Downregulation of EZH2 decreases growth of estrogen receptor-negative invasive breast carcinoma and requires BRCA1

Carcinoma of the breast with medullary-like features: diagnostic challenges and relationship with BRCA1 and EZH2 functions

This case presentation reviews the histologic distinction between pure medullary carcinoma and breast carcinomas with medullary-like features. This particular case prompts us to analyze the relationship among medullary carcinoma, basal-like breast carcinomas and carcinomas associated with germline BRCA1 mutations. In addition to now well-defined features, such as expression of high-molecular-weight cytokeratins and EGFR (epidermal growth factor receptor), basal-like tumors have a deficiency or dysfunction of BRCA1. This association in part explains the histologic features of BRCA1-associated breast cancers. Recent studies in our laboratory demonstrate that BRCA1 protein is regulated by a recently described gene, EZH2. These concepts illustrate the important relationships among histopathologic features; genomic profile; single gene abnormalities, such as BRCA1 and EZH2; and growth regulation in this subset of breast carcinomas.

Carcinoma of the breast with medullary-like features: diagnostic challenges and relationship with BRCA1 and EZH2 functions

This case presentation reviews the histologic distinction between pure medullary carcinoma and breast carcinomas with medullary-like features. This particular case prompts us to analyze the relationship among medullary carcinoma, basal-like breast carcinomas and carcinomas associated with germline BRCA1 mutations. In addition to now well-defined features, such as expression of high-molecular-weight cytokeratins and EGFR (epidermal growth factor receptor), basal-like tumors have a deficiency or dysfunction of BRCA1. This association in part explains the histologic features of BRCA1-associated breast cancers. Recent studies in our laboratory demonstrate that BRCA1 protein is regulated by a recently described gene, EZH2. These concepts illustrate the important relationships among histopathologic features; genomic profile; single gene abnormalities, such as BRCA1 and EZH2; and growth regulation in this subset of breast carcinomas.

Tumour-initiating cells: challenges and opportunities for anticancer drug discovery

The hypothesis that cancer is driven by tumour-initiating cells (popularly known as cancer stem cells) has recently attracted a great deal of attention, owing to the promise of a novel cellular target for the treatment of haematopoietic and solid malignancies. Furthermore, it seems that tumour-initiating cells might be resistant to many conventional cancer therapies, which might explain the limitations of these agents in curing human malignancies. Although much work is still needed to identify and characterize tumour-initiating cells, efforts are now being directed towards identifying therapeutic strategies that could target these cells. This Review considers recent advances in the cancer stem cell field, focusing on the challenges and opportunities for anticancer drug discovery.

BRCA1-deficient mammary tumor cells are dependent on EZH2 expression and sensitive to Polycomb Repressive Complex 2-inhibitor 3-deazaneplanocin A

Introduction

Treatment of breast cancer is becoming more individualized with the recognition of tumor subgroups that respond differently to available therapies. Breast cancer 1 gene (BRCA1)-deficient tumors are usually of the basal subtype and associated with poor survival rates, highlighting the need for more effective therapy.

Methods

We investigated a mouse model that closely mimics breast cancer arising in BRCA1-mutation carriers to better understand the molecular mechanism of tumor progression and tested whether targeting of the Polycomb-group protein EZH2 would be a putative therapy for BRCA1-deficient tumors.

Results

Gene expression analysis demonstrated that EZH2 is overexpressed in BRCA1-deficient mouse mammary tumors. By immunohistochemistry we show that an increase in EZH2 protein levels is also evident in tumors from BRCA1-mutation carriers. EZH2 is responsible for repression of genes driving differentiation and could thus be involved in the undifferentiated phenotype of these tumors. Importantly, we show that BRCA1-deficient cancer cells are selectively dependent on their elevated EZH2 levels. In addition, a chemical inhibitor of EZH2, 3-deazaneplanocin A (DZNep), is about 20-fold more effective in killing BRCA1-deficient cells compared to BRCA1-proficient mammary tumor cells.

Conclusions

We demonstrate by specific knock-down experiments that EZH2 overexpression is functionally relevant in BRCA1-deficient breast cancer cells. The effectiveness of a small molecule inhibitor indicates that EZH2 is a druggable target. The overexpression of EZH2 in all basal-like breast cancers warrants further investigation of the potential for targeting the genetic make-up of this particular breast cancer type.