title: Binding and internalization of thrombin by normal and transformed chick cells.
abstract: Thrombin stimulates cell proliferation in cultures of normal chick embryo fibroblasts but not in cells transformed with Rous sarcoma virus. Analysis of medium conditioned by Rous-sarcoma-virus-transformed cultures demonstrates that these cells do not secrete molecules that can inhibit or inactivate thrombin. The interaction of thrombin with these cells was investigated with enzymatically active 125I-thrombin. The amount of cell-associated 125I-thrombin was found to be three times greater with normal cells than with transformed cells. In both types of cell, greater than 50% of the total cell-associated 125I-thrombin was found as a component that was not dissociated from the cells by trypsin treatment, an observation suggesting that a significant portion was not on the cell surface. The amount of the trypsin-insensitive fraction increases with time up to 12 hr, whereas the trypsin-sensitive fraction is saturated after 1-4 hr. Autoradiography of thin sections of 125I-thrombin-treated cells observed by electron microscopy reveals that after 10 hr incubation greater than 70% of the label is localized in the cytoplasm of both normal and transformed cells. Autoradiograms of sodium dodecyl sulfate/polyacrylamide slab gels demonstrate that 40% of the intracellular label is the size of native thrombin with the remainder in two large fragments of 22,000 and 19,500 daltons.
mesh_terms: D000818:Animals; D001358:Avian Sarcoma Viruses; D002455:Cell Division; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D002642:Chick Embryo; D005347:Fibroblasts / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008854:Microscopy, Electron; D008938:Mitosis; D013696:Temperature; D013917:Thrombin / Q000378:metabolism*; D014357:Trypsin
chemical_list: D014357:Trypsin; D013917:Thrombin