Impaired secretion of mutant alpha 2-plasmin inhibitor (alpha 2 PI-Nara) from COS-7 and HepG2 cells: molecular and cellular basis for hereditary deficiency of alpha 2-plasmin inhibitor.
The elongated mutant of alpha 2-plasmin inhibitor (alpha 2 PI) designated as alpha 2 PI-Nara is caused by a frameshift mutation found near the 3' end of the coding region of the alpha 2 PI gene. To elucidate the mechanism by which this molecular abnormality leads to alpha 2 PI deficiency in plasma, we transfected an expression plasmid for alpha 2 PI-Nara into a monkey kidney cell line COS-7 or human hepatoma cell line HepG2 synthesizing alpha 2 PI, and analyzed the secretory process of the expressed alpha 2 PI-Nara by radioimmunoprecipitation followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography. The results obtained showed that the recombinant alpha 2 PI-Nara was retained within the cells for prolonged periods as an endoglycosidase H-sensitive precursor form, and only a small portion of the recombinant protein was secreted into the medium as a neuraminidase-sensitive mature form. These results suggest that instead of being secreted from the cells, most of the alpha 2 PI-Nara undergoes degradation within the cells while its transport is retarded in the intracellular secretory pathway; thus, alpha 2 PI-Nara should lead to the alpha 2 PI deficiency primarily by causing a block in the intracellular transport from the endoplasmic reticulum to the Golgi complex.
First Department of Internal Medicine, Tokyo Medical and Dental University, Japan.
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Miura
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Aoki
D001692:Biological Transport; D002460:Cell Line; D003001:Cloning, Molecular; D005341:Fibrinolysin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006596:Hexosaminidases / Q000378:metabolism; D006801:Humans; D008970:Molecular Weight; D009439:Neuraminidase / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000511:alpha-Macroglobulins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
D000511:alpha-Macroglobulins; C024668:plasmin-alpha(2)-macroglobulin complex; D006596:Hexosaminidases; D009439:Neuraminidase; D005341:Fibrinolysin