Damaged microtubules can inactivate BCL-2 by means of the mTOR kinase

• Published in: Oncogene Vol. 20; no. 43; pp. 6172 - 6180
• Main Authors: CALASTRETTI, Angela, BEVILACQUA, Anna, CERIANI, Cristina, VIGANO, Simona, ZANCAI, Paola, CAPACCIOLI, Sergio, NICOLIN, Angelo
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing 27.09.2001; Nature Publishing Group
• Subjects: Alzheimer's disease; Apoptosis; Apoptosis - drug effects; Bcl-2 protein; Biological and medical sciences; Blotting, Western; Cell cycle; Cell Cycle - drug effects; Cell Cycle Proteins - metabolism; Cell Division; Cell growth; Cell lines; Cell physiology; Cyclin-Dependent Kinase Inhibitor p27; Diploidy; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Enzyme Activation; Flow Cytometry; Fundamental and applied biological sciences. Psychology; Humans; Kinases; Lymphocytes B; Lymphoma; Metaphase; Microtubules; Microtubules - drug effects; Microtubules - metabolism; Molecular and cellular biology; mRNA; Nocodazole; Nocodazole - pharmacology; Paclitaxel; Paclitaxel - pharmacology; Phosphorylation; Phosphorylation - drug effects; Protein Kinases - metabolism; protein-serine/threonine kinase; Proteins; Proto-Oncogene Proteins c-bcl-2 - metabolism; Rapamycin; RNA, Messenger - metabolism; Signal transduction; Signal Transduction - drug effects; Sirolimus - pharmacology; Synchronization; Threonine; TOR protein; TOR Serine-Threonine Kinases; Tumor Cells, Cultured; Tumor Suppressor Proteins; Italy; Microtubule; Inactivation; Enzyme; Kinase; Transferases
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/sj.onc.1204751

Rapamycin, a specific inhibitor of the serine/threonine mTOR kinase, markedly inhibited both cell growth and apoptosis in human B-cell lines. Besides arresting cells in G(1) by increasing p27(kip1), rapamycin tripled the cellular level of the BCL-2 protein. The activity was dose-dependent and specific for the p27(kip1) and BCL-2 proteins. Rapamycin did not affect bcl-2 mRNA although it increased cellular BCL-2 concentration by inhibiting phosphorylation, a mechanism initiating the decay process. To add new insight, we combined rapamycin treatment with treatment by taxol, which, by damaging microtubules, can phosphorylate BCL-2 and activate apoptosis. It was found that the mTOR kinase was activated in cells treated with taxol or with nocodazole although it was inhibited in cells pre-treated with rapamycin. BCL-2 phosphorylation, apoptosis and hyperdiploidy were also inhibited by rapamycin. In contrast, taxol-induced microtubule stabilization or metaphase synchronization were not inhibited by rapamycin. Taken together, these findings indicate that mTOR belongs to the enzymatic cascade that, starting from damaged microtubules, phosphorylates BCL-2. By regulating apoptosis, in addition to the control of a multitude of growth-related pathways, mTOR plays a nodal role in signaling G(1) and G(2)-M events.