Dr. Alrasli inquired about p53 positive and negative cells. The breast carcinoma MCF-7 cells that have wt p53 may serve as both, p53 "negative" and positive cells. Becouse of high turnover of wt p53 in these cells its expression in the untreated cells is so low that is hardly detectable - approximately 10 % above the isotype control. When MCF-7 cells are treated with 0.15 uM campthotecin, after 4 -16 h of the treatment expression of their p53 increases (as measured by cytometry) by up to 50 -fold (see Deptala et al., Int. J. Oncol., 861-871, 1999). Similar increase may be induced by proteasome inhibitors. This dramatic range of increase provides a convenient standard that can be compared with other cell systems. Zbigniew Darzynkiewicz Brander Cancer Research Institute New York Medical College 19 Bradhurst Ave. Hawthorne, NY 10532 tel: 914-347-2801 fax: 914-347-2804 http://www.geocities.com/z_darzynkiewicz
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