Bombesin stimulates cholecystokinin secretion through mitogen-activated protein-kinase-dependent and -independent mechanisms in the enteroendocrine STC-1 cell line.
Bombesin has been reported to stimulate cholecystokinin (CCK) secretion from rat duodeno-jejunal I-cells. Bombesin was shown to activate mitogen-activated protein kinases (MAPKs) in cell types such as Swiss 3T3 fibroblasts and rat pancreatic acinar cells. No information is available on whether MAPK is activated in intestinal endocrine cells upon bombesin stimulation. This was studied by using the CCK-producing enteroendocrine cell line STC-1. Bombesin stimulated markedly and transiently both p42(MAPK) and p44(MAPK), with a maximum at 2 min, and a decrease to basal levels within 10 min. As expected, bombesin stimulated MAPK kinase 1 (MEK-1) activity. Activation of protein kinase C (PKC) with PMA also stimulated p42(MAPK), p44(MAPK) and MEK-1. Treatment of cells with PD 098059 (at 10 microM or 30 microM), which selectively inhibits MEK phosphorylation, blocked bombesin-induced p42(MAPK) and p44(MAPK) activation for at least 90 min. However, PD 098059 inhibited bombesin- and PMA-stimulated CCK secretion during the first 15 min, but failed to significantly reduce CCK release at later times. Inhibition of PKC with staurosporine, or PKC down-regulation by prolonged treatment with PMA, both drastically decreased MEK-1, p42(MAPK) and p44(MAPK) activation upon bombesin stimulation. Additionally, PKC activation appeared to be required for both MAPK-dependent (early) and -independent (late) CCK responses to bombesin. It is concluded that the early CCK secretory response of STC-1 cells to bombesin involves MAPK pathway activation through a PKC-dependent mechanism, whereas the late phase of bombesin-induced CCK secretion, that also requires PKC, appears to result from a MAPK-independent process.
Némoz-Gaillard
E
E
INSERM Unité 45, Hôpital Edouard-Herriot, Pavillon Hbis, 69437 Lyon Cédex 3, France.
Cordier-Bussat
M
M
Filloux
C
C
Cuber
J C
JC
Van Obberghen
E
E
Chayvialle
J A
JA
Abello
J
J
D016475:3T3 Cells; D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002766:Cholecystokinin / Q000378:metabolism*; D004703:Endocrine System / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D002766:Cholecystokinin; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D001839:Bombesin