MicroRNAs (miRNAs) are small non-coding RNAs which regulate gene expression by base-pairing to the 3 0 -UTR of the target mRNA. Recently, miRNAs have been shown to regulate cancer metastasis, however, central molecular mechanisms of this ability still need to be investigated. Epithelial to mesenchymal transition (EMT), which is characterized especially by repression of E-cadherin expression and increased cell motility, is an essential component of cancer metastasis and progression. In the present study, we found that Snai1, a known transcriptional repressor of E-cadherin and modulator of EMT, is post-transcriptionally targeted by miRNA-30a in non-small cell lung cancer (NSCLC). Consistent with this, microRNA30a expression was found inversely proportional to the invasive potential of various NSCLC cell lines, correlating positively with E-cadherin (epithelial marker) and negatively with N-cadherin (mesenchymal marker) expression. Forced re-introduction of miR-30a significantly altered cell morphology, in vitro invasion and migration of invasive cell lines, this being paralleled by a downregulation of Snai1 and upregulation of E-cadherin expression. Using a chicken embryonic metastasis assay, we found that miR-30a suppresses in vivo distant metastasis to the lungs and liver. Finally, we screened the expression of miR-30a in 64 consecutively resected NSCLC patients and found that, in 81% of the patients, expression of miR-30a was downregulated significantly (p < 0.0001) in tumors compared to corresponding normal tissues. These results suggest that miR-30a targets Snai1, inhibits invasion and metastasis, and is downregulated in NSCLC.Lung cancer is the most common cancer world wide in terms of both incidence and mortality. 1 The major problem in the management of lung cancer is metastatic disease, highlighting the importance of a better understanding of the biological processes that occur in tumor cells to promote the aggressive neoplastic phenotype. The hallmarks of malignant transformation are the capabilities of invasion and metastasis. In order to acquire these traits, tumor cells must be able to detach from the primary tumor, migrate, and disseminate to distant organs to form metastases. 2 Now it is clear that a transition of tumor cells at the invasive front, which is characterized by the loss of epithelial markers and the gain of a mesenchyme-like phenotype, plays a key role to induce invasion and metastasis. This transition is called epithelial to mesenchymal transition, or EMT.Epithelial cells are generally characterized by their arrangement as a sheet of cells abutting each other in a uniform fashion. As a result of regularly spaced cell-cell junctions between neighboring cells, epithelial cells cannot move away from the monolayer. On the other hand, mesenchymal cells generally lack tight intercellular adhesions and a regimented structure. The transition of epithelial cells into mesenchymal-like cells is orchestrated by a series of events finally leading to the release of epithelial cells from the surround...

A c c e p t e d M a n u s c r i p tLicenced copy. Copying is not permitted, except with prior permission and as allowed by law. © 2010 The Authors Journal compilation © 2010 Portland Press Limited AbstractCurcumin has promising potential in cancer prevention and therapy by interacting with proteins and modifying their expression and activity, which includes transcription factors, inflammatory cytokines, and factors of cell survival, proliferation, and angiogenesis. miR-21 is overexpressed in many tumors, promoting progression and metastasis. In the present study, we examined the potential of curcumin to regulate miR-21, tumor growth, invasion, and in vivo metastasis in colorectal cancer. In Rko and HCT116 cells, we identified two new transcriptional start sites of the miR-21 gene and delineated its promoter region. PMA stimulation induced miR-21 expression via motifs bound with AP-1 transcription factors. Curcumin treatment reduced miR-21 promoter activity and expression in a dose-dependent manner by inhibiting AP-1 binding to the promoter, and induced expression of tumor suppressor Pdcd4, which is a target of miR-21. Curcumin treated Rko and HCT116 cells were arrested in the G2/M phase with increasing concentrations. Furthermore, curcumin inhibited tumor growth, invasion and in vivo metastasis in the chicken-embryo-metastasis assay (CAM). Additionally, curcumin significantly inhibited miR-21 expression in primary tumors generated in vivo in the CAM assay by Rko and HCT116 cells (p<0.00006; p<0.035 respectively). Taken together, this is the first report to show that curcumin inhibits the transcriptional regulation of miR-21 via AP-1, suppresses cell proliferation, tumor growth, invasion, and in vivo metastasis, and stabilizes expression of tumor suppressor Pdcd4 in colorectal cancer.