Loss of CRBN expression in MM1.S cell line is associated with lenalidomide resistance. (A) Diagram of the karyotype evolution observed from MM1.S (lenalidomide-sensitive) to MM1.Sres cell line (lenalidomide-resistant). Red blocks represent the deletions on chromosome 3p, including CRBN (arrows indicate its location). Although 1 CRBN allele is present in the MM1.Sres cell line, there is a significant reduction of CRBN transcript (B) and lack of protein expression (C). (D) GEP comparison showed CRBN as one of the top 10 underexpressed genes in MM1.Sres compared with MM1.S. The lack of or very low CRBN expression was associated with lenalidomide (E) and pomalidomide (F) resistance.