Effects of NO on CXCR4 expression. Both MDA-MB-231 and SK-BR3 cells were treated with 1 mM DETA NONOate in the presence or absence of 5 mM L-NAME for various time periods and prepared for (A) real-time RT PCR analysis, and (B) western blot analysis, as described in Materials and Methods. Determinations were performed in triplicate and expressed as the mean of three experiments ± SD. Data are expressed as fold increase relative to control (untreated) cells. * indicates significant difference (p < 0.05) from control and/or L-NAME-treated cells.