Excess of a Rassf1-targeting microRNA, miR-193a-3p, perturbs cell division fidelity

Background: Several microRNA (miRNA) molecules have emerged as important post-transcriptional regulators of tumour suppressor and oncogene expression. Ras association domain family member 1 (RASSF1) is a critical tumour suppressor that controls multiple aspects of cell proliferation such as cell cycle, cell division and apoptosis. The expression of RASSF1 is lost in a variety of cancers due to the promoter hypermethylation. Methods: miR-193a-3p was identified as a RASSF1-targeting miRNA by a dual screening approach. In cultured human cancer cells, immunoblotting, qRT-PCR, luciferase reporter assays, time-lapse microscopy and immunofluorescence methods were used to study the effects of excess miR-193a-3p on RASSF1 expression and cell division. Results: Here, we report a new miRNA-mediated mechanism that regulates RASSF1 expression: miR-193a-3p binds directly to RASSF1-30UTR and represses the mRNA and protein expression. In human cancer cells, excess of miR-193a-3p causes polyploidy through impairment of the Rassf1-Syntaxin 16 signalling pathway that is needed for completion of cytokinesis. In the next cell cycle the miR-193a-3p-overexpressing cells exhibit multipolar mitotic spindles, mitotic delay and elevated frequency of cell death. Conclusions: Our results suggest that besides epigenetic regulation, altered expression of specific miRNAs may contribute to the loss of Rassf1 in cancer cells and cause cell division errors.