O-linked glycosylation modifies the association of apolipoprotein A-II to high density lipoproteins

• Published in: The Journal of biological chemistry Vol. 268; no. 9; pp. 6785 - 6790
• Main Authors: Remaley, A.T, Wong, A.W, Schumacher, U.K, Meng, M.S, Brewer, H.B. Jr, Hoeg, J.M
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 25.03.1993
• Subjects: AMINOAZUCARES; AMINOSUCRE; Animals; apolipoprotein A-II; Apolipoprotein A-II - metabolism; association; Centrifugation, Density Gradient; CHO Cells; Cricetinae; CULTIVO DE CELULAS; CULTURE DE CELLULE; Electrophoresis, Gel, Pulsed-Field; Electrophoresis, Gel, Two-Dimensional; Electrophoresis, Polyacrylamide Gel; GENERO HUMANO; GENRE HUMAIN; Glycosylation; Hep G2 cells; lipoprotein (high density); LIPOPROTEINAS; LIPOPROTEINE; Lipoproteins, HDL - metabolism; man; mutants; OLIGOSACARIDOS; OLIGOSACCHARIDE; OVAIRE; OVARIOS; Precipitin Tests; Protein Processing, Post-Translational; PROTEINAS; PROTEINE; REACCIONES QUIMICAS; REACTION CHIMIQUE; Recombinant Proteins - metabolism; RODENTIA; SECRECION; SECRETION
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)53318-4

O-linked glycosylation is a common post-translational modification of apolipoproteins, but no structural or functional role for it has been identified. We examined the biosynthesis of apolipoprotein (apo) A-II in Hep G2 cells and in glycosylation-defective Chinese hamster ovary (CHO) cell mutants transfected with apoA-II cDNA. Three monomeric isoforms of apoA-II with an apparent molecular mass of 8.5, 9.8, and 11.4 kDa were synthesized by Hep G2 cells and transfected wild-type CHO cells. The 9.8- and 11.4-kDa isoforms were sialylated but not the 8.5-kDa isoform. Transfected ldlD cells, which are defective in the biosynthesis of galactose and N-acetylgalactosamine, only produced the 8.5-kDa isoform; however, when grown in media supplemented with these sugars, ldlD cells produced all three isoforms of apoA-II. Pulse-chase analysis of ldlD cells showed that glycosylation was not necessary for secretion of apoA-II. Glycosylation did modify the association of apoA-II with nascent high density lipoprotein (HDL) secreted by Hep G2 cells. The sialylated isoforms were lipid-poor and were present in the lipoprotein-deficient density range, whereas the nonsialylated 8.5-kDa isoform was associated with LpA-I, A-II lipoprotein particles in the HDL density range. ApoA-II from transfected ldlD cells, regardless of glycosylation, were lipid-poor. When preincubated with HDL from serum, however, sialylated apoA-II from both ldlD cells and Hep G2 cells associated with lipoprotein particles within the HDL3 density, whereas nonsialylated apoA-II was found throughout the HDL density range. In summary, O-linked glycosylation is not necessary for the secretion of apoA-II but does modify the association of apoA-II to HDL and may, therefore, play an important role in the metabolism of HDL