Diversity of epidermal growth factor receptor-mediated activation of downstream molecules in human lung carcinomas

Abstract

The correlations among epidermal growth factor receptor (EGFR) gene amplification, gene mutation, overexpression/phosphorylation of EGFR protein and activation of its downstream molecules, signal transducers and activators of transcription 3 (Stat-3), Akt and extracellular signal-related protein kinase 1/2 (Erk1/2) were investigated in 28 cases of human lung carcinomas. In five cases of carcinomas with EGFR amplification, EGFR expression and phosphorylation levels were higher than other cases, and Stat-3 was activated in all five cases. Point mutations in the tyrosine kinase domain of EGFR were detected in five cases, one of which was also associated with gene amplification. In these five cases, both EGFR expression and phosphorylation were enhanced, and Akt was activated in four cases. In the remaining 19 cases, EGFR protein expression was upregulated in eight cases and phosphorylated in four cases, but neither EGFR nor phosphorylated-EGFR expression levels specifically correlated with activation of particular downstream molecules. In general, either Stat-3 or Akt, but not both, was activated reciprocally and complementarily to each other, as indicated by their phosphorylation. However, Erk1/2 was activated regardless of the status of Stat-3, Akt or EGFR proteins. The current data suggest that persistent Stat-3 activation may be a critical event downstream of EGFR that has been overexpressed by gene amplification. In contrast, tumor cells harboring the EGFR mutation may persistently activate a cascade via Akt. Finally, in the majority of cases that have no aberration of the EGFR, its downstream molecules function in reciprocal and/or complementary manner in the maintenance and/or progression of carcinomas. These overall results could provide novel insights into potential chemotherapeutic regimens for lung carcinomas, such as inhibitors of Stat-3, Akt and Erk1/2.

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.…”

“…Lysates were prepared from these fresh tissues as described, 7,22 and immunoblotting analysis was performed. Equal amounts (25 mg of lysates) of protein were used for blotting with anti-p-Akt (1:200 dilutions), anti-mTOR, anti-p-mTOR (both 1:500), anti-p-S6K, and anti-4E-BP1 (both 1:250 dilutions) antibodies.…”

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

“…2,4,5 In addition, mutation of EGFR was observed in 25% to 40% of adenocarcinomas (AC), and these tumors transduce signals predominantly through Akt. 2,6,7 These observations suggest that the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway plays a critical role downstream of EGFR in a defined population of NSCLC, in particular, those that harbor EGFR mutations. Akt transduces signals to various molecules, including the tuberous sclerosis complex (TSC) protein.…”

Impact of EGFR immunoexpression on STAT3 activation and association with proinflammatory/regulatory cytokine pattern in laryngeal squamous cell carcinoma

“…Our study shows that 37.8% of samples of the carcinoma expressed EGFR cytoplasmic staining. Based on a review of the literature overexpression of the EGFR protein is found in 34-93% of various types of human carcinomas (4,5,44,45). A dispersion of results report EGFR expression or its ligands which stems from different antibodies and methods that have been used.…”

“…It occurs as a transmembrane glycoprotein, which undergoes autophosphorylation and triggers signaling pathways involving the signal transducer and activator of transcription-3 (STAT3), phosphatydylinositol 3'-kinase/ protein kinase B (PI 3 K/Act), mitogen-activated protein kinase (MAPK), nuclear factor-κB (NF-κB), c-Myc, cyclin D1 and extracellular signal-related protein kinase 1/2 (Erk1/2) pathways (1)(2)(3)(4)(5)(6)(7). It is known as a key regulator of cellular proliferation and cell survival by cell cycle progression, inhibition of cell death, regulation of cell migration, tumor invasion and differentiation in a wide variety of human carcinoma types, such as head and neck carcinoma, cancer of the breast, colon, bladder, lung, kidney, esophagus, stomach and pancreas cancer (8)(9)(10).…”