THROMBIN AND PHORBOL ESTER INDUCE INTERNALIZATION OF THROMBIN RECEPTOR OF HUMAN MESANGIAL CELLS THROUGH DIFFERENT PATHWAYS

Thrombin is a potent activator of human mesangial cells probably by ac tivation of its functional receptor. Northern blot analysis demonstrat es the presence of mRNA encoding the functional thrombin receptor in m esangial cells, and surface expression of thrombin receptor antigen ha s been confirmed by immunocytochemistry. Using I-125-labeled ATAP2, a monoclonal antibody against the functional thrombin receptor, we found that thrombin and thrombin receptor agonist peptide (TRAP) induce hom ologous internalization of thrombin receptor in a dose-dependent manne r. Redistribution of thrombin receptor from the cell surface to vesicu lar structures in the cytoplasm has been followed by immunocytochemist ry. Additionally, a dose-dependent loss of cell surface thrombin recep tor is induced by phorbol 12-myristate 13-acetate (PMA), suggesting th at thrombin receptor undergoes heterologous internalization in respons e to PMA. The time course of thrombin-induced receptor internalization is different from that observed with TRAP and PMA. Protein kinase C i nhibitors, staurosporine and GF 109 203 X, do not affect thrombin rece ptor internalization induced by thrombin and TRAP but block receptor i nternalization stimulated by PMA. These data suggest that heterologous thrombin receptor internalization induced by PMA is mediated by prote in kinase C. However, activation of protein kinase C is not responsibl e for homologous thrombin receptor internalization caused by thrombin and TRAP. (C) 1995 Academic Press, Inc.