Intronic miRNA-641 controls its host Gene's pathway PI3K/AKT and this relationship is dysfunctional in glioblastoma multiforme.

MicroRNAs have established their role as important regulators of the epigenome. A considerable number of human miRNA genes are found in intronic regions of protein-coding host genes, in many cases adopting their regulatory circuitry. However, emerging evidence foreshadows an unprecedented importance for this relationship: Intronic miRNAs may protect the cell from overactivation of the respective host pathway, a setting that may trigger tumor development. AKT2 is a well-known proto-oncogene central to the PI3K/AKT pathway. This pathway is known to promote tumor growth and survival, especially in glioblastoma. Its intronic miRNA, hsa-miR-641, is scarcely investigated, however. We hypothesized that miR-641 regulates its host AKT2 and that this regulation may become dysfunctional in glioblastoma. We found that indeed miR-641 expression differs significantly between GBM tissue and normal brain samples, and that transfection of glioma cells with miR-641 antagonizes the PI3K/AKT pathway. Combining clinical samples, cell cultures, and biomolecular methods, we could show that miR-641 doesn't affect AKT2's expression levels, but down-regulates kinases that are necessary for AKT2-activation, thereby affecting its functional state. We also identified NFAT5 as a miR-641 regulated central factor to trigger the expression of these kinases and subsequently activate AKT2. In summary, our study is the first that draws a connecting line between the proto-oncogene AKT2 and its intronic miRNA miR-641 with implication for glioblastoma development.