Adelaide University: DNA enhancer HRR INT3 helps androgen receptor restrain ER+ breast cancer cells

Researchers at Adelaide University's School of Medicine, the South Australian immunoGENomics Cancer Institute (SAiGENCI) and SAHMRI, together with colleagues at the University of Bordeaux, identified a regulatory DNA region that supports the tumour-suppressor activity of the androgen receptor (AR) in oestrogen receptor-positive (ER⁺) breast cancer. The work, done in cell models and clinical specimens, was published in npj Breast Cancer doi.orgnpj Breast Cancerdoi.orgOpen source ↗. According to the university's release, up to 80% of breast cancers are ER⁺.

ZBTB16 expression and the androgen receptor

The AR represses cell cycle genes and restrains proliferation in ER⁺ breast cancer. The team had earlier proposed ZBTB16 as a candidate gene regulated by the AR. In clinical cohorts, ZBTB16 mRNA was lower in breast tumours than in normal tissue, and higher expression correlated with better survival in ER⁺ disease doi.orgnpj Breast Cancerdoi.orgOpen source ↗. Androgen treatment raised ZBTB16 protein in ER⁺ breast cancer cell lines doi.orgnpj Breast Cancerdoi.orgOpen source ↗.

However, knockdown or overexpression of ZBTB16 did not detectably change the anti-proliferative effect of the AR in the models tested doi.orgnpj Breast Cancerdoi.orgOpen source ↗. "The surprising finding was that ZBTB16 itself was not responsible for the growth-suppressing effect," said Dr Amy Dwyer of Adelaide University.

The HRR INT3 enhancer

The AR bound a conserved hormone response region in intron 3 of the ZBTB16 locus, named HRR INT3, in breast cancer models and clinical specimens. Binding was accompanied by androgen-dependent H3K27ac enrichment, consistent with an AR-responsive enhancer doi.orgnpj Breast Cancerdoi.orgOpen source ↗.

Using CRISPR/Cas9, the researchers deleted HRR INT3. The deletion prevented AR-dependent induction of ZBTB16, impaired AR-mediated growth suppression and attenuated activation of canonical AR target genes doi.orgnpj Breast Cancerdoi.orgOpen source ↗. Baseline proliferation increased in breast and prostate cancer cells, with upregulation of E2F targets doi.orgnpj Breast Cancerdoi.orgOpen source ↗. The authors describe HRR INT3 as a lineage-conserved enhancer contributing to AR-mediated tumour suppression across AR⁺ cancers doi.orgnpj Breast Cancerdoi.orgOpen source ↗.

"This tells us that the enhancer is doing much more than simply controlling ZBTB16," said co-author Dr Zeyad Nassar of SAiGENCI and SAHMRI. The researchers note that treatments activating the AR are already being investigated for advanced ER⁺ breast cancer, and say that understanding the molecular machinery behind the effect is important.