Hereditary alpha 2-plasmin inhibitor deficiency caused by a transport-deficient mutation (alpha 2-PI-Okinawa). Deletion of Glu137 by a trinucleotide deletion blocks intracellular transport

Abstract

alpha 2-Plasmin inhibitor is the most important physiological inhibitor of fibrinolysis; hence, its deficiency results in a severe hemorrhagic diathesis. We have cloned and characterized a mutant alpha 2-plasmin inhibitor gene from an individual homozygous for the deficiency. By sequencing all the coding exons and exon-intron boundaries of the gene, a trinucleotide deletion in exon VII that results in deletion of Glu137 was identified. We have designated this variant as alpha 2-plasmin inhibitor Okinawa. Using DNA samples amplified with the polymerase chain reaction, hybridization analysis by oligonucleotide probes confirmed the presence of this mutation in all the affected family members, including both parents. To elucidate the mechanism by which this mutation leads to the deficiency, a eukaryotic expression plasmid for alpha 2-plasmin inhibitor containing this mutation was constructed and transfected into COS-7 cells for transient expression analysis. Immunoprecipitation analysis and enzyme-linked immunosorbent assay revealed that the mutant alpha 2-plasmin inhibitor synthesized is mostly retained within the cells as an endoglycosidase H-sensitive form, and only a small portion of it is secreted into the medium as a neuraminidase-sensitive form. These results suggest that the Glu137 deletion leads to the alpha 2-plasmin inhibitor deficiency by causing a block in its intracellular transport from the endoplasmic reticulum to the Golgi complex.