Effect of RTVP-1 on the mesenchymal transformation of glioma stem cells (GSCs) and their self-renewal and migration.

Abstract

2073Background: Glioblastoma (GBM), the most aggressive primary brain tumors, exhibit increased invasiveness and resistance to anti-tumor treatments. GBM are categorized into proneural, neural, classical and mesenchymal subgroups, the latter being characterized by increased invasion and poor prognosis. We recently reported that RTVP-1 is highly expressed in GBM and its expression is correlated with astrocytic tumor grade. Methods: We employed promoter and Chip analyses, analysis of tumor specimens submitted to TCGA , GSC self-renewal and migration assays, mesenchymal and neural differentiation, gene array analysis and pull-down assay followed by FRET. Results: The RTVP-1 promoter binds STAT3 and C/EBPb, the transcription factors that regulate mesenchymal transformation of GBM. The expression of RTVP-1 is higher in mesenchymal GBM and is inversely correlated with patient survival in the proneural group. We examined the expression and functions of RTVP-1 in GSCs, a small population of cancer stem cells that are implicated in the increased migration, radio- and chemo-resistance of GSCs and tumor recurrence. RTVP-1 was expressed in the different GSCs but not in the normal human neural stem cells (NSCs). Overexpression of RTVP-1 in NSCs induced their mesenchymal transformation, whereas silencing of RTVP-1 in GSCs decreased their mesenchymal and increased their neural phenotypes. Moreover, RTVP-1 promoted the self-renewal and migration of GSCs. Using gene array analysis of RTVP-1 silenced cells we identified IL-6 and CXCR4 as major mediators of RTVP-1 effects on the mesenchymal transformation and self-renewal of GSCs. In addition, using a pull down assay with His-tagged RTVP-1 we identified N-WASP and hnRNPK as novel interacting proteins of RTVP-1 that mediate its effects on glioma cell migration. Conclusions: RTVP-1 expression is associated with mesenchymal transformation of GSCs. RTVP-1 promotes self-renewal and migration of GSCs and these effects are mediated by the increased expression of IL-6 and CXCR4 and via interaction with N-WASP and hnRNPK. Collectively, these results suggest that RTVP-1 may represent a novel diagnostic marker and a therapeutic target in GBM.