Grant: Master's Award: Canada Graduate Scholarships

Background:Glucocorticoid stress hormones activate glucocorticoid receptors (GR), which can suppress BRCA1, a critical gene for DNA repair using accurate homologous recombination (HR). Suppressed BRCA1 increases reliance on error-prone nonhomologous end joining (NHEJ). Mutated BRCA1 increases the risk of estrogen receptor-negative (ER?) and progesterone receptor-negative (PR?) breast cancers. High GR levels may improve outcomes in ER+ tumours but worsen prognosis in ER? tumours. Mechanisms linking stress and cancer initiation are unclear. This study explores how stress-activated GR affects BRCA1 expression and DNA repair in breast cancer subtypes. Objectives & Hypothesis:This research will assess how stimulated GR alters BRCA1 expression in ER+ and ER? breast cancers and investigate how GR-mediated BRCA1 suppression impacts DNA repair. I hypothesize that stimulated GR reduces BRCA1 gene expression and increases NHEJ, especially in ER? tumours. Methods:Breast cancer cell lines MCF-7 (ER+/PR+) and MCF-10A (ER?/PR?) will be treated with hydrocortisone (GR-activator), RU-486 (GR-blocker), ethanol control or onapristone (PR-antagonist). Western blotting and RT-qPCR will measure BRCA1 expression, and a luciferase reporter assay will measure how stimulated GR affects promoter activity. DNA repair efficiency will be assessed using NHEJ and HR assays with green (repaired DNA) and red (unrepaired DNA) fluorescent signals. CRISPR-Cas9 GR knockouts will study DNA repair differences in luminal differentiated vs progenitor breast cancer cells. Significance:This study contributes to mental health and cancer research in Canada. Exploring how stress-induced GR activation impacts BRCA1 expression and DNA repair could inform stress-management strategies and new breast cancer treatments.