MAD1L1

MAD1L1 encodes a core mitotic spindle assembly checkpoint (SAC) protein that enforces accurate chromosome segregation by recruiting MAD2 to unattached kinetochores (PMID:11181178, PMID:12042300). It localizes dynamically through the cell cycle, decorating kinetochores specifically in prometaphase and departing by metaphase/anaphase, while in interphase it co-localizes with nuclear pore complexes (PMID:11181178). MAD1L1 physically associates with MAD2 through two leucine zipper domains (residues 501–522 and 557–571), and this interaction is essential for checkpoint enforcement; a coding polymorphism at codon 558 (Arg→His) within the second leucine zipper reduces MAD1–MAD2 binding affinity and impairs nocodazole-induced mitotic arrest (PMID:12042300, PMID:20516147). Loss of MAD1L1 function compromises the checkpoint and drives chromosomal instability: a truncated dominant-negative mutant from lymphoma weakens the mitotic checkpoint (PMID:11423979), and biallelic germline loss-of-function abolishes full-length MAD1, producing a deficient SAC, profound aneuploidy in blood cells, mitochondrial stress, and systemic interferon and NFκB inflammatory signaling with clonal expansions bearing leukemic signatures (PMID:36322655). The MAD1L1 promoter is GC-rich and TATA-less, active in G1, responsive to mitogenic stimuli, and preferentially activated by a gain-of-function p53 mutant (PMID:11980658). Beyond mitosis, MAD1L1 engages non-checkpoint protein interactions, including binding to CHPF in glioma cells, whose functional role is not characterized in the available corpus (PMID:37851364).

1. 2001 High

   Establishing where MAD1L1 acts and what it partners with anchored it as a kinetochore-localized checkpoint component physically coupled to MAD2.

   Evidence Immunofluorescence co-labeling, subcellular fractionation, and reciprocal co-immunoprecipitation across cell lines

   PMID:11181178

   Open questions at the time

   • Did not map the MAD1–MAD2 interaction interface
   • Functional consequence of nuclear pore localization in interphase unresolved
2. 2001 Medium

   Demonstrating that a lymphoma-derived truncated MAD1L1 acts as a dominant-negative and weakens the checkpoint linked MAD1L1 loss of function to tumorigenic chromosome instability.

   Evidence Transfection of wild-type vs. mutant constructs with nocodazole mitotic index assays in HOS cells

   PMID:11423979

   Open questions at the time

   • Single dominant-negative allele; not a clean loss-of-function genetic test
   • Did not quantify aneuploidy directly
3. 2002 High

   Mapping two leucine zipper domains required for MAD2 binding and showing the codon-558 variant weakens it connected a defined protein region to checkpoint strength and a cancer-associated allele.

   Evidence Deletion/point-mutation mapping, Co-IP binding assays, mitotic arrest assay, and LOH analysis in breast cancer

   PMID:12042300

   Open questions at the time

   • No structural model of the bound interface
   • Population-level penetrance of the 558 variant not addressed
4. 2002 Medium

   Defining the MAD1L1 promoter architecture and its cell-cycle and p53-mutant responsiveness explained how checkpoint protein levels are coupled to proliferative signaling.

   Evidence Promoter deletion/mutational analysis with reporter assays and cell-cycle synchronization

   PMID:11980658

   Open questions at the time

   • Specific transcription factors binding the core region not identified
   • Mechanism of gain-of-function p53 activation unresolved
5. 2010 Medium

   Independent functional testing of the Arg558His variant confirmed it impairs checkpoint responses, corroborating the earlier binding-based prediction in a clinical-genetic context.

   Evidence Flow cytometry for 4N-DNA content and nocodazole mitotic index assays

   PMID:20516147

   Open questions at the time

   • Did not test endogenous heterozygous vs homozygous variant carriers
   • No direct aneuploidy measurement
6. 2017 Medium

   Characterizing a RARS–MAD1L1 fusion oncoprotein that activates FUBP1/c-Myc revealed MAD1L1 sequence in a gain-of-function rearrangement distinct from its checkpoint role.

   Evidence Co-IP, ChIP, in vitro proliferation/sphere assays, and xenografts with FUBP1 silencing and c-Myc inhibition

   PMID:29133573

   Open questions at the time

   • Contribution of the MAD1L1 portion to fusion activity not dissected
   • Relevance to wild-type MAD1L1 function unclear
7. 2022 High

   Identifying biallelic germline loss-of-function patients tied complete MAD1L1 deficiency to SAC failure, aneuploidy, and a systemic inflammatory/leukemic phenotype, establishing physiological consequences in humans.

   Evidence Germline mutation functional studies, SAC assays, protein expression, and single-cell RNA sequencing of patient cells

   PMID:36322655

   Open questions at the time

   • Mechanism linking aneuploidy to interferon/NFκB activation not fully resolved
   • Why specific chromosome gains undergo clonal expansion unknown
8. 2023 Medium

   Detecting a MAD1L1–CHPF physical interaction in glioma raised a candidate non-mitotic partnership for MAD1L1.

   Evidence Co-IP, GST pulldown, and LC-MS/MS in glioma cells

   PMID:37851364

   Open questions at the time

   • Functional consequence of the MAD1L1–CHPF interaction not established
   • Interaction not validated outside glioma context

• How MAD1L1-dependent aneuploidy is mechanistically translated into NFκB/interferon inflammatory signaling and selective clonal expansion remains unresolved.
• No defined signaling intermediary between mis-segregation and innate immune activation
• No structural basis for the MAD1–MAD2 kinetochore recruitment complex in the corpus