Small non-coding RNA molecules called microRNAs (miRs) have been identified as key regulators of cancer progression. In our laboratory, we used microRNA arrays to identify microRNAs that were associated with metastatic ability in the 4T1 syngeneic mouse model of breast cancer1 . mCherry expressing cells were grown as primary tumours, sorted by flow cytometry and subjected to microRNA array profiling using an Affymetrix platform.
Known oncogenic (eg. miR-155) and tumour suppressor (eg. miR-143~miR-145 cluster) were deregulated in metastatic 4T1.2 and 4T1.13 cells as expected. Of the less well studied microRNAs, we found that miR-193b was up-regulated in the epithelial cells of 4T1.2 and 4T1.13 tumours compared to weakly- and non-metastatic tumours. This was confirmed by quantitative stem-loop PCR in mCherry sorted tumour cells and in cell lines cultured in vitro.
Lentiviral-mediated knockdown of miR-193b activity in metastatic 4T1.13 cells reduced in vitro cell proliferation and migration. 4T1.13_miR-193b knockdown (KD) implanted orthotopically into Balb/c mice displayed reduced primary tumour growth rate with an associated reduction in distant metastasis. Reduced lung metastasis was also observed when 4T1.13_miR-193b KD cells were used in experimental metastasis (tail-vein) assays.
Transient over-expression of miR-193b in weakly metastatic 168FARN and 66cl4 cells dramatically reduced mRNA levels of putative target genes including cyclin-D1, DDB1 and CUL4-associated factor-7 (Dcaf7), urokinase plasminogen activator (uPa), and cell adhesion molecule-1 (Cadm1) / tumour suppressor in lung cancer-1 (Tslc1).
Finally, the analysis of a large human breast cancer dataset with over 10 years of clinical follow-up showed miR-193b expression was correlated with estrogen receptor positivity (ER+) and associated with reduced survival in both ER+ and ER- tumours (univariate analysis)2 .
1 Taken together, our data suggest that over-expression of miR-193b regulates both primary tumour proliferation and metastatic dissemination in vivo.