Inhibition of RNA polymerase II transcription in human cell extracts by cisplatin DNA damage

The anticancer drug cisplatin induces a spectrum of lesions in DNA. The eff ect of such DNA damage on transcription by RNA polymerase II (RNA pol II) i n human cell extracts was investigated at the level of initiation and elong ation. RNA pol II transcription directed from the adenovirus major late pro moter was inhibited following treatment of the promoter-containing template with increasing concentrations of cisplatin. Furthermore, transcription fr om an undamaged promoter fragment was depleted in the presence of increasin g amounts of cisplatin DNA damage on an exogenous plasmid, suggesting such damage may hijack an essential factor for transcription initiation. The eff ect of cisplatin damage on RNA pol II elongation was investigated using sit e-specifically-placed cisplatin adducts. The GTG adduct was an effective bl ock to RNA pol II elongation, inhibiting the polymerase by 80%. In contrast , RNA pol II completely bypassed the cisplatin GG intrastrand adduct. These studies suggest that the inhibition of RNA pol II transcription observed f ollowing the treatment of cells with cisplatin is likely to reflect the com bined effects of DNA damage at the level of both transcription initiation a nd elongation.