Survival and abrogation of E3 ubiquitin ligase activity. (A) Relative survival/proliferation of 32D cells expressing wild-type or mutant CBL constructs 48 hours after growth factor withdrawal as determined by MTS assay. (B) 32D cells expressing wild-type FLT3 and CBL constructs as indicated were transfected with HA-tagged ubiquitin and stimulated with FLT3 ligand. After lysis, FLT3 was immunoprecipitated, blotted, and probed with anti-HA. Total blots for FLT3 AND CBL are also shown.