Eukaryotic initiation factor 4E (eIF4E) is an oncogene over-expressed in a variety of cancers. It is responsible for regulation of synthesis of proteins involved in progression to the malignant phenotype, including cyclin D1, Mcl-1 and VEGF. The oncogenic activity of eIF4E has been shown to be dependent on phosphorylation at serine 209 by the mitogen-activating protein kinase signal integrating kinases (MNKs). This work investigates the role of the MNK proteins in the proliferation and survival of breast and kidney cancer cells. Inhibition of the MNKs with a chemical kinase inhibitor resulted in inhibition of proliferation through cell cycle arrest, with no induction of apoptosis. This is consistent with a reduction in cyclin D1 protein. Combination of mTOR inhibition and inhibition of the MNK proteins in kidney cancer cells resulted in an additive but not synergistic effect on inhibition of proliferation. siRNA knockdown of the MNKs resulted in a reduction in eIF4E phosphorylation but did not inhibit proliferation or induce cell cycle arrest in a renal cancer cell line. The generation of an eIF4E mutant with phospho-mimetic activity induced partial insensitivity to the MNK kinase inhibitor suggesting some specificity of activity of this agent through the MNK proteins. Inhibition of the MNKs resulted in a reduction in cyclin D1 mRNA with no reduction in transcription. An accumulation of cyclin D1 RNA was seen in the nuclear compartment following treatment with MNK inhibitor suggesting inhibition of nuclear export of cyclin D1 RNA and subsequent degradation. Gene expression array analysis revealed regulation of genes with key functions in cellular metabolism. The MNK kinases are thus worthy of further investigation as a therapeutic target in breast and renal cancer. More potent and specific inhibitors of the MNK kinases than CGP57380 are required for this to be clinically relevant.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:605717 |
| Date | January 2011 |
| Creators | Wheater, Matthew |
| Contributors | Blaydes, Jeremy ; Johnson, Peter |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/365941/ |
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