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 Internacional Meeting on Heme Oxygenase & Related Enzymes; 2012

DNA damage increases gene mutations and chromosomal aberrations disrupting normal growth control and favoring tumor development. The tumor suppressor Breast Cancer Susceptibility Gene 1 (BRCA1) is essential to prevent DNA damage accumulation due to its role in genomic stability maintenance. Recently, we reported that BRCA1 induces genes involved in stress response and resistance to genotoxic agents. In addition, other authors showed that BRCA1/Nrf2 protect cells against oxidative stress upregulating genes carrying antioxidant response elements (ARE). Since Heme oxygenase 1 (HO-1), an antioxidant enzyme 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 prostate cancer cell lines (PC3 or LNCaP). Using HO-1 luciferase reporter assays, we found that BRCA1 over-expressing PC3 cells significantly induced HO-1 promoter activity. As expected, Nrf2 also induced HO-1 promoter activity in PC3 cells. BRCA1 over-expressing cells also showed increased HO-1 mRNA and protein levels compared to control cells. Consistently, HO-1 induction was avoided after BRCA1 depletion by shRNA in both, PC3 and LNCaP cells. Furthermore, to study if BRCA1 modulates HO-1 function, we determined mRNA levels of HO-1 target genes by RT-qPCR. Accordingly, BRCA1 over-expression turned off some negative targets of HO-1, such as MMP9, uPA and Cyclin D1. Xenograft studies using PC3 cells showed that BRCA1 depletion resulted in increased tumor growth rate (12 fold induction). Surprisingly, BRCA1 depleted tumors showed low levels of HO-1 mRNA but highly increased expression of MMP9, uPA and Cyclin D1. Overall, our results suggest that BRCA1 might protect cells against oxidative stress via transcriptional activation of HO-1.