Replication Protein A (RPA) Mediates Radio-Resistance of Glioblastoma Cancer Stem-Like Cells.

Henriette Pedersen,Petra Hamerlik,Kirstine Juul Elbæk,Elisabeth Anne Adanma Obara,Kristoffer Vitting-Serup

doi:10.3390/ijms21051588

Abstract

Glioblastoma (GBM) is among the deadliest of solid tumors with median survival rates of approximately 12–15 months despite maximal therapeutic intervention. A rare population of self-renewing cells referred to as GBM cancer stem-like cells (GSCs) are believed to be the source of inevitable recurrence in GBM. GSCs exhibit preferential activation of the DNA damage response pathway (DDR) and evade ionizing radiation (IR) therapy by superior execution of DNA repair compared to their differentiated counterparts, differentiated GBM cells (DGCs). Replication Protein A (RPA) plays a central role in most of the DNA metabolic processes essential for genomic stability, including DNA repair. Here, we show that RPA is preferentially expressed by GSCs and high RPA expression informs poor glioma patient survival. RPA loss either by shRNA-mediated silencing or chemical inhibition impairs GSCs’ survival and self-renewal and most importantly, sensitizes these cells to IR. This newly uncovered role of RPA in GSCs supports its potential clinical significance as a druggable biomarker in GBM.

Highlights

A key feature that distinquishes cancer cells from most normal cells is their sustained proliferation
Replication stress (RS) occurs when replication forks encounter aberrant DNA structures, which either stall, block or prematurely terminate their progression, causing fork collapse and the formation of long stretches of single-stranded DNA [1,2]. ssDNA is bound with replication protein A (RPA), a heterotrimeric protein composed of three subunits, RPA14, RPA32 and RPA70
DNA damage response pathway (DDR) is primarily coordinated by two signaling cascades: ataxia telaniectasia mutated (ATM)-checkpoint kinase 2 (CHK2) pathway and ataxia telengiectasia and Rad3-related (ATR)-checkpoint kinase 1 (CHK1) pathway, of which the activation results in the phosphorylation of H2AX at Ser139 (H2AX), a marker for the double-strand DNA breaks (DSBs) [11]

Summary

Introduction

A key feature that distinquishes cancer cells from most normal cells is their sustained proliferation. In GBM, the CSCs (GBM cancer stem-like cells; GSCs), prospectively isolated based on the expression of cell surface makers such as CD133, exhibit superior DNA repair capacity, which protect them from the impact of genotoxic therapies such as ionizing radiation (IR) or chemotherapy by alkylating agent temozolomide [6,7,8,9]. IR, a standard of care for GBM, induces a plethora of DNA lesions, including oxidative base damages, ssDNA breaks and double-strand breaks (DSBs). In response to such DNA damage, a network of events collectively termed as the DNA damage response pathway (DDR) is activated and includes DNA damage recognition, activation of check-points, cell cycle arrest and cell death [2,10]. Upon DNA damage or RS, the activation of these pathways leads to hyperphosphorylation of RPA, which modulates its role in response to various genotoxic insults [3]

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