N-linked glycosylation of macrophage-derived PAF-AH is a major determinant of enzyme association with plasma HDL

Human plasma PAF-AH (platelet-activating factor-acetylhydrolase) is a Ca(2)+-independent phospholipase A2 of hematopoietic origin associated with LDL and HDL; it degrades PAF and oxidizes phospholipids. We show that human macrophages synthesize PAF-AH as a premedial Golgi precursor containing high mannose N-linked glycans. Secreted PAF-AH possesses a molecular mass of approximately 55 kDa and contains mature N-linked glycans. Secreted PAF-AH activity (90 +/- 4% of the total) bound to a wheat germ lectin column and could be eluted with N-acetylglucosamine, whereas digestion with N-acetylneuraminidase II completely abolished enzyme absorption. Tunicamycin significantly reduced cell-associated PAF-AH activity and inhibited enzyme secretion; but it did not alter the ratio of secreted to cell-associated enzyme (1.8 at 6 h and 3.1 at 24 h), suggesting that glycosylation is not essential for PAF-AH secretion. Digestion of cell-associated PAF-AH or secreted PAF-AH with peptide N-glycosidase F affected neither catalytic activity nor its resistance to proteolysis with trypsin or proteinase K; in addition, it did not affect PAF-AH association with LDL, but significantly increased its association with HDL. We suggest that macrophage-derived PAF-AH contains heterogeneous asparagine-conjugated sugar chain(s) involving sialic acid, which hinders its association with HDL but does not influence the secretion, catalytic activity, or resistance of PAF-AH to proteases.

SV40 large-T oncogene inhibits transcription of perlecan-related proteoglycans but stimulates hyaluronan synthesis in a temperature-sensitive renal-tubule principal cell line

We have analyzed the effects of SV40 large-T oncogene on proteoglycan (PG) synthesis in a temperature-sensitive SV40-transformed renal cell line. Cells shifted from permissive (33 degrees C) to restrictive (39.5 degrees C) temperature, acquired within 48 h the phenotype of principal cells of the renal collecting tubule. They then synthesized hyaluronan, a large-sized PG, small amounts of free GAG chains, and a major approximately 130-kDa heparan sulfate-PG. Sulfated PGs were localized in a basement membrane-like layer and possessed the same core protein (61-70 kDa) derived from perlecan. Expression of large-T oncogene at the permissive temperature induced dramatic alterations of the extracellular matrix, and a 4- and 12-fold reduction in cell-associated and medium-released sulfated PGs, due to a approximately 50% decrease in perlecan mRNA content and gene transcription. This contrasted with a 2-fold increase in actin gene transcription and a 10- and 2-fold rise in the hyaluronan content in cells and medium, respectively. These alterations did not occur in a control cell line (RC.SV3) derived from the same tubule segment but infected with wild-type SV40 strain. They are thus most likely related to the functional state of large-T oncogene and may take part in the early steps of transformation.