Activation of NOTCH signaling by tenascin-C promotes growth of human brain tumor-initiating cells

Elevated NOTCH signaling is implicated in tumorigenesis. The brain tumor- initiating cells (BTICs) present in malignant glioma exhibit elevated NOTCH activity but the mechanism of this activation is unknown. Here, we provide evidence that tenascin-C (TNC), an extracellular matrix protein prominent in malignant glioma, increases NOTCH activity in BTICs to promote their growth. We demonstrate the proximal localization of TNC and BTICs in human glioblastoma specimens, and in the brains of mice implanted with human BTIC intracranial xenografts. In culture, TNC was superior amongst several extracellular matrix proteins in enhancing the sphere-forming capacity of glioma patient-derived BTICs. Exogenously applied or autocrine TNC increased BTIC growth through an α2β1 integrin-mediated mechanism that elevated the NOTCH ligand, Jagged1 (JAG1). Microarray analyses and confirmatory PCR and Western blots in BTICs found that components of the NOTCH signaling pathway, including JAG1, ADAMTS15 and NICD1/2 were elevated in BITCs after TNC exposure. Inhibition of gamma secretase and metalloproteinase proteolysis in the NOTCH pathway, or knockdown of α2β1 integrin or JAG1, reduced the proliferative effect of TNC on BTIC. Collectively, our study has several novelties: the identification of TNC as a key initiator of the elevated NOTCH signaling in BTICs; the discovery that a prominent ECM component in malignant gliomas, TNC, is a promoter of BTIC growth; and the establishment of the TNC- α2β1 integrin - JAG1-NOTCH axis as a candidate for therapeutic interventions to improve the prognosis of patients with malignant glioma.

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