CRISPR/Cas9-Mediated Knockout of ZFP36L1 Impairs Cell Proliferation, Alters Cell-Cycle Progression, and Enhances DNA Damage Responses in MDA-MB-231 Triple-Negative Breast Cancer Cells

Background Zinc finger protein 36-like 1 (ZFP36L1) is an AU-rich element-binding RNA-binding protein that regulates post-transcriptional gene expression and has been implicated in tumor progression, cell-cycle regulation, and DNA damage responses. However, its functional role in triple-negative breast cancer (TNBC) remains poorly understood. This study investigated the effects of CRISPR/Cas9-mediated ZFP36L1 knockout on cell proliferation, doxorubicin (DOX) sensitivity, cell-cycle progression, and DNA damage responses in MDA-MB-231 TNBC cells. Methods Wild-type (WT) and CRISPR/Cas9-generated ZFP36L1 knockout (KO) MDA-MB-231 cells were cultured under standard conditions. Cellular proliferation was evaluated by cell counting over three weeks. Cell viability following DOX treatment was determined using the MTT assay, and half-maximal inhibitory concentration (IC50) values were calculated. Cell-cycle distribution was assessed by propidium iodide flow cytometry after 24 h of DOX exposure, while DNA damage was quantified by {gamma}-H2AX flow cytometric analysis. Statistical significance was determined using Student's t-test with P < 0.05 considered significant. Results ZFP36L1 knockout reduced the proliferative capacity of MDA-MB-231 cells compared with WT cells. Both cell lines exhibited dose-dependent decreases in viability following DOX treatment. KO cells demonstrated a higher mean IC50 than WT cells (9.64 vs. 8.40 M), indicating a trend toward reduced DOX sensitivity; however, this difference was not statistically significant (P = 0.569). Flow cytometric analysis revealed enhanced accumulation of KO cells in the S and G2/M phases following DOX treatment, suggesting altered cell-cycle checkpoint regulation. Furthermore, KO cells exhibited elevated basal {gamma}-H2AX expression and greater DOX-induced {gamma}-H2AX accumulation than WT cells, indicating increased DNA damage and impaired maintenance of genomic stability. Conclusions CRISPR/Cas9-mediated loss of ZFP36L1 suppresses proliferation, alters cell-cycle checkpoint dynamics, and enhances DNA damage accumulation in MDA-MB-231 TNBC cells. These findings indicate that ZFP36L1 plays a context-dependent role in regulating genomic stability and cellular responses to genotoxic stress, highlighting its potential as a biomarker and therapeutic target in triple-negative breast cancer.