Overexpression of phospho-eIF4E is associated with survival through AKT pathway in non-small cell lung cancer

Abstract

Purpose: The eukaryotic translation initiation factor complex 4E (eIF4E) is downstream in the mammalian target of rapamycin (mTOR) pathway. This study explored expression of eIF4E and its relationship with the PTEN/AKT and RAS/MEK/ERK pathways in non-small cell lung carcinoma (NSCLC).

Experimental design: The status of phosphorylated eIF4E (p-eIF4E), phosphorylated AKT (p-AKT), PTEN, phosphorylated tuberin (p-TSC2), phosphorylated mTOR (p-mTOR), phosphorylated S6 (p-S6), and phosphorylated Erk1/2 (p-Erk1/2) was studied using immunohistochemical analysis applied to a tissue microarray containing 300 NSCLCs. Staining results for each antibody were compared with clinical and pathologic features, and the relationship between staining results was explored.

Results: Overexpression of p-eIF4E, p-AKT, p-TSC2, p-mTOR, p-S6, and p-Erk1/2 in NSCLC was found in 39.9%, 78.8%, 5.1%, 46.7%, 27.1%, and 16.6% of tumors, respectively. The phenotype of p-eIF4E correlated positively with that of p-AKT, p-TSC2, and p-S6 (P < 0.001). Overall survival in NSCLC patients was significantly shorter in cases with overexpression of p-eIF4E and p-AKT alone and in combination (log-rank P < 0.001, each). Cases with underexpression of PTEN were limited (6.4%), and this phenotype did not correlate with any clinical variable. In cluster analysis, the p-AKT/p-mTOR/p-eIF4E/p-S6-positive group had significantly shorter survival compared with the survival of all cases (P < 0.001). Multivariate analysis showed that p-eIF4E overexpression is an independent prognostic factor for NSCLC (P = 0.004).

Conclusions: This study shows that p-eIF4E expression in addition to p-AKT predicts poor prognosis in NSCLC. Moreover, the correlation between expression of p-eIF4E with p-AKT, as well as p-TSC2 and p-S6, indicates that eIF4E activation through the AKT pathway plays an important role in the progression of NSCLC.

Fig. 1.

Representative examples of immunohistochemical staining by p-AKT, PTEN, p-TSC2, p-mTOR, p-eIF4E, p-S6, and p-Erk1/2 (from left column) of NSCLC specimens. The TMA cores of the first line show TS0 or TS2, those of the second line show TS3, and the third line shows TS4 or TS5 for each antibody. Diameter of tissue core, 0.6 mm. Photomicrographs of the bottom line show high magnification view of the third line TMA cores each. Original magnification, ×400.

Fig. 2.

Kaplan-Meier curve comparing overall survival for AKT, p-eIF4E, and various combinations of AKT and p-eIF4E: worse survival for p-eIF4E–positive patients (blue line) compared with p-eIF4E–negative patients (red line; A), worse survival for p-AKT–positive patients (blue line) compared with p-AKT–negative patients (red line; B), and worse survival for patients with a combination of p-AKT and p-eIF4E–positive tumors (green line; n = 83) compared with those with a combination of p-AKT– and p-eIF4E–negative tumors (red line; n = 31) and the other patients (blue line; n = 108; C).

Fig. 3.

Hierarchical cluster analysis for a seven-protein immunophenotype. Each row is a different tumor, and each column is a different immunohistochemical stain. Blue bars, marker positivity; red bars, negative staining for the marker. MST, median survival time; NA, not available.

Fig. 4.

Conventional PI3K-AKT-mTOR signaling pathway and RAS/MEK/ERK signaling pathway diagram derived from in vitro studies on NSCLC. AKT activation is most directly brought about by inhibition of TSC2, which results in the activation of S6 and e-IF4E signaling and enhanced protein synthesis through the activation of mTOR. mTOR may be affected by other genetic or metabolic changes. RTK, receptor tyrosine kinase; EGFR, epidermal growth factor receptor; PIP2/3, phosphatidylinositol 4,5-/3,4,5-phosphate; PI3K, phosphatidylinositol 3-kinase.