Genetic ablation of ataxin-2 increases several global translation factors in their transcript abundance but decreases translation rate

Abstract

Spinocerebellar ataxia type 2 (SCA2) and amyotrophic lateral sclerosis (ALS) are neurodegenerative disorders, caused or modified by an unstable CAG-repeat expansion in the SCA2 gene, which encodes a polyglutamine (polyQ) domain expansion in ataxin-2 (ATXN2). ATXN2 is an RNA-binding protein and interacts with the poly(A)-binding protein PABPC1, localizing to ribosomes at the rough endoplasmic reticulum. Under cell stress, ATXN2, PABPC1 and small ribosomal subunits are relocated to stress granules, where mRNAs are protected from translation and from degradation. It is unknown whether ATXN2 associates preferentially with specific mRNAs or how it modulates RNA processing. Here, we investigated the RNA profile of the liver and cerebellum from Atxn2 knockout (Atxn2−/−) mice at two adult ages, employing oligonucleotide microarrays. Prominent increases were observed for Lsm12/Paip1 (>2-fold), translation modulators known as protein interactor/competitor of ATXN2 and for Plin3/Mttp (>1.3-fold), known as apolipoprotein modulators in agreement with the hepatosteatosis phenotype of the Atxn2−/− mice. Consistent modest upregulations were also observed for many factors in the ribosome and the translation/secretion apparatus. Quantitative reverse transcriptase PCR in liver tissue validated >1.2-fold upregulations for the ribosomal biogenesis modulator Nop10, the ribosomal components Rps10, Rps18, Rpl14, Rpl18, Gnb2l1, the translation initiation factors Eif2s2, Eif3s6, Eif4b, Pabpc1 and the rER translocase factors Srp14, Ssr1, Sec61b. Quantitative immunoblots substantiated the increased abundance of NOP10, RPS3, RPS6, RPS10, RPS18, GNB2L1 in SDS protein fractions, and of PABPC1. In mouse embryonal fibroblasts, ATXN2 absence also enhanced phosphorylation of the ribosomal protein S6 during growth stimulation, while impairing the rate of overall protein synthesis rates, suggesting a block between the enhanced translation drive and the impaired execution. Thus, the physiological role of ATXN2 subtly modifies the abundance of cellular translation factors as well as global translation.Electronic supplementary materialThe online version of this article (doi:10.1007/s10048-015-0441-5) contains supplementary material, which is available to authorized users.

Mammalian ataxin-2 modulates translation control at the pre-initiation complex via PI3K/mTOR and is induced by starvation

“…These reductions may simply be due to less vigorous growth of the clonal fibroblast lines under study and may be unrelated to ataxin-2 effects on translation. However, they certainly coincide with our previously published observation that the incorporation rate of radioactively labelled amino acids is diminished by 34% in Atxn2 -KO MEFs [31]. It can be concluded safely from these data that ataxin-2 is not a prerequisite for ribosome assembly.…”

“…A previous report from our team showed the ratio of phosphorylated RPS6 versus total RPS6 increased in serum-starved Atxn2 -KO MEFs both at the basal state and after insulin administration [31]. As before, we now found elevated RPS6 phosphorylation in KO-MEFs (Figure 6A).…”

“…Several lines of evidence implicate ataxin-2 in growth receptor regulation and RNA metabolism [25-28]. Recent expression profiling efforts in Atxn2 -knockoout mouse tissues demonstrated a selective downregulation of mitochondrial matrix components global proteome profiles and a preferential downregulation of calcium homeostasis factors together with an upregulation of mRNA translation factors in global transcriptomics [29-31]. The structure of ataxin-2 contains a PAM2 motif which mediates association with the poly(A)-binding protein PABP [12, 13, 32], thought to promote ataxin-2 association with polyribosomes [33].…”

Ataxin-2 (Atxn2)-Knock-Out Mice Show Branched Chain Amino Acids and Fatty Acids Pathway Alterations

“…also in hepatocytes (1)(2)(3)(4). The structure of the human ATXN2 protein is characterized (1) by the N-terminal polyQ domain (5), (2) by dispersed proline-rich-domains that mediate association with various SH3-motif containing proteins of the tyrosine kinase receptor endocytosis machinery and thus modulate neuro-trophic signaling (6, 7), (3) by a C-terminal PAM2 motif that mediates interaction with the poly(A)-binding protein PABPC1 that is crucial for mRNA translation (8) and (4) by Lsm and Lsm-AD sequences that mediate the association with RNAs (9 -11).…”

Motor Dysfunctions and Neuropathology in Mouse Models of Spinocerebellar Ataxia Type 2: A Comprehensive Review

“…Indeed, although they are not the focus of this work, simple models like yeast, C. elegans and D. melanogaster were among the very first models used and have been crucial to infer on the ubiquitous functions of ataxin-2, such as: the embryonic development (Kiehl et al, 2000; Ciosk et al, 2004); the translation regulation and mRNA metabolism (Mangus et al, 1998; Satterfield and Pallanck, 2006); the regulation of circadian rhythms (Lim and Allada, 2013; Zhang et al, 2013); and modulating the formation of stress granules (Ralser et al, 2005). Likewise, the creation and characterization of two murine KO models of ATXN2 have provided precious new insights into the functions and pathways of this protein (Kiehl et al, 2006; Lastres-Becker et al, 2008a; Huynh et al, 2009; Fittschen et al, 2015; Halbach et al, 2016; Meierhofer et al, 2016) including a putative role in insulin resistance and obesity, which was validated in humans through Genome-wide association studies (Auburger et al, 2014). Finally, the development of iPSCs lines from SCA2 patients was recently reported, as well as CRISPR-Cas9 corrected isogenic iPSCs, to serve as suitable controls.…”