The chloroethylating anticancer drug ACNU induces FRA1 that is involved in drug resistance of glioma cells

Abstract

FRA1 belongs, together with c-Fos and FosB, to the family of Fos proteins that form with members of the ATF and Jun family the transcription factor AP-1 (activator protein 1). Previously we showed that c-Fos protects mouse embryonic fibroblasts against the cytotoxic effects of ultraviolet (UV) light by induction of the endonuclease XPF, leading to enhanced nucleotide excision repair (NER) activity. Here, we analyzed the regulation of FRA1 in glioma cells treated with the anticancer drug nimustine (ACNU) and its role in ACNU-induced toxicity. We show that FRA1 is upregulated in glioblastoma cells following ACNU on mRNA and protein levels. Knockdown of FRA1 by either siRNA or shRNA clearly sensitized glioma cells towards ACNU-induced cell death. Despite decreased AP-1 binding activity upon FRA1 knockdown, this effect is independent on regulation of the AP-1 target genes fasL, ercc1 and xpf. In addition, FRA1 knockdown does not affect DNA repair capacity. However, lack of FRA1 attenuated the ACNU-induced phosphorylation of CHK1 and led to a reduced arrest of cells in G2/M and, thereby, presumably leads to enhanced cell death in the subsequent cell cycle.