Disease relevance of MAD2L1

• Novel mutational hotspots in human Mad2 genes were discovered for the gastric cancers and these mutations caused the functional defects in the spindle checkpoint suggesting that these mutations might be involved in the development and progression of gastric cancer [1].
• Gene expression levels of the MAD2 and BUB1 mitotic spindle checkpoint genes were assessed in 37 Barrett's patients (with histology ranging from metaplasia to adenocarcinoma) by real-time RT-PCR [2].
• Overexpressed genes included two cell cycle checkpoint genes, CDC2 and MAD2L1, which have previously been described in association with lymph node metastasis in other cancer types [3].
• Expression and mutational analyses of the human MAD2L1 gene in breast cancer cells [4].
• Significance of MAD2 expression to mitotic checkpoint control in ovarian cancer cells [5].

High impact information on MAD2L1

• Depletion of PICH causes the selective loss of Mad2 from kinetochores and completely abrogates the spindle checkpoint, resulting in massive chromosome missegregation [6].
• In addition, in vitro cdk1-phosphorylated Cdc20 interacts with Mad2 rather than APC/ C [7].
• When injected into Xenopus embryos, hMAD2 arrests cells at mitosis with an inactive APC [8].
• The template model proposes that Mad1-Mad2 at kinetochores acts as a template to change the conformation of another binding molecule of Mad2 [9].
• Arrest with ICRF-193 is not accompanied by recruitment of Mad2 or Bub1 to kinetochores, nor by phosphorylation of the histone H2AX, indicating arrest by ICRF-193 is not due to activation of the spindle assembly checkpoint, nor is it a response to DNA damage [10].

Chemical compound and disease context of MAD2L1

• Mad2beta, an alternative variant of Mad2 reducing mitotic arrest and apoptosis induced by adriamycin in gastric cancer cells [11].

Biological context of MAD2L1

• We conclude that expression changes in mitotic arrest deficiency genes (MAD1, MAD2L1, and MAD2L2) play a role in renal carcinogenesis characterized by multiple numerical chromosome abnormalities [12].
• Assignment of mitotic arrest deficient protein 2 (MAD2L1) to human chromosome band 5q23.3 by in situ hybridization [13].
• We show that RNAi-mediated suppression of Mad1 function in mammalian cells causes loss of Mad2 kinetochore localization and impairment of the spindle checkpoint [14].
• MAD2 is a key component of the spindle checkpoint that delays the onset of anaphase until all the kinetochores are attached to the spindle [15].
• These data suggest that the phosphorylation state of Mad2 regulates its checkpoint activity by modulating its association with Mad1 and the APC/C [16].

Anatomical context of MAD2L1

• Most significantly, a partial repression of either MAD1 or MAD2 confers resistance to nocodazole, a drug that inhibits microtubule attachment [17].
• Surprisingly, unlike any other known mitotic checkpoint proteins, HsMad1 and HsMAD2 were found localized at nuclear pores throughout interphase [18].
• Mad2 was mutated in 44.9% of gastric cancer tissues and one gastric cancer cell line, N87, but not Bub1 [1].
• Overexpression of mutant Mad2 in HeLa cells led to the appearance of aneuploid cells in the presence of nocodazole, and this indicated that these mutations caused a defect in MAD2 protein [1].
• Sequence analysis of MAD2L1 cDNA in these as well as nine additional aneuploid breast cancer and five immortalized normal human mammary epithelial cell lines revealed one heterozygous frameshift (572 del A) mutation in a cancer cell line that demonstrated a high level of transcript expression [4].

Associations of MAD2L1 with chemical compounds

• In addition, the association of Mad2 with the APC/C(cdc20) complex and the accumulation of Pds1, an anaphase inhibitor, were remarkably reduced in arsenite-arrested mitotic cells as compared with nocodazole-arrested mitotic cells [19].
• To additionally understand the significance of the MAD2 to mitotic checkpoint control, we established an inducible expression system in which MAD2 was induced by the addition of ponasterone A [5].
• Further, we have identified a unique polyhistidine motif with metal binding property adjacent to this second binding domain that may be important for maintaining the overall conformation of Cdc20 for its binding to Mad2 [20].
• Previously, we first reported that a key regulator of the mitotic checkpoint, mitotic arrest deficient-2 (MAD2), was a mediator of cisplatin sensitivity in human cancer cells [21].

Physical interactions of MAD2L1

• The Mad2 spindle checkpoint protein undergoes similar major conformational changes upon binding to either Mad1 or Cdc20 [14].
• Mad2 is a component of the SAC effector complex that sequesters Cdc20 to halt anaphase [22].
• More interestingly, REV7 interacts with hMAD2 and therefore might function in the cell cycle control by affecting the activation of APC (anaphase promoting complex) [23].
• The structure of the O-Mad2-C-Mad2 conformational dimer is consistent with a catalytic model in which a C-Mad2 template facilitates the binding of O-Mad2 to Cdc20, the target of Mad2 in the spindle checkpoint [24].
• Depletion of Tpr in HeLa cells disrupts the NPC localization of Mad1 and Mad2 during interphase and decreases the levels of Mad1-bound Mad2 [25].

Regulatory relationships of MAD2L1

• The mitotic arrest deficiency 2 (Mad2) spindle checkpoint protein inhibits APC/C through binding to its mitotic-specific activator, Cdc20 [26].

Other interactions of MAD2L1

• Mad1 and Cdc20 contain Mad2 binding motifs that share a common consensus [14].
• Binding of one of these ligands, MBP1, triggers an extensive rearrangement of the tertiary structure of Mad2 [14].
• In addition, we have identified an interaction between hREV7 and hMAD2 but not hMAD1 [27].
• These observations provide a simple explanation of why BubR1 and Mad2 are essential for checkpoint function following spindle destruction, yet Bub1 and aurora B kinase activity are not [28].
• Analysis of BubR1 complexes suggests that both of these arms converge on the mitotic checkpoint complex (MCC), which includes BubR1, Bub3, Mad2 and Cdc20 [28].

Analytical, diagnostic and therapeutic context of MAD2L1

• The WD repeats of the Bub3 and Cdc20 kinetochore proteins are important for the physical interactions of these proteins with Mad2 and BubR1 to yield a kinetochore protein complex capable of delaying anaphase by inhibiting ubiquitin ligation via the anaphase-promoting complex/cyclosome [29].
• The presence of mutations in Bub1 and Mad2 coding sequences was primarily detected by RT-PCR-SSCP and subsequently confirmed by automatic sequencing of either the RT-PCR products and/or the PCR products from genomic DNA [1].
• Wild type and mutant MAD2 protein displayed distinct mobility on two-dimensional gel electrophoresis [1].
• Microinjection of Mad2 antibodies results in premature anaphase onset [9,10], and excess Mad2 protein causes arrest in mitosis [5,11] [30].
• By injecting PtK1 cells in nocodazole with GST-Mad1F10 and processing the cells for immunofluorescence microscopy after anaphase sister chromatid separation in nocodazole we found that Mad2, BubR1, cytoplasmic dynein, CENP-E and the 3F3/2 phosphoepitope remain on kinetochores [31].

References