Screening of genes responsible for EV secretion in resistant MM cells. (A) Flow diagram for the selection of candidate genes related to EV secretion. (B) Illustration of the method used for EV secretion-related gene screening. (C) Heatmap showing the 118 genes highly expressed in lenalidomide-resistant cell lines (resistant, KMS21R, KMS27R, KMS34, and KMS34R; sensitive, KMS21 and KMS27). (D) Cell viability assay of cells with knockdown of the 13 selected genes in the presence of lenalidomide. (E) Caspase activity assay of cells with knockdown of the 13 selected genes in the presence of lenalidomide. (F) ExoScreen assay of cells with knockdown of the selected 8 genes. The values were normalized to those of the negative control (NC). (G) Western blotting for SORT1, LAMP2, VLA-4, STAT3, p-STAT3, and β-actin in the 6 cell lines used in this study. Proteins were loaded at 15 μg per lane. (H) Quantitative reverse transcription polymerase chain reaction analysis of the expression levels of LAMP2 and SORT1. Each expression value was normalized to that in the corresponding parental cell line.