The RNA-binding protein QKI-7 recruits the poly(A) polymerase GLD-2 for 3′ adenylation and selective stabilization of microRNA-122

Abstract

MicroRNA-122 (miR-122) is highly expressed in hepatocytes, where it plays an important role in regulating cholesterol and fatty acid metabolism, and it is also a host factor required for hepatitis C virus replication. miR-122 is selectively stabilized by 3′ adenylation mediated by the cytoplasmic poly(A) polymerase GLD-2 (also known as PAPD4 or TENT2). However, it is unclear how GLD-2 specifically stabilizes miR-122. Here, we show that QKI7 KH domain-containing RNA binding (QKI-7), one of three isoforms of the QKI proteins, which are members of the signal transduction and activation of RNA (STAR) family of RNA-binding proteins, is involved in miR-122 stabilization. QKI down-regulation specifically decreased the steady-state level of mature miR-122, but did not affect the pre-miR-122 level. We also found that QKI-7 uses its C-terminal region to interact with GLD-2 and its QUA2 domain to associate with the RNA-induced silencing complex protein Argonaute 2 (Ago2), indicating that the GLD-2–QKI-7 interaction recruits GLD-2 to Ago2. QKI-7 exhibited specific affinity to miR-122 and significantly promoted GLD-2–mediated 3′ adenylation of miR-122 in vitro. Taken together, our findings indicate that miR-122 binds Ago2–interacting QKI-7, which recruits GLD-2 for 3′ adenylation and stabilization of miR-122.

RNA-binding proteins in tumor progression

“…Compared with normal tissues, the expression of QKI is significantly reduced in lung cancer, which is associated with a poor prognosis [ 129 – 132 ]. QKI binds to QKI response element [QRE, 5′-A (C/A) UAA-3] and exerts multifunctional effects on target RNAs, including localization, stability, translation efficiency, and microRNA (miRNA) processing [ 133 , 134 ]. In normal cells, QKI can compete with the core splicing factor SF1, selectively suppress the splicing of exon 12 of NUMB mRNA, and upregulate the expression of NUMB isoforms, thereby inhibiting cell proliferation and preventing the activation of Notch signaling pathway [ 135 , 136 ].…”

Structures of mammalian GLD-2 proteins reveal molecular basis of their functional diversity in mRNA and microRNA processing

“…Like in cytoplasmic polyadenylation, the selectivity of GLD-2 on miRNA substrates may be also dependent on the binding with other partners. A recent study suggests that an isoform of QKI7 KH domain-containing RNA binding protein (QKI-7) is responsible for the selective adenylation of miR-122 by GLD-2 in Huh7 cells ( 58 ). The adenylation activity of GLD-2 on miR-122 is found to be counterbalanced by deadenylation mediated by CUG-binding protein 1 (CUGBP1) and PARN ( 59 ).…”

Regulation of RNA stability at the 3′ end

“…et al 2014). In humans, TENT2 is recruited by QKI-7 (protein quaking isoform 7) to stabilize the miRNA miR-122 in the liver and fibroblasts through monoadenylation (D'Ambrogio et al 2012;Hojo et al 2020;Katoh et al 2009), where its depletion significantly lowers miR-122 levels (Gebert et al 2014). Interestingly, TENT2 activity is regulated by Akt1 catalyzed phosphorylation, providing a first example of the regulation of miRNA metabolism by Akt1 (Chung et al 2019a).…”