The E2F4 Knockout NCI-H1975 Polyclonal Cells represent a CRISPR/Cas9-edited polyclonal knockout cell population derived from the NCI-H1975 human lung adenocarcinoma cell line, engineered to disrupt the E2F4 gene. E2F4 encodes a transcriptional repressor that regulates cell cycle progression from G0 to G1 phase by forming repressor complexes with pocket proteins p130 (RBL2) and p107 (RBL1) to silence E2F target genes. This knockout model enables loss-of-function studies of E2F4-mediated transcriptional repression in a physiologically relevant lung cancer background.
The parental NCI-H1975 cell line is a well-established model of non-small cell lung adenocarcinoma, originally isolated from a non-smoking female patient. These epithelial cells harbor activating EGFR mutations (L858R and T790M) that drive constitutive kinase signaling and are commonly used in research on EGFR-targeted therapies, tyrosine kinase inhibitor resistance, and lung cancer pathogenesis. The presence of these oncogenic drivers provides a defined genetic context for dissecting cell cycle regulatory networks.
Mechanistically, E2F4 functions as a key component of the DREAM complex and RB family pathway, where it heterodimerizes with TFDP1 or TFDP2 and associates with RBL2 (p130) or RBL1 (p107) to recruit chromatin modifiers such as HDAC1 and SIN3A. This repressor module silences E2F-responsive genes including CCNA2, CCNE1, CDC6, MCM5, and PCNA, thereby restraining entry into S phase. E2F4 activity is modulated by upstream signals such as Cyclin D-CDK4/6-mediated phosphorylation, TGF-beta signaling, and p53-dependent checkpoints, which collectively relieve repression and allow cell cycle progression. Disruption of E2F4 thus perturbs this checkpoint, removing a negative regulatory brake on proliferation.
In the NCI-H1975 background, where EGFR signaling converges on Cyclin D-CDK4/6 activation and downstream RB pathway inactivation, E2F4 knockout may synergistically enhance dysregulation of the G1/S restriction point. This compound perturbation??combining oncogenic EGFR mutations with loss of a key transcriptional repressor??mimics aspects of RB pathway inactivation, potentially altering sensitivity to CDK4/6 inhibitors and EGFR tyrosine kinase inhibitors. The polyclonal nature of the knockout population captures a spectrum of editing events, providing a heterogeneous model that can uncover dominant phenotypic effects and facilitate studies of clonal dynamics under drug pressure.
This model enables quantitative cell cycle analysis via flow cytometry, expression profiling of E2F targets (CCNA2, CCNE1, etc.) by RT-qPCR and RNA-seq, ChIP-qPCR assessment of E2F4 binding, and Western blot detection of E2F4 and pocket proteins. Functional assays such as MTT or BrdU proliferation measurements and drug sensitivity testing with EGFR inhibitors (e.g., osimertinib, gefitinib) reveal phenotypic consequences. Co-immunoprecipitation can interrogate E2F4 complex dynamics. For additional information, contact Ascent Research.
