The role of E3 ubiquitin ligases in the development and progression of glioblastoma

Luke M Humphreys,Paul Smith,Shahd Fouad,Zhuoyao Chen,Vincenzo D’Angiolella

doi:10.1038/s41418-020-00696-6

Abstract

Despite recent advances in our understanding of the disease, glioblastoma (GB) continues to have limited treatment options and carries a dismal prognosis for patients. Efforts to stratify this heterogeneous malignancy using molecular classifiers identified frequent alterations in targetable proteins belonging to several pathways including the receptor tyrosine kinase (RTK) and mitogen-activated protein kinase (MAPK) signalling pathways. However, these findings have failed to improve clinical outcomes for patients. In almost all cases, GB becomes refractory to standard-of-care therapy, and recent evidence suggests that disease recurrence may be associated with a subpopulation of cells known as glioma stem cells (GSCs). Therefore, there remains a significant unmet need for novel therapeutic strategies. E3 ubiquitin ligases are a family of >700 proteins that conjugate ubiquitin to target proteins, resulting in an array of cellular responses, including DNA repair, pro-survival signalling and protein degradation. Ubiquitin modifications on target proteins are diverse, ranging from mono-ubiquitination through to the formation of polyubiquitin chains and mixed chains. The specificity in substrate tagging and chain elongation is dictated by E3 ubiquitin ligases, which have essential regulatory roles in multiple aspects of brain cancer pathogenesis. In this review, we begin by briefly summarising the histological and molecular classification of GB. We comprehensively describe the roles of E3 ubiquitin ligases in RTK and MAPK, as well as other, commonly altered, oncogenic and tumour suppressive signalling pathways in GB. We also describe the role of E3 ligases in maintaining glioma stem cell populations and their function in promoting resistance to ionizing radiation (IR) and chemotherapy. Finally, we consider how our knowledge of E3 ligase biology may be used for future therapeutic interventions in GB, including the use of blood–brain barrier permeable proteolysis targeting chimeras (PROTACs).

Highlights

Glioma is an umbrella term for primary brain tumours which are classified according to their cell of origin, and include astrocytic tumours, ependymomas and oligodendrogliomas
Upon binding its cognate ligand (TNF-α or lymphotoxin-α), trimerization of tumour necrosis factor receptor 1 (TNFR1) leads to the recruitment of TNF receptor type 1-associated death domain (TRADD) protein which acts as a scaffold facilitating the recruitment of several proteins including the E3 ligases TRAF2, BIRC2 and BIRC3 to form complex I [110,111,112,113,114]
Loss of RIPK1 abrogates the tumour-forming capability of these cells in an in vivo orthotopic model of GB. These results suggest that the oncogenicity of the EGFRvIII mutation in GB may require the recruitment of the E3 ligase-RIP1 complex [133]

Summary

Introduction

Glioma is an umbrella term for primary brain tumours which are classified according to their cell of origin, and include astrocytic tumours, ependymomas and oligodendrogliomas. Upon binding its cognate ligand (TNF-α or lymphotoxin-α), trimerization of TNFR1 leads to the recruitment of TNF receptor type 1-associated death domain (TRADD) protein which acts as a scaffold facilitating the recruitment of several proteins including the E3 ligases TRAF2, BIRC2 and BIRC3 to form complex I [110,111,112,113,114] This complex includes RIPK1, which undergoes BIRC2- and BIRC3-mediated K11, K48 and K68 linked ubiquitylation [115,116,117,118]. Loss of RIPK1 abrogates the tumour-forming capability of these cells in an in vivo orthotopic model of GB These results suggest that the oncogenicity of the EGFRvIII mutation in GB may require the recruitment of the E3 ligase-RIP1 complex [133].

Conclusions and future perspectives

Findings

Compliance with ethical standards