Abstract
Lung cancer is the leading cause of cancer death in the world as well as Taiwan. Abnormal expression of epidermal growth factor receptor (EGFR) is reported in most of lung cancer cases and is correlated with poor prognosis. MicroRNA (miRNA), a novel class of gene regulator, has been shown to play significant roles in tumor progression through functioning as either tumor suppressor or oncogene. We hypothesized that a microRNA profile could mediate EGFR induced lung cancer progression. Through miRNA microarray study to search for miRNAs regulated by EGFR in lung cancer, we identified that miR-7 is one of the most significantly downregulated miRNAs in EGFR silencing lung cancer cells. It has been reported that miR-7 modulates EGFR mediated Drosophila eye development by blocking Yan expression. In lung cancer cells, we found that both MEK1/ERK inhibitor (PD98059) and EGFR tyrosine kinas inhibitor (AG1478) attenuated miR-7 expression, suggesting that EGFR mediated MAPK activity was involved in miR-7 regulation. Overexpression of miR-7 promoted cell growth and colony formation in soft agar. However, ERF, a tumor suppressor and possible mammalian counterpart of Yan, was upregulated in EGFR silencing cells. Interestingly, overexpression of miR-7 attenuated ERF expression and promoted tumor formation in nude mice. Nonetheless, knockdown of miR-7 induced ERF expression, suggesting that ERF could be the direct target of miR-7 in lung cancer. Luciferase reporter assay further demonstrated that 3\\\\\\\\\\\\\\\\#8217;UTR of ERF contained possible miR-7 target sites. Through real time PCR analysis, we found miR-7 was overexpressed in lung cancer specimen. From these results, we have identified an evolutionarily conservative regulatory network of EGFR induced miR-7 expression in human lung cancer, which is comparable for the effect of EGFR-mediated miR-7 in Drosophila eye development. These data supports that miR-7 functions as an oncomiR to modulate EGFR mediated lung cancer progression in part through downregulation of tumor suppressor ERF.