FIG 3.
The knockdown of Syk expression sensitizes DG75 B lymphoma cells to oxidative stress-induced apoptosis and degradation of Bcl-xL mRNA. (A) DG75 B lymphoma cells (−) or DG75 cells stably expressing shRNA targeted against Syk (+) were treated with 5 mM H2O2 for the indicated times. Cell lysates were analyzed by RT-PCR to measure the levels of Bcl-xL and Bcl-xS mRNA (top) or by Western blotting to detect endogenous Syk (bottom). (B) Comparison of relative levels of Bcl-xL to Bcl-xS mRNA. Ratios were normalized to a value of 1.0 for wild-type DG75 B cells at time zero. Bars represent means ± SEMs from three replicate experiments. *, P < 0.05; **, P < 0.01. (C) DG75 B lymphoma cells (−) or DG75 cells stably expressing shRNA targeted against Syk (+) were treated with 5 mM H2O2 for the indicated times. Cell lysates were analyzed by SDS-PAGE and Western blotting with antibodies against PARP. The cleaved form of PARP is indicated by the arrow (top). The expression level of endogenous Syk was probed by Western blotting with antibodies against Syk (bottom). (D) DG75 B lymphoma cells (−) or DG75 cells stably expressing shRNA targeted against Syk (+) were transiently transfected with a Bcl-xL expression plasmid (+) or empty vector (−) and then treated with 5 mM H2O2 for the indicated times. Cell lysates were analyzed by SDS-PAGE and Western blotting with antibodies against PARP (top), Syk (middle), or Bcl-xL (bottom). The cleaved form of PARP is indicated by the arrow.