Inhibition of Gli1 results in altered c-Jun activation, inhibition of cisplatin-induced upregulation of ERCC1, XPD and XRCC1, and inhibition of platinum–DNA adduct repair

Abstract

The transcription of ERCC1 and other nucleotide excision repair (NER) genes is strongly influenced by c-jun. C-jun is transcriptionally regulated by Gli proteins of the Hedgehog pathway. We therefore studied the possible relationships between Gli1, c-jun, and the upregulation of ERCC1, XPD and XRCC1 in cisplatin-resistant human ovarian cancer cells. We studied the paired human ovarian cancer cell lines A2780 and A2780-CP70. We used a shRNA construct that specifically degrades Gli1 message. Genes we assessed for mRNA and/or protein levels included: c-jun, ERCC1, XPD, XRCC1, Gli1, Gli2, SHH, IHH, GAPDH and α-tubulin. Platinum-DNA adduct repair was assessed by atomic absorbance spectrometry with Zeeman background correction. Use of the anti-Gli1 shRNA in cisplatin-resistant cells resulted in a block of the cell's ability to upregulate genes in response to cisplatin treatment, including: c-jun, ERCC1, XPD and XRCC1. This block in upregulation of c-jun was concurrent with a change in the phosphorylation pattern of the c-jun protein, shifting that pattern from a Ser63/73 dominant pattern, to a Thr91/93 dominant pattern. A2780-CP70 cells were treated at their cisplatin IC50, and DNA repair was assessed after pretreatment with anti-Gli1 shRNA or scrambled shRNA control. Control cells repaired 78% of platinum-DNA adducts at 12 h, compared with 33% repair in cells pretreated with anti-Gli1 shRNA resulting in a 2.4-fold difference. Pretreatment of A2780-CP70 cells with anti-Gli1 shRNA resulted in supra-additive cell killing with cisplatin; shifting the cisplatin IC50 (half maximal inhibitory concentration) from 30 μM to 5 μM. Pretreatment of these cells with cyclopamine did not shift the cisplatin IC50. We conclude that the transcriptional protein Gli1 is important in the upregulation of these three DNA repair genes in human ovarian cancer cells, and that Gli1 strongly influences platinum-DNA adduct repair, and cellular sensitivity to cisplatin. This Gli1 role has c-jun as an intermediate in the pathway. In all, inhibition of Gli1 by a specific shRNA inhibits the upregulation of c-jun Ser63/73, and also inhibits the upregulation of three genes essential to NER (ERCC1, XPD) and base excision repair (XRCC1).