The stem cell–specific protein TRIM71 inhibits maturation and activity of the prodifferentiation miRNA let-7 via two independent molecular mechanisms

Abstract

The stem cell–specific RNA-binding protein TRIM71/LIN-41 was the first identified target of the prodifferentiation and tumor suppressor miRNA let-7. TRIM71 has essential functions in embryonic development and a proposed oncogenic role in several cancer types, such as hepatocellular carcinoma. Here, we show that TRIM71 regulates let-7 expression and activity via two independent mechanisms. On the one hand, TRIM71 enhances pre-let-7 degradation through its direct interaction with LIN28 and TUT4, thereby inhibiting let-7 maturation and indirectly promoting the stabilization of let-7 targets. On the other hand, TRIM71 represses the activity of mature let-7 via its RNA-dependent interaction with the RNA-induced silencing complex (RISC) effector protein AGO2. We found that TRIM71 directly binds and stabilizes let-7 targets, suggesting that let-7 activity inhibition occurs on active RISCs. MiRNA enrichment analysis of several transcriptomic data sets from mouse embryonic stem cells and human hepatocellular carcinoma cells suggests that these let-7 regulatory mechanisms shape transcriptomic changes during developmental and oncogenic processes. Altogether, our work reveals a novel role for TRIM71 as a miRNA repressor and sheds light on a dual mechanism of let-7 regulation, uncovering a bistable switch between TRIM71 and let-7 miRNAs that regulates the balance between proliferation and differentiation.

Circ_0007429/miR‐637/TRIM71/Ago2 axis participates in the regulation of proliferation, migration, invasion, apoptosis, and aerobic glycolysis of HCC

“…Ago2 is one of the Argonaute proteins that interact with microRNAs, forming a miRNA-induced silencing complex (miRISC), stem cells (mESCs). 19,31,32 Here, we found that knockdown of circ_0007429 increased Ago2 expression at the protein, but not at the mRNA, level; this effect was counteracted by overexpression of TRIM71 in addition to circ_0007429 knockdown. We found that knockdown or overexpression of TRIM71 alone affected Ago2…”

“…Ago2 is one of the Argonaute proteins that interact with microRNAs, forming a miRNA‐induced silencing complex (miRISC), to repress posttranscriptional target gene expression. TRIM71 inhibits Ago2 production during self‐renewal of mouse embryonic stem cells (mESCs) 19,31,32 . Here, we found that knockdown of circ_0007429 increased Ago2 expression at the protein, but not at the mRNA, level; this effect was counteracted by overexpression of TRIM71 in addition to circ_0007429 knockdown.…”

New Tricks with Old Dogs: Computational Identification and Experimental Validation of New miRNA–mRNA Regulation in hiPSC-CMs

“…The TRIM71 protein promotes stem cell proliferation and is strongly downregulated during exit from pluripotency [ 42 , 43 , 44 ]. We measured TRIM71 levels following miR-99a-5p mimic transfections at an early and late timepoint post hiPSC differentiation start.…”

Fraternity of old‐timers: How ubiquitin regulates miRNA functions

“…Regulation is carried out in different ways and outcomes in the suppression or enhancement of miRNA repressive functions. Through interaction with Ago, the proteins NHL-2 and Trim32 of nematode and human, respectively, [78,82] enhance miRNA-mediated gene regulation, while murine Trim71 suppresses it [79][80][81]83,84] ; Drosophila Mei-P26 both suppresses and activates, depending on the cellular environment. [85,86] TRIM-HNL proteins do not regulate the functioning of all miRNAs, but only particular ones; for some cases, this proved to be highly conserved let-7, [78,79,82,84,87] whose biological role is largely related to the change of cell programs during stem cell differentiation.…”

“…Through interaction with Ago, the proteins NHL-2 and Trim32 of nematode and human, respectively, [78,82] enhance miRNA-mediated gene regulation, while murine Trim71 suppresses it [79][80][81]83,84] ; Drosophila Mei-P26 both suppresses and activates, depending on the cellular environment. [85,86] TRIM-HNL proteins do not regulate the functioning of all miRNAs, but only particular ones; for some cases, this proved to be highly conserved let-7, [78,79,82,84,87] whose biological role is largely related to the change of cell programs during stem cell differentiation. [22,88] It is important to note that TRIM-NHL-dependent regulation, despite the presence of a RING domain in the protein, generally is not associated with the ubiquitylation of Ago or other proteins: the ubiquitin ligase property of NHL-2 and Trim32 is not required for miRISC activation [78,82] ,…”