Sources of cell lines are as previously described (21 (link)). All cell lines have been maintained in a central bank at Moffitt Cancer Center since 2008, authenticated by STR analysis (ACTG Inc, Wheeling, IL) as of September 2010, and are routinely tested and negative for mycoplasma (PlasmoTest, InvivoGen, San Diego, CA). Experiments were conducted <15 passages post thaw. Viability assays were conducted with Cell Titer Glo assay kits (Promega) and read on Spectramax M5 plate reader. For siRNA-mediated knockdown, On-Target Smartpools (Dharmacon) were used and transfections performed with Lipofectamine RNAiMax (Invitrogen).