Sequences of shRNA are shown in Table 1 . Lentiviral vector production and transduction were performed as described earlier (37) . Viral vectors were pelleted by ultracentrifugation at 50 000g at 4 C for 3 h and resuspended in a volume of PBS that was 1% of the original medium volume. The titers of the concentrated vectors were then measured with a p24 ELISA kit (ZeptoMetrix, Buffalo, NY, USA).