CCNG2

CCNG2 (cyclin G2) is an atypical cyclin that functions as a growth-inhibitory, tumor-suppressive regulator of the G0/G1 transition across diverse epithelial and neural cancers (PMID:24248541, PMID:24307622, PMID:29720957). Unlike its nuclear paralog cyclin G1, CCNG2 protein localizes predominantly to the cytoplasm (PMID:10216255). Forced expression of CCNG2 imposes G0/G1 arrest, reduces survival, and lowers CDK2 protein levels, indicating that it restrains cell cycle progression in part by promoting CDK2 degradation (PMID:24248541, PMID:24307622, PMID:24289643); in glioma it additionally induces apoptosis and suppresses xenograft tumor growth, and its expression is held down by AKT activity such that CCNG2 knockdown reverses the anti-proliferative effect of AKT inhibition (PMID:29720957). CCNG2 acts as a convergence node controlled by multiple transcriptional and post-transcriptional inputs: it is directly transactivated by PTOV1 through an AT-hook-like motif in its promoter (PMID:30922918), by the androgen-receptor-driven clock factor BHLHE40 as part of an AR–BHLHE40–CCNG2 axis mediating androgen-induced senescence (PMID:38902772), and by PATZ1, whose abundance is limited by SMURF1-mediated degradation; loss of this input derepresses β-catenin signaling, while CCNG2 overexpression reduces β-catenin and suppresses malignant phenotypes (PMID:39617210). CCNG2 is repressed epigenetically by the LINC00460–EZH2/LSD1 complex at its promoter (PMID:32059342) and post-transcriptionally by multiple miRNAs, most prominently miR-1246 and miR-17-5p, which directly target its 3'UTR to license proliferation, invasion, and drug resistance (PMID:34598688, PMID:34497267, PMID:29216623, PMID:39285403).

1. 1999 Medium

   Established that cyclin G2 is a distinct cyclin family member with cytoplasmic, rather than nuclear, localization, distinguishing it functionally from cyclin G1.

   Evidence GFP fusion live imaging in NIH3T3 cells plus genomic cloning and FISH mapping of mouse Ccng2

   PMID:10216255

   Open questions at the time

   • Does not define a molecular function or interaction partner
   • Localization shown only for overexpressed fusion protein in one cell type
2. 2013 Medium

   Defined CCNG2 as a growth suppressor by showing its overexpression forces G0/G1 arrest and lowers CDK2 across gastric, colorectal, and thyroid cancer cells, linking it to CDK2 turnover.

   Evidence Lentiviral overexpression with MTT, flow cytometry cell cycle analysis, and CDK2 Western blot in SGC-7901, SW480, and K1 lines

   PMID:24248541 PMID:24289643 PMID:24307622

   Open questions at the time

   • CDK2 degradation inferred from protein loss, not directly demonstrated mechanistically
   • No physical CCNG2–CDK2 interaction shown
   • Gain-of-function only
3. 2018 Medium

   Placed CCNG2 downstream of AKT signaling, showing AKT suppresses CCNG2 and that CCNG2 is required for the anti-proliferative effect of AKT inhibition in glioma.

   Evidence Overexpression/knockdown, MK-2206 AKT inhibitor treatment, colony formation, flow cytometry, and murine xenograft

   PMID:29720957

   Open questions at the time

   • Mechanism by which AKT lowers CCNG2 (transcriptional vs post-transcriptional) not resolved
   • Single lab
4. 2019 Medium

   Identified the first direct transcriptional activator of CCNG2, showing PTOV1 binds its promoter through an AT-hook-like motif.

   Evidence ChIP, EMSA, promoter mutation analysis, and immunohistochemistry

   PMID:30922918

   Open questions at the time

   • Functional consequence of PTOV1-driven CCNG2 on cell cycle not directly tested in this study
   • Single lab
5. 2024 High

   Integrated CCNG2 into androgen-receptor and clock signaling by defining an AR→BHLHE40→CCNG2 axis driving androgen-induced senescence as a tumor-suppressive program.

   Evidence RNA-seq, ChIP-seq, Co-IP, translocation analysis, xenograft, and 3D spheroids in prostate cancer

   PMID:38902772

   Open questions at the time

   • Direct BHLHE40 occupancy at the CCNG2 promoter inferred from ChIP-seq within one study
   • Generalizability beyond prostate cancer untested
6. 2024 Medium

   Connected CCNG2 to Wnt/β-catenin control via a SMURF1→PATZ1→CCNG2 cascade, showing CCNG2 restrains β-catenin and malignant phenotypes.

   Evidence Overexpression, SMURF1/PATZ1 knockdown, promoter/luciferase assays, T cell co-culture, and Wnt agonist rescue in esophageal squamous cell carcinoma

   PMID:39617210

   Open questions at the time

   • Mechanism by which CCNG2 reduces β-catenin not defined
   • Single lab
7. 2020 Medium

   Showed CCNG2 is epigenetically silenced, with LINC00460 recruiting EZH2 and LSD1 to its promoter to promote tumor proliferation.

   Evidence RNA-seq, RIP, ChIP, Western blot, and knockdown/overexpression with in vitro and in vivo proliferation assays in gastric cancer

   PMID:32059342

   Open questions at the time

   • Direct chromatin mark changes at the CCNG2 locus not fully resolved
   • Single lab
8. 2014 Medium

   Established post-transcriptional repression of CCNG2 by miR-1246, linking its loss to drug resistance and cancer stem cell-like behavior.

   Evidence miRNA overexpression/knockdown, drug sensitivity and sphere formation assays, in vivo tumorigenicity in pancreatic cancer

   PMID:25117811

   Open questions at the time

   • Direct 3'UTR binding not shown in this study
   • Single lab
9. 2017 Medium

   Demonstrated direct miR-1246 targeting of the CCNG2 3'UTR and intercellular transfer of this repression via exosomes from metastatic to non-malignant cells.

   Evidence Luciferase reporter assay, Western blot, exosome transfer, invasion/viability assays in breast cell models

   PMID:29216623

   Open questions at the time

   • Single lab
   • Endogenous stoichiometry of EV-delivered miR-1246 unaddressed
10. 2021 Medium

    Expanded the miRNA control of CCNG2, showing METTL3-driven maturation of miR-1246 and direct miR-17-5p 3'UTR targeting both repress CCNG2 to drive cell cycle progression.

    Evidence Dual-luciferase reporter, RT-qPCR, Western blot, flow cytometry, METTL3 knockdown/overexpression, and xenograft in ovarian and HNSCC models

    PMID:34497267 PMID:34598688

    Open questions at the time

    • Relative contribution of each miRNA to endogenous CCNG2 levels not quantified
    • Single lab per study
11. 2024 Medium

    Showed extracellular vesicle-delivered miR-1246 directly represses CCNG2 to enhance melanoma invasion, reinforcing CCNG2 loss as a pro-invasive event transferable between cells.

    Evidence NGS, luciferase reporter, Matrigel spheroid invasion, Boyden chamber, and sphingomyelinase inhibition of EV secretion

    PMID:39285403

    Open questions at the time

    • Single lab
    • In vivo metastasis not tested

• How cytoplasmic CCNG2 mechanistically promotes CDK2 degradation and lowers β-catenin—its direct protein partners and any CDK-binding or adaptor activity—remains undefined.
• No direct CCNG2 binding partner identified
• No structural model
• CDK2 and β-catenin reduction shown only at the protein-level readout, not biochemically dissected