The Chfr mitotic checkpoint protein functions with Ubc13-Mms2 to form Lys63-linked polyubiquitin chains

• Published in: Oncogene Vol. 22; no. 46; pp. 7101 - 7107
• Main Authors: Bothos, John, Summers, Matthew K, Venere, Monica, Scolnick, Daniel M, Halazonetis, Thanos D
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 16-10-2003
• Subjects: Cancer; Cell Cycle - genetics; Cell Cycle - physiology; Cell Cycle Proteins - metabolism; Cell Cycle Proteins - physiology; Cellular stress response; Chromosomes; Cloning, Molecular; DNA Repair - genetics; Electrophoretic mobility; Enzymes; Escherichia coli - genetics; Fungal Proteins - physiology; Humans; Kinases; Microtubules - physiology; Microtubules - ultrastructure; Mitosis; Mitotic Index; Neoplasm Proteins; Osteosarcoma; Phosphorylation; Poly-ADP-Ribose Binding Proteins; Proteasomes; Proteins; Recombinant Proteins - metabolism; Saccharomyces cerevisiae Proteins; Signal transduction; Tumor Cells, Cultured; Ubiquitin; Ubiquitin - metabolism; Ubiquitin-conjugating enzyme; Ubiquitin-Conjugating Enzymes - physiology; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases; United States > US
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/sj.onc.1206831

We recently described a novel checkpoint pathway that functions early in mitosis to delay chromosome condensation in response to microtubule poisons. The only gene implicated so far in this checkpoint pathway is chfr, whose protein product contains a RING domain and has ubiquitin ligase activity in vitro. The significance of this activity in vivo is unclear. A recent report suggested that the Chfr protein targets itself for proteasome-dependent degradation in mitotic cells through autoubiquitination. However, we observe that in mitosis Chfr exhibits a phosphorylation-dependent electrophoretic mobility shift with no change in overall protein levels. Further analysis of its ubiquitin ligase activity revealed that Chfr can catalyse the formation of noncanonical Lys63-linked polyubiquitin chains with Ubc13-Mms2 acting as the ubiquitin-conjugating enzyme. Ubc13-Mms2 and Lys63-polyubiquitin chains are not associated with targeting proteins to the proteasome, but rather with signaling cellular stress. We propose that Chfr may have a role in signaling the presence of mitotic stress induced by microtubule poisons.