TDP-43 regulates <i>β-adducin</i> (<i>Add2</i>) transcript stability

TDP-43 is an RNA-binding protein involved in several steps of mRNA metabolism including transcription, splicing and stability. It is also involved in ALS and FTD, neurodegenerative diseases characterized by TDP-43 nuclear depletion. We previously identified TDP-43 as a binder of the downstream element (DSE) of the <i>β-Adducin</i> (<i>Add2</i>) brain-specific polyadenylation site (A4 PAS), suggesting its involvement in pre-mRNA 3′ end processing. Here, by using chimeric minigenes, we showed that TDP-43 depletion in HeLa and HEK293 cells resulted in down-regulation of both the chimeric and endogenous <i>Add2</i> transcripts. Despite having confirmed TDP-43-DSE in vitro interaction, we demonstrated that the in vivo effect was not mediated by the TDP-43-DSE interaction. In fact, substitution of the <i>Add2</i> DSE with viral <i>E-SV40</i> and <i>L-SV40</i> DSEs, which are not TDP-43 targets, still resulted in decreased <i>Add2</i> mRNA levels after TDP-43 downregulation. In addition, we failed to show interaction between TDP-43 and key polyadenylation factors, such as CstF-64 and CPSF160 and excluded TDP-43 involvement in pre-mRNA cleavage and regulation of polyA tail length. These evidences allowed us to exclude the pre-hypothesized role of TDP43 in modulating 3′ end processing of <i>Add2</i> pre-mRNA. Finally, we showed that TDP-43 regulates <i>Add2</i> gene expression levels by increasing <i>Add2</i> mRNA stability. Considering that <i>Add2</i> in brain participates in synapse assembly, synaptic plasticity and their stability, and its genetic inactivation in mice leads to LTP, LTD, learning and motor-coordination deficits, we hypothesize that a possible loss of Add2 function by TDP-43 depletion may contribute to ALS and FTD disease states.