Protein Kinase C α Is a Central Signaling Node and Therapeutic Target for Breast Cancer Stem Cells

• Inhibition of PKCα preferentially targets breast cancer stem cells
• Activation of an EMT program induces a shift from EGFR to PDGFR signaling
• Activation of an AP-1 molecular switch involves c-FOS and FRA1 in CSCs
• FRA1 is required for the EMT phenotype and tumor-initiation ability

SummaryThe epithelial-mesenchymal transition program becomes activated during malignant progression and can enrich for cancer stem cells (CSCs). We report that inhibition of protein kinase C α (PKCα) specifically targets CSCs but has little effect on non-CSCs. The formation of CSCs from non-stem cells involves a shift from EGFR to PDGFR signaling and results in the PKCα-dependent activation of FRA1. We identified an AP-1 molecular switch in which c-FOS and FRA1 are preferentially utilized in non-CSCs and CSCs, respectively. PKCα and FRA1 expression is associated with the aggressive triple-negative breast cancers, and the depletion of FRA1 results in a mesenchymal-epithelial transition. Hence, identifying molecular features that shift between cell states can be exploited to target signaling components critical to CSCs.

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