The Role of ESC-Specific MicroRNA, miR-302, in the Induction of Stemness Property of Brain Tumor Cells
Objective: Recent studies have identified a subset of ES cell-associated transcription regulators including Oct-3/4, Sox2, Nanog and their targets, that are highly expressed in poorly differentiated tumors. However, the underlying molecular mechanisms, by which these genes contribute to stem cell-like phenotypes shown by many tumors, are not well understood. On the other hand, by considering the role of microRNAs in regulation of stem cell identity, it is of great interest whether ESC-specific miRNAs allow continued tumor growth through the suppression of differentiation and the maintenance of the stem cell-like properties of cancer stem cells.
To test this idea, we examined the expression and the role of microRNA-302 members, which are expressed at high levels in ESCs and are transcriptionally regulated by Oct-3/4 and Sox2, in human brain cell lines.
Materials and Methods: The expression of miR-302 members in brain tumor cell lines, 1321N1, Daoy, A172 and U87MG, was evaluated by means of real-time RT-PCR. For further analyzing the role of this miRNA, an expression vector of miR-302 members was also constructed and successfully transfected into brain tumor cell lines.
Results: The qRT-PCR assay demonstrated the expression of miR-302 members in brain cell lines. By introducing miR-302 overxpression vector into these cells, we detected the expression of several well known ESC-specific markers such as Oct-4 variants, Sox2, Nanog, Rex1 and Lin28 in transfected cells in comparision with the absence or low expression level in untransfected cells. Furthermore, the expression of CyclinD1, as one of the main miR-302 target, was decreased in miR-302 transfected cells.
Conclusion: Our data suggest the presence of a small subpopulation of tumor cells expressing miR-302 that may probably have stem cell properties. In addition, it seems that miR-302 may play a role in cancer stem-like cell behavior, such as self-renewal and maintenance of an undifferentiated state of tumor cells. These observations provide a new strategy to target cancer stem cell subpopulation in patients.