Purpose: This study aims to identify novel biomarkers and therapeutic targets for lung cancer. Experimental Design: We carried out gene expression profile analysis of 120 lung cancers to screen for genes encoding transmembrane/secretory molecules that are commonly transactivated in lung cancers. Epstein-Barr virus-induced gene 3 (EBI3), which encodes a secretory glycoprotein, was selected as a good candidate. Immunohistochemical staining using tissue microarray consisting of 414 non-small cell lung cancers was applied to examine the expression level and prognostic value of EBI3. Serum EBI3 levels in 400 individuals for training assays (274 lung cancers and 126 healthy volunteers) and those in 173 individuals for validation analysis (132 lung cancers and 41 healthy volunteers) were measured by ELISA. The role of EBI3 in cancer cell growth was examined by siRNA and cell growth assays, using cells stably expressing exogenous EBI3.Results: Immunohistochemical staining of EBI3 using tissue microarrays revealed that a high level of EBI3 expression was associated with a poor prognosis of lung cancer (P ¼ 0.0014) and multivariate analysis confirmed it to be an independent prognostic factor (P ¼ 0.0439). Serum levels of EBI3 in the training set were found to be significantly higher in lung cancer patients than in healthy volunteers; this result was also observed in the validation set. Furthermore, reduction in EBI3 expression by siRNA suppressed cancer cell proliferation whereas induction of exogenous EBI3 conferred growth-promoting activity.Conclusions: EBI3 is a potential serum and tissue biomarker as well as therapeutic target for lung cancer.

Genome-wide gene expression profiling revealed that the Ras and EF-hand domain containing (RASEF) transcript was significantly transactivated in the majority of lung cancers. Using lung cancer cells, transient expression of RASEF promoted cell growth, whereas RASEF knockdown not only reduced its expression but resulted in growth suppression of the cancer cells. Immunohistochemical staining using tumor tissue microarrays consisting of 341 archived non-small cell lung cancers (NSCLC) revealed the association of strong RASEF positivity with poor prognosis (P ¼ 0.0034 by multivariate analysis). Mechanistically, RASEF interacted with extracellular signal-regulated kinase (ERK) 1/2 and enhanced ERK1/2 signaling. Importantly, inhibiting the interaction between RASEF and ERK1/2 using a cell-permeable peptide that corresponded to the ERK1/2-interacting site of RASEF, suppressed growth of lung cancer cells. This study demonstrates that elevated RASEF promoted cell growth via enhanced ERK signaling and is associated with poor prognosis of NSCLC.