The distribution of individual miRNA species between high-molecular weight and low-molecular weight RISC complexes by small RNA sequencing in thyroid cancer cell lines

Thyroid cancer is the most prevalent malignancy of the endocrine system. We and others have shown that several microRNAs, which are ~21-24nt post-transcriptional gene regulators, are aberrantly expressed in anaplastic thyroid cancer (ATC) and papillary thyroid cancer (PTC) tissues and cell lines. In the cell, miRNAs are bound to Argonaute (AGO) proteins as low molecular weight RNA Induced Silencing Complexes (LMW-RISCs) that can then assemble into high molecular weight RISCs (HMW-RISCs) that also include additional proteins and mRNA. In this study, we sought to analyze the association of miRNAs across RISC complexity in ATC and PTC. For both ATC and PTC lines, miRNAs were enriched in HMW-RISC and LMW-RISC fractions compared with intermediate fractions or very low molecular weight (AGO-poor) fractions. Furthermore, 60% of all miRNAs were more abundant in LMW-RISC versus HMW- RISC fractions by ~2-4 fold. Surprisingly, miR-21-5p, one of the most abundant miRNAs in both ATC and PTC lines, was consistently one the least abundant miRNAs in HMW-RISC and the most enriched miRNA in LMW-RISC fractions. These findings suggest that miR-21 may be uniquely distributed in RISCs relative to other miRNAs. Furthermore, the methodology described here is a useful way to assess the relative magnitude of miR-21association with HMW and LMW-RISCs and may help to reveal the true roles of this miRNA in thyroid cancer development, progression, and treatment. Total RNA was extracted from SW1736 and TPC-1 cell line fractionated lysates. HMW-RISC and LMW-RISC fractions. Input, Medium Molecular weight (MMW-RISC), and RISC-poor fractions were included as controls.