Different Signaling Pathways Are Involved in CCKB Receptor-Mediated MAP Kinase Activation in COS-7 Cells

Abstract

Abstract Recently, the involvement of the MAP kinase ERK in mitogenic signaling of cholecystokininB (CCKB) receptors has been shown. However, the intracellular effector systems involved in this signaling pathway are poorly defined. In this study, we used COS-7 cells transiently transfected with the human CCKB receptor to investigate cholecystokinin-induced MAP kinase activation. CCK-8 induced activation of ERK2 which is associated with its phosphorylation and localization in the nucleus. The CCK-8-dependent ERK stimulation is sensitive to wortmannin an inhibitor of phosphoinositide 3-kinases (PI3Ks) indicating the involvement of PI3K activity. To identify the PI3K species involved in mitogenic signaling of the CCKB receptor several dominant-negative mutants of PI3K regulatory and catalytic subunits were transiently expressed. Surprisingly, different catalytically inactive mutants of the G protein-sensitive PI3Kγ did not affect ERK stimulation induced by CCK, whereas a dominant-negative mutant of the regulatory p85 subunit induced significant inhibition of CCK-dependent ERK activity. These results indicate an involvement of PI3K class 1A species α, β or/and δ in signal transduction via CCKB receptors. In addition, protein kinase C (PKC)-dependent signaling pathways contribute to CCKB-mediated MAP kinase signaling as shown by inhibition of CCK-8-induced ERK activation by the PKC inhibitor bisindolylmaleimide.