YAP, CTGF and Cyr61 are overexpressed in tamoxifen-resistant breast cancer and induce transcriptional repression of ERα

About 70% of breast cancers overexpress estrogen receptor alpha (ER alpha, encoded by ESR1). Tamoxifen, a competitive inhibitor of estrogen that binds to ER, has been widely used as a treatment for ER-positive breast cancer. However, 20-30% of breast cancer is resistant to tamoxifen treatment. The mechanisms underlying tamoxifen resistance remain elusive. We found that Yes-associated protein (YAP; also known as YAP1), connective tissue growth factor (CTGF; also known as CCN2) and cysteine-rich angiogenic inducer 61 (Cyr61; also known as CCN1) are overexpressed, while ER alpha is downregulated in tamoxifen-resistant breast cancer. Inhibition of YAP, CTGF and Cyr61 restored ER alpha expression and increased sensitivity to tamoxifen. Overexpression of YAP, CTGF, and Cyr61 led to downregulation of ERa and conferred resistance to tamoxifen in ER-positive breast cancer cells. Mechanistically, CTGF and Cyr61 downregulated ER alpha expression at the transcriptional level by directly binding to the regulatory regions of the ER alpha-encoding gene, leading to increased tamoxifen resistance. Also, CTGF induced Glut3 (also known as SLC2A3) expression, leading to increased glycolysis, which enhanced cell proliferation and migration in tamoxifen-resistant cells. Together, these results demonstrate a novel role of YAP, CTGF and Cyr61 in tamoxifen resistance and provide a molecular basis for their function in tamoxifen-resistant breast cancer.

Automated summary

The study found that in tamoxifen-resistant breast cancer, YAP, CTGF, and Cyr61 are overexpressed while ER alpha is downregulated. Inhibition of YAP, CTGF, and Cyr61 can restore ER alpha expression and increase sensitivity to tamoxifen. CTGF and Cyr61 downregulate ER alpha expression at the transcriptional level by directly binding to the regulatory regions of the ER alpha-encoding gene, leading to increased tamoxifen resistance.