title: The deubiquitylase Ataxin-3 restricts PTEN transcription in lung cancer cells.
abstract: The phosphatidylinositol-3-kinase (PI3K) pathway is commonly hyperactivated in cancer. One mechanism by which this occurs is by silencing of the phosphatase and tensin homolog (PTEN), a tumor suppressor and major antagonist of the pathway, through genetic, epigenetic or posttranscriptional mechanisms. Here, we used an unbiased siRNA screen in non-small-cell lung cancer cells to identify deubiquitylases (DUBs) that have an impact on PI3K signaling by regulating the abundance of PTEN. We found that PTEN expression was induced by depleting any of three members of the Josephin family DUBs: ataxin 3 (ATXN3), ataxin 3-like (ATXN3L) and Josephin domain containing 1 (JOSD1). However, this effect is not mediated through altered PTEN protein stability. Instead, depletion of each DUB increases expression of both the PTEN transcript and its competing endogenous RNA, PTENP1. In ATXN3-depleted cells, under conditions of transcriptional inhibition, PTEN and PTENP1 mRNAs rapidly decay, suggesting that ATXN3 acts primarily by repressing their transcription. Importantly, the PTEN induction observed in response to ATXN3 siRNA is sufficient to downregulate Akt phosphorylation and hence PI3K signaling. Histone deacetylase inhibitors (HDACi) have been suggested as potential mediators of PTEN transcriptional reactivation in non-small-cell lung cancer. Although PTEN exhibits a very limited response to the broad-spectrum HDACi Vorinostat (SAHA) in A549 cells, we find that combination with ATXN3 depletion enhances PTEN induction in an additive manner. Similarly, these interventions additively decrease cell viability. Thus, ATXN3 provides an autonomous, complementary therapeutic target in cancers with epigenetic downregulation of PTEN.
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: J J
authors.initials: JJ
authors.lastname: Sacco
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: T Y
authors.initials: TY
authors.lastname: Yau
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: S
authors.initials: S
authors.lastname: Darling
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: V
authors.initials: V
authors.lastname: Patel
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: S
authors.initials: S
authors.lastname: Urbé
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Clague
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Coulson
mesh_terms: D000067699:Ataxin-3; D045744:Cell Line, Tumor; D002470:Cell Survival; D015536:Down-Regulation; D004795:Enzyme Stability; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D006801:Humans; D008175:Lung Neoplasms; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics* / Q000378:metabolism; D020871:RNA Stability; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; C092341:ATXN3 protein, human; D000067699:Ataxin-3