Processing and assembly of the integrin, glycoprotein IIb-IIIa, in HEL cells
We examined the biosynthetic processing and assembly of the platelet glycoprotein (GP) IIb-IIIa complex in (/sup 35/S)methionine-labeled HEL cells, a human cell line with features of megakaryocytes. Both GPIIb and GPIIIa were synthesized as single-chain precursors to which high mannose N-linked oligosaccharides were added in the endoplasmic reticulum (ER). A 5-fold excess of the major IIb precursor, preIIb, was synthesized relative to GPIIIa. Two smaller proteins immunologically related to GPIIb were synthesized in smaller amounts. Assembly of the GPIIb and GPIIIa precursors required 4-6 h for completion. All GPIIIa molecules were eventually assembled; the excess GPIIb precursors were degraded without reaching the cell surface. Following assembly, preIIb-IIIa complexes were rapidly transported to the Golgi apparatus where preIIb underwent modification of high mannose chains into complex oligosaccharides and proteolytic cleavage to yield disulfide-linked heavy and light chains. Pretreating cells with the ionophore monensin blocked cleavage of preIIb but not its carbohydrate modification or its assembly with GPIIIa. These studies suggest that (1) assembly of the precursors of GPIIb and GPIIIa in the ER is a slow process requiring conformational maturation of one or both subunits, and (2) only heterodimers assembled in the ER are transported to the Golgi apparatus for additional processing and, ultimately, expression on the cell surface.
- Research Organization:
- Institut National de la Sante et de la Recherche Medicale, Paris (France)
- OSTI ID:
- 5822492
- Journal Information:
- J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 264:21; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANIMAL CELLS
ANIMALS
ANTIBODIES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOSYNTHESIS
BONE MARROW CELLS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
CHELATING AGENTS
CONNECTIVE TISSUE CELLS
DAYS LIVING RADIOISOTOPES
DRUGS
EDTA
EVEN-ODD NUCLEI
GLYCOPROTEINS
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
LIPOTROPIC FACTORS
MAMMALS
MAN
MEMBRANES
METHIONINE
MONOCLONAL ANTIBODIES
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANOIDS
PRIMATES
PROTEINS
RADIOISOTOPES
SOMATIC CELLS
SULFUR 35
SULFUR ISOTOPES
SYNTHESIS
TRACER TECHNIQUES
VERTEBRATES