α-adrenergic-mediated activation of human reconstituted fibrinogen receptor (integrin αllbβ3) in Chinese hamster ovary cells

This work reports the functional studies of CHO cells coexpressing alpha-adrenergic (alphaAR) and human fibrinogen (Fg) receptors (integrin alphaIIbbeta3). Stimulation of these cells with alpha-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 alpha-adrenergic-induced activation of alphaIIbbeta3 in CHO-alphaIIbbeta(3)-alphaAR increased the rate of adhesion and extension of cells onto Fg coated plates, and also induced a soluble Fg- and alphaIIbbeta3-dependent formation of cell aggregates, whereas no effects were observed by the stimulation of CHO-alphaIIbbeta3 cells. alpha-Adrenergic antagonists, the ligand mimetic peptide RGDS, pertussis toxin (PTX), or EDTA, they all prevented the alpha-adrenergic stimulation of adhesion and aggregation. However, inhibition of PKC prevented the alpha-adrenergic stimulation of cell adherence, whereas blocking the intracellular Ca++ mobilization impeded the stimulation of cell aggregation. The alpha-adrenergic activation was associated with phosphorylation of a protein of similar to100 kDa and proteins of the MAPK family. The former was selectively phosphorylated by alpha-adrenergic stimulation whereas the latter were phosphorylated by the binding of cells to Fg and markedly intensified by alpha-adrenergic stimulation.