LCOR

LCOR is a multifunctional transcriptional regulator that serves as a ligand-dependent corepressor of nuclear receptors, a context-dependent coactivator, a PRC2.1 accessory subunit stimulating H3K27 trimethylation, and an IFN-independent activator of antigen presentation genes. LCOR is recruited to agonist-bound nuclear receptors (e.g., ERα) via a single LXXLL motif and assembles repressor complexes containing HDAC3, HDAC6, and CtBP corepressors to attenuate hormone-driven transcription; the helix-turn-helix (HTH) domain mediates interaction with RIP140 and C/EBPβ for repression of estrogen-inducible genes, breast cancer cell proliferation, and early adipogenesis (PMID:12535528, PMID:19744931, PMID:28414308, PMID:28972158). LCOR also encodes a longer isoform, PALI1, that functions as a vertebrate-specific PRC2.1 subunit essential for mouse development, promoting EZH2-mediated H3K27 trimethylation and defining a PRC2 subtype antagonistic to AEBP2-containing PRC2.2 (PMID:29628311). Independently of interferon signaling, LCOR binds IFN-stimulated response elements to activate antigen processing and presentation machinery genes, directly modulating tumor immunogenicity and responsiveness to immune checkpoint blockade (PMID:35301507).

1. 2003 High

   Establishing that LCOR is a novel ligand-dependent corepressor recruited to agonist-bound nuclear receptors via an LXXLL motif, assembling HDAC- and CtBP-containing repressor complexes—this defined the gene's founding molecular activity and distinguished it from classical corepressors.

   Evidence In vitro binding assays, Co-IP, mutagenesis, reporter gene assays with TSA treatment, and confocal colocalization in mammalian cells

   PMID:12535528

   Open questions at the time

   • Structural basis of LXXLL-mediated recognition not resolved
   • Genome-wide target repertoire unknown
   • In vivo physiological relevance not tested
2. 2009 High

   Demonstrating that HDAC6 is a direct LCOR partner co-recruited to ERα target promoters in a hormone-dependent manner extended the corepressor complex composition beyond HDAC3 and CtBP.

   Evidence In vitro binding, Co-IP, ChIP, re-ChIP, siRNA knockdown, and reporter assays in MCF7 cells

   PMID:19744931

   Open questions at the time

   • Relative contributions of HDAC3 versus HDAC6 to repression not disentangled
   • Whether HDAC6 catalytic activity or scaffold function is required is unclear
3. 2012 High

   Identifying KLF6 as a transcription factor partner that recruits LCOR-CtBP1-HDAC complexes to CDKN1A and CDH1 promoters showed LCOR operates beyond nuclear receptors to regulate cell cycle and adhesion gene expression.

   Evidence Yeast two-hybrid screen, Co-IP, ChIP, reporter assays, and siRNA knockdown

   PMID:22277651

   Open questions at the time

   • Physiological context for KLF6-LCOR interaction in vivo not established
   • Whether LCOR-KLF6 cooperation is tissue-specific is unknown
4. 2017 High

   Defining the HTH domain as essential for LCOR-mediated transcriptional repression and showing RIP140 is required for LCOR's anti-proliferative effects in breast cancer cells revealed the modular architecture of the LCOR repressor complex.

   Evidence In vitro interaction, Co-IP, proximity ligation assay, mutagenesis, reporter and proliferation assays in breast cancer cell lines

   PMID:28414308

   Open questions at the time

   • Whether HTH domain functions independently of CtBP/HDAC recruitment is unresolved
   • RIP140-LCOR stoichiometry and structural interface unknown
5. 2017 High

   Demonstrating that miR-199a directly represses LCOR to maintain stemness by blocking LCOR-mediated interferon response priming connected LCOR to stem cell differentiation and established a post-transcriptional regulatory layer.

   Evidence miRNA target validation, luciferase reporter, gain/loss-of-function, in vivo tumor initiation and metastasis assays

   PMID:28530657

   Open questions at the time

   • How LCOR activates interferon response genes mechanistically was not resolved
   • Whether other miRNAs regulate LCOR in additional stem cell contexts is unknown
6. 2017 High

   Showing LCOR interacts with C/EBPβ via its HTH domain and suppresses adipogenic gene promoters through CtBP recruitment and histone modification changes extended LCOR's regulatory repertoire to adipocyte differentiation.

   Evidence Affinity purification/mass spectrometry, Co-IP, ChIP, mutagenesis, and differentiation assays in 3T3-L1 cells

   PMID:28972158

   Open questions at the time

   • In vivo adipogenesis phenotype not tested
   • Whether LCOR regulates later stages of adipocyte maturation is unclear
7. 2018 High

   Discovering that LCOR encodes PALI1, a vertebrate-specific PRC2.1 accessory subunit that stimulates H3K27me3 and is essential for mouse development, revealed an entirely separate function from its nuclear receptor corepressor role and defined a PRC2 subtype antagonistic to PRC2.2.

   Evidence In vitro methyltransferase assay, Co-IP, mouse genetic knockout, ChIP-seq

   PMID:29628311

   Open questions at the time

   • How PALI1 stimulates EZH2 catalytic activity at the structural level is unknown
   • Tissue-specific contributions of PALI1 versus AEBP2-PRC2.2 not delineated
   • Relationship between PALI1/PRC2.1 function and LCOR's corepressor activity is unresolved
8. 2018 High

   Showing LCOR acts as a coactivator for PPARγ-RXRα heterodimers through noncanonical motifs demonstrated context-dependent switching between corepressor and coactivator functions.

   Evidence Luciferase reporter, Co-IP, Lcor-null mouse placenta analysis, AF2 domain mutagenesis

   PMID:29463649

   Open questions at the time

   • Full spectrum of genes coactivated by LCOR-PPARγ-RXRα is unknown
   • Structural basis for rexinoid-mediated inhibition of the interaction not resolved
9. 2022 High

   Establishing that LCOR binds ISREs and activates antigen processing/presentation genes independently of IFN signaling resolved how LCOR primes interferon-like responses and directly linked LCOR expression to tumor immunogenicity and immune checkpoint therapy responsiveness.

   Evidence Genetic overexpression/knockdown, ChIP at ISREs, flow cytometry for APM markers, in vivo tumor models with anti-PD-L1

   PMID:35301507

   Open questions at the time

   • Whether LCOR binds ISREs directly as a monomer or requires cofactors is unresolved
   • Structural basis of LCOR-ISRE recognition unknown
   • Whether PALI1 isoform also binds ISREs is not tested
10. 2025 Medium

    Demonstrating that LCOR interacts with RUNX1 to relieve RUNX1-mediated repression of PLCL1, inhibiting lipid accumulation and tumor progression in ccRCC, expanded LCOR's transcription factor partnership repertoire to include RUNX1.

    Evidence Co-IP, ChIP-qPCR, in vitro and in vivo functional assays in clear cell renal cell carcinoma models

    PMID:40083699

    Open questions at the time

    • Mechanism by which LCOR relieves RUNX1 repression (competitive displacement versus complex remodeling) is not established
    • Single study without independent replication
    • Generalizability beyond ccRCC untested

• The relationship between LCOR's PRC2.1/PALI1 function and its nuclear receptor corepressor and ISRE-binding activities remains mechanistically unresolved, as does the structural basis for LCOR's context-dependent switching between corepressor and coactivator roles.
• No structural model of full-length LCOR or its domains in complex with partners
• Isoform-specific functions (PALI1 versus shorter LCOR) not systematically dissected
• Genome-wide direct target map integrating all reported LCOR functions is lacking