γ-Glutamylcyclotransferase is transcriptionally regulated by c-Jun and controls proliferation of glioblastoma stem cells through Notch1 levels

Glioblastoma stem cells (GSCs) have been reported to cause poor prognosis of glioblastoma by contributing to therapy-resistance. γ-Glutamylcyclotransferase (GGCT) is highly expressed in various cancer types, including glioblastoma, and its inhibition suppresses cancer cell growth. However, the mechanism of GGCT overexpression and its function in GSCs are unknown. In this study, we show that GGCT is highly expressed in GSCs established from a mouse glioblastoma model and its knockdown suppresses their proliferation. We also found that c-Jun transcription factor at the downstream of NRas regulates GGCT promoter activity via its consensus sequence. Gene expression analysis revealed that GGCT knockdown showed a repressive effect on the Delta-Notch pathway and decreased Notch1 expression. Notch1 knockdown alone inhibited the GSC proliferation, confirming that Notch1 is functional in this model. Forced expression of the Notch1 intracellular domain restored the growth inhibitory effect of GGCT knockdown. Moreover, GGCT knockdown inhibited GSC tumorigenic potential in vivo. These results indicate that GGCT, whose expression is promoted by c-Jun, plays an important role in the proliferation and tumorigenic potential of GSCs, and that the phenotype caused by its knockdown is contributed by a decrease in Notch1. Thus, GGCT may represent a novel therapeutic target for attacking GSCs. To test the effect of suppression of GGCT on the gene expression, murine GSC was tranducted with lentiviral non-target (control) or GGCT shRNA. GGCT knockdown GSCs were compared to control cells.