Characterization of two mutations of the protein S gene observed in Japanese thrombophilic patients.

Abstract

Two missense mutations, Thr37Met and Cys206Phe, have been found in the protein S (PS) gene of two patients with a PS deficiency associated with deep vein thrombosis.The two patients were both heterozygous for the respective mutations.To determine whether these mutations play a causative role in the PS deficiency of the patient, the PS molecule harboring the mutation was stably expressed in the human embryo kidney (HEK) 293 cells.The amount of the Thr37Met mutant PS protein in the culture medium was as much as that of the mild-type, while its specific activity was decreased to 33% of that of the wild-type.On the other hand, the Cys206Phe mutant secreted into the medium was determined below the dectection limit.Because a chimera molecule of Cys206Phe mutatnt PS and green flueorescence protein (GFP) was found to accumulate in the HEK 293 cells, secretion of the Cys206Phe mutant into the medium may be impaired.These results suggest that the Thr37Met and Cys206Phe mutations are responsible at least in part for the observed PS deficiency in the respective patients.