Mature microRNA-binding protein QKI promotes microRNA-mediated gene silencing

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• Argonaute (AGO) proteins are central to microRNA (miRNA) function.
• However, AGO-free mature miRNAs interacting with RNA-binding proteins (RBPs) suggest complex regulatory mechanisms.
• Investigating novel RBPs involved in miRNA pathways is crucial for understanding gene regulation.

Purpose of the Study:

• To globally identify microRNA-binding proteins (miRBPs).
• To characterize the role of RBP quaking (QKI) in miRNA-mediated gene silencing.
• To elucidate QKI's function as a potential tumor suppressor.

Main Methods:

• Analysis of PAR-CLIP data sets to identify QKI as a let-7b binding protein.
• Validation of AGO-free miRNAs in AGO-depleted human and mouse cells.
• Single-molecule level analysis of AGO2/miRNA/target mRNA complex dynamics.

Main Results:

• QKI was identified as a novel RBP that binds let-7b, functioning independently of AGO.
• QKI acts as an auxiliary factor, enhancing AGO2/let-7b-mediated gene silencing and mRNA decay.
• QKI suppresses let-7b dissociation from AGO2 and slows complex assembly, while QKI overexpression inhibits cMYC and reduces cell proliferation.

Conclusions:

• QKI is a novel type of RBP involved in versatile miRNA-mediated gene silencing.
• QKI functions as a complementary factor in miRNA-mediated mRNA decay.
• QKI acts as a tumor suppressor by augmenting let-7b activity, impacting cell proliferation and migration.