Temozolomide Induces Senescence and Repression of DNA Repair Pathways in Glioblastoma Cells via Activation of ATR-CHK1, p21, and NF-κB.

Dorthe Aasland,Maja T Tomicic,Laura Götzinger,Bernd Kaina,Simon Schneider,Markus Christmann,Emelie E Reuber,Wynand P Roos,Laura Hauck,Melanie Effenberger,Jessica Meyer,Nancy Berte

doi:10.1158/0008-5472.can-18-1733

Abstract

The DNA-methylating drug temozolomide, which induces cell death through apoptosis, is used for the treatment of malignant glioma. Here, we investigate the mechanisms underlying the ability of temozolomide to induce senescence in glioblastoma cells. Temozolomide-induced senescence was triggered by the specific DNA lesion O6-methylguanine (O6MeG) and characterized by arrest of cells in the G2-M phase. Inhibitor experiments revealed that temozolomide-induced senescence was initiated by damage recognition through the MRN complex, activation of the ATR/CHK1 axis of the DNA damage response pathway, and mediated by degradation of CDC25c. Temozolomide-induced senescence required functional p53 and was dependent on sustained p21 induction. p53-deficient cells, not expressing p21, failed to induce senescence, but were still able to induce a G2-M arrest. p14 and p16, targets of p53, were silenced in our cell system and did not seem to play a role in temozolomide-induced senescence. In addition to p21, the NF-κB pathway was required for senescence, which was accompanied by induction of the senescence-associated secretory phenotype. Upon temozolomide exposure, we found a strong repression of the mismatch repair proteins MSH2, MSH6, and EXO1 as well as the homologous recombination protein RAD51, which was downregulated by disruption of the E2F1/DP1 complex. Repression of these repair factors was not observed in G2-M arrested p53-deficient cells and, therefore, it seems to represent a specific trait of temozolomide-induced senescence. SIGNIFICANCE: These findings reveal a mechanism by which the anticancer drug temozolomide induces senescence and downregulation of DNA repair pathways in glioma cells.

Highlights

The success of cancer therapy with genotoxic anticancer drugs rests on their potency to induce cell death
We showed that O6MeG is the initial trigger of temozolomide-induced apoptosis, which is mediated through the DNA damage response (DDR) [22]
Because the isogenic lines only differ in the methylguanine-DNA methyltransferase (MGMT) repair capacity and, thereby, the amount of O6MeG following temozolomide treatment, we conclude that this lesion is responsible for inducing temozolomideinduced cell death [9], and for senescence

Summary

Introduction

The success of cancer therapy with genotoxic anticancer drugs rests on their potency to induce cell death. Genotoxic anticancer drugs induce death, but are effective in activating other pathways such as cellular senescence, which allows cancer cells to survive without proliferation [1]. We have shown that glioblastoma cells treated with the methylating anticancer drug temozolomide undergo apoptosis and, in the same dose range and time period, senescence [2]. Evidence for induction of senescence by temozolomide was provided in other studies with glioma cells [3,4,5]. The finding that not all tumor cells can be killed through anticancer drug treatment is of importance in view of the dismal prognosis of patients with glioblastoma with a median.

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