Internalization of factor J and cellular signalization after factor J-cellinteraction

Factor J (FJ) is a cationic glycoprotein with inhibitory activity in vitro against both classical and alternative pathways of complement activation. R ecently FJ has been implicated in adhesion to several cell lines, through a membrane receptor identified as nucleolin, In the present work we study th e events that follow the binding of FJ to cells. After incubation of K562 w ith FJ, this protein was internalized actively and localized in the cytopla sm and nucleus, Adhesion to immobilized FJ induced tyrosine phosphorylation of several intracellular proteins in Jurkat cell line with a similar patte rn to that induced by fibronectin (FN), an extracellular matrix protein. Th is effect was maximal at 5 min and decreased after 10 min, and inhibited by anti-FJ monoclonal antibody (mAb), These results suggest that the binding of FJ to cells may play an important role in transduction of biochemical si gnals across the plasma membrane to the cell interior, (C) 1999 Academic Pr ess.