Biosynthesis and shedding of epiglycanin: a mucin-type glycoprotein of the mouse TA3Ha mammary carcinoma cell.
Epiglycanin is a mucin-type glycoprotein present at the surface of TA3Ha mouse mammary tumour cells. It is a long rod-like glycoprotein with a molecular mass of 500 kDa. Its function has not yet been established but its overexpression can affect cell-cell and cell-matrix adhesion. To understand better the biological function of epiglycanin, we have studied the biochemical structure and biosynthesis of epiglycanin in TA3Ha cells. Pulse-chase labelling experiments with [(3)H]threonine revealed an early precursor with a molecular mass of approx. 300 kDa containing approx. 5-10 kDa of N-linked glycans. The precursor was gradually converted into a high-molecular-mass mature form, owing mainly, if not entirely, to O-glycosylation. The mature molecule consists of two major glycoforms that differ in sialylation. Unlike secreted mucins, epiglycanin did not form cysteine-bound multimers, providing further evidence that epiglycanin belongs to the class of membrane-associated mucins. The mature form, but not the precursor form, is shed from the cell surface. The half-life of epiglycanin on the cell surface was found to be approx. 60 h. These results provide the first detailed analysis of the biochemical structure and biosynthesis of epiglycanin.
Thingstad
T
T
Division of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Vos
H L
HL
Hilkens
J
J
D000818:Animals; D003545:Cysteine / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006026:Glycoside Hydrolases / Q000378:metabolism; D006031:Glycosylation; D006207:Half-Life; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008970:Molecular Weight; D009077:Mucins / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D019158:N-Acetylneuraminic Acid / Q000032:analysis / Q000378:metabolism; D009439:Neuraminidase / Q000378:metabolism; D011498:Protein Precursors / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D014407:Tumor Cells, Cultured
D004220:Disulfides; D008562:Membrane Glycoproteins; D009077:Mucins; D011498:Protein Precursors; C016424:epiglycanin protein, mouse; D006026:Glycoside Hydrolases; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid; D003545:Cysteine