Abstract 4559: Phosphodeficient NRF1 mutant suppresses the susceptibility of the breast epithelial cells to develop tumors when exposed to estrogen - a major breast cancer risk factor

Although several nuclear regulatory proteins may be targeted by estrogen, our efforts have focused on the redox nuclear respiratory factor-1 (NRF-1), because our recent study showed that NRF-1 gene expression significantly increases with the progression of breast tumor grades. NRF-1 overexpression supported in vitro tumor formation. To determine if NRF-1 is required for 17 beta estradiol (E2)-induced neoplastic phenotype, we have generated NRF-1 mutants by site directed mutagenesis. We have generated stable clones that express NRF-1 mutant. The in vitro tumor formation was detected by anchorage independent growth and 3D spheroid assays. NRF-1 overexpression enhanced in vitro tumor spheroid formation, cell migration and cell invasion. Our flow cytometry analysis showed that overexpression of wild-type NRF-1 increased the percent of transformed MCF-10A cells in S phase compared to vector alone. Dominant negative NRF-1 protein showed reduction in the tumor formation. In addition, shRNA targeting NRF-1 resulted in the inhibition of anchorage independent growth of MCF-10A cells in both vehicle control and E2-treated cells. Since NRF-1 is a substrate of the kinase AKT, we determined whether NRF-1 phosphorylation was increased in MCF-10A cells after treatment with a carcinogenic regimen of E2. We observed more than a 2-fold increase in phospho-NRF-1 in E2 treated (100pg/ml for 30 min) MCF-10A cells and phosphorylation of NRF-1 was inhibited by co-treatment with either biological (CAT or MnSOD) or chemical (20μM ebselen) ROS modifiers. These results suggest that E2-induced phosphorylation of NRF-1 is influenced by ROS signaling messengers. We found that E2 treated MCF-10A cells showed increased NRF-1 binding to the promoters of Cdc2, PRC1, PCNA, Cyclin B1, and CDC25C genes. NRF-1 binding induced by E2 treatment was inhibited by the overexpression of CAT and MnSOD. NRF-1 phosphorylation site specific to kinase AKT, Thr-109, was mutated to Asp (D) or Ala (A), and the NRF-1 acetylation site specific to acetyl-transferase PCAF, Lys- 89, was mutated to Gln (glutamine)-Q or Ala (A). We examine the effect of one of the NRF-1 mutants on E2-induced in vitro tumor formation. We observed that the expression of NRF-1 (T109A) phosphodeficient mutant (NRF-1PMT) significantly inhibited E2-induced cell transformation, whereas empty vector did not influence E2-induced colony formation. Together these findings support the idea that NRF-1 may play an important role in E2-induced malignant transformation of breast epithelial cells. Thus, our data is consistent with the hypothesis that in addition to the estrogen receptor activity, NRF-1 activation contributes to the susceptibility to develop malignant phenotype in response to exposure to estrogen. This work was in part supported by a VA MERIT Review (VA BX001463) grant to DR Citation Format: Lazaro Mesa, Jayanta Das, Alok Deoraj, Victor Okoh, Deodutta Roy. Phosphodeficient NRF1 mutant suppresses the susceptibility of the breast epithelial cells to develop tumors when exposed to estrogen - a major breast cancer risk factor. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4559. doi:10.1158/1538-7445.AM2015-4559