Dual Role of Integrin Alpha-6 in Glioblastoma: Supporting Stemness in Proneural Stem-Like Cells While Inducing Radioresistance in Mesenchymal Stem-Like Cells.

Elisabetta Stanzani,Fina Martínez-Soler,Anna Esteve-Codina,Lorena Passoni,Guillaume Bourmeau,Núria De La Iglesia,Leire Pedrosa,Giorgio Seano,Michela Matteoli,Oceane Anezo,Avelina Tortosa,Aleix Noguera-Castells

doi:10.3390/cancers13123055

Abstract

Simple SummaryGlioblastoma stem-like cells (GSCs) are responsible for most of the malignant characteristics of glioblastoma, including therapeutic resistance, tumour recurrence, and tumour cellular heterogeneity. Therefore, increased understanding of the mechanisms regulating GSCs aggressiveness may help to improve patients’ outcomes. Here, we investigated the role of integrin a6 in controlling stemness and resistance to radiotherapy across proneural and mesenchymal molecular subtypes. We observed that integrin a6 had a clear role in stemness maintenance in proneural but not in mesenchymal GSCs. In addition, we proved a crucial role of integrin a6 in supporting mesenchymal GSCs resistance to ionizing radiation. Finally, we highlighted that integrin a6 may control different stem-associated features in GSCs, depending on the molecular subtype. The inhibition of integrin a6 limits stem-like malignant characteristics in both GSCs subtypes and thus may potentially control tumour relapse following conventional treatment.Therapeutic resistance after multimodal therapy is the most relevant cause of glioblastoma (GBM) recurrence. Extensive cellular heterogeneity, mainly driven by the presence of GBM stem-like cells (GSCs), strongly correlates with patients’ prognosis and limited response to therapies. Defining the mechanisms that drive stemness and control responsiveness to therapy in a GSC-specific manner is therefore essential. Here we investigated the role of integrin a6 (ITGA6) in controlling stemness and resistance to radiotherapy in proneural and mesenchymal GSCs subtypes. Using cell sorting, gene silencing, RNA-Seq, and in vitro assays, we verified that ITGA6 expression seems crucial for proliferation and stemness of proneural GSCs, while it appears not to be relevant in mesenchymal GSCs under basal conditions. However, when challenged with a fractionated protocol of radiation therapy, comparable to that used in the clinical setting, mesenchymal GSCs were dependent on integrin a6 for survival. Specifically, GSCs with reduced levels of ITGA6 displayed a clear reduction of DNA damage response and perturbation of cell cycle pathways. These data indicate that ITGA6 inhibition is able to overcome the radioresistance of mesenchymal GSCs, while it reduces proliferation and stemness in proneural GSCs. Therefore, integrin a6 controls crucial characteristics across GBM subtypes in GBM heterogeneous biology and thus may represent a promising target to improve patient outcomes.

Highlights

Glioblastoma (GBM) is the most common and most malignant primary brain tumour in adults
To better understand the significance of integrin a6 in GBM, we analysed in silico the ITGA6 expression in the two most important GBM subtypes
Even taking into consideration the recent integrative model that tuned the previous classification into four molecular subtypes [45], ITGA6-expressing cells were enriched in the MES-like state (Figure S1D)

Summary

Introduction

Glioblastoma (GBM) is the most common and most malignant primary brain tumour in adults. It is characterized by high recurrence rates even after maximal resection and multimodal treatment [1]. Key players among the various cellular elements are the GBM stem-like cells (GSCs), which are commonly believed to be at the origin of tumorigenesis, invasion, angiogenesis, immune evasion, and treatment resistance [5,6,7,8,9,10,11]. GSCs are characterized by specific biological features which confer them an outstanding capacity to cope with radiation-induced cell-damage [7,12,13]

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