α-Adrenergic-mediated activation of human reconstituted fibrinogen receptor (integrin αIibβ3) in Chinese hamster ovary cells

This work reports the functional studies of CHO cells coexpressing a-adrenergic (aAR) and human fibrinogen (Fg) receptors (integrin αIibβ3). Stimulation of these cells with a-agonists produced a transient rise in the free cytosolic calcium (Ca++) accompanied by enhanced binding to soluble Fg, and these effects were prevented by specific aAR antagonists. The a- adrenergic-induced activation of αIibβ3 in CHO-αIibβ3-aAR increased the rate of adhesion and extension of cells onto Fg coated plates, and also induced a soluble Fg- and αLIIba3-dependent formation of cell aggregates, whereas no effects were observed by the stimulation of CHO-αIibβ3 cells.a-Adrenergic antagonists, the ligand mimetic peptide RGDS, pertussis toxin (PTX), or EDTA, they all prevented the a-adrenergic stimulation of adhesion and aggregation. However, inhibition of PKC prevented the a-adrenergic stimulation of cell adherence, whereas blocking the intracellular Ca++ mobilization impeded the stimulation of cell aggregation.The α-adrenergic activation was associated with phosphorylation of a protein of ~100 kDa and proteins of the MAPK family. The former was selectively phosphorylated by α-adrenergic stimulation whereas the latter were phosphorylated by the binding of cells to Fg and markedly intensified by a-adrenergic stimulation.