The serine 2481-autophosphorylated form of mammalian Target Of Rapamycin (mTOR) is localized to midzone and midbody in dividing cancer cells

Using a high-resolution, automated confocal high-content imaging system, we investigated the sub-cellular localization of the Serine 2481-autophosphorylated form of mTOR (PP-mTOR Ser2481) during mitosis and cytokinesis in human cancer cells. PP-mTOR Ser2481 exhibited a punctate nuclear distribution in interphase cancer cells, with the number of PP-mTOR Ser2481 nuclear speckles positively relating with the proliferative capacity of cancer cells. PP-mTOR Ser2481 expression dynamically rearranged within the cytoplasm in a close association near and between separating chromosomes during early stages of mitosis. Towards the end of anaphase and in telophase, PP-mTOR Ser2481 drastically focused on the midzone and ultimately in the centre of the midbody at the presumptive cleavage furrow. In cells at cytokinesis, PP-mTOR Ser2481 appeared as a doublet facing each other at the apical ends of two daughter cells. Three-dimensional analysis confirmed that PP-mTOR Ser2481 positioned at a ring structure wrapped round by microtubule bundles to connect daughter cells. These results reveal for the first time that PP-mTOR Ser2481 may be unexpectedly involved in the terminal stages of cytokinesis.