EYA1 phosphatase function is essential to drive breast cancer cell proliferation through cyclin D1

Area of Science:

• Molecular Biology
• Oncology
• Cell Biology

Background:

• Eyes Absent Homologue 1 (EYA1) is a phosphatase involved in the retinal determination gene network.
• Cyclin D1 regulates cell cycle progression by phosphorylating and inactivating the pRb protein.

Purpose of the Study:

• To investigate the role of EYA1 in breast cancer, specifically its association with cyclin D1 and its impact on tumor growth.
• To elucidate the molecular mechanisms by which EYA1 influences cell proliferation, apoptosis, and cyclin D1 expression.

Main Methods:

• Comparative analysis of EYA1 and cyclin D1 expression in normal breast tissue versus luminal B breast cancer.
• In vivo mouse models to assess EYA1's effect on tumor growth.
• In vitro studies to evaluate EYA1's impact on cellular proliferation, apoptosis, and contact-independent growth.
• Chromatin immunoprecipitation (ChIP) assays to determine EYA1 recruitment to the cyclin D1 promoter and its effect on transcriptional complex formation.

Main Results:

• EYA1 is overexpressed with cyclin D1 in the luminal B breast cancer subtype.
• EYA1 enhances breast tumor growth in vivo, an effect dependent on its phosphatase domain.
• EYA1 promotes cellular proliferation and cyclin D1 abundance while inhibiting apoptosis, with proliferation and cyclin D1 induction requiring its phosphatase activity.
• EYA1-mediated cyclin D1 transcription occurs via the AP-1-binding site and requires EYA1 phosphatase function, leading to recruitment of CBP, RNA polymerase II, and H3K9 acetylation.

Conclusions:

• EYA1 acts as an oncogene in luminal B breast cancer by upregulating cyclin D1 expression.
• The phosphatase activity of EYA1 is critical for its oncogenic functions, including promoting proliferation and cyclin D1 induction.
• EYA1 regulates cell-cycle control through the formation of transcriptional complexes at the cyclin D1 promoter.