LHPP impedes energy metabolism by inducing ubiquitin-mediated degradation of PKM2 in glioblastoma

摘要

Phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) is a new-found tumor suppressor in a variety of tumors. While, it is still unknown about its role in glioma. In this study, we found that LHPP is abnormally decreasing or absent in glioblastoma, and the low expression of LHPP is associated with poor median survival in glioma patients. Functional assay revealed that LHPP-overexpression significantly inhibited U87MG and U118MG growth in vitro and in vivo. As to the mechanism, mass-spectrometric analysis indicated that the LHPP interacting proteins were mainly enriched in regulation of energy metabolism, including Carbon metabolism, Oxidative phosphorylation, and Glycolysis. Seahorse assay and metabolites detection confirmed that LHPP-overexpression obviously impeded glycolysis and respiration in U87MG and U118MG cells. For the further study, western blot assay showed that the protein level of PKM2 at dimeric, tetrameric, and total protein, were all decreased significantly, and its enzymatic activity was decreased as well. ChIP and RNAseq integrated analysis indicated that the decreased protein level of PKM2 was independent of PKM2 transcription, and LHPP did not reprogram transcription level of metabolic genome. Co-IP and immunofluorescence assay manifested that LHPP interacted with PKM2, and this interaction interfered the protein stability, then induced ubiquitin-mediated degradation of PKM2. Rescue assay confirmed that restoring the expression of PKM2 effectively reversed the restrained energy metabolism and the inhibited cancer cell growth caused by LHPP-overexpression in U87MG and U118MG cells. Taking together, we demonstrated that LHPP impedes the glycolysis and respiration during energy metabolic process via inducing ubiquitin-mediated degradation of PKM2, thus inhibits the growth of glioblastoma.