title: RRR-alpha-tocopherol succinate down-regulates oncogenic Ras signaling.
abstract: alpha-Tocopherol succinate (TS), an analogue of vitamin E, has growth-inhibitory activity in a wide spectrum of in vitro and in vivo cancer models. Here, we report that modulation of oncogenic Ras is associated with TS activity. TS inhibits the proliferation and induces apoptosis of NIH3T3 cells stably transfected with oncogenic K-Ras and H-Ras, but not NIH3T3 cells expressing empty vector. TS treatment resulted in decreased Ras protein levels in oncogenic Ras expressing NIH3T3 cells but not in parental NIH3T3 cells. Treatment with TS suppressed the levels of phospho-Akt and phospho-Erk1/2 in oncogenic Ras expressing NIH3T3 cells. Overexpression of constitutively active phosphoinositide-3-kinase, Akt, and Mek1/2 significantly attenuated TS growth inhibition of oncogenic Ras-transformed NIH3T3 mouse fibroblast cell lines. In addition, transcriptional targets of oncogenic Ras such as c-Myc, cyclin D1, and E2F1 were down-regulated by TS in oncogenic Ras-expressing cells. The above TS effects on oncogenic Ras signaling were also observed in endogenous oncogenic K-Ras expressing HCT 116 (human colon cancer) and MDA-MB-231 (human breast cancer) cells. Taken together, these data show that TS down-regulation of the Ras signaling pathways that are mediated by Mek/Erk and phosphoinositide-3-kinase/Akt plays, at least in part, a critical role in TS inhibition of proliferation and survival of transformed cells. This data supports further investigation of the chemopreventive and therapeutic potential of TS in tumors that are dependent on activated Ras signaling and identifies phosphor-Erk and phosphor-Akt as potential biomarkers of TS activity.
authors.affiliation: Gastrointestinal Tumor Program, Division of Gastrointestinal Tumors, Department of Interdisciplinary Oncology, University of South Florida, Tampa, Florida 33612, USA.
authors.forename: Sreenivasa
authors.initials: S
authors.lastname: Donapaty
authors.forename: Somaja
authors.initials: S
authors.lastname: Louis
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Horvath
authors.forename: Jiang
authors.initials: J
authors.lastname: Kun
authors.forename: Said M
authors.initials: SM
authors.lastname: Sebti
authors.forename: Mokenge P
authors.initials: MP
authors.lastname: Malafa
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000037:antagonists & inhibitors; D015536:Down-Regulation; D050684:E2F Transcription Factors / Q000037:antagonists & inhibitors; D006801:Humans; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects; D024505:Tocopherols; D015533:Transcriptional Activation; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D019938:Cyclin D1; D050684:E2F Transcription Factors; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D016271:Proto-Oncogene Proteins c-myc; D024505:Tocopherols; D014810:Vitamin E; D018631:ras Proteins