The AXL-PYK2-PKCa axis as a nexus of stemness circuits in TNBC

Cancer stem cells (CSCs) are implicated in tumor initiation, metastasis and drug resistance, and are considered as attractive targets for cancer therapy. We identified a clinically relevant signaling nexus mediated by PYK2 and its impact on stemness in triple negative breast cancer (TNBC). PYK2 depletion in multiple mesenchymal TNBC cell lines markedly reduced the expression of PKCa and AXL proteins and reduced the number of mammosphere-forming cells and cells harboring CSCs characteristic markers. PYK2 and PKCa cooperate at a convergence point of multiple stemness-inducing pathways to regulate AXL levels and concomitantly the levels/activation of key transcription factors implicated in stemness including STAT3, TAZ, FRA1 and SMAD3 as well as the pluripotent transcription factors Nanog and Oct4, and in-turn affect their target genes. Targeting the AXL-PYK2-PKCa circuit could be a promising strategy to eliminate CSCs in TNBC and possibly overcome drug resistance. Overall design: PYK2 (PTK2B) was knocked-down in the triple negative breast cancer cell line MDA-MB-231 using shRNA. The empty lentiviral vector (PLKO) was used as control. Experiment was done in duplicates.