title: Characterization of regions in hsMAD1 needed for binding hsMAD2. A polymorphic change in an hsMAD1 leucine zipper affects MAD1-MAD2 interaction and spindle checkpoint function.
abstract: In eukaryotes, the mitotic spindle assembly checkpoint provides a monitor for the fidelity of chromosomal segregation. In this context, the mitotic arrest deficiency protein 2 (MAD2) censors chromosomal mis-segregation by monitoring microtubule attachment/tension, a role that requires its attachment to kinetochores. Studies in yeast have shown that binding of MAD1 to MAD2 is important for the checkpoint function of the latter. The interactions between human MAD1 (hsMAD1) and human MAD2 (hsMAD2) have, however, remained poorly characterized. Here we report that two leucine zipper domains (amino acids 501-522 and 557-571) in hsMAD1 are required for its contact with hsMAD2. Interestingly, in several cancer cell lines, we noted the frequent presence of a coding single nucleotide Arg to His polymorphism at codon 558 located within the second leucine zipper of hsMAD1. We found that hsMAD1H558 is less proficient than hsMAD1R558 in binding hsMAD2 and in enforcing mitotic arrest. We also document a first example of loss-of-heterozygosity for a spindle checkpoint gene (at the hsMAD1 558 locus) in a human breast cancer. Based on our findings, it is possible that hsMAD1H558 could be an at-risk polymorphism that contributes to attenuated spindle checkpoint function in human cells.
authors.affiliation: Molecular Virology Section, Laboratory of Molecular Microbiology, NIAID/National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892-0460, USA.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Iwanaga
authors.forename: Takefumi
authors.initials: T
authors.lastname: Kasai
authors.forename: Karen
authors.initials: K
authors.lastname: Kibler
authors.forename: Kuan-Teh
authors.initials: KT
authors.lastname: Jeang
mesh_terms: D000595:Amino Acid Sequence; D000782:Aneuploidy; D001483:Base Sequence; D001665:Binding Sites; D001943:Breast Neoplasms / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D003062:Codon; D003110:Colonic Neoplasms / Q000235:genetics; D003198:Computer Simulation; D006367:HeLa Cells; D006801:Humans; D016350:Leucine Zippers; D019656:Loss of Heterozygosity; D064246:Mad2 Proteins; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000502:physiology*; D013329:Structure-Activity Relationship
chemical_list: D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D003062:Codon; C501384:MAD1L1 protein, human; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012097:Repressor Proteins