Chromatin modifications sequentially enhance ErbB2 expression in ErbB2-positive breast cancers

Area of Science:

• Oncology
• Epigenetics
• Molecular Biology

Background:

• ErbB2 (Human Epidermal growth factor Receptor 2) gene amplification in 20%-25% of breast cancers leads to overexpression, a target for therapies improving patient survival.
• Therapeutic resistance to ErbB2-targeted treatments can emerge, necessitating alternative therapeutic strategies.
• Epigenetic mechanisms, including histone modifications, can regulate oncogene expression and represent druggable targets.

Purpose of the Study:

• To investigate the role of histone modifications in ErbB2 overexpression, independent of gene amplification.
• To identify epigenetic regulators of ErbB2 activation and explore their therapeutic potential.

Main Methods:

• Analysis of histone modifications (H3K4me3, H3K9ac) on the erbB2 promoter in breast carcinomas.
• Targeting WD repeat domain 5 (Wdr5), a key regulator of H3K4me3 enrichment.
• Assessment of Wdr5 silencing effects on ErbB2 overexpression and tumor cell growth, alone and in combination with trastuzumab or chemotherapy.

Main Results:

• ErbB2-overexpressing breast cancers exhibit H3K4me3 enrichment on the erbB2 promoter.
• Receptor-amplified tumors show H3K9ac acquisition, dependent on H3K4me3.
• Targeting Wdr5 decreased ErbB2 overexpression by reducing H3K4me3 enrichment.
• Wdr5 silencing synergized with trastuzumab or chemotherapy to inhibit ErbB2-positive breast tumor cell growth.

Conclusions:

• Epigenetic modifications, specifically H3K4me3 and H3K9ac, are crucial in ErbB2 overexpression in breast cancer.
• Wdr5 is a critical epigenetic regulator of ErbB2 activation and a potential therapeutic target.
• Targeting Wdr5 offers a promising strategy to overcome resistance and enhance the efficacy of ErbB2-targeted therapies.