Presentation Authors: Sei Naito*, Osamu Ichiyanagi, Ito Hiromi, Michinobu Ozawa, Masaki Ushijima, Mayu Yagi, Takafumi Narisawa, Hidenori Kanno, Yuta Kurota, Tomoyuki Kato, Norihiko Tsuchiya, Yamagata, Japan
Introduction: The eukaryotic initiation factor 4E (eIF4E) is a 5â€™-cap component binding to mRNA. It is regulated by two pathways; mTOR/4EBP1/eIF4E and MNK/eIF4E pathway. The mTOR/4EBP1/eIF4E pathway promotes cell proliferation and anti-apoptotic behavior in clear cell renal cell carcinoma (ccRCC). This pathway does not affect eIF4E phosphorylation. Besides, MNKs phosphorylate eIF4E, which also promote translation in a different manner from Akt/mTOR pathway. However, the role of MNK pathway remains unknown in ccRCC. Our objectives are to investigate the role of eIF4E phosphorylation in ccRCC.
Methods: Firstly, we evaluated phospho-eIF4E (p-eIF4E) expression in 290 localized RCC surgical specimens using immunohistochemistry (IHC) and compared the recurrence rate. Secondly, western blotting, scratch assay, and invasion assay in RCC cell lines were performed with or without MNK inhibition which suppresses phosphorylation of eIF4E. Lastly, MAPK family protein (ERK1/2, p38, and ERK5) and mTOR inhibitors were administered onto ccRCC cell lines, and estimated p-eIF4E status using WB, since previous reports in other cancers mentioned that MAPK family proteins activate MNKs and mTOR suppresses MNKs.
Results: Patients with low expression of p-eIF4E has higher recurrence rate (p = 0.024, Fig 1), and low p-eIF4E expression was an independent indicator for ccRCC recurrence after nephrectomy. Inhibition of MNK using siRNA or MNK inhibitor up-regulated vimentin and N-cadherin expression which are involved in cell migration (Fig 2). Scratch assay showed that MNK2 inhibition enhanced cell migration (Fig 3). These results indicate that eIF4E phosphorylation suppresses migration and metastasis in ccRCC. In regard to regulation of MNKs, ERK5 inhibitor promoted phosphorylation of eIF4E, while ERK1/2 or p38 inhibitors did not affect it. mTOR inhibitor rapamycin also promote eIF4E phosphorylation (Fig 4).
Conclusions: Low p-eIF4E is a biomarker for ccRCC recurrence after nephrectomy. Inhibition of eIF4E phosphorylation via MNK knockdown enhances ccRCC migration. ERK5 or mTOR inhibition could enhance eIF4E phosphorylation and be a promising strategy for prevention of ccRCC recurrence.