MicroRNA-22 (miR-22), a short non-coding RNA that post-transcriptionally regulates mRNA stability and protein synthesis, has been shown to enhance metastatic potential and to suppress HER-3, an important mRNA marker for non-small cell lung cancer (NSCLC). However, the effect of miR-22 has not been investigated in lung adenocarcinoma (LADC), the most common type of NSCLC in the Far East. In this study, we analyzed the role of miR-22 expression in LADC patients. Expression of miR-22 was detected

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... y reverse-transcription polymerase chain reaction (RT-PCR), and confirmed by cDNA sequencing. Signals of miR-22 in LADC sections were identified using in situ hybridization (ISH). The association between miR-22 expression and survival was evaluated by the log-rank test. Induction of miR-22 expression and the effect on HER-3 levels, as well as the subsequent cell behavior were also investigated in vitro. Two types of miR-22: miR-22 and miR-22H, were detected by RT-PCR. The miR-22H had extra 13 bases, 5'-TGTGTTCAGTGGT-3', at the 3'end, and this segment was named miR-22E. Using ISH, miR-22E overexpression was detected in 225 (83.0%) of 271 LADC patients. A significant difference was found in cumulative survival between patients with high miR-22E levels and those with low miR-22E levels (p < 0.0001). In vitro, epidermal growth factor induced miR-22, but reduced HER-3 expression. Expression of miR-22 increased cell movement ability. In conclusion, expression of miR-22 is closely associated with * Corresponding author. H.-Y. Fang et al. 363 tumor recurrence, metastasis and overall survival in LADC patients by suppressing HER-3 protein expression to enhance epithelial-mesenchymal transition and metastasis.