Smad4 mediates activation of mitogen-activated protein kinases by TGF-beta in pancreatic acinar cells.
Transforming growth factor-beta (TGF-beta) inhibits pancreatic acinar cell growth. In many cell types, TGF-beta mediates its growth inhibitory effects by activation of Smad proteins. Recently, it has been reported that Smad proteins may interact with the mitogen-activated protein (MAP) kinase signaling pathways. In this study, we report on the interactions between the TGF-beta and MAP kinase signaling pathways in isolated rat pancreatic acinar cells. TGF-beta activated the MAP kinases extracellular signal-related kinases (ERKs) and p38 in pancreatic acinar cells, but had no effect on c-jun NH2-terminal kinase activity. Activation of MAP kinase by TGF-beta was maximal 4 h after treatment. The ability of TGF-beta to activate ERKs was concentration dependent and dependent on protein synthesis. TGF-beta's stimulation of ERK activation was blocked by PD-98059, an inhibitor of MAP kinase kinase 1, and by adenoviral transfer of dominant negative RasN17. Furthermore, adenoviral-mediated expression of dominant negative Smad4 blocked the ability of TGF-beta to activate acinar cell MAP kinase, demonstrating that this activation is downstream of Smads. The biological relevance of ERK activation by TGF-beta was indicated by demonstrating that inhibition of ERK signaling by PD-98059 blocked the ability of TGF-beta to activate the transcription factor activator protein-1. These studies provide new insight into the signaling mechanisms by which TGF-beta mediates biological actions in pancreatic acinar cells.
Simeone
D M
DM
Department of Surgery, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA. simeone@umich.edu
Zhang
L
L
Graziano
K
K
Nicke
B
B
Pham
T
T
Schaefer
C
C
Logsdon
C D
CD
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002766:Cholecystokinin / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D017930:Genes, Reporter; D015151:Immunoblotting; D066298:In Vitro Techniques; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010179:Pancreas / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D051901:Smad4 Protein; D015534:Trans-Activators / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D011500:Protein Synthesis Inhibitors; D051901:Smad4 Protein; C490811:Smad4 protein, rat; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D002766:Cholecystokinin; D003513:Cycloheximide; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one