Role of basal calcium in the EGF activation of MAP kinases

The role of intracellular Ca2+ pools in the regulation of growth factor sig nal transduction pathways and mitogenesis is not well understood. We have e xamined the roles of basal and transiently mobilized Ca2+ in the regulation of MAP kinases by EGF, To assess the influence of Ca2+ transients we utili zed Plcg1(-/-) and Plcg1(+/+) mouse embryonic fibroblasts, while BAPTA/AM w as employed to chelate total intracellular Ca2+ in the same cell lines, The MAP kinases erk-1, erk-2 and erk-5 exhibited similar patterns of activatio n in wild-type and Plcg1(-/-) cells treated with EGF, However, pretreatment with BAPTA/AM significantly increased and prolonged erk-1 and erk-2 activa tion in both cell types, In contrast, BAPTA/AM prevented the EGF activation of erk-5 in wild-type and Plcg1(-/-) cells. These data indicate that basal Ca2+, but not growth factor provoked Ca2+ transients, has a significant in fluence on the activation of these MAP kinases, AG1478, a specific EGF rece ptor kinase inhibitor, abolished the prolonged erk-1 and erk-2 activation p roduced by EGF in cells pretreated with BAPTA/AM, This indicates that the p rolonged activation of erk-1 and erk-2 produced in the presence of BAPTA/AM requires continuous signaling from the EGF receptor kinase.