Nucleolin is required for Syk-dependent stabilization of Bcl-x L mRNA. (A) Tet-responsive MDA-MB-231 cells were untreated (control [Ctrl]) or infected with one of a set of lentiviruses encoding shRNAs for nucleolin (shNCL). Nucleolin levels were measured by Western blotting. The level of GAPDH was measured as a loading control. Results from three different populations of infected cells are shown. (B) Tet-responsive MDA-MB-231 cells and two of the three sets of Tet-responsive cells carrying the nucleolin shRNA (shNCL2 and shNCL3) were either uninduced (−) or induced with doxycycline to express Syk-EGFP (+) and then 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. (C) DG75 B cells were untreated (control) or infected with a lentivirus encoding shRNA directed against nucleolin. Nucleolin levels were measured by Western blotting. The level of GAPDH was measured as a loading control. (D) DG75 cells either infected (+) or not infected (−) with the lentivirus carrying the nucleolin shRNA were 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. (E) Tet-responsive MCF7 cells were untreated (control) or infected with a set of lentiviruses encoding shRNAs for nucleolin. Nucleolin levels were measured by Western blotting. Results from two different populations of infected cells are shown. (F) Tet-responsive MCF7 cells and the two sets of Tet-responsive cells carrying the nucleolin shRNA (shNCL1 and shNCL2) were either uninduced (−) or induced with doxycycline to express Syk-EGFP (+) and then 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.