Flash Talk + Poster Presentation 37th Lorne Cancer Conference 2025

Sex Hormone-Mediated Regulation of ZBTB16, a Candidate Tumour Suppressor in Estrogen Receptor Positive Breast Cancer (#268)

Maliha Wajahat 1 , Carmela Ricciardelli 1 2 , Amy Dwyer 1 , Wayne Tilley 1 , Theresa Hickey 1
  1. Dame Roma Mitchell Cancer Research Laboratories, Adelaide Medical School, Faculty of Health and Medical Sciences, , University of Adelaide, Adelaide, SA, Australia
  2. The Reproductive Cancer Group, Adelaide Medical School, Robinson Research Institute, Adelaide , SA, Australia, University of Adelaide , Adelaide , SA, Australia

The androgen receptor (AR) and progesterone receptor (PR) act as tumour suppressors in ER+ breast cancers [1-3] but AR and PR target genes that mediate tumour suppression have yet to be identified and validated. Herein, we analysed ChIP-seq and RNA-seq data from ER+ breast cancer models treated with estrogen, androgen, or progesterone and identified ZBTB16 as a candidate AR and PR target gene likely to have a role in tumour suppression. ZBTB16 was among AR- and PR-associated gene signatures predicting better outcomes for ER+ breast cancer [1, 2] and has been implicated as a tumour suppressor in other cancers [4-6]. Analysis of clinical datasets revealed higher expression of ZBTB16 in normal versus malignant breast tissues and in early versus advanced stages of breast cancer, consistent with a tumour suppressive role. A hormone regulatory element (HRE) within intron 3 of ZBTB16 is bound by AR or PR and is associated with strong H3K27ac signals, indicative of an active enhancer. CRISPR-Cas9 was used to delete this HRE in ER+ T-47D cells, generating HRE knockout (KO) clonal lines with ER, PR and AR expression comparable to parental cells. Androgen-induced ZBTB16 expression (mRNA, protein) and AR-mediated growth suppression was lost in HRE-KO lines, but progesterone-induced activity remained intact due to a PR-specific upstream enhancer. RNA-seq confirmed impaired AR signalling in HRE-KO cells, but siRNA-mediated knockdown of androgen-induced ZBTB16 in parental cells did not affect AR-mediated growth suppression nor induction of other AR-regulated genes. Collectively, these data validate ZBTB16 as a direct AR and PR and target gene in ER+ breast cancer but indicate differential regulatory mechanisms. The intron 3 HRE is only critical for AR-mediated induction of ZBTB16, which accords with a study of prostate cancer cells [7]. Our data further indicates that this HRE plays a larger role in AR signalling and AR-mediated tumour suppression than up-regulation of ZBTB16 in a cell line context. The clinical data analysis suggests that AR or PR-mediated regulation of ZBTB16 may be more important at earlier stages of ER+ breast cancer and may be useful as a biomarker of response to AR or PR agonist drugs.

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