BRCA1 protects cells against oxidative stress upregulating HO-1 transcription.

LABANCA E; DE LUCA P; GUERON G; ZALAZAR F; VAZQUEZ E; DE SIERVI A

Edimburgo

Congreso; 7th INTERNATIONAL MEETING ON HEME OXYGENASE & RELATED ENZYMES; 2012

DNA damage increases gene mutations and chromosomal aberrations disrupting normal cell growth. The tumor suppressor Breast Cancer Susceptibility Gene 1 (BRCA1) is essential to prevent DNA damage given its role in genomic stability maintenance. Recently, we reported that BRCA1 induces genes involved in stress response and resistance to genotoxic agents in prostate cancer (PCa). In addition, BRCA1/Nrf2 protects cells against oxidative stress genes carrying antioxidant response elements (ARE). Since Heme oxygenase 1 (HO-1), crucial in the maintenance of cellular homeostasis, contains ARE sites in its promoter, our goal was to investigate HO-1 transcriptional regulation by BRCA1/Nrf2. We generated BRCA1 over-expressing or depleted stable transfected PCa cell lines. HO-1 luciferase reporter assays showed that BRCA1 over-expressing PCa cells significantly induced HO-1 promoter activity. As expected, Nrf2 also induced HO-1 promoter activity in PCa cells. BRCA1 over-expressing cells also displayed increased HO-1 mRNA and protein levels compared to control cells. Consistently, HO-1 induction was avoided after BRCA1 depletion by shRNA. To study if BRCA1 modulates HO-1 function, we determined mRNA levels of HO-1 target genes by RT-qPCR. BRCA1 over-expression turned-off downstream targets of HO-1 (MMP9, uPA and Cyclin D1). Xenograft studies using PC3 cells showed that BRCA1 depletion increased tumor growth rate. Accordingly, BRCA1 depleted tumors showed lower levels of HO-1 mRNA with highly increased expression of MMP9, uPA and Cyclin D1. Collectively, these results indicate that BRCA1 might trigger an anti-oxidative stress gene signature via transcriptional activation of HO-1, determining its ultimate effect on cell survival.