CRBN and plasma cell myeloma: Interestingly, the protein levels of CRBN and its neo-substrate IKZF1/3 were unaffected in TRAF2 knockout myeloma cells, although these TRAF2 knockout cells were resistant to both lenalidomide and pomalidomide (66), which suggested that the nonubiquitin functions of CRBN were crucial for cellular responses, such as proliferation.