CCNL1

CCNL1 (Cyclin L1) is a nuclear speckle-localized cyclin that partners with the kinase CDK11 to regulate cell cycle progression, particularly the G2-M transition, where defective CCNL1 accumulation shortens mitotic time (PMID:36278408). Its abundance is controlled by opposing post-translational mechanisms: it is targeted for ubiquitination and degradation by the SCF-FBXW7 E3 ligase complex, such that FBXW7 loss-of-function cells accumulate CCNL1 and become hypersensitive to CDK11 inhibition (PMID:36278408), while OGT-mediated O-GlcNAcylation stabilizes CCNL1 to support proliferation and cell cycle progression (PMID:41348282). Consistent with its nuclear speckle localization, CCNL1 co-localizes with the splicing-associated proteins TFIP11 and EWSR1, linking it to pre-mRNA splicing (PMID:19122807). Across cancer contexts CCNL1 levels modulate proliferation and survival signaling: it is a direct target of repressive microRNAs that constrain cell cycle progression (PMID:35260070), and its perturbation influences ERK/AKT/STAT3 survival signaling and chemotherapy resistance (PMID:35804923). Beyond these themes, the CCNL1-CDK11 link to RNA Polymerase II CTD phosphorylation and downstream transcriptional roles remains only partially characterized in the available corpus.

1. 2006 Low

   Establishing where CCNL1 acts in the cell was the first step toward a functional hypothesis; localizing it to nuclear speckles tied it to RNA processing machinery rather than bulk nucleoplasm.

   Evidence Immunofluorescence with a CCNL1-specific antibody in head and neck squamous carcinoma cells

   PMID:16598186

   Open questions at the time

   • Single immunofluorescence method without functional validation of a splicing role
   • No identification of associated splicing factors
2. 2008 Medium

   To connect speckle localization to a molecular function, CCNL1 was placed in physical proximity to splicing-associated proteins, supporting participation in pre-mRNA splicing.

   Evidence Yeast two-hybrid (cited prior work) and confocal co-localization with TFIP11 and EWSR1

   PMID:19122807

   Open questions at the time

   • No reciprocal Co-IP or functional splicing assay
   • Direct splicing substrates of a CCNL1-containing complex not defined
3. 2015 Low

   Cancer-context loss-of-function studies began testing whether CCNL1 levels drive proliferation; microRNA targeting linked CCNL1 downregulation to suppressed growth and cell cycle progression.

   Evidence miR-199b-5p mimic transfection with proliferation/invasion/apoptosis assays in Ewing's sarcoma cells

   PMID:26043836

   Open questions at the time

   • Direct target validation method not explicitly established
   • Downstream effector mechanism not defined
4. 2022 High

   The core cell cycle mechanism was defined: CCNL1 functions with CDK11 at G2-M and is degraded by SCF-FBXW7, establishing both a kinase partner and the ubiquitin-ligase controlling its turnover, and revealing a synthetic-lethal vulnerability.

   Evidence Genome-wide CRISPR synthetic-lethal screens, biochemical ubiquitination characterization, FBXW7-mutant cell cycle analysis, and CDK11 inhibitor treatment

   PMID:36278408

   Open questions at the time

   • Structural basis of CCNL1-CDK11 complex not resolved
   • Direct enzymatic substrates of the CCNL1-CDK11 kinase not enumerated
5. 2022 Medium

   CCNL1 was linked to chemotherapy response, showing that its loss rewires survival signaling and confers drug resistance.

   Evidence Genome-wide CRISPR knockout screening and targeted CCNL1 knockout with ERK/AKT/STAT3 pathway analysis in pancreatic cancer lines

   PMID:35804923

   Open questions at the time

   • Mechanism connecting CCNL1 loss to pathway activation not resolved
   • Limited to gemcitabine context
6. 2022 Medium

   A second microRNA axis reinforced CCNL1's role in promoting the G1/S transition via rescue experiments and in vivo validation.

   Evidence Luciferase reporter validation, CCK-8 and flow cytometry, plus xenograft model in prostate cancer cells

   PMID:35260070

   Open questions at the time

   • Molecular effectors downstream of CCNL1 in G1/S not defined
7. 2024 Low

   A transcriptional role was probed by testing whether CCNL1 supports viral gene expression through RNA Polymerase II CTD phosphorylation.

   Evidence RNAi knockdown in primary human hepatocytes, pull-down, and ChIP-PCR on HBV cccDNA (preprint)

   PMID:bio_10.1101_2024.10.23.619969

   Open questions at the time

   • Preprint; CTD kinase activity not reconstituted in vitro
   • Direct versus indirect contribution of CCNL1 to RNAPII Ser2 phosphorylation unresolved
8. 2025 Medium

   CCNL1 stability control was extended by identifying OGT-mediated O-GlcNAcylation as a stabilizing modification supporting proliferation.

   Evidence Co-IP, molecular docking, CCK-8, flow cytometry, and OGT/CCNL1 rescue experiments

   PMID:41348282

   Open questions at the time

   • O-GlcNAcylation not reconstituted in vitro
   • Modified residues not mapped
9. 2026 Low

   A direct interaction with DVL3 was reported to couple CCNL1 to NF-kB and PI3K/AKT signaling in breast cancer invasion and chemosensitivity.

   Evidence Co-IP, overexpression, Transwell/wound-healing assays, and rescue in breast cancer cells

   PMID:41632921

   Open questions at the time

   • Single Co-IP without reciprocal validation or reconstitution
   • Epistasis linking interaction to pathway activation not established

• Whether CCNL1's cell cycle, splicing, and signaling activities are mechanistically unified through a single CCNL1-CDK11 catalytic output remains unresolved.
• No structural model of the CCNL1-CDK11 complex
• Direct catalytic substrates and splicing targets not defined
• Mechanistic basis linking CCNL1 abundance to ERK/AKT/STAT3, NF-kB, and Wnt pathway outputs unknown