Monopolar spindle 1 (MPS1) protein-dependent phosphorylation of RecQ-mediated genome instability protein 2 (RMI2) at serine 112 is essential for BLM-Topo III α-RMI1-RMI2 (BTR) protein complex function upon spindle assembly checkpoint (SAC) activation during mitosis.

Abstract

Genomic instability and a predisposition to cancer are hallmarks of Bloom syndrome, an autosomal recessive disease arising from mutations in the BLM gene. BLM is a RecQ helicase component of the BLM-Topo III α-RMI1-RMI2 (BTR) complex, which maintains chromosome stability at the spindle assembly checkpoint (SAC). Other members of the BTR complex include Topo IIIa, RMI1, and RMI2. All members of the BTR complex are essential for maintaining the stable genome. Interestingly, the BTR complex is posttranslationally modified upon SAC activation during mitosis, but its significance remains unknown. In this study, we show that two proteins that interact with BLM, RMI1 and RMI2, are phosphorylated upon SAC activation, and, like BLM, RMI1, and RMI2, are phosphorylated in an MPS1-dependent manner. An S112A mutant of RMI2 localized normally in cells and was found in SAC-induced coimmunoprecipitations of the BTR complex. However, in RMI2-depleted cells, an S112A mutant disrupted the mitotic arrest upon SAC activation. The failure of cells to maintain mitotic arrest, due to lack of phosphorylation at Ser-112, results in high genomic instability characterized by micronuclei, multiple nuclei, and a wide distribution of aberrantly segregating chromosomes. We found that the S112A mutant of RMI2 showed defects in redistribution between the nucleoplasm and nuclear matrix. The phosphorylation at Ser-112 of RMI2 is independent of BLM and is not required for the stability of the BTR complex, BLM focus formation, and chromatin targeting in response to replication stress. Overall, this study suggests that the phosphorylation of the BTR complex is essential to maintain a stable genome.

• Authors: Arun Pradhan, Thiyam Ramsing Singh, Abdullah Mahmood Ali, Kebola Wahengbam, Amom Ruhikanta Meetei
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 288 Issue 47 Pg. 33500-33508 (Nov 22 2013) ISSN: 1083-351X [Electronic] United States
• PMID: 24108125 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Carrier Proteins
• Cell Cycle Proteins
• DNA-Binding Proteins
• Multiprotein Complexes
• Nuclear Proteins
• RMI1 protein, human
• RMI2 protein, human
• Serine
• Protein-Tyrosine Kinases
• Protein Serine-Threonine Kinases
• TTK protein, human
• Bloom syndrome protein
• RecQ Helicases
• DNA Topoisomerases, Type I

Topics

• Amino Acid Substitution
• Carrier Proteins (genetics, metabolism)
• Cell Cycle Proteins (genetics, metabolism)
• Chromosomal Instability (physiology)
• DNA Topoisomerases, Type I (genetics, metabolism)
• DNA-Binding Proteins (genetics, metabolism)
• HEK293 Cells
• HeLa Cells
• Humans
• M Phase Cell Cycle Checkpoints (physiology)
• Multiprotein Complexes (genetics, metabolism)
• Mutation, Missense
• Nuclear Proteins (genetics, metabolism)
• Phosphorylation (physiology)
• Protein Serine-Threonine Kinases (genetics, metabolism)
• Protein-Tyrosine Kinases (genetics, metabolism)
• RecQ Helicases (genetics, metabolism)
• Serine (genetics, metabolism)
• Spindle Apparatus (genetics, metabolism)