Geranylgeranyltransferase I regulates HIF-1α promoting glioblastoma cell migration and invasion

Emerging trends in post-translational modification: Shedding light on Glioblastoma multiforme

Recent multi-omics studies, including proteomics, transcriptomics, genomics, and metabolomics have revealed the critical role of post-translational modifications (PTMs) in the progression and pathogenesis of Glioblastoma multiforme (GBM). Further, PTMs alter the oncogenic signaling events and offer a novel avenue in GBM therapeutics research through PTM enzymes as potential biomarkers for drug targeting. In addition, PTMs are critical regulators of chromatin architecture, gene expression, and tumor microenvironment (TME), that play a crucial function in tumorigenesis. Moreover, the implementation of artificial intelligence and machine learning algorithms enhances GBM therapeutics research through the identification of novel PTM enzymes and residues. Herein, we briefly explain the mechanism of protein modifications in GBM etiology, and in altering the biologics of GBM cells through chromatin remodeling, modulation of the TME, and signaling pathways. In addition, we highlighted the importance of PTM enzymes as therapeutic biomarkers and the role of artificial intelligence and machine learning in protein PTM prediction.

The HIF1α/JMY pathway promotes glioblastoma stem-like cell invasiveness after irradiation

Human glioblastoma (GBM) is the most common primary malignant brain tumor. A minor subpopulation of cancer cells, known as glioma stem-like cells (GSCs), are thought to play a major role in tumor relapse due to their stem cell-like properties, their high resistance to conventional treatments and their high invasion capacity. We show that ionizing radiation specifically enhances the motility and invasiveness of human GSCs through the stabilization and nuclear accumulation of the hypoxia-inducible factor 1α (HIF1α), which in turn transcriptionally activates the Junction-mediating and regulatory protein (JMY). Finally, JMY accumulates in the cytoplasm where it stimulates GSC migration via its actin nucleation-promoting activity. Targeting JMY could thus open the way to the development of new therapeutic strategies to improve the efficacy of radiotherapy and prevent glioma recurrence.

FRK suppresses human glioma growth by inhibiting ITGB1/FAK signaling

Fyn-related kinase (FRK), a member of the Src-related tyrosine kinase family, functions as a tumor suppressor in several malignancies. We previously showed that FRK overexpression inhibited the growth of glioma cells. However, it is unknown whether FRK is equally effective against intracranial glioma in vivo, and the mechanism by which FRK influences glioma cell growth remains unclear. In this study, we found that tumor volume was reduced by about one-third in mice with FRK overexpression, which showed improved survival relative to controls. Immunofluorescence analysis revealed that FRK overexpression inhibited glioma cell proliferation and induced their apoptosis. Importantly, in vitro we further found that FRK decreased the expression of integrin subunit β1 (ITGB1) at both the mRNA and protein levels. FRK also inhibited transactivation by ITGB1, resulting in the suppression of its target proteins AKT and focal adhesion kinase (FAK). ITGB1 overexpression promoted glioma cell growth and partially reduced FRK-induced growth suppression. These results indicate that FRK inhibits human glioma growth via regulating ITGB1/FAK signaling and provide a potential therapeutic target for the treatment of glioma.

The Role of Hypoxia in Glioblastoma Invasion

Glioblastoma multiforme (GBM), a grade IV astrocytoma, is the most common and deadly type of primary malignant brain tumor, with a patient's median survival rate ranging from 15 to 17 months. The current treatment for GBM involves tumor resection surgery based on MRI image analysis, followed by radiotherapy and treatment with temozolomide. However, the gradual development of tumor resistance to temozolomide is frequent in GBM patients leading to subsequent tumor regrowth/relapse. For this reason, the development of more effective therapeutic approaches for GBM is of critical importance. Low tumor oxygenation, also known as hypoxia, constitutes a major concern for GBM patients, since it promotes cancer cell spreading (invasion) into the healthy brain tissue in order to evade this adverse microenvironment. Tumor invasion not only constitutes a major obstacle to surgery, radiotherapy, and chemotherapy, but it is also the main cause of death in GBM patients. Understanding how hypoxia triggers the GBM cells to become invasive is paramount to developing novel and more effective therapies against this devastating disease. In this review, we will present a comprehensive examination of the available literature focused on investigating how GBM hypoxia triggers an invasive cancer cell phenotype and the role of these invasive proteins in GBM progression.

ZEB1 Promotes Invasion in Human Fetal Neural Stem Cells and Hypoxic Glioma Neurospheres

Diffuse spread through brain parenchyma and the presence of hypoxic foci rimmed by neoplastic cells are two cardinal features of glioblastoma, and low oxygen is thought to drive movement of malignant gliomas in the core of the lesions. Transcription factors associated with epithelial-to-mesenchymal transition (EMT) have been linked to this invasion, and we found that hypoxia increased in vitro invasion up to fourfold in glioblastoma neurosphere lines and induced the expression of ZEB1. Immunohistochemical assessment of 295 surgical specimens consisting of various types of pediatric and adult brain cancers showed that ZEB1 expression was significantly higher in infiltrative lesions than less invasive tumors such as pilocytic astrocytoma and ependymoma. ZEB1 protein was also present in human fetal periventricular stem and progenitor cells and ZEB1 inhibition impaired migration of in vitro propagated human neural stem cells. The induction of ZEB1 protein in hypoxic glioblastoma neurospheres could be partially blocked by the HIF1alpha inhibitor digoxin. Targeting ZEB1 blocked hypoxia-augmented invasion of glioblastoma cells in addition to slowing them in normoxia. These data support the role for ZEB1 in invasive and high-grade brain tumors and suggest its key role in promoting invasion in the hypoxic tumor core as well as in the periphery.

Lovastatin and perillyl alcohol inhibit glioma cell invasion, migration, and proliferation--impact of Ras-/Rho-prenylation

Alterations in small GTPase mediated signal transduction pathways have emerged as a central step in the molecular pathogenesis of glioblastoma (GBM), the most common malignant brain tumor in adults. Farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) are derived from mevalonate, whose production is catalyzed by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Prenylation by FPP and GGPP is required for membrane insertion and oncogenic function of Ras- and Rho-proteins, within the stimulation of the Ras-Raf-MEK-ERK pathway. A straightforward prediction from HMG-CoA reductase inhibitor studies is that statins decrease FPP and GGPP levels and diminish ERK signaling ensuring less proliferation and migration of cancer cells. Perillyl alcohol (POH), a naturally occurring monoterpene inhibits prenyltransferases and is able to inhibit cancer cell growth, but the underlying mechanism is still unclear. We here report that lovastatin (LOV) and POH impair the regulation of the mevalonate- and the Ras-Raf-MEK-ERK pathway in U87 and U343 glioblastoma cells. Both compounds affected the post-translational modification of H-Ras and Rac1. While LOV diminished the substrates of the transferase reaction that catalyze prenylation, POH inhibited the enzymes itself. Our data highlight the impact of isoprenoids for post-translational modification of small GTPases promoting proliferation, migration and invasion capabilities in glioma cells.

FRK inhibits migration and invasion of human glioma cells by promoting N-cadherin/β-catenin complex formation

Fyn-related kinase (FRK), a member of Src-related tyrosine kinases, is recently reported to function as a potent tumor suppressor in several cancer types. Our previous study has also shown that FRK over-expression inhibited the migration and invasion of glioma cells. However, the mechanism of FRK effect on glioma cell migration and invasion, a feature of human malignant gliomas, is still not clear. In this study, we found that FRK over-expression increased the protein level of N-cadherin, but not E-cadherin. Meanwhile, FRK over-expression promoted β-catenin translocation to the plasma membrane, where it formed complex with N-cadherin, while decreased β-catenin level in the nuclear fraction. In addition, down-regulation of N-cadherin by siRNA promoted the migration and invasion of glioma U251 and U87 cells and abolished the inhibitory effect of FRK on glioma cell migration and invasion. In summary, these results indicate that FRK inhibits migration and invasion of human glioma cells by promoting N-cadherin/β-catenin complex formation.

Systematic review of protein biomarkers of invasive behavior in glioblastoma

Glioblastoma (GBM) is an aggressive and incurable brain tumor with a grave prognosis. Recurrence is inevitable even with maximal surgical resection, in large part because GBM is a highly invasive tumor. Invasiveness also contributes to the failure of multiple cornerstones of GBM therapy, including radiotherapy, temozolomide chemotherapy, and vascular endothelial growth factor blockade. In recent years there has been significant progress in the identification of protein biomarkers of invasive phenotype in GBM. In this article, we comprehensively review the literature and survey a broad spectrum of biomarkers, including proteolytic enzymes, extracellular matrix proteins, cell adhesion molecules, neurodevelopmental factors, cell signaling and transcription factors, angiogenic effectors, metabolic proteins, membrane channels, and cytokines and chemokines. In light of the marked variation seen in outcomes in GBM patients, the systematic use of these biomarkers could be used to form a framework for better prediction, prognostication, and treatment selection, as well as the identification of molecular targets for further laboratory investigation and development of nascent, directed therapies.