Nutrition & Food Science
Permanent URI for this communityhttp://hdl.handle.net/1903/2267
null
Browse
2 results
Search Results
Item Selenium compounds activate early barriers of tumorigenesis(2011) WU, MIN; Cheng, Wen-Hsing; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Selenium chemoprevention by apoptosis has been well studied, but it is not clear whether selenium can activate early barriers of tumorigenesis, namely senescence and DNA damage response. To test this hypothesis, we treated normal and cancerous cells with a gradient concentration of sodium selenite, methylseleninic acid and methylselenocysteine for 48 h, followed by a recovery of 1-7 days. Here we show that selenium compounds at doses of ≤LD50 can induce cellular senescence, as evidenced by the expression of senescence-associated β-galactosidase and 5-bromo-2-deoxyuridine incorporation, in normal but not cancerous cells. In response to clastogens, the ataxia telangiectasia mutated (ATM) protein is rapidly activated, which in turn initiates a cascade of DNA damage response. We found that the ATM pathway is activated by the selenium compounds, and the kinase activity is required for the selenium induced senescence response. Pretreatment of the MRC-5 non-cancerous cells with the antioxidant N-acetylcysteine or 2,2,6,6-tetramethylpiperidine-1-oxyl suppresses the selenium induced ATM activation and senescence. Taken together, the results suggest a novel role of selenium in the activation of early tumorigenesis barriers specific in non-cancerous cells, whereby selenium induces an ATM-dependent senescence response that depends on reactive oxygen species. The tumor suppressor p53 is a substrate of the ATM kinase and plays an important role in senescence. To determine mechanism by which selenium induces the ATM-dependent senescence, we employed shRNA knockdown approach and other DNA damage assays to determine the role of p53 in the senescence response. Results from senescence-associated expression of β-galactosidase assay indicate that p53 shRNA MRC-5 cells did not show senescent phenotype with a series of concentrations of methylseleninic acid (0-10 μM) after 7-day recovery. However, loss of p53 renders MRC-5 cells more resistant to MSeA treatment and increased its genomic instability. We also observe that MSeA can cause increased irreversible G2/M arrest in scramble MRC-5 cells but treated p53 shRNA MRC-5 can recover back to non-treated status after 7-day recovery. Taken together, p53 is involved in the ATM-dependent senescence in the response of MRC-5 normal cells to selenium compounds.Item THE FUNCTION OF MRN (MRE11-RAD50-NBS1) COMPLEX DURING WRN (WERNER) FACILITATED ATM (ATAXIA-TELANGIECTASIA MUTATED) ACTIVATION(2009) Ma, Junhao; Cheng, Wen-Hsing; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)WRN (Werner) protein is a member of the RecQ family showing helicase and exonuclease activity. WRN protein may lose function upon mutation and causes Werner syndrome (WS) which is an autosomal recessive, cancer-prone and premature aging disease. ATM (Ataxia-Telangiectasia mutated) protein initiates a signaling pathway in response to DNA double strand breaks (DSBs). Genomic disorder ataxia-telangiectasia (A-T) is associated with defective ATM. WRN protein is involved in ATM pathway activation when cells are exposed to DSBs associated with replication fork collapse. Because the Mre11-Rad50-Nbs1 (MRN) complex, a sensor of DSBs, is known to interact with WRN and ATM, we investigated whether the MRN complex mediates the WRN-dependent ATM pathway activation. In this study, we employed short-hairpin RNA to generate WRN- and Nbs1-deficient U-2 OS (osteosarcoma) cells. Cells were treated with clastogens which induce collapsed replication forks, thus provided proof for whether WRN facilitates ATM activation via MRN complex. This study serves as a basis for future investigation on the correlation between ATM, MRN complex and WRN, which will ultimately help understand the mechanism of aging and cancer.