Secretion of the lysosomal acid triacylglycerol hydrolase precursor by J774 macrophages.
J774, thioglycollate-elicited mouse peritoneal and BCG-induced rabbit alveolar macrophages all contain high levels of a triacylglycerol hydrolase (EC 3.1.1.3) (TGase) with optimal activity at pH 6.5. The J774 macrophages, a cell line deficient in the calcium-independent mannose 6-phosphate receptor, were found to secrete large quantities of the TGase into the culture medium. In contrast, mouse peritoneal and rabbit alveolar macrophages, which are both mannose 6-phosphate receptor-competent cell types, secreted much lower amounts of neutral TGase. The enzyme was localized in the lysosomes of rabbit alveolar macrophages. Addition of 25 mM NH4Cl induced a 6-fold increase in TGase secretion by alveolar macrophages, while 50 mM NH4Cl induced a 12-fold increase in TGase secretion. NH4Cl had no effect on TGase secretion by J774 macrophages. The TGase secreted by J774 macrophages was internalized by I-cell disease fibroblasts, increasing the cellular content of TGase 10-fold after 8 h. Internalization was inhibited 70% by the addition of 2 mM mannose 6-phosphate to the culture medium, but was not affected by 2 mM mannose or glucose 6-phosphate. After internalization, the neutral TGase was converted to a TGase with a pH optimum of 5.1. These data are consistent with the spontaneous release of a lysosomal enzyme precursor from a calcium-independent mannose 6-phosphate receptor-deficient cell line, indicating that the neutral TGase previously reported in several types of macrophages may be the precursor of the lysosomal acid TGase.
Goldberg
D I
DI
Department of Medicine, University of California, San Diego, La Jolla 92093-0613.
Khoo
J C
JC
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000172:deficiency; D002460:Cell Line; D002478:Cells, Cultured; D004792:Enzyme Precursors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D008049:Lipase / Q000096:biosynthesis*; D008247:Lysosomes / Q000201:enzymology*; D008264:Macrophages / Q000201:enzymology*; D051379:Mice; D008899:Mineral Oil / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000166:cytology; D011817:Rabbits; D017527:Receptor, IGF Type 2; D013864:Thioglycolates / Q000494:pharmacology
D002352:Carrier Proteins; D004792:Enzyme Precursors; D017527:Receptor, IGF Type 2; D013864:Thioglycolates; D000643:Ammonium Chloride; D008899:Mineral Oil; D008049:Lipase; D002118:Calcium