Effect of aggretin on endothelial ERK 1/2 phosphorylation. The integrin α2β1 agonist aggretin was purified from the venom of Calloselasma rhodostoma as described under “Purification of aggretin” in “Materials and methods.” To assess the activity of the purified protein, HUVECs were incubated with 0.15 μM aggretin for various times. Cell extracts were prepared and separated using 10% SDS-PAGE, then transferred to PVDF membranes. Membranes were immunoblotted with antibodies specific for phospho-ERK 1/2 (A) or total ERK 1/2 (B). Aggretin induced rapid phosphorylation of ERK 1/2. Similar observations were noted when mAbs JSB2 or TS2/16 were used as agonists.