CCNL1 encodes cyclin L1, a regulatory component of the cyclin L1-CDK11 complex that controls transcription and pre-mRNA splicing processes. The protein localizes to nuclear speckles, consistent with its role in RNA processing 1. CCNL1 functions as a substrate of the SCF-FBXW7 E3 ligase complex, and the CCNL1-CDK11 complex is critical during the G2-M phase of the cell cycle, where defective CCNL1 accumulation leads to shortened mitotic time 2. In prostate cancer, CCNL1 forms a complex with CDK19 and facilitates RNA polymerase II serine-2 phosphorylation, promoting transcription of metastasis-related genes 3. CCNL1 demonstrates oncogenic properties in multiple cancer types, being overexpressed in 57% of head and neck squamous cell carcinomas with amplification in 26% of tumors 1. In osteosarcoma, CCNL1 promotes cell proliferation, migration, and adriamycin resistance through activation of the PI3K/AKT-mTOR pathway 4. Genetic variants near CCNL1 are associated with birth weight regulation and diabetic retinopathy risk 56. The synthetic lethality between FBXW7 mutations and CCNL1 dependency suggests potential therapeutic vulnerabilities in FBXW7-deficient cancers through CDK11 inhibition 2.