Investigating the Involvement of RNA-Binding Protein ZFP36L1 in Breast Cancer Progression

ZFP36L1 is an RNA-binding protein which functions as a mRNA decaying protein through binding to the adenylate-uridylate rich elements (AREs) located in the 3’ untranslated region (3’UTR) of mRNAs, thereby mediating mRNA decaying. ZFP36L1 has emerged as a breast cancer driver gene, exhibiting tumour-suppressing properties. Notably, ZFP36L1 has been reported to be significantly mutated and downregulated in various tumour types. In our comprehensive study, we identified the novel role of the ZFP36L1 gene in regulating the tumorigenic traits of breast cancer, with a particular focus on hormone-positive and HER2-negative breast cancer subtypes. Furthermore, our research explored the therapeutic potential of ZFP36L1 in combination with tamoxifen, an antiestrogenic drug used as a standard treatment for the luminal breast cancer subtype. To explore functional aspects of ZFP36L1, we generated CRISPR Cas9-derived knockout of ZFP36L1 in the MCF-7 breast cancer cell line, characterised by luminal A molecular subtype. Functional assays demonstrated that the loss of ZFP36L1 in MCF-7 cells reduced the cell migration capacity and reduced cell population in the G1 phase of the cell cycle. Subsequent RNA-sequencing study and western blot analysis revealed that ZFP36L1 absence leads to upregulation of cell-cycle-related genes, including cyclin D1, CDK6 and tumour suppressor p53. Notably, cyclin D1 and CDK6 transcripts contain ARE sequences in the 3’ UTR, suggesting that they could be the direct targets of ZFP36L1 in MCF-7 cells. Similarly, we observed an upregulation of several ARE-rich genes associated with cell migration and extracellular matrix in the absence of ZFP36L1 in MCF-7 cells. These findings collectively illustrated that ZFP36L1 might be crucially involved in regulating key oncogenic transcripts encoding cell migration and extracellular matrix in MCF-7 cells. Our study also reported that ZFP36L1 depletion reduced the response of MCF-7 cells to tamoxifen, a standard drug used in endocrine therapy. Specifically, we found that while tamoxifen treatment decreased the cell migration capacity of MCF-7 cells, this effect was mitigated by the loss of ZFP36L1. Western blot analysis further confirmed that tamoxifen treatment reduced cyclin D1 expression in MCF-7 cells. Conversely, when ZFP36L1 expression was inhibited, the tamoxifen-induced reduction in cyclin D1 expression was decreased, resulting in increased cyclin D1 levels compared to tamoxifen-treated wild-type counterparts. Moreover, ZFP36L1 knockout MCF-7 cells exhibited higher IC50 values than WT MCF-7 cells. Conclusively, using molecular and transcriptomic approaches, our study convincingly demonstrates that ZFP36L1 exerts control over transcripts encoding key tumorigenic traits in MCF-7 cells and highlights the potential of synergistically combining ZFP36L1 with tamoxifen, offering potential treatment opportunities for hormone-positive breast cancer subtypes.