Disrupting two cancer hallmarks with one target: DHX36, the major G-quadruplex helicase

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PROJECT SUMMARY This proposal uses innovative approaches and novel mouse models to define an underlying mechanism of tumorigenesis. This proposal further seeks to identify the major G-quadruplex helicase, DHX36 (aliases: G4R1 and RHAU), as a novel therapeutic target. G-quadruplexes (G4s) are dynamic, “knot-like” DNA or RNA structures that shut down transcription and translation, respectively. Of relevance to cancer, genes that promote cell proliferation and survival (i.e. oncogenes) are more likely to contain G4 sequences, while genes that suppress cell proliferation and survival (i.e. tumor suppressor genes) are depleted of G4s. Therefore, G4s represent an epigenetic feature that generally distinguishes oncogenes from tumor suppresser genes. As such, G4s are attractive cancer therapeutic targets. Moreover, >80% of tumors rely on telomerase to prevent telomere shortening, which confers cellular immortality, a classic hallmark of cancer. Extensive G4 structures form in telomere DNA that inhibit telomerase. Taken together, G4 structures reduce oncogene expression and cellular immortality. Conversely, G4 helicases unwind G4 structures increasing oncogene expression and limiting telomere elongation. DHX36 accounts for the majority of G4 helicase activity in human cells and is commonly overexpressed in cancer. DHX36-overexpression is correlated with a significantly reduction in patient survival. Thus, DHX36 is a prime candidate to explore as a therapeutic target. In this proposal, we will pursue two aims to determine the potential of DHX36 as a therapeutic target. In the first aim, we hypothesize that DHX36- overexpression initiates tumors and exacerbates tumor progression. In the second aim, we hypothesize that decreased DHX36 expression alone or in combination with G4 ligands will reduce oncogene expression, telomere elongation, and result in tumor remission. We will test these hypotheses using a novel Dhx36- overexpression mouse as well as a Dhx36-knockout mouse crossed to a transgenic mouse tumor line. The proposed studies will be the first to determine the role of DHX36 in tumorigenesis using mouse models. This work is poised to identify DHX36 as a novel therapeutic target that inhibition of will disrupt two fundamental cancer pathways: oncogene expression and telomere elongation. Undergraduate and graduate students will be integrated at every stage of the project allowing them to gain authentic experience with innovative mouse and bioinformatics technologies applied to a deadly human disease.