Targeting Cell Death Mechanism Specifically in Triple Negative Breast Cancer Cell Lines

The carcinogenic capacity of arsenic in normal epithelial breast cells and double-positive breast cancer cells

Background and aims

The carcinogenic effect of arsenic is a subject of controversy in relation to breast cancer. In our current research, we aimed to simulate the effects of chronic low-level arsenic exposure on breast cells by intoxicating MCF-10A and MCF-7 cells with 1 μM Arsenic trioxide (As2O3) for 3 weeks (3w) and 6 weeks (6w), respectively.

Methods

We assessed the cellular responses to As2O3 through various assays, including confocal fluorescence microscopy, flow cytometry for cell cycle analysis, Transwell invasion assay, scratch assay, and colony assay. Additionally, we analyzed the mutation burden in all the exposed cells by using the next generation sequencing technology.

Results

Our findings indicate that As2O3 has a minor carcinogenic effect in normal cells, with no definitive evidence of malignant transformation observed after 6 weeks of exposure. In the case of breast cancer cells, As2O3 exhibits a dual effect, both inhibitory and stimulatory. It leads to reduced colony formation ability at 6 weeks, while enhancing the cells' ability for invasion. The mutations triggered by As2O3 exposure are distributed across genes with both tumor-suppressive and oncogenic functions. Five mutations are common to both cell lines, involving the following genes: Kinase Insert Domain Receptor (KDR) (c.798+54G>A), Colony Stimulating Factor 1 Receptor (CSF1R) (c.*37AC>C, c.*35C>TC), SWI/SNF-Related Matrix-Associated Actin-Dependent Regulator of Chromatin Subfamily B Member 1 (SMARCB1) (c.1119-41C>T), and Fms-like Tyrosine Kinase 3 (FLT3) (c.1310-3T>C). Additionally, Human Epidermal Growth Factor Receptor 4 (ERBB4/HER4) (c.421+58A>G) and Human Epidermal Growth Factor Receptor 2 (HER2/ERBB2) (c.2307+46A>G) mutations were exclusively found in MCF-10A cells exposed to As2O3. Furthermore, MCF-7 cells exhibited unique mutations in the KIT Proto-Oncogene (KIT) (c.1594G>A) and TP53 (c.215C>G).

Conclusion

In summary, our study reveals that a 6-weeks exposure to arsenic has a limited carcinogenic effect in normal breast cells and a dual role in breast cancer cells.

OTUD7B knockdown inhibits the proliferation and stemness of breast cancer cells by destabilizing FOXM1

Breast cancer is a leading cause of cancer-related death in women worldwide; therefore, there is an urgent need to develop novel therapies and drugs that prolong the survival and improve the quality of life of patients with breast cancer. In the present study, the effects and underlying mechanisms of OTU domain-containing 7B (OTUD7B) knockdown on breast cancer were investigated using MDA-MB-468, MDA-MB-453 and MCF7 cell lines. The results of Cell Counting Kit 8, colony formation and tumor sphere formation experiments showed that OTUD7B knockdown caused a significant decrease in the proliferation and sphere formation ability of MDA-MB-468, MDA-MB-453 and MCF7 cells in vitro. Moreover, western blotting results showed that CD44, EpCAM, SOX2 and Nanog protein levels were significantly decreased following OTUD7B knockdown. These findings indicated that OTUD7B knockdown reduced the proliferation and stemness of breast cancer cells. Co-immunoprecipitation assays demonstrated that OTUD7B interacted with forkhead box protein M1 (FOXM1) and reduced the polyubiquitylation of FOXM1 in breast cancer cells; accordingly, FOXM1 protein levels were significantly decreased by OTUD7B knockdown. Furthermore, the overexpression of FOXM1 reduced the inhibitory effects of OTUD7B knockdown on breast cancer cells. The findings of the present study provide new insights into the oncogenic role of OTUD7B in breast cancer and indicate that OTUD7B may serve as a therapeutic target for breast cancer.