Molecular context of the EGFR mutations: evidence for the activation of mTOR/S6K signaling.
OBJECTIVE
Activating somatic mutations in the epidermal growth factor receptor (EGFR) gene are present in a small subset of lung adenocarcinomas. These mutations cluster in specific regions and confer sensitivity to inhibitors of the tyrosine kinase activity of EGFR. To further determine the genetic and molecular characteristics of tumors carrying EGFR gene mutations, we investigated the EGFR gene status in lung adenocarcinomas and evaluated its association with specific characteristics of the patients and tumors, such as mutations at KRAS and p53, EGFR and ErbB2 gene amplification, levels of EGFR and HER2 proteins, and levels of downstream effectors of EGFR, such as phospho-extracellular signal-regulated kinase and phospho-S6 proteins.


METHODS
The mutational status of EGFR was determined by direct sequencing in 86 primary lung adenocarcinomas and 12 lung cancer cell lines, and was correlated with a number of variables relating to the tumor and patient. A tissue microarray containing 37 lung tumors was constructed to determine, by fluorescence in situ hybridization analysis, the number of copies of EGFR and ErbB2 genes and, by immunohistochemistry, the levels of EGFR, HER2, phospho-ERK, and phospho-S6 proteins.


RESULTS
EGFR gene mutations were identified in 13% of the primary tumors. The type and clustering of the mutations were identical to those previously reported. Amplification of the EGFR occurred in 14% of the tumors and could arise in tumors with EGFR mutations. Interestingly, mTOR activation, as measured indirectly by augmented levels of phospho-S6 protein, was more frequent in tumors with gene alterations in either EGFR or KRAS (P = 0.00005; Fisher's exact test) than in their wild-type counterparts.


CONCLUSIONS
Our data agree with the accumulation of EGFR mutations in a subset of patients with lung cancer. Moreover, we report EGFR gene amplification in EGFR-mutant tumors and a positive correlation between EGFR or KRAS alterations and activation of mTOR signaling.
Conde
Esther
E
Lung Cancer Group, Spanish National Cancer Centre, Hospital Universitario 12 de Octubre, Madrid, Spain.
Angulo
Barbara
B
Tang
Moying
M
Morente
Manuel
M
Torres-Lanzas
Juan
J
Lopez-Encuentra
Angel
A
Lopez-Rios
Fernando
F
Sanchez-Cespedes
Montserrat
M
D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004252:DNA Mutational Analysis; D066246:ErbB Receptors / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases
D004247:DNA; D011494:Protein Kinases; C546842:MTOR protein, human; D066246:ErbB Receptors; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases