SOX10high Cells within Mammary Tumo

SOX10high Cells within Mammary Tumors Exhibit Dedifferentiated and EMT-like FeaturesEctopic overexpression of SOX10 reprograms mammary epithelial cells into a mesenchymal-like cell state (Dravis et al., 2015). Strikingly, analysis of sections from C3-1 mammary tumors revealed that SOX10high cells expressed low levels of epithelial cytokeratins, whereas cells with lower SOX10 expression retained epithelial markers (Figures 5A and 5B ). To better quantify the relationship between SOX10 and epithelial markers, we dissociated C3-1 mammary tumors to single cells, and found that >80%–90% of SOX10high cells had undetectable levels of KRT8 and KRT14 (Figures 5C and 5D). SOX10high tumor cells form tumorspheres in 3D culture conditions at low efficiency, and these tumorspheres exhibited high levels of SOX10 and low levels of cytokeratins (Figure 5E). Thus SOX10high cells in these basal-like mammary tumors showed reduced levels of keratin markers associated with the epithelial state and mammary cell differentiation We analyzed the PY230 mammary tumor model to determine the generality of the relationship between Sox10 expression and loss of epithelial features. Notably, SOX10high PY230 mammary tumor cells also exhibited significant decreases in multiple epithelial and luminal mammary cell markers compared with SOX10low mammary tumor cells (Figure 5F). SOX10high cells also had increased expression of the mesenchymal/EMT markers Vim, Snai2, and Twist1. As ectopic expression of SOX10 in normal mammary cells also elicits dedifferentiation and mesenchymal-like features with similar corresponding gene expression changes (Dravis et al., 2015), we infer that SOX10 directly contributes to this cell state change.Because SOX10 overexpression can also induce motility and mammary cell delamination in 3D culture (Dravis et al., 2015), we determined whether SOX10high cells also locally invade in mouse tumor models in vivo. Strikingly, significant numbers of SOX10high cells in PY230 tumors were found outside the primary tumor margin and in close proximity to tumor vasculature (Figure 5G and Video S1). We examined the TCGA database to determine whether SOX10 is similarly linked to EMT and dedifferentiation in human breast cancer. We generated a rank-order list of human genes based on the correlation of their expression with SOX10 expression across a panel of human breast tumors. Many EMT-related genes positively correlated with SOX10 expression, whereas many epithelial/differentiation-related genes negatively correlated with SOX10 expression (Figures 5H and S5E). Consistent with these data, SOX10 expression in malignant tissue correlated with undetectable or low expression of K14 and K8, compared with adjacent benign mammary tissue on the section, in the same human ER−PR−HER2− breast cancer sample (Figures 3G and S4C). Clear expression of the mesenchymal marker VIM could also be detected in many of the SOX10+ tumor cells (Figure 5I).Taken together, these data establish a link between SOX10 and partial EMT/dedifferentiation in breast cancer. The data further indicate links between SOX10 and local invasion and metastasis, critical features of cancer-associated mortality.