RARα2 expression increases in myeloma stem cells. (A) Cell growth between CD138⁺ and CD138⁻ cells from ARK and KMS11 was compared with a hemocytometer for 5 days. Cells from the CD138⁺ fraction exhibited higher proliferation than CD138⁻ cells. All results were expressed as means ± SD of 3 independent experiments. (B) A supervised hierarchical cluster showed 291 significant differentially expressed genes between CD138⁺ and CD138⁻ cells from 8 myeloma cell lines. Red for a gene indicates expression above the median and blue indicates expression below the median. Myeloma cell lines were plotted on the vertical axis and the gene probe sets are listed on top along the horizontal axis. (C) The expression of Oct4, Sox2, Nanog, and Lin28A was examined in CD138⁻ and CD138⁺ cells of ARP1, KMS28PE, and OPM2 myeloma lines by real-time PCR. (D) RARα expression (Y-axis) was compared between CD138⁻ cells with CD138⁺ cells in 8 myeloma cell lines using GEP analysis. (E) RARα2 expression was compared in the CD138⁻ fraction vs the CD138⁺ fraction of 8 MM cell lines using real-time-PCR. (F) Real-time PCR showed that expression of RARα2, Oct4, Sox2, Nanog, Lin28A, TCF1, Gli1, and ABCC3 was increased in MMSCs (SP/κ⁺) cells compared with non-SP/κ⁺cells in a primary MM patient sample. (G) A Heatmap showed the expression of RARα2, Oct4, Sox2, Nanog, Lin28A, TCF1, Gli1, and ABCC3 genes in 23 primary MM samples as detected by RT-PCR.