ATF5 and squamous cell carcinoma: Representative immunoblot (of three independent biological replicates) shows level of ubiquitinated proteins in the radio-immunoprecipitation assay (RIPA)-insoluble fraction of S51, S51A, and S51A-ATF5 squamous cell carcinoma [SCC] cells in the absence or proteotoxic stress or following 24 hr recovery from a 6 hr bortezomib pulse.