Abstract
Background:
The incidence of esophageal adenocarcinoma (EAC) has increased more than sevenfold in the United States and Western countries over the past four decades; however, patient prognosis remains poor, with a five-year survival rate of less than 20%. Dysregulation of mRNA translation, especially the cap-dependent mechanism mediated by eIF4F complex, was found in many human cancers. Aberrant expression and phosphorylation of eIF4E, the rate-limiting component of eIF4F complex, has been evidenced to promote oncogenic translation programs in human cancers. Constitutive overexpression of NEK2, a serine/threonine kinase of the NEK protein kinase family, has been reported to mediate tumor progression and drug resistance in cancer cells. Our study aims to investigate the role of NEK2 in regulating cap-dependent mRNA translation and translational significance of NEK2/eIF4E signaling in EAC.
Methods and Results:
We first confirmed activation of the cap-dependent translation using a luciferase reporter assay and increased protein levels of its key factors, such as p-eIF4E, eIF4E, p-4EBP1, and 4EBP1, by western blotting, in the scenarios with either transient or repeated ABS exposure. However, the levels of p-mTOR, mTOR, eIF4A, and eIF4G remained unchanged. Meanwhile, intrinsic overexpression of NEK2 protein was observed in EAC patients, esophageal cell lines of dysplasia/EAC, and ABS-exposure-induced cell models. Overexpression and silence of NEK2 underlined its role in mediating activation of cap-dependent translation under reflux conditions. The co-overexpression of NEK2 and eIF4E was identified by immunofluorescent staining in EAC cells and immunohistochemistry staining in human TMA, indicating their potential interaction. Mechanically, we discovered that NEK2 contributes to cap-dependent translation by stabilizing eIF4E protein and regulated its phosphorylation in an MNK-dependent manner. Exotic overexpression of NEK2 significantly promoted colony formation capacities of tumor cells, while NEK2 silencing greatly suppressed tumor growth and expansion in cells/3D tumor spheres. Moreover, activation of NEK2/eIF4E signaling was proved to facilitate tumor cell survival in the presence of oxaliplatin. NEK2 silencing re-sensitized resistant EAC cells to chemotherapeutic drugs by magnifying apoptosis. Remarkably, the combination therapy of oxaliplatin and pharmacological inhibitor of NEK2, T-1101, synergized in inducing cell death, with minimized interruption on non-neoplastic cells. This finding was further confirmed in EAC-cell-line-derived xenograft models.
Conclusion:
Our data elucidates novel functions of NEK2/eIF4E signaling axis in promoting cancer progression and drug resistance. Combination therapy of chemotherapeutic drugs with NEK2 inhibitor provides a promising strategy for treatment of EAC patients.