Cisplatin-DNA adducts inhibit ribosomal RNA synthesis by hijacking the transcription factor human upstream binding factor.

Several eukaryotic cellular proteins recognize DNA modified by the anticancer drug cisplatin (cis-diamminedichloroplatinum(II) or cis-DDP); among these proteins is a class of DNA-binding molecules containing the HMG (high-mobility group) box DNA recognition motif. We have previously reported the extraordinarily high binding activity to cisplatin adducts by human upstream binding factor (hUBF), an HMG box containing transcription factor that stimulates ribosomal RNA synthesis (Treiber et al. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 5672-5676). In the present study, we discovered that (1) hUBF interacted selectively with DNA lesions formed by therapeutically effective platinum compounds [Pt(en)Cl2] and [Pt(dach)Cl2], in addition to the lesions formed by cis-DDP, suggesting a possible association with their anticancer effect; (2) multiple HMG boxes contributed additively to the hUBF-adduct interaction, providing a possible explanation for the unusually high affinity of hUBF for cis-DDP adducts as compared to the lower affinities of other HMG box proteins; and (3) ribosomal RNA transcription in a reconstituted system is specifically inhibited in the presence of cis-DDP adducts. In this third experiment, a ratio of adducts/promoter of approximately 4:1 completely abolished the transcription activated by hUBF. Taken together, these data lend support to the view that transcription factors involved in cellular growth regulation, such as ribosomal RNA transcription, may be hijacked by cis-DDP adducts resulting in functional inhibition.