The effect of alphaB-crystallin and Hsp27 on the availability of translation initiation factors in heat-shocked cells.
The mechanism of the translational thermotolerance provided by the small heat shock proteins (sHsps) alphaB-crystallin or Hsp27 is unknown. We show here that Hsp27, but not alphaB-crystallin, increased the pool of mobile stress granule-associated enhanced green fluorescent protein (EGFP)-eukaryotic translation initiation factor (eIF)4E in heat-shocked cells, as determined by fluorescence recovery after photobleaching. Hsp27 also partially prevented the sharp decrease in the pool of mobile cytoplasmic EGFP-eIF4G. sHsps did not prevent the phosphorylation of eIF2alpha by a heat shock, but promoted dephosphorylation during recovery. Expression of the C-terminal fragment of GADD34, which causes constitutive dephosphorylation of eIF2alpha, fully compensated for the stimulatory effect of alphaB-crystallin on protein synthesis in heat-shocked cells, but only partially for that of Hsp27. Our data show that sHsps do not prevent the inhibition of protein synthesis upon heat shock, but restore translation more rapidly by promoting the dephosphorylation of eIF2alpha and, in the case of Hsp27, the availability of eIF4E and eIF4G.
Doerwald
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L
Department of Biochemistry 271, NCMLS, Radboud University Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands, N.Lubsen@science.ru.nl.
van Genesen
S T
ST
Onnekink
C
C
Marín-Vinader
L
L
de Lange
F
F
de Jong
W W
WW
Lubsen
N H
NH
D000818:Animals; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000235:genetics; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D018869:Heat-Shock Response / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation; D038203:alpha-Crystallin B Chain / Q000235:genetics / Q000502:physiology*; D000099190:MAP-Kinase-Activated Kinase 2
D000943:Antigens, Differentiation; D018797:Cell Cycle Proteins; D015852:Eukaryotic Initiation Factor-2; D039603:Eukaryotic Initiation Factor-4G; D047908:Intracellular Signaling Peptides and Proteins; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases; D038203:alpha-Crystallin B Chain; D000099190:MAP-Kinase-Activated Kinase 2; C087519:PPP1R15A protein, human