Pattern of cell-to-cell transfer of microRNA by gap junction and its effect on the proliferation of glioma cells.

MicroRNA is expected to be a novel therapeutic tool for tumors. Gap junctions facilitate the transfer of microRNA, which exerts biological effects on tumor cells. However, the length of microRNA that can pass through certain gap junctions composed of specific connexin remains unknown. To address this question, the present study investigated the permeability of gap junctions composed of various connexins, including connexin 43, connexin 32 or connexin 37, to microRNAs consisting of 18-27 nucleotides in glioma cells and cervical cancer cells. Results indicated that all of the microRNAs were able to be transferred from donor glioma cells to neighboring cells through the connexin 43 composed gap junction, but not the gap junctions composed of connexin 32 or connexin 37, in cervical cancer cells. Downregulation of the function of gap junctions comprising connexin 43 by pharmacological inhibition and shRNA significantly decreased the transfer of these microRNAs. In contrast, gap junction enhancers and overexpression of connexin 43 effectively increased these transfers. In glioma cells, cell proliferation was inhibited by microRNA-34a. Additionally, these effects of microRNA-34a were significantly enhanced by overexpression of connexin 43 in U251 cells, indicating that gap junctions play an important role in the antitumor effect of microRNA by transfer of microRNA to neighboring cells. Our data are the first to clarify the pattern of microRNA transmission through gap junctions and provide novel insights to show that antitumor microRNAs should be combined with connexin 43 or a connexin 43 enhancer, not connexin 32 or connexin 37, in order to improve the therapeutic effect.