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Toll-like receptor 9 (TLR9) has been shown to have a significant role in cancer. MicroRNAs (miRNAs), a group of small non-coding RNAs that fine tune translation of multiple target mRNAs, are involved in the development and progression of human cancers. The present study was undertaken to determine the roles of TLR9 on lung cancer and whether miR-26a is involved in TLR9‑mediated lung cancer growth and migration. The lung cancer models were elicited by injecting human lung cancer cells into the left ventricle. The expression of TLR9 and miR-26a in lung cancer tissues obtained from lung cancer patients was increased. TLR9 ligand CpG-oligodeoxynucleotides (CpG-ODN) caused an increase in the mean tumor weight and the size of tumor mass in nude mice, and the proliferation and migration of H460 human lung cancer cells. CpG-ODN also induced an increase in the expression of miR-26a in H460 cells. The overexpression of miR-26a increased the weight and size of the tumor mass in the nude mice, and the proliferation and migration of H460 cells. Expression of phosphoinositide 3 kinase (PI3K) and phosphorylation of protein kinase B (Akt) was increased after miR-26a overexpression in the H460 cells. PI3K inhibitor wortmannin (WM) or Akt inhibitor triciribine hydrate (TCN) eliminated the increase in the proliferation and migration induced by the overexpression of miR-26a in H460 cells. These results suggested that miR-26a is involved in the TLR9‑mediated growth and migration of lung cancer through the PI3K-Akt signaling pathway.

Aldehyde dehydrogenase isoform 1 (ALDH1) has been proved useful for the identification of cancer stem cells. However, our knowledge of the expression and activity of ALDH1 in common epithelial cancers and their corresponding normal tissues is still largely absent. Therefore, we characterized ALDH1 expression in 24 types of normal tissues and a large collection of epithelial tumor specimens (six cancer types, n = 792) by immunohistochemical staining. Using the ALDEFUOR assay, ALDH1 activity was also examined in 16 primary tumor specimens and 43 established epithelial cancer cell lines. In addition, an ovarian cancer transgenic mouse model and 7 murine ovarian cancer cell lines were analyzed. We found that the expression levels and patterns of ALDH1 in epithelial cancers are remarkably distinct, and they correlate with their corresponding normal tissues. ALDH1 protein expression levels are positively correlated with ALDH1 enzymatic activity measured by ALDEFLUOR assay. Long-term in vitro culture doesn't significantly affect ALDH1 activity in epithelial tumor cells. Consistent with research on other cancers, we found that high ALDH1 expression is significantly associated with poor clinical outcomes in serous ovarian cancer patients (n = 439, p = 0.0036). Finally, ALDH(br) tumor cells exhibit cancer stem cell properties and are resistant to chemotherapy. As a novel cancer stem cell marker, ALDH1 can be used for tumors whose corresponding normal tissues express ALDH1 in relatively restricted or limited levels such as breast, lung, ovarian or colon cancer.