Abstract
MicroRNAs (miRNA) control numerous physiological and pathological processes. Typically, the primary miRNA (pri-miRNA) transcripts are processed by nuclear Drosha complex into ~70-nucleotide stem-loop precursor miRNAs (pre-miRNA), which are further cleaved by cytoplasmic Dicer complex into ~21-nucleotide mature miRNAs. However, it is unclear how nascent pre-miRNAs are protected from ribonucleases, such as MCPIP1, that degrade pre-miRNAs to abort miRNA production. Here, we identify Sjögren syndrome antigen B (SSB)/La as a pre-miRNA-binding protein that regulates miRNA processing in vitro. All three RNA-binding motifs (LAM, RRM1, and RRM2) of La/SSB are required for efficient pre-miRNA binding. Intriguingly, La/SSB recognizes the characteristic stem-loop structure of pre-miRNAs, of which the majority lack a 3' UUU terminus. Moreover, La/SSB associates with endogenous pri-/pre-miRNAs and promotes miRNA biogenesis by stabilizing pre-miRNAs from nuclease (e.g. MCPIP1)-mediated decay in mammalian cells. Accordingly, we observed positive correlations between the expression status of La/SSB and Dicer in human cancer transcriptome and prognosis. These studies identify an important function of La/SSB as a global regulator of miRNA expression, and implicate stem-loop recognition as a major mechanism that mediates association between La/SSB and diverse RNA molecules.
Highlights
MicroRNA biogenesis is a multistep process regulated by RNA-binding proteins
The primary miRNA transcripts are processed by nuclear Drosha complex into ϳ70-nucleotide stem-loop precursor miRNAs, which are further cleaved by cytoplasmic Dicer complex into ϳ21-nucleotide mature miRNAs
At the final purification step, only a single protein of ϳ50 kDa appeared on the silverstained polyacrylamide gel (PAGE), and correlated closely with the miRNA regulatory activity (Fig. 1C)
Summary
MicroRNA biogenesis is a multistep process regulated by RNA-binding proteins. Results: Sjögren syndrome antigen B (SSB)/La binds stem-loop precursor microRNAs (pre-miRNA) and is required for microRNA expression. We observed positive correlations between the expression status of La/SSB and Dicer in human cancer transcriptome and prognosis These studies identify an important function of La/SSB as a global regulator of miRNA expression, and implicate stem-loop recognition as a major mechanism that mediates association between La/SSB and diverse RNA molecules. The binding of La/SSB protects pre-tRNAs from nonspecific exonuclease digestion and ensures correct processing of the 5Ј and 3Ј leader sequences of pre-tRNAs by specific ribonucleases, such as RNase P and RNase Z (36 –38) Both Drosophila and human La/SSB contain three RNAbinding motifs, a highly conserved La motif (LAM) [39], a canonical RNA recognition motif (RRM1), and an atypical RRM2, as well as a variable carboxyl (C) terminus. These significant findings provide fresh insights into the basic process of miRNA biogenesis, the diverse functions of La/SSB in RNA metabolism, and possibly the pathogenesis of cancer and autoimmune diseases
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call