MYCT1

MYCT1 is a multifunctional membrane-associated and nuclear protein that integrates endosomal trafficking, cytoskeletal regulation, transcriptional repression, and translational control to restrain cell proliferation, preserve stem cell identity, and suppress tumor progression. At endosomal membranes, MYCT1 moderates endocytosis and interacts with IFITM2/3 to limit endolysosomal nutrient degradation and mTORC1 signaling, and with ZO-1 to regulate Rho GTPase-dependent actin dynamics and endothelial motility (PMID:38839950, PMID:41880193, PMID:33658356). In the nucleus, MYCT1 partners with MAX to repress transcription of targets including RUNX1, and interacts with RACK1 to selectively promote translation of glycogen-shunt enzymes PGM1, UGP2, and GSK3A (PMID:38172714, PMID:35281731). MYCT1 expression is directly activated by c-Myc and VDR, repressed by YY1 and CREB at the promoter level or silenced by promoter hypermethylation, and its protein is turned over by MARCH1-mediated ubiquitination and proteasomal degradation (PMID:21998677, PMID:22672838, PMID:28485541, PMID:37664593, PMID:40533483).

1. 2003 Medium

   Identification of MYCT1 as a novel c-Myc-associated gene established its existence and initial localization, providing the molecular entry point for all subsequent functional studies.

   Evidence Cloning from laryngeal cancer cells, RT-PCR, subcellular localization, bioinformatics identification of c-Myc binding sites and NLS

   PMID:12673574

   Open questions at the time

   • No functional domain identified beyond NLS
   • Localization studied in only one cell line
   • No interaction partners identified
2. 2003 Medium

   Demonstrating that MYCT1 overexpression promoted apoptosis in gastric cancer cells established the first functional phenotype and framed MYCT1 as a potential tumor suppressor.

   Evidence Overexpression in BGC823 cells, TUNEL assay

   PMID:14562369

   Open questions at the time

   • Single cell line and single method (TUNEL)
   • Mechanism of apoptosis induction unknown
   • No loss-of-function data
3. 2011 High

   Establishing that c-Myc directly binds E-box elements in the MYCT1 promoter resolved how MYCT1 is transcriptionally activated and confirmed it as a bona fide c-Myc target gene.

   Evidence Luciferase reporter, EMSA, ChIP, site-directed mutagenesis, RNAi in multiple cell lines

   PMID:21998677

   Open questions at the time

   • Whether c-Myc activates or represses MYCT1 in different contexts not resolved
   • Other transcription factors at the promoter not yet identified
4. 2012 High

   Showing that promoter CpG methylation blocks c-Myc binding and silences MYCT1 explained the frequent downregulation of MYCT1 in cancers and linked epigenetic regulation to its tumor-suppressive loss.

   Evidence Bisulfite-specific PCR, EMSA, ChIP, mutagenesis, 5-aza-C demethylation rescue

   PMID:22672838

   Open questions at the time

   • Whether methylation is a driver or passenger event in tumorigenesis
   • Methylation status across diverse tumor types not systematically assessed
5. 2017 High

   Identifying YY1 as a direct transcriptional repressor of MYCT1 expanded the regulatory logic at the MYCT1 promoter and demonstrated that MYCT1 mediates YY1's oncogenic effects in laryngeal cancer.

   Evidence ChIP, dual luciferase, epistasis rescue (MYCT1 KD reverses YY1-silencing phenotypes), proliferation and migration assays

   PMID:28485541

   Open questions at the time

   • Whether YY1 and c-Myc compete at the same promoter region not tested
   • Downstream effectors of MYCT1 in this context unknown
6. 2018 High

   Demonstrating that CREB represses MYCT1 to de-repress NAT10 and that MYCT1 overexpression induces G0/G1 arrest and intrinsic apoptosis in AML cells broadened the tumor-suppressive repertoire of MYCT1 to hematological malignancies and identified cell cycle and apoptosis machinery as downstream effectors.

   Evidence ChIP and luciferase for CREB-MYCT1 promoter; lentiviral overexpression in AML lines with cell cycle, apoptosis, and xenograft readouts

   PMID:29563811 PMID:30283340

   Open questions at the time

   • How MYCT1 mechanistically regulates cyclin D/E and Bcl-2 family members not resolved
   • NAT10 downstream pathway poorly defined
7. 2019 Medium

   Identifying MYCT1's interaction with MAX as a co-transcriptional mechanism and its post-transcriptional regulation by miR-632 revealed both nuclear effector function (driving miR-181a/NPM1 apoptosis axis) and an additional silencing route via 3′UTR targeting.

   Evidence Luciferase, ChIP, miRNA inhibitor/overexpression rescue for MYCT1-MAX-miR-181a-NPM1 axis; dual luciferase 3′UTR assay for miR-632 targeting

   PMID:30982352 PMID:31152622

   Open questions at the time

   • MYCT1-MAX interaction inferred functionally but not validated by direct Co-IP in 2019 study
   • Whether MYCT1-MAX complex is stoichiometric or transient unknown
8. 2020 Medium

   Mapping the MYCT1→SP1→miR-629-3p→ESRP2 pathway and confirming YY1-mediated MYCT1 repression in a second cancer type (HCC) established MYCT1's anti-EMT function and validated the generalizability of its transcriptional regulation.

   Evidence ChIP, luciferase, Transwell migration, EMT marker analysis in laryngeal cancer; YY1/miR-34a-5p epistasis in HCC

   PMID:32659265 PMID:32778238

   Open questions at the time

   • How MYCT1 suppresses SP1 expression mechanistically unknown
   • Whether ESRP2 is a direct or indirect target not fully resolved
9. 2021 High

   Discovery that MYCT1 physically interacts with ZO-1 and regulates Rho GTPase-actin dynamics in endothelium, with endothelial-specific knockout enhancing antitumor immunity, pivoted understanding of MYCT1 from a purely cancer-cell-intrinsic suppressor to a regulator of endothelial biology and the tumor microenvironment.

   Evidence Co-IP for MYCT1-ZO-1, endothelial-specific Myct1 knockout mice, in vivo tumor models, motility and trans-endothelial migration assays

   PMID:33658356

   Open questions at the time

   • Which Rho GTPase is the direct target not specified
   • How ZO-1 interaction is regulated unclear
   • Role in non-tumor vasculature not defined
10. 2022 Medium

    Demonstrating that MYCT1 promotes translation of glycogen-shunt enzymes via RACK1 interaction, with global knockout causing hepatic glycogen accumulation, established MYCT1 as a translational regulator with metabolic consequences in vivo.

    Evidence Myct1 global KO mice, metabolic intermediate analysis, translational efficiency assays, RACK1 interaction studies in hepatic cells

    PMID:35281731

    Open questions at the time

    • Whether RACK1 interaction is direct or within a larger ribosomal complex not resolved
    • Full spectrum of RACK1-dependent MYCT1 translational targets unknown
    • Single lab finding
11. 2023 High

    Identifying VDR as a direct transcriptional activator of MYCT1 and showing that MYCT1 attenuates renal fibrosis via SP1/TGF-β1/SMAD3 suppression extended MYCT1's physiological relevance to diabetic kidney disease.

    Evidence ChIP and luciferase for VDR-MYCT1 promoter, AAV-Myct1 in diabetic db/db mice, Western blot and siRNA in tubular epithelial cells

    PMID:37664593

    Open questions at the time

    • Whether VDR-MYCT1 axis operates in non-renal tissues unknown
    • Direct molecular link between MYCT1 and SP1 suppression still unresolved
12. 2024 High

    Localizing MYCT1 to endosomal membranes in human HSCs and showing it restrains endocytosis to preserve stemness fundamentally reframed MYCT1 as a membrane-associated endosomal gatekeeper rather than a purely nuclear factor.

    Evidence Lentiviral KD/OE in cord blood HSPCs, scRNA-seq, endosomal membrane imaging, Co-IP with trafficking regulators, endocytosis assays, xenograft engraftment

    PMID:38839950

    Open questions at the time

    • Specific endosomal trafficking regulators interacting with MYCT1 not all named
    • Whether endosomal localization is universal across cell types or HSC-specific unclear
13. 2024 High

    Confirming MYCT1-MAX physical interaction by Co-IP and showing it represses RUNX1 transcription in DLBCL validated the nuclear transcriptional repressor arm of MYCT1 function with direct protein-protein evidence.

    Evidence Co-IP, immunofluorescence, ChIP, dual-luciferase, flow cytometry, CCK-8 in DLBCL cells

    PMID:38172714

    Open questions at the time

    • Whether MYCT1 alters MAX-MYC versus MAX-MXD1 complex equilibrium unknown
    • Genome-wide MYCT1-MAX target repertoire not defined
14. 2025 High

    Identifying MARCH1 as the E3 ligase that ubiquitinates and degrades MYCT1 protein resolved a major gap in understanding how MYCT1 protein levels are controlled post-translationally, explaining another route of MYCT1 inactivation in AML.

    Evidence Co-IP, ubiquitination assay, gain/loss-of-function, in vivo AML mouse model, POU2F2-MARCH1 luciferase axis

    PMID:40533483

    Open questions at the time

    • Ubiquitination site(s) on MYCT1 not mapped
    • Whether other E3 ligases target MYCT1 unknown
15. 2025 High

    Demonstrating that MYCT1 interacts with IFITM2/3 at endolysosomes to restrain nutrient trafficking and mTORC1 signaling in endothelium, with loss causing defective white adipose energy storage, provided a molecular mechanism for MYCT1's endosomal gatekeeper function and linked it to systemic metabolic regulation.

    Evidence Endothelial-specific MYCT1 deletion, Co-IP for MYCT1-IFITM2/3, endosomal trafficking assays, mTORC1 activity measurement, TSC1-KO phenocopy, WAT expansion assay

    PMID:41880193

    Open questions at the time

    • Structural basis of MYCT1-IFITM2/3 interaction unknown
    • Whether MYCT1-IFITM interaction is regulated by post-translational modifications not tested
    • Relevance to non-endothelial MYCT1 functions not established

• How MYCT1 coordinates its dual endosomal and nuclear functions — whether these represent distinct protein pools, cell-type-specific roles, or a shuttling mechanism — remains unresolved, and no structural model of MYCT1 or its complexes exists.
• No crystal structure or cryo-EM model of MYCT1
• Dual localization (endosome vs. nucleus) mechanism unexplained
• Full interactome not defined by unbiased proteomics
• Relative importance of transcriptional, translational, and trafficking functions in different tissues not delineated