FIG. 5.

Serines 927 and 932 are required for TNF-α to trigger p105 ubiquitination. (A) HeLa cells stably transfected with HA-p105 were pretreated for 1 h with LLnL proteasome inhibitor or vehicle control (dimethyl sulfoxide [DMSO]). Cells were then stimulated for 15 min with TNF-α or control medium. HA-p105 was isolated from cell lysates by immunoprecipitation, resolved by SDS-6% PAGE, and then Western blotted with anti-p105C antibody. Ip, immunoprecipitates; WT, wild type. (B) The indicated HeLa clones were pretreated with LLnL inhibitor and stimulated with TNF-α as described for that in panel A. Anti-HA immunoprecipitates were Western blotted with anti-p105C antibody.