Ca2+]i as a potential downregulator of alpha2beta1-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 alpha2beta1-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 alpha2beta1-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.