cgp-57380 and Cell-Transformation--Neoplastic

Dysregulated mRNA translation is implicated in the pathogenesis of many human cancers including chronic myelogenous leukemia (CML). Because our prior work has specifically implicated translation initiation in CML, we tested compounds that could modulate translation initiation and polysomal mRNA assembly. Here, we evaluated the activity of one such compound, CGP57380, against CML cells and explored its mechanisms of action. First, using polysomal mRNA profiles, we found that imatinib and CGP57380 could independently, and cooperatively, impair polysomal mRNA loading. Imatinib and CGP57380 also synergistically inhibited the growth of Ba/F3-Bcr-Abl and K562 cells via impaired cell cycle entry and increased apoptosis. Mechanistically, CGP57380 inhibited efficient polysomal assembly via two processes. First, it enhanced imatinib-mediated inhibition of eukaryotic initiation factor 4F induction, and second, it independently impaired phosphorylation of ribosomal protein S6 on the preinitiation complex. We also identified multiple substrates of the mTOR, Rsk, and Mnk kinases as targets of CGP57380. Finally, we found a novel negative-feedback loop to the mitogen-activated protein kinase/Mnk pathway that is triggered by CGP57380 and demonstrated that an interruption of the loop further increased the activity of the combination against imatinib-sensitive and -resistant CML cells. Together, this work supports the inhibition of translation initiation as a therapeutic strategy for treating cancers fueled by dysregulated translation.

Topics: Aniline Compounds; Apoptosis; Benzamides; Cell Cycle; Cell Proliferation; Cell Transformation, Neoplastic; Drug Resistance, Neoplasm; Drug Synergism; Enzyme Activation; Eukaryotic Initiation Factor-4F; Feedback, Physiological; Humans; Imatinib Mesylate; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mitogen-Activated Protein Kinases; Peptide Chain Initiation, Translational; Phosphorylation; Piperazines; Polyribosomes; Protein Kinases; Purines; Pyrimidines; Ribosomal Protein S6; RNA Caps; RNA Transport; RNA, Messenger; Signal Transduction; Substrate Specificity; TOR Serine-Threonine Kinases

The eukaryotic translation initiation factor eIF4E is dysregulated in a wide variety of human cancers. In the cytoplasm, eIF4E acts in the rate-limiting step of translation initiation whereas in the nucleus, eIF4E forms nuclear bodies and promotes the nucleo-cytoplasmic export of a subset of growth-promoting mRNAs including cyclin D1. The only known post-translational modification of eIF4E is its phosphorylation at S209. Many studies have examined the role of phosphorylation on cap-dependent translation. However, no studies to date have explored the role of phosphorylation on the ability of eIF4E to transform cells. Using mutagenesis and separately a small molecular inhibitor of eIF4E phosphorylation, we show that eIF4E phosphorylation enhances both its mRNA transport function and its transformation activity in cell culture. Thus, phosphorylation of nuclear eIF4E seems to be an important step in control of the mRNA transport and thus the transforming properties of eIF4E.

Topics: Aniline Compounds; Animals; Cell Transformation, Neoplastic; Cyclin D1; Eukaryotic Initiation Factor-4E; Mice; Mutagenesis; NIH 3T3 Cells; Phosphorylation; Purines; RNA Transport; RNA, Messenger