Tight expression regulation of senataxin, linked to motor neuron disease and ataxia, is required to avert cell-cycle block and nucleolus disassembly

Abstract

The Senataxin (SETX) protein exhibits strong sequence conservation with the helicase domain of the yeast protein Sen1p, and recessive SETX mutations cause a severe ataxia, known as Ataxia with Oculomotor Apraxia type 2, while dominant SETX mutations cause Amyotrophic Lateral Sclerosis type 4. SETX is a very low abundance protein, and its expression is tightly regulated, such that large increases in mRNA levels fail to significantly increase protein levels. Despite this, transient transfection in cell culture can boost SETX protein levels on an individual cell basis. Here we found that over-expression of normal SETX, but not enzymatically-dead SETX, is associated with S-phase cell-cycle arrest in HEK293A cells. As SETX interacts with the nuclear exosome to ensure degradation of incomplete RNA transcripts, and SETX localizes to sites of collision between the DNA replication machinery and the RNAP II complex, altered dosage or aberrant function of SETX may impede this process to promote S-phase cell-cycle arrest. Because neurons are enriched for long transcripts with additional antisense regulatory transcription, collisions of RNAP II complexes may occur in such post-mitotic cells, underscoring a role for SETX in maintaining neuron homeostasis.

SUMOylated Senataxin functions in genome stability, RNA degradation, and stress granule disassembly, and is linked with inherited ataxia and motor neuron disease

“…Yet, despite tight SETX regulation, transient transfection can boost SETX levels on an individual cell basis. We found that by transient transfection of HEK293 cells, GFP-SETX was localized to the nucleoplasm, as expected (Bennett et al, 2020). But surprisingly, the nucleolus marker fibrillarin was diffused within the nucleus, coincident with SETX transfection.…”

“…Curiously, the SETX-induced fibrillarin redistribution appeared typical of prophase induction (Hernandez-Verdun, 2011), prompting us to test cell cycle progression with propidium iodide staining and flow cytometry. We found that GFP-SETX positive cells were S-phase arrested, without evidence of increased cell death (Bennett et al, 2020).…”

Transcriptional targets of senataxin and E2 promoter binding factors are associated with neuro-degenerative pathways during increased autophagic flux

“…In another study, Bennet et al induced SETX over-expression that disrupted the cell cycle of HEK 293 cells and they concluded that neurons due to their long RNA transcripts (i.e. propensity for R-loops) may be particularly vulnerable if SETX expression is outside the optimal range [50].…”

Transcriptional targets of senataxin and E2 promoter binding factors are associated with neuro-degenerative pathways during increased autophagic flux

“…In another study, Bennet et al induced SETX over-expression that disrupted the cell cycle of HEK 293 cells and they concluded that neurons due to their long RNA transcripts (i.e. propensity for R-loops) may be particularly vulnerable if SETX expression is outside the optimal range 52 .…”