RESUMO
PURPOSE: ATM activates the NF-κB transcriptional complex in response to genotoxic and oxidative stress. The purpose of this study was to examine if the NF-κB target gene and critical antioxidant SOD2 (MnSOD) in cultured mammary epithelium is also ATM-dependent, and what phenotypes arise from deletion of ATM and SOD2 within the mammary gland. METHODS: SOD2 expression was studied in human mammary epithelial cells and MCF10A using RNAi to knockdown ATM or the NF-κB subunit RelA. To study ATM and SOD2 function in mammary glands, mouse lines containing Atm or Sod2 genes containing LoxP sites were mated with mice harboring Cre recombinase under the control of the whey acidic protein promoter. Quantitative PCR was used to measure gene expression, and mammary gland structure was studied using histology. RESULTS: SOD2 expression is ATM- and RelA-dependent, ATM knockdown renders cells sensitive to pro-oxidant exposure, and SOD mimetics partially rescue this sensitivity. Mice with germline deletion of Atm fail to develop mature mammary glands, but using a conditional knockout approach, we determined that Atm deletion significantly diminished the expression of Sod2. We also observed that these mice (termed AtmΔ/Δ) displayed a progressive lactation defect as judged by reduced pup growth rate, aberrant lobulo-alveolar structure, diminished milk protein gene expression, and increased apoptosis within lactating glands. This phenotype appears to be linked to dysregulated Sod2 expression as mammary gland-specific deletion of Sod2 phenocopies defects observed in AtmΔ/Δ dams. CONCLUSIONS: We conclude that ATM is required to promote expression of SOD2 within the mammary epithelium, and that both ATM and SOD2 play a crucial role in mammary gland homeostasis.
Assuntos
Neoplasias da Mama/genética , Superóxido Dismutase/genética , Fator de Transcrição RelA/genética , Animais , Proteínas Mutadas de Ataxia Telangiectasia/genética , Neoplasias da Mama/patologia , Diferenciação Celular/genética , Proliferação de Células/genética , Feminino , Regulação Neoplásica da Expressão Gênica , Homeostase , Humanos , Integrases/genética , Glândulas Mamárias Animais/metabolismo , Glândulas Mamárias Animais/patologia , Camundongos , Estresse Oxidativo/genéticaRESUMO
Reduced ATM function has been linked to breast cancer risk, and the TRIM29 protein is an emerging breast cancer tumor suppressor. Here we show that, in cultured breast tumor and non-tumorigenic mammary epithelial cells, TRIM29 is up-regulated in response to hypoxic stress but not DNA damage. Hypoxia-induced up-regulation of TRIM29 is dependent upon ATM and HIF1α and occurs through increased transcription of the TRIM29 gene. Basal expression of TRIM29 is also down-regulated in cells expressing diminished levels of ATM, and findings suggest that this occurs through basal NF-κB activity as knockdown of the NF-κB subunit RelA suppresses TRIM29 abundance. We have previously shown that the activity of the TWIST1 oncogene is antagonized by TRIM29 and now show that TRIM29 is necessary to block the up-regulation of TWIST1 that occurs in response to hypoxic stress. This study establishes TRIM29 as a hypoxia-induced tumor suppressor gene and provides a novel molecular mechanism for ATM-dependent breast cancer suppression.
