Protein Sumoylation with SUMO1 Promoted by Pin1 in Glioma Stem Cells Augments Glioblastoma Malignancy

Background: The tumorigenic potential of glioma stem cells (GSCs) is associated with multiple reversible molecular alternations, but the role of post-translational protein sumoylation in GSCs has not been elucidated. The development of GSC-targeting drugs relies on the discovery of GSC-preferential molecular modifications and the relevant signaling pathways. In this work, we investigated the protein sumoylation status, the major sumoylated substrate and the key regulatory enzyme in GSCs to explore the therapeutic potential of disrupting protein sumoylation for glioblastoma (GBM) treatment.

Methods: Patient-derived GSCs, primary GBM sections, and intracranial GBM xenografts were used to determine protein sumoylation and the related molecular mechanisms by immunoblot, quantitative PCR, immunoprecipitation, immunofluorescence and immunohistochemistry. Orthotopic GBM xenograft models were applied to investigate the inhibition of tumor growth by disrupting protein sumoylation with shRNAs or molecular inhibitors.

Results: We show that high levels of SUMO1- but not SUMO2/3-modified sumoylation are preferentially present in GSCs. The promyelocytic leukaemia protein (PML) is a major SUMO1-sumoylated substrate in GSCs, whose sumoylation facilitates its interaction with c-Myc to stabilize c-Myc proteins. The prolyl-isomerase Pin1 is preferentially expressed in GSCs and functions as the key enzyme to promote SUMO1-sumoylation. Disruption of SUMO1-sumoylation by Pin1 silencing with shRNAs or inhibition with its inhibitor Juglone markedly abrogated GSC maintenance and mitigated GSC-driven tumor growth.

Conclusions: Our findings indicate that high SUMO1-modified protein sumoylation as a feature of GSCs is critical for GSC maintenance, suggesting that targeting SUMO1-sumoylation may effectively improve GBM treatment.

Keywords: Glioma stem cells; PML; Pin1; Post-translational modification; Protein sumoylation.