Proliferative effects of cholecystokinin in GH(3) pituitary cells mediatedby CCK2 receptors and potentiated by insulin

1 Proliferative effects of CCK peptides have been examined in rat anterior pituitary GH(3) cells, which express CCK2 receptors. 2 CCK-8s, gastrin(1-17) and its glycine-extended precursor G(1-17)-Gly, pre viously reported to cause proliferation via putative novel sites on AR4-2J and Swiss 3T3 cells, elicited significant dose dependent increases of simil ar magnitude in [H-3]thymidine incorporation over 3 days in serum-free medi um of 39+/-10% (P<0.01, n=20), 37+/-8% (P<0.01, n=27) and 41+/-6% (P<0.01, n=36) respectively. 3 CCK-8s and gastrin potentially stimulated mitogenesis (EC50 values 0.12 n M and 3.0 nM respectively), whilst G-Gly displayed similar efficacy but mar kedly lower potency. L-365,260 consistently blocked each peptide. The CCK2 receptor affinity of G-Gly in GH(3) cells was 1.09 mu M (1.01; 1.17, n=6) a nd 5.53 mu M (3.71; 5.99, n=4) in guinea-pig cortex. 4 1 mu M G-Gly weakly stimulated Ca2+ increase, eliciting a 104 +/- 21% inc rease over basal Ca2+ levels, and was blocked by 1 mu M L-365,260 whilst CC K-8s (100 nM) produced a much larger Ca2+ response (331 +/- 14%). 5 Insulin dose dependently enhanced proliferative effects of CCK-8s with a maximal leftwards shift of the CCK-8s curve at 100 ng ml(-1) (17 nM) (EC50 decreased 500 fold, from 0.1 nM to 0.2 pM; P<0.0001). 10 mu g ml(-1) insuli n was supramaximal reducing the EC50 to 5 pM (P=0.027) whilst 1 ng ml(-1) i nsulin was ineffective. Insulin weakly displaced [I-125]BHCCK binding to GH (3) CCK2 receptors (IC50 3.6 mu M). 6 Results are consistent with mediation of G-Gly effects via CCK2 receptors in GH(3) cells and reinforce the role of CCK2 receptors in control of cell growth. Effects of insulin in enhancing CCK proliferative potency may sugg est that CCK2 and insulin receptors converge on common intracellular target s and indicates that mitogenic stimuli are influenced by the combination of extracellular factors present.