title: Control of cellular GADD34 levels by the 26S proteasome.
abstract: GADD34, the product of a growth arrest and DNA damage-inducible gene, is expressed at low levels in unstressed cells. In response to stress, the cellular content of GADD34 protein increases and, on termination of stress, rapidly declines. We investigated the mechanisms that control GADD34 levels in human cells. GADD34 proteins containing either an internal FLAG or a C-terminal green fluorescent protein epitope were degraded at rates similar to endogenous GADD34. However, the addition of epitopes at the N terminus or deletion of N-terminal sequences stabilized GADD34. N-terminal peptides of GADD34, either alone or fused to heterologous proteins, exhibited rapid degradation similar to wild-type GADD34, thereby identifying an N-terminal degron. Deletion of internal PEST repeats had no impact on GADD34 stability but modulated the binding and activity of protein phosphatase 1. Proteasomal but not lysosomal inhibitors enhanced GADD34 stability and eukaryotic initiation factor 2alpha (eIF-2alpha) dephosphorylation, a finding consistent with GADD34's role in assembling an eIF-2alpha phosphatase. GADD34 was polyubiquitinated, and this modification enhanced its turnover in cells. A stabilized form of GADD34 promoted the accumulation and aggregation of the mutant cystic fibrosis transmembrane conductance regulator (CFTRDeltaF508), highlighting the physiological importance of GADD34 turnover in protein processing in the endoplasmic reticulum and the potential impact of prolonged GADD34 expression in human disease.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Brush
authors.forename: Shirish
authors.initials: S
authors.lastname: Shenolikar
mesh_terms: D000943:Antigens, Differentiation / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004721:Endoplasmic Reticulum; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000502:physiology*; D054645:Protein Phosphatase 1 / Q000378:metabolism; D055550:Protein Stability; D014407:Tumor Cells, Cultured; D054875:Ubiquitination
chemical_list: D000943:Antigens, Differentiation; C505032:CFTR protein, human; D018797:Cell Cycle Proteins; D015852:Eukaryotic Initiation Factor-2; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C087519:PPP1R15A protein, human; D054645:Protein Phosphatase 1; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
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