VITAMIN-K-DEPENDENT PROTEIN-S IN LEYDIG-CELLS OF HUMAN TESTIS

Protein S is an anticoagulant plasma protein, functioning as a cofacto r to activated protein C in the regulation of blood coagulation. In ad dition, protein S forms a complex with the complement regulatory prote in, C4b-binding protein. Protein S is unique among the vitamin K-depen dent proteins in being structurally similar to androgen binding protei ns. Protein S immunoreactivity was demonstrated in Leydig cells of hum an testis. In Northern blotting experiments, the presence of protein S mRNA in human testis tissue could be shown. In situ hybridization exp eriments localized protein S mRNA to the Leydig cells, demonstrating t ranscription of the protein S gene in these cells. Five protein S clon es were isolated from a human testis cDNA library, partially sequenced and characterized by restriction enzyme mapping. Three unique clones contained information for the entire coding sequence and approximately two-thirds of the 5' and 3' non-coding sequences. The results indicat e the nucleotide sequences of testis and liver protein S mRNA to be id entical. No binding of androgens to protein S could be demonstrated. I n conclusion, we demonstrate the presence of protein S immunoreactivit y as well as protein S mRNA in the Leydig cells of human testis. These results suggest local synthesis of protein S in Leydig cells of human testis which may be Functionally important for local anticoagulation.