Four missense mutations identified in the protein S gene of thrombosis patients with protein S deficiency - Effects on secretion and anticoagulant activity of protein S

Four missense Mutations, G54R, T5891, K155E, and Y595C, were identified in the protein S (PS) gene of the patients with PS deficiency and venous thrombosis. Three patients were heterozygous for the novel mutations, G54R, T5891, and Y595C, while a remaining one patient was homozygous for the K155E mutation, which is known to be a polymorphism in the Japanese population. A family study revealed that the Y595C mutation was associated with a Type I PS deficiency and the K155E mutation with a Type II PS deficiency, while no family study was performed for the patients with the G54R and T5891 mutations. To determine whether these four mutations play a causative role in PS deficiency, the four PS mutants and wild-type PS were stably expressed in human embryo kidney (HEK) 293 cells. Pulse-chase experiments showed intracellular degradation and decreased secretion of the Y595C mutant. In the activated protein C(APC) cofactor assays, the specific activity of the K155E mutant decreased to 58% of that of wild-type PS. The APC cofactor activity of the three mutants, G54R, K155E, and T5891, were inhibited by C4b-binding protein (C4BP) with a dose dependency similar to that of wild-type PS, These results indicate that the Y595C and the K155E mutations are responsible for a secretion defect and a decreased anticoagulant activity of PS, respectively. The remaining two mutations, G54R and T5891, however, did not produce any definite abnormality leading to a low plasma PS activity. (C) 2002 Elsevier Science Ltd. All rights reserved.