The stem cell-specific protein TRIM71 inhibits maturation and activity of the pro-differentiation 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 pro-differentiation 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 datasets 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 the precise mechanistic dual regulation of let-7.

Reactivation of the progenitor gene Trim71 enhances the mitotic and hair cell-forming potential of cochlear supporting cells

“…The shared list of upregulated genes included well-known let-7 targets such as Hmga2, Arid3a, Igf2bp1, Ccnd2 and Trim71 itself (table S3) (Figure 3D), suggesting that in cochlear organoid culture TRIM71 may inhibit the expression or activity of mature let-7 miRNAs or both. Recent studies found that TRIM71 represses mature let-7 miRNA expression by binding LIN28A or LIN28B proteins and enhancing their inhibition of let-7 biogenesis (Torres Fernandez et al, 2021). Our pull-down experiments using HEK293T cells revealed that NHL or Coiled-Coil deficient TRIM71 proteins failed to bind LIN28B (Figure S3), which correlated with the inability of NHL or Coiled-Coil deficient TRIM71 to upregulate the expression of the let-7 target Hmga2 in cochlear organoids (Figure 3E).…”

“…Recent studies revealed that TRIM71 interferes with the expression and function of mature let-7 miRNAs through enhancing LIN28A and LIN28B-mediated repression of let-7 biogenesis (Torres Fernandez et al, 2021) and through limiting the expression of AGO2, an essential component of miRNA-mediated gene silencing (Liu et al, 2021). Indeed, our transcriptomic profiling revealed that many of the up-regulated genes that were shared between TRIM71 and LIN28B were known or predicted targets of let-7 -mediated gene silencing.…”

“…Lin28b and Trim71 are evolutionary conserved targets of let-7 mediated gene silencing (Reinhart et al, 2000, Lin et al, 2007). Recent studies suggest that like LIN28B, TRIM71 interferes with the processing and activity of let-7 miRNAs (Liu et al, 2021, Torres Fernandez et al, 2021, Rybak et al, 2009). Whether reactivation of Trim71 enhances the regenerative capacity of cochlear supporting cells has yet to be determined.…”

Ubiquitin ligases and a processive proteasome facilitate protein clearance during the oocyte-to-embryo transition in Caenorhabditis elegans

“…A new twist is that recent studies suggest that mammalian LIN-41/TRIM71 can inhibit the accumulation of let-7 microRNAs (Liu et al . 2021; Torres-Fernandez et al . 2021b), suggesting its involvement as a component of a bistable developmental switch.…”