β-catenin is aberrantly expressed in MM, and its down-regulation by the use of shRNA knockdown increases sensitivity to chemotherapeutic agents. (A) Affymetrix analysis of β-catenin mRNA expression in normal plasma cells (PC) and multiple myeloma primary tumors (MMPT). (B) Immunoblot of β-catenin protein in PC and MMPT (1-6) cells. Immunoglobulin heavy chain (IgH) and a nonspecific protein were used as loading markers. (C) Nuclear (N) and cytoplasmic (C) protein fractions of MM1.S and OPM1 cells. Lamin B was used as nuclear fraction loading control. (D) Immunofluorescent staining of total β-catenin (green) in MM1.S (60×) and OPM1 (100×) cells. DAPI is shown in blue. (E) Immunoblot of β-catenin knockdown by stable lentiviral shRNA transduction in MM1.S and OPM1 cells. GFP was used as a whole-cell lysate transduction efficiency marker, whereas Actin and Lamin B were used as whole-cell lysate loading and nuclear fraction loading controls markers, respectively. Note reduced β-catenin levels in both cytoplasmic (C) and nuclear fractions (N). (F) MM1.S control or β-catenin shRNA cells were cocultured with BM stromal cells and treated with different drugs followed by MTT assays to measure metabolism.