Identifying Small Organic Compounds that Induce an Alternative Structure in Precursor miRNA-92b

MicroRNAs (miRNA) are a form of small non-coding RNA that downregulates protein translation. They do this by directly binding to messenger RNA targets in an RNA-induced silencing complex (RISC). The biogenesis of miRNAs relies on two cleavage events, one of which is the cleavage of a precursor miRNA (pre-miRNA) by the enzyme Dicer. For Dicer to cleave, it needs to recognize the two nucleotide 3’ overhang of the pre-miRNA when it is in the canonical stem-loop structure. However, recent studies have shown some pre-miRNAs can form non-canonical guanine-quadruplex (G4) structures that lack this overhang, including pre-miR-92b.  miRNA-92b is a clinically important miRNA due to its upregulation in multiple types of cancer, which has been correlated with an increased resistance to certain chemotherapies. We have identified small organic compounds that selectively bind to the G4 forming pre-miR-92b through small molecule microarray analysis. These compounds are being analyzed for their ability to bind to and stabilize the G4 structure of pre-miR-92b through biochemical and biophysical means, including fluorimeter titrations. Furthermore, we are examining how this change in pre-miRNA structure alters miRNA-92b maturation, specifically examining how Dicer cleavage of pre-miR-92b is affected.