Abstract
The let-7 family of miRNAs has been shown to be crucial in many aspects of biology, from the regulation of developmental timing to cancer. The available methods to regulate this family of miRNAs have so far been mostly genetic and therefore not easily performed experimentally. Here, we describe a small molecule screen designed to identify regulators of let-7 targets in human cells. In particular, we focused our efforts on the identification of small molecules that could suppress let-7 targets, as these could serve to potentially intercede in tumors driven by loss of let-7 activity. After screening through roughly 36,000 compounds, we identified a class of phosphodiesterase inhibitors that suppress let-7 targets. These compounds stimulate cAMP levels and raise mature let-7 levels to suppress let-7 target genes in multiple cancer cell lines such as HMGA2 and MYC. As a result, these compounds also show growth inhibitory activity on cancer cells.
Highlights
Lin28A and Lin28B are RNA-binding proteins with two types of nucleic acid interacting domains: a cold shock domain (CSD) followed by two repeats of CCHC-type zinc-binding motifs[1]
In addition to its role in development, LIN28 has been shown to be activated in 15% of human tumors and its expression correlates with tumor progression and poor prognosis[13]
The Renilla luciferase is flanked by 8 repeats of let-7 target sequence and its mRNA will be subject to a higher rate of degradation in the presence of a higher let-7 activity
Summary
Lin28A and Lin28B are RNA-binding proteins with two types of nucleic acid interacting domains: a cold shock domain (CSD) followed by two repeats of CCHC-type zinc-binding motifs[1]. Lin28A recruits the TUTase Zcchc[11] to inhibit the maturation of precursor let-7 (pre-let-7)[5] These let-7 family members of miRNA are known to regulate developmental timing and cell-fate decisions in less complex organisms. Let-7 family members have identical seed sequences and divergent stem-loop regions Their targets include many oncogenes (C-MYC, N-MYC, RAS, and HMGA2), cell-cycle regulators (CYCLIND1, D2), as well as other developmental regulators including LIN28A and LIN28B8,9. Their mutual inhibition with Lin[28] forms a powerful regulatory loop that is thought to have broad effects on developmental maturity. We describe small molecule screening for compound that affect the expression of let-7 targets
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