MXD4

MXD4 (Mad4) is a transcriptional repressor that antagonizes MYC-driven proliferation: it heterodimerizes with Max, binds CACGTG E-box sequences to repress transcription from such promoters, interacts with mSin3, and suppresses c-Myc-dependent cell transformation (PMID:8521822). This MYC-antagonist activity makes MXD4 a brake on proliferation across multiple cell systems—enforced expression impairs hematopoietic progenitor development by reducing proliferation and arresting cells in G0/G1 (PMID:21782766), while its loss in keratinocyte precursors elevates MYC and enhances proliferative and clonogenic capacity (PMID:36007550). Because MXD4 opposes MYC, its levels are tightly held down in proliferating and malignant cells through several converging mechanisms: a c-Myc–Miz-1 complex bound to the MXD4 initiator element represses its transcription, with Miz-1 alone activating the promoter and c-Myc antagonizing this activation (PMID:12418961); the UHRF1–SAP30 epigenetic complex represses MXD4 to sustain leukemogenesis via the MYC pathway (PMID:36302855); and METTL16-mediated m6A deposition on MXD4 mRNA destabilizes the transcript, lowering MXD4 protein to favor MYC-MAX complex formation in AML (PMID:40946103). MXD4 protein stability is also positively controlled, being protected from c-IAP1-mediated degradation by Sin3B (PMID:22895069) and increased through an OX40-driven phosphorylation event that promotes nuclear translocation and supports T-cell survival (PMID:21400495).

1. 1995 High

   Established MXD4's core molecular identity—whether it acts as a MYC antagonist—by showing it dimerizes with Max, binds E-boxes, represses transcription, and blocks Myc-driven transformation.

   Evidence Co-IP, reporter repression assays, and rat embryo fibroblast transformation assays

   PMID:8521822

   Open questions at the time

   • Did not define endogenous target genes repressed by MXD4
   • Mechanism of mSin3 corepressor recruitment not detailed
2. 2003 High

   Answered how MXD4 expression is held low in proliferating cells, showing a c-Myc–Miz-1 complex represses its promoter at the initiator element.

   Evidence Reporter and initiator-element mutagenesis assays in MEL cells

   PMID:12418961

   Open questions at the time

   • Did not establish chromatin/epigenetic state at the endogenous promoter
   • In vivo relevance during differentiation not tested genetically
3. 2004 Medium

   Identified a tissue-specific physical partner, TCP10L, expanding the MXD4 interactome beyond Max/mSin3.

   Evidence Yeast two-hybrid screen confirmed by co-IP and subcellular co-localization

   PMID:15469726

   Open questions at the time

   • Functional consequence of the TCP10L–MXD4 interaction not determined
   • Single lab, no reciprocal validation in a physiological liver context
4. 2011 Medium

   Showed MXD4 protein stability is an actively regulated node, with OX40 signaling driving a stabilizing phosphorylation that promotes nuclear translocation and T-cell survival.

   Evidence Ex vivo murine T-cell analysis, protein stability assays, siRNA knockdown with cell-death readout

   PMID:21400495

   Open questions at the time

   • Kinase responsible for the phosphorylation not identified
   • Direct transcriptional targets driving survival not defined
5. 2011 Medium

   Tested MXD4's cell-cycle function in hematopoiesis, demonstrating that gain-of-function impairs progenitor proliferation via G0/G1 arrest.

   Evidence Doxycycline-inducible gain-of-function in ES-derived hematopoietic cells with cell-cycle analysis

   PMID:21782766

   Open questions at the time

   • Loss-of-function consequence in normal hematopoiesis not addressed
   • Direct E-box targets mediating the arrest not mapped
6. 2012 Medium

   Resolved a post-translational control mechanism, showing Sin3B stabilizes MXD4 by protecting it from c-IAP1-mediated degradation.

   Evidence siRNA knockdown, co-transfection, co-IP, and protein stability assays in GBM cells

   PMID:22895069

   Open questions at the time

   • Whether c-IAP1 directly ubiquitinates MXD4 versus an indirect route not fully resolved
   • In vivo relevance in glioma not established
7. 2022 High

   Placed MXD4 as a functional effector downstream of the UHRF1–SAP30 repressor complex in leukemia, using epistasis to show its de-repression depends on this complex.

   Evidence Co-IP, SRA-domain mutagenesis, knockdown, leukemia PDX, and genetic rescue

   PMID:36302855

   Open questions at the time

   • Direct UHRF1/SAP30 occupancy at the MXD4 locus not shown at base-pair resolution
   • Generality beyond the leukemia context untested
8. 2022 Medium

   Defined MXD4 as a regulator of MYC-dependent stemness balance in human epidermis, with knockdown raising MYC and proliferative/clonogenic potential.

   Evidence shRNA knockdown in keratinocytes, clonogenic assays, and 3D organoid generation

   PMID:36007550

   Open questions at the time

   • Direct MXD4 target genes in keratinocytes not identified
   • Mechanism linking MXD4 loss to MYC upregulation not dissected
9. 2025 High

   Identified an RNA-level control of MXD4, showing METTL16-deposited m6A destabilizes MXD4 mRNA to favor MYC-MAX activity in AML.

   Evidence Transcriptome-wide m6A mapping, METTL16 depletion/inhibition, mRNA stability and MYC-target rescue assays in AML cells

   PMID:40946103

   Open questions at the time

   • The m6A reader interpreting the MXD4 mark not identified
   • Whether this axis operates in non-AML contexts unknown

• The genome-wide set of MXD4 direct target genes and the structural basis of its corepressor recruitment remain undefined across the corpus.
• No ChIP-based genome-wide target map
• No structural model of the MXD4–Max–mSin3 repressive complex