14-3-3 sigma and 14-3-3 zeta plays an opposite role in cell growth inhibition mediated by transforming growth factor-beta 1.
The expression of 14-3-3 proteins is dysregulated in various types of cancer. This study was undertaken to investigate the effects of 14-3-3 zeta and 14-3-3 sigma on cell growth inhibition mediated by transforming growth factor-beta 1 (TGF-beta1). Mouse mammary epithelial cells (Eph4) that are transformed with oncogenic c-H-Ras (EpRas) and no longer sensitive to TGF-beta1-mediated growth inhibition displayed increased expression of 14-3-3 zeta and decreased expression of 14-3-3 sigma compared with parental Eph4 cells. Using small interfering RNA-mediated knockdown and overexpression of 14-3-3 sigma or 14-3-3 zeta, we showed that 14-3-3 sigma is required for TGF-beta1-mediated growth inhibition whereas 14-3-3 zeta negatively modulates this growth inhibitory response. Notably, overexpression of 14-3-3 zeta increased the level of Smad3 protein that is phosphorylated at linker regions and cannot mediate the TGF-beta1 growth inhibitory response. Consistent with this finding, mutation of the 14-3-3 zeta phosphorylation sites in Smad3 markedly reduced the 14-3-3 zeta-mediated inhibition of TGF-beta1-induced p15 promoter-reporter activity and cell cycle arrest, suggesting that these residues are critical targets of 14-3-3 zeta in the suppression of TGF-beta1-mediated growth. Taken together, our findings indicate that dysregulation of 14-3-3 sigma or 14-3-3 zeta contributes to TGF-beta1 resistance in cancer cells.
Hong
Hye-Young
HY
Department of Biochemistry, College of Natural Sciences, Kangwon National University, Chuncheon, 200-701, Korea.
Jeon
Woo-Kwang
WK
Bae
Eun-Jin
EJ
Kim
Shin-Tae
ST
Lee
Ho-Jae
HJ
Kim
Seong-Jin
SJ
Kim
Byung-Chul
BC
D048948:14-3-3 Proteins / Q000502:physiology*; D000818:Animals; D001665:Binding Sites; D002453:Cell Cycle; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000235:genetics; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects*; D005260:Female; D055785:Gene Knockdown Techniques; D011905:Genes, ras; D008321:Mammary Glands, Animal / Q000166:cytology; D051379:Mice; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000037:antagonists & inhibitors / Q000502:physiology*
D048948:14-3-3 Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D034741:RNA, Small Interfering; C499130:Sfn protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D053773:Transforming Growth Factor beta1; D050760:Cyclin-Dependent Kinase Inhibitor p27