NF-κB activation is reduced in Tax transgenic mouse tumors treated with PS-341 in vitro. Nuclear extracts were prepared from Tax transgenic tissues, and representative results from 5 transgenic spleens and tumors and 5 nontransgenic splenocytes are shown. Tissues used included tumors arising on the nose, leg, or foot, as well as spleens with tumor involvement or nontransgenic splenocytes. (A) ELISA was performed as described in “Materials and methods.” Values are represented as means of 1 of 3 separate experiments. Error bars correspond to SEM between 5 animals in each group. The statistical significance of the inhibition was evaluated by a paired t test: P ≤ .05 for untreated compared to sodium salicylate treatments and P ≤ .05 for untreated compared to PS-341 treatments. (B) F8 cells were cultured with 10^-7 M PS-341, harvested at 0, 30, 60, 90, and 120 minutes, washed, and lysed to prepare total cell extracts. For detection of phospho-IκB, IκB, and actin, cell lysates were subjected to electrophoresis on a 10% SDS-PAGE, transferred to nitrocellulose membrane, and immunoblotted with antiphospho-IκB, IκB, and actin (loading reference) antibodies. Blots were developed using a chemiluminescent substrate.