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

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 O-methylguanine (OMeG) and characterized by arrest of cells in the G-M phase.

Repair gene O -methylguanine-DNA methyltransferase is controlled by SP1 and up-regulated by glucocorticoids, but not by temozolomide and radiation.

Therapy of malignant glioma relies on treatment with the O -methylating agent temozolomide (TMZ) concomitant with ionizing radiation followed by adjuvant TMZ. For the treatment of recurrences, DNA chloroethylating drugs are also used. The main killing lesion induced by these drugs is O -alkylguanine.

Adaptive upregulation of DNA repair genes following benzo(a)pyrene diol epoxide protects against cell death at the expense of mutations.

A coordinated and faithful DNA damage response is of central importance for maintaining genomic integrity and survival. Here, we show that exposure of human cells to benzo(a)pyrene 9,10-diol-7,8-epoxide (BPDE), the active metabolite of benzo(a)pyrene (B(a)P), which represents a most important carcinogen formed during food preparation at high temperature, smoking and by incomplete combustion processes, causes a prompt and sustained upregulation of the DNA repair genes DDB2, XPC, XPF, XPG and POLH. Induction of these repair factors on RNA and protein level enhanced the removal of BPDE adducts from DNA and protected cells against subsequent BPDE exposure.

Apoptosis induced by temozolomide and nimustine in glioblastoma cells is supported by JNK/c-Jun-mediated induction of the BH3-only protein BIM.

The outcome of cancer therapy strongly depends on the complex network of cell signaling pathways, including transcription factor activation following drug exposure. Here we assessed whether and how the MAP kinase (MAPK) cascade and its downstream target, the transcription factor AP-1, influence the sensitivity of malignant glioma cells to the anticancer drugs temozolomide (TMZ) and nimustine (ACNU). Both drugs induce apoptosis in glioma cells at late times following treatment.

The bacterial alkyltransferase-like (eATL) protein protects mammalian cells against methylating agent-induced toxicity.

In both pro- and eukaryotes, the mutagenic and toxic DNA adduct O(6)-methylguanine (O(6)MeG) is subject to repair by alkyltransferase proteins via methyl group transfer. In addition, in prokaryotes, there are proteins with sequence homology to alkyltransferases, collectively designated as alkyltransferase-like (ATL) proteins, which bind to O(6)-alkylguanine adducts and mediate resistance to alkylating agents. Whether such proteins might enable similar protection in higher eukaryotes is unknown.

Translesion polymerase η is upregulated by cancer therapeutics and confers anticancer drug resistance.

DNA repair processes are a key determinant of the sensitivity of cancer cells to DNA-damaging chemotherapeutics, which may induce certain repair genes as a mechanism to promote resistance. Here, we report the results of a screen for repair genes induced in cancer cells treated with DNA crosslinking agents, which identified the translesion polymerase η (PolH) as a p53-regulated target acting as one defense against interstrand crosslink (ICL)-inducing agents. PolH was induced by fotemustine, mafosfamide, and lomustine in breast cancer, glioma, and melanoma cells in vitro and in vivo, with similar inductions observed in normal cells such as lymphocytes and diploid fibroblasts.

Three prime exonuclease I (TREX1) is Fos/AP-1 regulated by genotoxic stress and protects against ultraviolet light and benzo(a)pyrene-induced DNA damage.

Cells respond to genotoxic stress with the induction of DNA damage defence functions. Aimed at identifying novel players in this response, we analysed the genotoxic stress-induced expression of DNA repair genes in mouse fibroblasts proficient and deficient for c-Fos or c-Jun. The experiments revealed a clear up-regulation of the three prime exonuclease I (trex1) mRNA following ultraviolet (UV) light treatment.

A role for UV-light-induced c-Fos: Stimulation of nucleotide excision repair and protection against sustained JNK activation and apoptosis.

UV light (UV-C) is a potent inducer of the c-fos gene. Cells lacking c-Fos are hypersensitive to the cytotoxic effect of UV-C indicating a protective role of c-fos induction. Here we show that cells deficient in c-Fos (fos-/-) are unable to remove cyclobutane pyrimidine dimers (CPDs) from DNA and undergo apoptosis at high frequency via the Fas pathway.

Analysis of the leukemia inhibitory factor receptor functional domains by chimeric receptors and cytokines.

In contrast to other hematopoietic cytokine receptors, the leukemia inhibitory factor receptor (LIFR) possesses two cytokine binding modules (CBMs). Previous studies suggested that the NH(2)-terminal CBM and the Ig-like domain of the LIFR are most important for LIF binding and activity. Using the recently engineered designer cytokine IC7, which induces an active heterodimer of the LIFR and gp130 after binding to the IL-6R, and several receptor chimeras of the LIFR and the interleukin-6 receptor (IL-6R) carrying the CBM of the IL-6R in place of the COOH-terminal LIFR CBM, we could assign individual receptor subdomains to individual binding sites of the ligand.

The upper cytokine-binding module and the Ig-like domain of the leukaemia inhibitory factor (LIF) receptor are sufficient for a functional LIF receptor complex.

To elucidate the function of the two cytokine-binding modules (CBM) of the leukemia inhibitory factor receptor (LIFR), receptor chimeras of LIFR and the interleukin-6 receptor (IL-6R) were constructed. Either the NH(2)-terminal (chimera RILLIFdeltaI) or the COOH-terminal LIFR CBM (chimera RILLIFdeltaII) were replaced by the structurally related CBM of the IL-6R which does not bind LIF. Chimera RILLIFdeltaI is functionally inactive, whereas RILLIFdeltaII binds LIF and mediates signalling as efficiently as the wild-type LIFR.