Stabilization of Pin1 by USP34 promotes Ubc9 isomerization and protein sumoylation in glioma stem cells to augment glioblastoma malignancy

he unique prolyl isomerase Pin1 that promotes protein conformational changes is a pivotal therapeutic target in many cancers, but little is known about the regulation of Pin1 protein stability. We previously found that Pin1 was highly expressed in glioma stem cells (GSCs) relative to non-stem tumor cells (NSTCs). Interestingly, treatment of the proteasome inhibitor MG132 markedly restored Pin1 protein expression in NSTCs to a level similar to GSCs. We therefore sought to identify the molecular regulators controlling the proteasomal degradation of Pin1 by mass spectrometry analysis of Pin1-interacting proteins in GSCs. The results showed that Pin1 interacts with a deubiquitinase USP34 in GSCs, suggesting that Pin1 may be stabilized by USP34.