Direct evidence that Ataxin-2 is a translational activator mediating cytoplasmic polyadenylation

Abstract

The RNA-binding protein Ataxin-2 binds to and stabilizes a number of mRNA sequences, including that of the transactive response DNA binding protein 43 kDa (TDP-43). Ataxin-2 is additionally involved in several processes requiring translation such as germline formation, long term habituation and circadian rhythm formation. However, it has yet to be unambiguously demonstrated that Ataxin-2 is actually involved in activating the translation of its target mRNAs. Here we provide direct evidence from a polysome profile analysis showing that Ataxin-2 enhances translation of target mRNAs. Our recently established method for transcriptional pulse-chase analysis under conditions of suppressing deadenylation revealed that Ataxin-2 promotes post-transcriptional polyadenylation of the target mRNAs. Furthermore, Ataxin-2 binds to a poly(A) binding protein PABPC1 and a noncanonical poly(A) polymerase PAPD4 via its intrinsically disordered region (906–1095 aa) to recruit PAPD4 to the targets. Posttranscriptional polyadenylation by Ataxin-2 explains not only how it activates translation but also stabilizes target mRNAs, including TDP-43 mRNA. Ataxin-2 is known to be a potent modifier of TDP-43 proteinopathies and to play a causative role in the neurodegenerative disease Spinocerebellar ataxia type 2, so these findings suggest that Ataxin-2-induced cytoplasmic polyadenylation and activation of translation might impact neurodegeneration (i.e., TDP-43 proteinopathies) and this process could be a therapeutic target for Ataxin-2-related neurodegenerative disorders.

RNA Modifications and RNA Metabolism in Neurological Disease Pathogenesis

“…Deviant axonal transport of mRNAs associated with TDP-43 (Map1b, Nefl) or with FUS (e.g., Fosb) contributes to ALS and frontotemporal lobar degeneration (FTLD) [73,74]. Interestingly, translational activation of CyclinD1 and TDP-43 mRNAs via Ataxin2-mediated polyadenylation in association with the Poly-A binding protein PAPD4 can induce TDP-43 proteinopathies, such as the Tau aggregation typical of FTLD, ALS, and AD [75,76]. Together, this evidence establishes dysregulated mRNA transport/translation as a crucial factor in several neurological diseases.…”

Ataxin-2 gene: a powerful modulator of neurological disorders

“…ATXN2 and TDP43 interact through RNA molecules (Fig. 4 ) [ 40 , 41 , 42 ▪ , 43 ]. In spinal cord neurons of ALS patients, ataxin-2 and TDP43 are abnormally localized.…”

“…In turn, TDP43 protein accelerates deadenylation of target mRNAs, which is a critical step in the RNA degradation. Therefore, regulating the length of the of the poly(A) tail plays a key role in the control of the mRNA stability [ 42 ▪ ]. This provides evidence for a common cellular process where both proteins cooperate with antagonistic functions regulating common substrates.…”

The ATXN2 Orthologs CID3 and CID4, Act Redundantly to In-Fluence Developmental Pathways throughout the Life Cycle of Arabidopsis thaliana

“…This binding improves the stability of target mRNAs and consequently increases levels of target proteins [ 13 ]. Ataxin-2 also interacts with POLY(A) POLYMERASE (PAP)D4, a noncanonical PAP, resulting in an extended poly(A) tail of specific mRNAs and a consequent improvement of translation and the stability of target mRNAs [ 14 ].…”