Transforming growth factor-beta-mediated tumor necrosis factor-related apoptosis-inducing ligand expression and apoptosis in hepatoma cells requires functional cooperation between Smad proteins and activator protein-1.
Transforming growth factor-beta (TGF-beta) has been shown to induce apoptotic cell death in normal and transformed hepatocytes. We recently identified tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as an important mediator of TGF-beta-induced apoptosis in hepatoma cells. In this study, we have further explored the mechanism by which TGF-beta up-regulates TRAIL expression. The 5'-flanking region of the TRAIL gene was isolated and characterized. Deletion mutants of the 5'-untranslated region of the TRAIL gene revealed a region comprising nucleotides -1950 to -1100 responsible for TRAIL induction following treatment with TGF-beta. Within this region, we have identified an activator protein-1 (AP-1) site indispensable for TGF-beta-mediated induction of TRAIL. Activation of this AP-1 site is mediated by a JunD.FosB heterodimer. Expression of DNSmad4, DNJunD, or DNFosB significantly impairs TGF-beta-mediated activation of the TRAIL promoter. Furthermore, with tRNA interference targeting Smad4, junD, FosB, we could abolish TRAIL expression and, subsequently, TGF-beta-induced TRAIL-mediated apoptosis in hepatoma cells. Our results reveal a new AP-1 site within the TRAIL promoter functionally involved in TGF-beta-induced TRAIL expression and apoptosis in hepatomas and thus provide evidence for the underlying mechanism by which TGF-beta might regulate cell death in liver cancer.
Herzer
Kerstin
K
Department of Internal Medicine, Johannes Gutenburg University, Mainz, Germany.
Grosse-Wilde
Anne
A
Krammer
Peter H
PH
Galle
Peter R
PR
Kanzler
Stephan
S
D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D004273:DNA, Neoplasm; D020868:Gene Silencing / Q000187:drug effects; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D051785:Smad Proteins / Q000378:metabolism*; D051901:Smad4 Protein / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics*; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D004273:DNA, Neoplasm; D051785:Smad Proteins; D051901:Smad4 Protein; D053221:TNF-Related Apoptosis-Inducing Ligand; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta