Small differences in amplitude, duration, and temporal patterns of change in the concentration of free intracellular Ca2+ ([Ca 2+]i) can profoundly affect cell physiology, altering programs of gene expression, cell proliferation, secretory activity, and cell survival. We report a novel mechanism for amplitude modulation of [Ca 2+]i that involves mitogen-activated protein kinase (MAPK). We show that epidermal growth factor (EGF) potentiates gastrin-(1-17) (G17)-stimulated Ca2+ release from intracellular Ca2+ stores through a MAPK-dependent pathway. G17 activation of the cholecystokinin/gastrin receptor (CCK2R), a G protein-coupled receptor, stimulates release of Ca2+ from inositol 1,4,5-triphosphate-sensitive Ca2+ stores. Pretreating rat intestinal epithelial cells expressing CCK2R with EGF increased the level of G17-stimulated Ca2+ release from intracellular stores. The stimulatory effect of EGF on CCK2R-mediated Ca2+ release requires activation of the MAPK kinase (MEK)1,2/extracellular signal-regulated kinase (ERK)1,2 pathway. Inhibition of the MEK1,2/ERK1,2 pathway by either serum starvation or treatment with selective MEK1,2 inhibitors PD98059 and U0126 or expression of a dominant-negative mutant form of MEK1 decreased the amplitude of the G17-stimulated Ca2+ release response. Activation of the MEK1,2/ERK1,2 pathway either by pretreating cells with EGF or by expression of constitutively active K-ras (K-rasV12G) or MEK1 (MEK1*) increased the amplitude of G17-stimulated Ca2+ release. Although EGF, MEK1*, and K-rasV12G activated the MEK1,2/ERK1,2 pathway, they did not increase [Ca2+]i in the absence of G17. These data demonstrate that the activation state of the MEK1,2/ERK1,2 pathway can modulate the amplitude of the CCK2R-mediated Ca2+ release response and identify a novel mechanism for cross-talk between EGF receptor- and CCK 2R-regulated signaling pathways.
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