A mitogenic action for fibrinogen mediated through intercellular adhesion molecule-1

Intercellular adhesion molecule-1 (ICAM-1) is a cell surface ligand for α(L)β₂ and α(M)β₂ integrins and has a key role in leukocyte adhesion to the vascular endothelium. The plasma protein fibrinogen has also been shown to interact with ICAM-1. We have investigated the effect of fibrinogen binding to ICAM-1-expressing cells on cell proliferation. The inclusion of 200-800 nM fibrinogen but not fibronectin to the culture medium of Raji induced a 2-4-fold increase in [³H]thymidine incorporation after 8 h. Cell proliferation in cultures containing fibrinogen was also confirmed by direct cell counting. The proliferative response in Raji was abrogated by an anti- ICAM-1 mAb 84H10 which maps to the first Ig domain of ICAM-1. A purified truncated form of ICAM-1 containing the first two Ig-like domains and a peptide with amino acid sequence corresponding to ICAM-1 (822) was also able to block the proliferative action of fibrinogen on Raji. 200 nM fibrinogen induced a 3-fold increase in [³H]thymidine incorporation by 293 cells transfected with ICAM-1 cDNA but not control nontransfected 293 cells. Comparable mitogenic effects were achieved with fibrinogen fragments X and D₁₀₀, and with a synthetic peptide with an amino acid sequence matching fibrinogen γ chain (117-133). These results indicate that interaction between discrete sequences within ICAM-1 and fibrinogen result in cellular proliferation.