Fig. 2

E-cadherin/SOX9 axis regulates CSCs in human MM-derived cells. A–D SOX9 was depleted in RPMI 8226 cells expressing high endogenous SOX9 using lentiviral particles carrying shSOX9 or non-target sequence (WT-control). A Western blot analysis of SOX9 and ABCG2 levels. β-actin was used as a loading control. The significant decrease in SOX9 and ABCG2 levels was detected in shSOX9 cells compared to WT cells (^**p < 0.01; two-tailed Student’s t-test). B Western blot analysis of Akt and MAPK family proteins. The significant decrease in p-Akt, p-p38, and p-p44/42 levels was detected in shSOX9 cells compared to WT cells (^*p < 0.05; two-tailed Student’s t-test). C Representative micrographs showing MM colonies under clonogenic assay (see also Additional file 2: Figure S7 for quantitative analysis). Scale bar = 200 μm. D SP analysis using flow cytometry based on Hoechst 33342 dye efflux (see also Additional file 2: Figure S8 for quantitative analysis). E–H Rescue experiments were performed in CDH1-KO RPMI 8226 cells by transfection of the cells with SOX9 plasmid. Cells with SOX9 restoration were designated SOX9-CDH1-KO cells. E Western blot analysis of SOX9 and ABCG2 levels. β-actin was used as a loading control. The significant increase in SOX9 and ABCG2 levels was detected in SOX9-CDH1-KO cells compared to CDH1-KO cells (see also Additional file 2: Figure S9 for quantitative analysis). F Western blot analysis of Akt and MAPK family proteins. The significant increase in p-Akt, p-p38, and p-p44/42 levels was detected in SOX9-CDH1-KO cells compared to CDH1-KO cells (see also Additional file 2: Figure S10 for quantitative analysis). G Representative micrographs showing MM colonies under clonogenic assay (see also Additional file 2: Figure S11 for quantitative analysis). Scale bar = 200 μm. H SP analysis using flow cytometry based on Hoechst 33342 dye efflux (see also Additional file 2: Figure S12 for quantitative analysis). I Schematic illustration of how E-cadherin/SOX9 axis governs cell growth and self-renewal of CSCs, in part via Akt and MAPK signaling, in MM cells. It is worth noting that other molecules might be involved in this regulatory axis, which requires further investigation