EIF3i promotes colon oncogenesis by regulating COX-2 protein synthesis and β-catenin activation.
Translational control of gene expression has recently been recognized as an important mechanism controlling cell proliferation and oncogenesis, and it mainly occurs in the initiation step of protein synthesis that involves multiple eukaryotic initiation factors (eIFs). Many eIFs have been found to have aberrant expression in human tumors and the aberrant expression may contribute to oncogenesis. However, how these previously considered house-keeping proteins are potentially oncogenic remains elusive. In this study, we investigated the expression of eIF3i in human colon cancers, tested its contribution to colon oncogenesis and determined the mechanism of eIF3i action in colon oncogenesis. We found that eIF3i expression was upregulated in both human colon adenocarcinoma and adenoma polyps as well as in model inducible colon tumorigenic cell lines. Overexpression of ectopic eIF3i in intestinal epithelial cells causes oncogenesis by directly upregulating the synthesis of cyclooxygenase-2 (COX-2) protein and activates the β-catenin/T-cell factor 4 signaling pathway that mediates the oncogenic function of eIF3i. Together, we conclude that eIF3i is a proto-oncogene that drives colon oncogenesis by translationally upregulating COX-2 and activating the β-catenin signaling pathway. These findings imply that proto-oncogenic eIFs likely exert their tumorigenic function by regulating/altering the synthesis level of downstream tumor suppressor or oncogenes.
Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, USA.
J
J
Qi
Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, USA.
Z
Z
Dong
Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, USA.
J
J
Liu
Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, USA.
J-T
JT
Zhang
D000236:Adenoma / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D003110:Colonic Neoplasms / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000090063:Proto-Oncogene Mas; D015398:Signal Transduction; D051176:beta Catenin / Q000378:metabolism*
C495270:CTNNB1 protein, human; D039621:Eukaryotic Initiation Factor-3; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D051176:beta Catenin; C096013:EIF3I protein, human; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human