Critical and diverse involvement of Akt/mammalian target of rapamycin signaling in human lung carcinomas

Abstract

BACKGROUND: Aberrant signaling cascades emanating from epidermal growth factor receptor (EGFR) are involved in the complex network of oncogenic signaling in lung carcinomas. One representative cascade is the phosphatidylinositol 3‐kinase/Akt/mammalian target of rapamycin (mTOR) pathway. METHODS: The authors investigated the involvement of mTOR in the pathobiologic profiles of 150 specimens of lung carcinoma by immunohistochemistry and immunoblotting in correlation with the upstream and downstream proteins Akt and p70S6‐kinase (S6K), respectively. RESULTS: Immunohistochemistry revealed Akt activation in 44% of tumors and mTOR expression in 68.7% of tumors, and the preponderance of activation was observed in adenocarcinoma (AC) (100%). Phosphorylated mTOR (p‐mTOR) was observed in 53.3% of tumors and had the highest frequency in AC (89.7%). In AC, the frequency of p‐mTOR staining was higher in the well differentiated subtype, in particular, in the acinar structure. However, little correlation was observed between the activation of mTOR and Akt, except in the 5 AC specimens that harbored an EGFR gene mutation, which exhibited constitutive activation of both Akt and mTOR. Conversely, in squamous cell carcinomas, mTOR activation was associated with a significantly higher frequency of lymph node metastasis. CONCLUSIONS: The results of this study suggested the dual functions of mTOR. First, mTOR may function not only in the proliferation of tumor cells as an effector molecule downstream of EGFR but also possibly in the morphogenesis of AC. Second, the activation of mTOR may play a key role in metastasis in squamous cell carcinoma. Overall, the current results demonstrated the potential for the application of rapamycin, an mTOR inhibitor, as an additional novel component of chemotherapy for a defined subset of patients with lung carcinoma. Cancer 2009. © 2008 American Cancer Society.

Expression of p-AKT and p-mTOR in a large series of bronchopulmonary neuroendocrine tumors

“…Other studies have also investigated the p-AKT/p-mTOR pathway in BP-NETs, but their analysis of the percentage of immunoreactive tumor cells was combined with the staining intensity of the cells (26)(27)(28)(29). We decided to analyze our cases using only the percentage of positive cells, as our experience has indicated that the scoring system is highly subjective.…”

EGFR-dependent and independent activation of Akt/mTOR cascade in bone and soft tissue tumors

“…The sensitivity and the specificity of these antibodies were earlier validated on a variety of cell lines and the tissue specimens by immunohistochemical and immunoblotting analysis. 7,22,23 Antibodies were visualized by a ChemMate Envision/ peroxidase complex kit (DAKO Japan, Kyoto, Japan). Immunohistochemical expression was evaluated by two of us (YD, SS) and the intensity of reactivity was evaluated as 'significant' or 'not-significant': 'significant' was defined as definite staining with higher intensity than that observed in non-neoplastic cells.…”

“…Furthermore, 'immunohistochemical expression level' was scored by three-tier system: negative (score 0), o10%; low (score 1), 10% or more, but o50%; high (score 2), 50% or more tumor cells with 'significant' staining. 7,23,24 When scores were classified into two groups for statistical analysis, 'low' and 'high' were combined as 'positive'.…”

“…In this study, protein expression was interpreted as 'upregulated' (for mTOR expression) or 'activated' (for p-Akt, pmTOR, p-S6K, and p-4E-BP1) when (i) detectable expression was observed only in tumor tissue and the level was higher than the highest value in any of the non-neoplastic tissues or (ii) the 'protein index' was higher than 1.5. 7,23,25 Statistical Analysis…”

“…23,26 Differences in the rate of positive immunostaining between two groups were analyzed by Fisher's test. Correlations between the immunohistochemical score and clinicopathological factors were evaluated by MannWhitney U-test or Kruskal-Wallis tests.…”