MYOCD

MYOCD (myocardin) is a transcriptional coactivator that partners with SRF and lineage-specific transcription factors to drive smooth muscle and cardiac contractile gene programs and to control cellular phenotype in development and disease (PMID:26047103, PMID:39663419). In the cardiovascular and smooth muscle context, the SRF–MYOCD complex activates contractile genes and maintains the differentiated VSMC state, with this output gated by upstream regulators such as the FOXO3A–MSX1/2 axis (PMID:39663419); in cardiomyocytes MYOCD partners with SALL4 and SRF to bind cell-cycle gene loci (Cdk1, Ccnb1) and promote proliferation (PMID:38014633), and in cardiac stem cells MYOCD cooperates with GATA4 and TBX5 to induce cardiac differentiation (PMID:26047103). MYOCD expression is required for smooth muscle differentiation programs in vivo, acting downstream of BMP4/GATA6/FOXF1 signaling in ureteric smooth muscle precursors (PMID:35905011) and being required for airway smooth muscle hypertrophy and hyperplasia in chronic asthma (PMID:36484734). MYOCD activity is tuned post-transcriptionally by miRNAs miR-9 and miR-139-5p, which bind its 3'-UTR to repress expression and promote contractile-to-synthetic phenotypic switching (PMID:26147104, PMID:35926758). In cancer, MYOCD has context-dependent roles: it directly binds SMAD3 and sustains nuclear SMAD3/SMAD4 complexes in a positive feedback loop that drives TGF-β-induced EMT and metastasis in NSCLC (PMID:32029901), while at the TGFBR2 promoter it recruits the PRMT5/MEP50 complex to epigenetically silence TGFBR2 and suppress lung cancer stemness (PMID:33995678).

1. 2015 Medium

   Established that MYOCD acts as a combinatorial cardiac coactivator, defining which transcription-factor partners convert progenitor cells toward cardiac identity.

   Evidence Inducible lentiviral overexpression of MYOCD with GATA4/MEF2C/TBX5 combinations and cardiac protein readouts in adult mouse Sca1+ cardiac stem cells

   PMID:26047103

   Open questions at the time

   • Does not define the genomic loci directly bound by MYOCD in these cells
   • Pairwise efficacy measured by marker expression, not functional cardiomyocyte conversion
2. 2015 Medium

   Showed MYOCD is post-transcriptionally repressible, identifying miR-9 as a direct 3'-UTR regulator that drives smooth muscle phenotypic switching.

   Evidence Luciferase 3'-UTR reporter assay with miR-9 knockdown/overexpression and myocardin rescue in rat pulmonary artery smooth muscle cells

   PMID:26147104

   Open questions at the time

   • Single cell type; whether miR-9 regulation operates in vivo not established
   • Downstream contractile targets affected not enumerated
3. 2020 High

   Resolved a direct mechanistic link between MYOCD and TGF-β signaling, showing MYOCD sustains SMAD3/SMAD4 nuclear complexes in a feed-forward loop driving EMT.

   Evidence Reciprocal Co-IP, reporter assays, CRISPR silencing of SMAD3/SMAD4 and in vivo metastasis assay in NSCLC cells

   PMID:32029901

   Open questions at the time

   • The MYOCD domain mediating SMAD3 binding not mapped
   • Reconciliation with MYOCD's tumor-suppressive role in lung cancer not addressed
4. 2021 Medium

   Demonstrated a chromatin-level repressive function for MYOCD, occupying the TGFBR2 promoter and recruiting PRMT5/MEP50 to silence it.

   Evidence ChIP promoter occupancy and complex recruitment with in vitro/in vivo functional assays in lung cancer stem cells

   PMID:33995678

   Open questions at the time

   • Single study, single lab
   • How MYOCD switches between coactivator and repressor at different loci is unresolved
5. 2022 Medium

   Placed Myocd within a developmental signaling cascade, showing it is a required transcriptional output of BMP4/GATA6/FOXF1 for ureteric smooth muscle differentiation.

   Evidence Conditional Gata6 knockout with molecular profiling and gain-of-function in mouse ureteric smooth muscle precursors

   PMID:35905011

   Open questions at the time

   • Direct binding of GATA6 to the Myocd locus not shown
   • Whether Myocd loss alone phenocopies Gata6 loss not tested here
6. 2022 Medium

   Identified a second miRNA, miR-139-5p, as a direct MYOCD 3'-UTR repressor linking toxicant exposure to VSMC phenotype switching.

   Evidence Dual-luciferase 3'-UTR assay with qRT-PCR and western blot in A7r5 VSMCs

   PMID:35926758

   Open questions at the time

   • Single cell line
   • In vivo relevance of DBP–miR-139-5p–MYOCD axis not established
7. 2023 High

   Extended MYOCD's coactivator function into cell-cycle control, showing a SALL4–MYOCD–SRF complex directly drives proliferation genes in cardiomyocytes.

   Evidence Co-IP, ChIP-seq and RNA-seq in ΔSall4 loss-of-function mice with proliferation readouts at Cdk1/Ccnb1 loci

   PMID:38014633

   Open questions at the time

   • Relative contribution of MYOCD versus SALL4 to complex targeting not dissected
   • Whether this proliferative role is reactivatable for cardiac regeneration untested
8. 2023 High

   Provided in vivo genetic proof that Myocd is required for pathological airway smooth muscle remodeling.

   Evidence Lung mesenchyme-specific conditional Myocd knockout in a chronic ovalbumin asthma model with histological phenotyping

   PMID:36484734

   Open questions at the time

   • Direct transcriptional targets mediating hypertrophy/hyperplasia not identified
   • Whether MYOCD acts through SRF in this setting not addressed
9. 2024 Medium

   Defined upstream control of the SRF–MYOCD contractile output via a FOXO3A–MSX1/2 repressive axis relieved pharmacologically.

   Evidence Carotid ligation model plus VSMC phenotype assays dissecting the FOXO3A–MSX1/2–SRF–MYOCD axis with colchicine

   PMID:39663419

   Open questions at the time

   • Direct molecular mechanism of MSX1/2 repression of the complex not fully resolved
   • Single lab
10. 2024 Medium

    Linked SRF–MYOCD to MLCK transcription as a determinant of ferroptosis resistance in neutrophils during acute lung injury.

    Evidence RNA-seq, promoter binding and MYOCD/SRF/MLCK knockdown in a mouse ALI model with ferroptosis markers

    PMID:39196520

    Open questions at the time

    • Single study
    • Mechanism connecting MLCK to ferroptosis resistance not fully defined
11. 2025 Low

    Identified NEXN as a physical MYOCD partner modulating EMT via WNT/β-catenin in hepatocellular carcinoma.

    Evidence Co-IP for NEXN–MYOCD binding with overexpression/knockdown EMT readouts and in vivo tumor assay

    PMID:41399508

    Open questions at the time

    • Single Co-IP without reciprocal/structural validation of the interaction
    • Mechanistic link to β-catenin only partially inferred

• How MYOCD is switched between transcriptional coactivation, chromatin-level repression, and partner-dependent context outputs at the molecular level remains unresolved.
• No structural model of MYOCD with its partners
• No unified mechanism explaining its opposing tumor-promoting (SMAD3) versus tumor-suppressing (TGFBR2 silencing) roles in lung cancer
• Domains mediating distinct partner interactions not mapped