EVIDENCE FOR A PROTEIN-S RECEPTOR(S) ON HUMAN VASCULAR SMOOTH-MUSCLE CELLS - ANALYSIS OF THE BINDING CHARACTERISTICS AND MITOGENIC PROPERTIES OF PROTEIN-S ON HUMAN VASCULAR SMOOTH-MUSCLE CELLS

The presence of specific binding sites for the coagulation factor prot ein S (PS) on the surface of human vascular smooth muscle cells (HVSMC ) is described. The binding characteristics of I-125-PS to HVSMC were studied and found to be saturable, reversible and, as described by the Hill equation, co-operative (h 1.74; K-d 0.33 nM). Autoradiographic a nalysis of detergent extracts of HVSMC chemically cross-linked with I- 125-PS and separated by SDS/PAGE revealed radioactivity associated wit h two proteins with apparent molecular masses of 220 and 230 kDa respe ctively. The mitogenic activity of PS on HVSMC was also investigated. Protein S was shown to stimulate DNA synthesis of growth-arrested HVSM C and to support their proliferation under low-serum conditions in a s ustained and dose-dependent manner.