Epidermal Growth Factor Potentiates Cholecystokinin/Gastrin Receptor-mediated Ca²⁺ Release by Activation of Mitogen-activated Protein Kinases

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.