Coordinated inhibition of C/EBP by Tribbles in multiple tissues is essential for Caenorhabditis elegans development

Abstract

BackgroundTribbles proteins are conserved pseudokinases that function to control kinase signalling and transcription in diverse biological processes. Abnormal function in human Tribbles has been implicated in a number of diseases including leukaemia, metabolic syndromes and cardiovascular diseases. Caenorhabditis elegans Tribbles NIPI-3 was previously shown to activate host defense upon infection by promoting the conserved PMK-1/p38 mitogen-activated protein kinase (MAPK) signalling pathway. Despite the prominent role of Tribbles proteins in many species, our knowledge of their mechanism of action is fragmented, and the in vivo functional relevance of their interactions with other proteins remains largely unknown.ResultsHere, by characterizing nipi-3 null mutants, we show that nipi-3 is essential for larval development and viability. Through analyses of genetic suppressors of nipi-3 null mutant lethality, we show that NIPI-3 negatively controls PMK-1/p38 signalling via transcriptional repression of the C/EBP transcription factor CEBP-1. We identified CEBP-1’s transcriptional targets by ChIP-seq analyses and found them to be enriched in genes involved in development and stress responses. Unlike its cell-autonomous role in innate immunity, NIPI-3 is required in multiple tissues to control organismal development.ConclusionsTogether, our data uncover an unprecedented crosstalk involving multiple tissues, in which NIPI-3 acts as a master regulator to inhibit CEBP-1 and the PMK-1/p38 MAPK pathway. In doing so, it keeps innate immunity in check and ensures proper organismal development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0320-z) contains supplementary material, which is available to authorized users.

Distinct cis elements in the 3′ UTR of the C. elegans cebp-1 mRNA mediate its regulation in neuronal development

“…On the other hand, only CEBP-1 expressed from ΔD2 transgene fully rescued the axon regeneration defect. Previous observations have revealed that cebp-1 acts in other dosage-dependent processes influencing larval development and axon regeneration (Kim et al, 2016, data not shown). These results indicate that the ability of the animal to tolerate changes in cebp-1 levels is minimal, and that precise control over cebp-1 levels may be accomplished by using multiple cis regulatory elements.…”

“…S1B). As cebp-1 is expressed in many tissues (Kim et al, 2016), to address 3′ UTR-mediated regulation specifically in the nervous system, we used the pan-neuronal rgef-1 promoter to drive transgene expression. We initially analyzed transgenic lines generated as high-copy extra-chromosomal arrays.…”

“…We first identified cebp-1 as necessary for axon regeneration, and this function is also reported for C/EBPδ in a mammalian axon regeneration model (Lopez de Heredia and Magoulas, 2013; Yan et al, 2009). The activity of cebp-1 can be regulated at transcriptional and post-transcriptional levels (Kim et al, 2016; Yan et al, 2009). Here, we focused on post-transcriptional regulation involving the 3′ UTR of cebp-1 , and our data reveal several cis elements contributing to context-dependent regulation of cebp-1 function in the nervous system.…”

“…6). Since cebp-1 has been found to function in other tissues as well as neurons, the cebp-1 3′ UTR may allow tissue and temporal specific regulation through different cis elements (Kim et al, 2016; McEwan et al, 2016). Overall, our findings on the cebp-1 3′ UTR are consistent with studies on the roles of post-transcriptional regulation mediated by 3′ UTR in other neuronal models.…”

The Drosophila melanogaster tribbles pseudokinase is necessary for proper memory formation

“…These pseudokinases are thought to both link substrate binding to specific protein stability by recruiting ubiquitin ligases and as regulators of MAPK and AKT/FOXO - signaling (Eyers et al, 2016). There is one version of the trbl pseudokinase in Drosophila melanogaster and Caenorhabditis elegans (Kim, Thakur, Piggott, Omi, Polanowska, Jin, & Pujol, 2016; Mata, Curado, Ephrussi, & Rorth, 2000; Pujol, Cypowyj, Ziegler, Millet, Astrain, Goncharov, Jin, Chisholm, & Ewbank, 2008). Mouse and man have three, named trbl 1, 2, and 3 (Boudeau, Miranda-Saavedra, Barton, & Alessi, 2006; Eyers et al, 2016).…”