[Ca2+]i as a potential downregulator of α2β1-integrin-mediated A2058 tumor cell migration to type IV collagen

We have investigated cellular Ca2+ regulation during A2058 human melanoma cell chemotaxis to type IV collagen (CIV). We have identified alpha (2)beta (1)-integrin as the primary mediator of A2058 cell response to CIV in vitro. Integrin ligation initiated a characteristic intracellular Ca2+ concentration ([Ca2+](i)) response consisting of an internal release and a receptor-mediated Ca2+ entry. Thapsigargin (TG) pretreatment drained overlapping and CIV-inducible internal Ca2+ stores while initiating a store-operated Ca2+ release (SOCR). CIV-mediated Ca2+ entry was additive to TG-SOCR, suggesting an independent signaling mechanism. Similarly, ionophore application in a basal medium containing Ca2+ initiated a sustained influx. Elevated [Ca2+](i) from TG-SOCR or ionophore significantly attenuated cell migration to CIV by recruiting the Ca2+/calcineurin-mediated signaling pathway. Furthermore, low [Ca2+](i) induced by EGTA application in the presence of ionophore fully restored cell motility to CIV. Together, these results suggest that [Ca2+](i) signaling accompanying A2058 cell response to alpha (2)beta (1)-integrin ligation is neither necessary nor sufficient and that elevated [Ca2+](i) downregulates cell motility via a calcineurin-mediated mechanism in A2058 cell chemotaxis to CIV.