Coordinated Regulation of Cap-Dependent Translation and MicroRNA Function by Convergent Signaling Pathways

Abstract

Cell growth and proliferation require the coordinated activation of many cellular processes, including cap-dependent mRNA translation. MicroRNAs oppose cap-dependent translation and set thresholds for expression of target proteins. Emerging data suggest that microRNA function is enhanced by cellular activation due in part to induction of the RNA-induced silencing complex (RISC) scaffold protein GW182. In the current study, we demonstrate that increased expression of GW182 in activated or transformed immune cells results from effects of phosphoinositol 3-kinase-Akt-mechanistic target of rapamycin (PI3K-AktmTOR) and Jak-Stat-Pim signaling on the translation of GW182 mRNA. Both signaling pathways enhanced polysome occupancy and eukaryotic initiation factor 4E (eIF4E) binding to the 5= 7mG cap of GW182 mRNA. The effect of Jak-Stat-Pim signaling on polysome occupancy and expression of GW182 protein was greater than that of PI3K-Akt-mTOR signaling, likely resulting from enhanced eIF4A-dependent unwinding of G-quadruplexes in the 5= untranslated region of GW182 mRNA. Consistent with this, GW182 expression and microRNA function were reduced by inhibition of mTOR or Pim kinases, translation initiation complex assembly, or eIF4A function. Taken together, these data provide a mechanistic link between microRNA function and cap-dependent translation that allows activated immune cells to maintain microRNA-mediated repression of targets despite enhanced rates of protein synthesis.

Distinct temporal expression of the GW182 paralog TNRC6A in neurons regulates dendritic arborization

“…We observed that the amount of GW182 mRNA remains unchanged during neuronal development, suggesting a role for translation regulatory mechanisms in controlling GW182 levels during neuronal development. However, we cannot rule out the possibility of degradation mechanisms, as previous studies have indicated that GW182 levels can be regulated translationally as well as through ubiquitin-mediated proteasomal degradation (Li et al, 2014;Olejniczak et al, 2016). Our expression profile studies indicate that the developmental reduction in GW182 expression correlates with the emergence of synaptic circuitry and neuronal activity.…”

ARS2-directed alternative splicing mediates CD28 driven T cell glycolysis and effector function

“…Since the primary function of ARS2 bound to the CBC is recruitment of RNA processing factors to nascent transcripts 11,12,17,24,29 , we determined the effect of ARS2 on splicing factor association with Pkm pre-mRNA. For these experiments T cell activation was modeled by IL-3 stimulation of FL5.12.xL cells as previously described 32 . Similar to T cell activation, IL-3 stimulated FL5.12.xL cells upregulated ARS2 and preferentially spliced Pkm to favor Pkm2 expression (Extended Data Fig.…”

The Role of Dynamic miRISC During Neuronal Development

“…Another mechanism of regulating miRISC is via protein-protein interactions. AGO2-GW182 interaction is highly regulated by various extracellular cues (Olejniczak et al, 2013(Olejniczak et al, , 2016Wu et al, 2013;La Rocca et al, 2015;Bridge et al, 2017;Rajgor et al, 2018). AGO2 interaction with RBPs, as well as the modulation of miRISC activity by RBPs are shown to be regulated by different signals like hypoxia, arsenite stress, FIGURE 2 | The role of miRISC in cue mediated protein synthesis during neurodevelopment.…”