Synthesis and glycosylation of fibronectin in hepatocytes from vitamin A-deficient rats.
Recent work from our laboratory (Kim and Wolf, J Biol Chem 262:365-371, 1987) has shown increased uptake of labeled amino acids into fibronectin (FN), increased net synthesis of FN and increased levels of FN-mRNA in primary cultures of hepatocytes from vitamin A-deficient rats compared to controls. We now find, surprisingly, decreased uptake of labeled sugars into the oligosaccharide chains of FN from vitamin A-deficient hepatocytes. This decrease could be reversed by added retinoic acid at physiological concentration. At the same time, FN from deficient hepatocytes (-A.FN) was more susceptible to proteolytic degradation. Decreased uptake of the core sugar mannose into -A.FN was similar to that of glucosamine, yet the percent of label in sialic acid was the same as in + A.FN, suggesting a smaller number of oligosaccharide chains per molecule of -A.FN. Upon enzymatic removal of oligosaccharide and labeling with sodium borotritide, it was found that both -A.FN and +A.FN had biantennary oligosaccharide structures. Selective enzymatic removal of sialic acid showed that +A.FN had both sialic acids in an alpha 2----3 linkage, whereas -A.FN apparently had one alpha 2----3 and one alpha 2----6-linked sialic acid. The borotritide experiments allowed us to calculate that +A.FN appeared to have 5 oligosaccharide chains per FN monomer, whereas the -A.FN showed only 4 chains. These results would account for the decreased glycosylation and increased susceptibility to proteolysis of the -A.FN. We conclude that vitamin A controls both the rate of synthesis of the polypeptide chain of FN via its mRNA, as well as the rate of its glycosylation.
Kirven
M J
MJ
Department of Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge 02139.
Wolf
G
G
D000209:Acute-Phase Proteins / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D005353:Fibronectins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D006868:Hydrolysis; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D019158:N-Acetylneuraminic Acid; D009844:Oligosaccharides / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012794:Sialic Acids / Q000737:chemistry; D014802:Vitamin A Deficiency / Q000378:metabolism*
D000209:Acute-Phase Proteins; D005353:Fibronectins; D009844:Oligosaccharides; D012333:RNA, Messenger; D012794:Sialic Acids; D019158:N-Acetylneuraminic Acid