TGFB1 and neoplasm: MIR-663 targets TGFB1 and regulates the expression of PTEN, a tumour suppressor gene30 and downregulates BCL-2 to induce apoptosis.31 Consequently, in U266 cells, mtDNA depletion significantly decreases the expression of interferon-related genes, reduces P53 suppressor activity and activates tumour-suppressing micro-RNAs, which alter the tumorigenic state of U266 cells.