyl-recognition system that mediates uptake of lysosomal enzymes includes: (a) its pinocytosis is inhibited by the same compounds that competitively inhibit enzyme pinocytosis (mannose-6-phosphate and phosphomannan from saccharomyces cerevisiae mutant mnn-1); (b) alkaline phosphatase treatment greatly reduces its susceptibility to pinocytosis; (c) its pinocytosis is competitively inhibited by high-uptake human beta-glucuronidase; and (d) this inhibition by high-uptake enzyme is dramatically reduced by prior treatment of the enzyme with alkaline phosphatase or endoglycosidase-H. Endoglycosidase-H treatment human beta-glucuronidase dramatically reduced its susceptibility to pinocytosis by fibroblasts. The phosphomannosyl components of high- uptake enzyme released by endoglycosidase-H treatment were much less effective inhibitors of polyphosphomonoester pinocytosis than when present on the phosphomannyl-enzyme. These results suggest that high-uptake acid hydrolases may be polyvalent ligands analogous to the polyphosphomonoester mannan fragment whose pinocytosis depends on interaction of more than one phospho-mannosyl recognition marker with pinocytosis receptors on fibroblasts.
mesh_terms: D000469:Alkaline Phosphatase / Q000494:pharmacology; D005347:Fibroblasts; D005966:Glucuronidase / Q000378:metabolism*; D006600:Hexosephosphates / Q000378:metabolism*; D006801:Humans; D008351:Mannans / Q000378:metabolism* / Q000494:pharmacology; D008360:Mannosephosphates / Q000378:metabolism* / Q000494:pharmacology; D010873:Pinocytosis / Q000187:drug effects; D011134:Polysaccharides / Q000378:metabolism*; D011955:Receptors, Drug / Q000378:metabolism*
chemical_list: D006600:Hexosephosphates; D008351:Mannans; D008360:Mannosephosphates; D011134:Polysaccharides; D011955:Receptors, Drug; D000469:Alkaline Phosphatase; D005966:Glucuronidase