Syk expression protects MCF7 cells from oxidative stress-induced apoptosis and degradation of Bcl-x L mRNA. (A) MCF7-BD cells lacking Syk (−) or stably expressing Syk-EGFP (+) were treated with 5 mM H 2 O 2 for the indicated times. Cell lysates were analyzed by SDS-PAGE and Western blotting with antibodies against PARP (top). The cleaved form of PARP is indicated by the arrow. The expression of Syk-EGFP was visualized by Western blotting of cell lysates (bottom). (B) MCF7-BD cells lacking Syk (−) or stably expressing Syk-EGFP (+) were exposed to 5 mM H 2 O 2 for 30 min (pulse) and then moved to fresh medium for the indicated total incubation times or treated with 5 mM H 2 O 2 for the indicated times. Cell lysates were analyzed by RT-PCR to measure the levels of Bcl-x L and Bcl-x S mRNA (top) or by Western blotting to detect expressed Syk-EGFP (bottom). (C) Comparison of relative levels of Bcl-x L mRNA. Changes in the ratio of Bcl-x L mRNA to Bcl-x S mRNA were normalized to their relative levels of expression in Syk-deficient cells at time zero, which was set equal to a value of 1.0. Bars represent means ± SEMs from three replicate experiments. Significant differences between pairs were determined using an unpaired, two-tailed Student's t test. *, P