Platinum-seq: High-throughput mapping of small-molecule platinum adducts on cellular RNA
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Methods to map small-molecule interactions with cellular RNAs are important for understanding endogenous activation, such as in riboswitches, as well as the potential for exogenous compounds to target RNA. Cisplatin is one of the most widely used of the platinum anticancer drugs that are prescribed in approximately 40-50% of all chemotherapy treatments (Dyson and Sava, 2006; Harper et al., 2010). Despite nearly 40 years of experience with this class of drugs, we still lack a comprehensive understanding of the targets of Pt compounds and their effects on cells. Pt(II) compounds are well-known DNA and RNA crosslinking agents, but the latter area is under-studied. In order to better understand the impacts of cisplatin and other platinum(II)-derived small molecules on cellular RNA, we have developed a technique we call “Platinum-seq,” which couples reverse transcription mapping of platinated RNAs to high-throughput sequencing. Chapter 1 is a study of cisplatin and a novel click-functionalized platinum compound (2-ADAP Pt) binding to the HDV ribozyme, a small catalytic RNA. Chapter 2 moves our platinum mapping approaches from low-throughput, sequencing gel based methods into next-generation sequencing for high-throughput analysis of all platinum sites in cellular RNA, a method we have named “Platinum-seq.” Chapter 3 is a study of differential gene expression of Saccharomyces cerevisiae treated with cisplatin and a second novel platinum(II) compound (azaplatin), using data acquired from the work in Chapter 2. Chapter 4 describes recent efforts to implement pre-enrichment of sequencing targets using click chemistry followed by DNA hybridization, in order to enrich for platinated fragments before sequencing library construction. Together, this work represents a significant step forward in advancing analysis of Pt(II) binding to cellular RNA, a potentially important target for this widely used class of anticancer compounds. Methods developed here are broadly applicable to genome-wide identification of platinum accumulation on DNA as well, which has not been pursued despite the extensive use of these compounds.