TGF-beta signaling in colon cancer cells.
Transforming growth factor-betas (TGF-betas), cytokines expressed in the colon, play important roles as tumor suppressors and tumor promoters during colorectal carcinogenesis. TGF-beta signaling pathway involves activation of Smad2 and Smad3 by the type I receptor and formation of Smad2/3/4 heteromeric complexes that enter the nucleus to regulate transcription. Most human colorectal cancers are resistant to the tumor suppressor effects of TGF-beta, and a subset of human colorectal cancers have mutations in Smad2 and Smad4. The purpose of this study was to determine whether Smads are required for TGF-beta signaling in colon cancer cells. First, we selected a colon cancer cell line (MC-26) that has a functional TGF-beta signaling pathway. We found that MC-26 cells expressed Smad2, Smad3, and Smad4 mRNAs by reverse transeription-polymerase chain reaction and confirmed that the TGF-beta signaling pathway is functional using a transient transfection assay with 3TP-Lux reporter plasmid. TGF-beta also inhibited cell growth and induced apoptosis in MC-26 cells. When MC-26 cells were transiently transfected with dominant-negative carboxyl-terminal truncation mutants of Smad2, Smad3, and Smad4, TGF-beta-induced 3TP-Lux reporter activity was significantly reduced, suggesting that Smad2, Smad3, and Smad4 are attractive novel therapeutic targets for regulating TGF-beta signaling in colorectal cancers. Because MC-26 cells express TGF-beta activated Smads, have a functional TGF-beta signaling pathway, and are sensitive to the growth inhibitory and apoptotic effects of TGF-beta, they can serve as an excellent model to examine TGF-beta signaling in colorectal cancers.
Li
Fazhi
F
Department of Surgery, The University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas, 77555-0737, USA.
Cao
Yanna
Y
Townsend
Courtney M
CM
Ko
Tien C
TC
D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000502:physiology*
D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D051785:Smad Proteins; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta