VEGF–neuropilin-2 signaling promotes stem-like traits in breast cancer cells by TAZ-mediated repression of the Rac GAP β2-chimaerin

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Science Signaling  01 May 2018:
Vol. 11, Issue 528, eaao6897
DOI: 10.1126/scisignal.aao6897

A Rac-TAZ loop drives cancer stem cells

In various cancers, stem-like cells called CSCs may drive tumor growth, metastasis, recurrence, and drug resistance; thus, blocking the survival and proliferation of CSCs may enhance the efficacy of anticancer therapies in patients. Elaimy et al. found that CSC phenotypes in breast cancer cells are supported by VEGF, a growth factor that is associated with poor prognosis in breast cancer patients. Through its receptor NRP2 and subsequent activation of the kinase FAK and the protein Rac1, VEGF activated the Hippo pathway transcription cofactor TAZ, which bound and repressed the promoter of the gene encoding the enzyme β2-chimaerin. β2-chimaerin effectively shuts off Rac1; thus, its loss promoted sustained Rac1 activity in a self-perpetuating loop that promoted CSC-like behavior in cells and correlated with stem-like and metastatic markers in patient tumors.


The role of vascular endothelial growth factor (VEGF) signaling in cancer is not only well known in the context of angiogenesis but also important in the functional regulation of tumor cells. Autocrine VEGF signaling mediated by its co-receptors called neuropilins (NRPs) appears to be essential for sustaining the proliferation and survival of cancer stem cells (CSCs), which are implicated in mediating tumor growth, progression, and drug resistance. Therefore, understanding the mechanisms involved in VEGF-mediated support of CSCs is critical to successfully treating cancer patients. The expression of the Hippo effector TAZ is associated with breast CSCs and confers stem cell–like properties. We found that VEGF-NRP2 signaling contributed to the activation of TAZ in various breast cancer cells, which mediated a positive feedback loop that promoted mammosphere formation. VEGF-NRP2 signaling activated the GTPase Rac1, which inhibited the Hippo kinase LATS, thus leading to TAZ activity. In a complex with the transcription factor TEAD, TAZ then bound and repressed the promoter of the gene encoding the Rac GTPase-activating protein (Rac GAP) β2-chimaerin. By activating GTP hydrolysis, Rac GAPs effectively turn off Rac signaling; hence, the TAZ-mediated repression of β2-chimaerin resulted in sustained Rac1 activity in CSCs. Depletion of β2-chimaerin in non-CSCs increased Rac1 activity, TAZ abundance, and mammosphere formation. Analysis of a breast cancer patient database revealed an inverse correlation between β2-chimaerin and TAZ expression in tumors. Our findings highlight an unexpected role for β2-chimaerin in a feed-forward loop of TAZ activation and the acquisition of CSC properties.

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