CRISPR/Cas9-Mediated BRCA1 Knockdown Adipose Stem Cells Promote Breast Cancer Progression

The tumor microenvironment within the breast is rich in adipose elements. The interaction between adipose cells and breast cancer is poorly understood, particularly as it pertains to patients with genetic susceptibility to breast cancer. This study focuses on the phenotype of human adipose-derived stem cells with the BRCA1 mutation and the effect they may have on breast cancer cell behavior.

CRISPR/Cas9 was used to generate de novo BRCA1-knockdown human adipose-derived stem cells. The effect of the BRCA1 knockdown on the adipose-derived stem cell phenotype was compared to wild-type adipose-derived stem cells and patient-derived breast adipose-derived stem cells with known BRCA1 mutations. Interactions between adipose-derived stem cells and the MDA-MB-231 breast cancer cell line were evaluated.

BRCA1-knockdown adipose-derived stem cells stimulated MDA-MB-231 proliferation (1.4-fold increase on day 4; p = 0.0074) and invasion (2.3-fold increase on day 2; p = 0.0171) compared to wild-type cells. Immunofluorescence staining revealed higher levels of phosphorylated ataxia telangiectasia-mutated activation in BRCA1-knockdown cells (72.9 ± 5.32 percent versus 42.9 ± 4.97 percent; p = 0.0147), indicating higher levels of DNA damage. Beta-galactosidase staining demonstrated a significantly higher level of senescence in BRCA1-knockdown cells compared with wild-type cells (7.9 ± 0.25 percent versus 0.17 ± 0.17 percent; p < 0.0001). Using quantitative enzyme-linked immunosorbent assay to evaluate conditioned media, the authors found significantly higher levels of interleukin-8 in BRCA1-knockdown cells (2.57 ± 0.32-fold; p = 0.0049).

The authors show for the first time that the BRCA1 mutation affects the adipose-derived stem cell phenotype. Moreover, CRISPR/Cas9-generated BRCA1-knockdown adipose-derived stem cells stimulate a more aggressive behavior in breast cancer cells than wild-type adipose-derived stem cells. This appears to be related to increased inflammatory cytokine production by means of a DNA damage-mediated cell senescence pathway.