Disease relevance of MAD2

• Finally, T47D, a human breast tumor cell line that is sensitive to taxol and nocodazole, had reduced MAD2 expression and failed to arrest in mitosis after nocodazole treatment [1].
• 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 [2].

High impact information on MAD2

• We find that Orc2 depletion causes a delay in progression through mitosis, reflecting activation of both the DNA-damage and Mad2-spindle checkpoints [3].
• Recent experiments shed important insight into how Mad2 molecules bound to centromeres through their association with a protein called Mad1 might be transferred to Cdc20 and thereby inhibit securin's destruction [4].
• Kinetochores that have not yet attached to microtubules catalyze the sequestration of Cdc20 by an inhibitor called Mad2 [4].
• MAD1 and MAD2 act in a surveillance mechanism that mediates a metaphase delay in response to nonexchange chromosomes, whereas MAD3 acts as a crucial meiotic timer, mediating a prophase delay in every meiosis [5].
• Therefore MAD2 and BET2 gene products may physically interact to form a geranylgeranyl transferase complex [6].

Biological context of MAD2

• In addition, the difference between the phenotypes of mad2-1 and mad2-2ts suggests that MAD2 has distinct roles in protein transport and the mitotic feedback control [6].
• We have cloned the MAD2 gene, which encodes a protein of 196 amino acids that remains at a constant level during the cell cycle [7].
• These data support the view that the spindle assembly checkpoint encompasses regulation of distinct mitotic steps, including a MAD2-directed block to anaphase initiation and a BUB2-directed block to TEM1-dependent exit [8].
• Deletion of MAD1 or MAD2 did not affect steady-state nucleocytoplasmic distribution of a classical nuclear localization signal-containing reporter, a nuclear export signal-containing reporter, or Ran localization [9].
• We conclude that Mad1 and Mad2 are required to detect bipolar orientation and/or tension at kinetochores, whereas Mad3 is not [10].

Anatomical context of MAD2

• The MAD2 branch of the pathway responds to kinetochore microtubule interactions and the BUB2 branch of the pathway operates within the cytoplasm, responding to spindle misorientation [11].
• Ran GTPase regulates Mad2 localization to the nuclear pore complex [9].
• The human homolog of MAD2 was isolated and shown to be a necessary component of the mitotic checkpoint in HeLa cells by antibody electroporation experiments [1].
• Mad1 may anchor Mad2 to the nuclear membrane and regulate its entry into the nucleus [12].

Associations of MAD2 with chemical compounds

• Mad2 is present in two separate complexes in cells arrested in mitosis with nocodazole [13].
• Bet2p forms a complex with Mad2p that appears to bind geranylgeranyl pyrophosphate, but not farnesyl pyrophosphate [14].

Physical interactions of MAD2

• Accumulation of Mad2-Cdc20 complex during spindle checkpoint activation requires binding of open and closed conformers of Mad2 in Saccharomyces cerevisiae [15].
• On the basis of these results and genetic analysis of double mutants, we propose a model in which Mad1p bound to a Nup53p-containing complex sequesters Mad2p at the NPC until its release by activation of the spindle checkpoint [16].

Enzymatic interactions of MAD2

• In addition, Mad2p binds to all of the different phosphorylated isoforms of Mad1p that can be resolved on SDS-PAGE [7].

Regulatory relationships of MAD2

• Budding yeast Bub2 is localized at spindle pole bodies and activates the mitotic checkpoint via a different pathway from Mad2 [17].
• The Cdc14 liberation from the nucleolus was inhibited by the Mad2 checkpoint and by the Bub2 checkpoint in a different manner when microtubule organization was disrupted [18].
• Genetic interactions with checkpoint and apc mutants suggest Cdc28 may regulate checkpoint arrest downstream of the MAD2 and BUB2 pathways [19].

Other interactions of MAD2

• Overexpression of BUB1, which interacts genetically with BUB3 and which is involved in the same checkpoint pathway, also rescues the cold sensitivity of tub1-729, but another checkpoint gene, MAD2, does not [20].
• We demonstrate that Mad3p function is required for the overexpression of Mad2p to result in a metaphase arrest [21].
• The spindle checkpoint is composed of two independent pathways, one leading to inhibition of the metaphase-to-anaphase transition by checkpoint proteins, including Mad2, and the other to inhibition of mitotic exit by Bub2 [22].
• CDH1 showed genetic interactions with MAD2 and PDS1, genes encoding components of the mitotic spindle assembly checkpoint that acts at metaphase to prevent premature chromosome segregation [23].
• RAM2 is also homologous to MAD2, a yeast gene whose product has been implicated in the feedback control of mitosis [14].

Analytical, diagnostic and therapeutic context of MAD2

• Gel filtration and co-immunoprecipitation analyses reveal that Mad2p tightly associates with another spindle checkpoint component, Mad1p [7].
• Microinjection of cells with anti-Mad2 antibody normally induces premature anaphase onset resulting in catastrophic nondisjunction of the chromosomes [24].
• Mutagenesis and NMR titration experiments show that a C-terminal flexible region of Mad2 is required for binding to Cdc20 [25].
• Using deletion mutagenesis and peptide mapping, we have identified the sequences in Cdc20 that target it to Mad2 and the APC, respectively [26].

References