MYCBP

MYCBP is a small adaptor protein that operates at the intersection of transcriptional regulation, cAMP/PKA signaling, membrane trafficking, and Hedgehog pathway control. It binds the N-terminal transactivation domain of C-MYC and stimulates E-box-dependent transcription without directly recognizing DNA, and its protein levels are stabilized by circ_0002669 through protection from ubiquitin-mediated degradation (PMID:9797456, PMID:38570856). MYCBP associates with AKAPs (AKAP84, AKAP95, AKAP149) and the RII regulatory subunit of PKA, competitively excluding the PKA catalytic subunit to suppress PKA activity, and is directed to mitochondria via S-AKAP84 or to the trans-Golgi network via the ARF-GEF BIG2 (PMID:12414807, PMID:11483602, PMID:16866877). In Hedgehog signaling, MYCBP resides in a nuclear complex with Gli and Sufu; upon pathway activation and Sufu/p66β dissociation, MYCBP promotes Gli-dependent target gene expression, and its Drosophila ortholog is required for germline stem cell maintenance and Dpp/BMP signaling (PMID:25403183, PMID:41325460).

1. 1998 High

   Identifying MYCBP as a direct C-MYC-binding partner established that an 11-kDa protein could stimulate MYC/Max-dependent transcription without itself recognizing DNA, raising the question of how it modulates transcription mechanistically.

   Evidence Co-immunoprecipitation, yeast two-hybrid mapping of binding domains, and E-box reporter assays in mammalian cells

   PMID:9797456

   Open questions at the time

   • No structural basis for how MYCBP enhances MYC transactivation
   • Whether MYCBP binds chromatin directly or solely through MYC is unresolved
   • Endogenous stoichiometry of the MYCBP-MYC complex unknown
2. 1998 Medium

   Demonstrating cell-cycle-dependent nuclear translocation of MYCBP during S phase linked its subcellular localization to C-MYC expression dynamics, suggesting regulated compartmentalization as a functional control mechanism.

   Evidence Immunofluorescence with cell-cycle synchronization in transfected cells

   PMID:9797456

   Open questions at the time

   • Nuclear import mechanism (NLS, carrier) not identified
   • Single overexpression system; endogenous protein not tracked
   • Functional consequence of nuclear translocation on specific MYC target genes not tested
3. 2000 Medium

   Showing that MYCBP overexpression drives erythroid differentiation in K562 cells established a functional role beyond simple transcriptional coactivation, implicating it in lineage commitment.

   Evidence Stable overexpression with ε-globin RT-PCR and hemoglobin accumulation assays

   PMID:10639579

   Open questions at the time

   • Whether the differentiation effect is MYC-dependent or independent was not resolved
   • Loss-of-function experiment not performed
   • Single cell line tested
4. 2001 High

   Discovery that MYCBP binds the RII-binding region of AKAPs (AKAP149/S-AKAP84) and localizes to mitochondria through this interaction revealed a second, non-transcriptional function linked to cAMP/PKA scaffolding.

   Evidence Yeast two-hybrid, in vitro binding, co-IP, and immunofluorescence/subcellular fractionation in HeLa cells and sperm

   PMID:11483602

   Open questions at the time

   • Functional consequence of mitochondrial MYCBP on organelle biology not established
   • Whether MYCBP-AKAP and MYCBP-MYC interactions are mutually exclusive unknown
5. 2002 High

   Establishing that MYCBP competitively excludes the PKA catalytic subunit from AKAP/RII complexes defined a biochemical mechanism by which it suppresses PKA signaling, placing it as a negative modulator of cAMP-dependent phosphorylation.

   Evidence Co-IP, in vitro binding competition assays, and PKA enzymatic activity measurements

   PMID:12414807

   Open questions at the time

   • Physiological targets of PKA suppression by MYCBP not identified
   • In vivo consequences of MYCBP-mediated PKA inhibition not tested in animal models
   • Structural basis for competitive exclusion not resolved
6. 2002 High

   Identification of a quaternary complex (MYCBP/S-AKAP84/RII/AAT-1α) at mitochondria with PKA-dependent phosphorylation of AAT-1α provided the first candidate downstream event of MYCBP-scaffolded signaling in the testis.

   Evidence Yeast two-hybrid, co-IP, colocalization, in vivo and in vitro phosphorylation assays

   PMID:12223483

   Open questions at the time

   • Functional significance of AAT-1α phosphorylation unknown
   • Role of this complex in spermatogenesis not tested genetically
7. 2006 High

   Demonstrating that BIG2 (but not BIG1) recruits MYCBP to the trans-Golgi network expanded its compartment-specific functions to membrane trafficking, with BIG2 knockdown displacing MYCBP from the TGN.

   Evidence Co-IP, RNAi knockdown of BIG2, immunofluorescence localization, in vitro binding

   PMID:16866877

   Open questions at the time

   • What MYCBP does at the TGN functionally (e.g., vesicle budding, ARF regulation) is not known
   • Whether TGN and mitochondrial pools of MYCBP are independently regulated is unclear
8. 2014 High

   Proteomic identification of MYCBP in the Sufu/Gli complex and demonstration that Hh-induced Sufu/p66β dissociation licenses MYCBP to promote Gli activity established MYCBP as a positive nuclear effector of Hedgehog signaling downstream of Smoothened.

   Evidence Sufu interactome by co-IP/proteomics, ChIP, cell-based Hh reporter assays, zebrafish epistasis experiments

   PMID:25403183

   Open questions at the time

   • How MYCBP biochemically activates Gli (coactivator recruitment, chromatin remodeling) is unresolved
   • Whether MYCBP's MYC-coactivator and Hh-effector roles are coordinated or independent is unknown
9. 2019 Medium

   Placing MYCBP transcription under β-catenin/LEF1 control, suppressed by EYA4-mediated dephosphorylation of β-catenin, connected Wnt signaling to MYCBP expression and revealed its role in hepatocellular carcinoma proliferation.

   Evidence Phosphatase assay, siRNA knockdown/overexpression rescue, co-IP, luciferase reporter in HCC cells

   PMID:31385398

   Open questions at the time

   • Whether Wnt-driven MYCBP upregulation acts through MYC, Hh, or PKA pathways in HCC was not dissected
   • Single cancer type; generalizability not established
10. 2024 Medium

    Showing that circ_0002669 binds MYCBP protein and shields it from ubiquitin-mediated proteasomal degradation revealed a post-translational stabilization mechanism that amplifies MYC target gene expression in osteosarcoma.

    Evidence Biotin pulldown, mass spectrometry, RNA immunoprecipitation, ubiquitination assay in osteosarcoma cells

    PMID:38570856

    Open questions at the time

    • The E3 ubiquitin ligase targeting MYCBP is not identified
    • Whether circRNA-mediated stabilization operates in non-cancer contexts is unknown
    • Single study; independent confirmation needed
11. 2025 High

    Genetic analysis in Drosophila revealed that MYCBP forms complexes with Sakura and Otu and is essential for germline stem cell maintenance via Dpp/BMP signaling, bam regulation, and sex-lethal splicing, establishing conserved roles in stem cell biology and RNA processing.

    Evidence Co-IP defining binary/ternary complexes, null mutant and germline-specific RNAi in Drosophila, signaling reporter assays

    PMID:41325460

    Open questions at the time

    • Whether the Sakura/Otu complex is conserved in mammals is unknown
    • Mechanism by which MYCBP influences sex-lethal splicing not defined
    • Whether BMP-pathway role in Drosophila GSCs reflects a mammalian Hedgehog or TGFβ function is unresolved

• How MYCBP's distinct interaction modalities — MYC coactivation, AKAP/PKA scaffolding, BIG2-mediated TGN targeting, and Gli activation — are coordinated within a single cell, and which E3 ligase targets MYCBP for degradation, remain open mechanistic questions.
• No structural model of MYCBP alone or in any complex
• Conditional knockout phenotype in mammalian systems not reported
• Integration of multiple signaling roles into a unified model lacking