Roles of YB-1 under arsenite-induced stress: translational activation of HSP70 mRNA and control of the number of stress granules.
BACKGROUND
When cells become stressed, they form stress granules (SGs) and show an increase of the molecular chaperone HSP70. The translational regulator YB-1 is a component of SGs, but it is unclear whether it contributes to the translational induction of HSP70 mRNA. Here we examined the roles of YB-1 in SG assembly and translational regulation of HSP70 mRNA under arsenite-induced stress.


METHODS
Using arsenite-treated NG108-15 cells, we examined whether YB-1 was included in SGs with GluR2 mRNA, a target of YB-1, and investigated the interaction of YB-1 with HSP70 mRNA and its effect on translation of the mRNA. We also investigated the distribution of these mRNAs to SGs or polysomes, and evaluated the role of YB-1 in SG assembly.


RESULTS
Arsenite treatment reduced the translation level of GluR2 mRNA; concomitantly, YB-1-bound HSP70 mRNA was increased and its translation was induced. Sucrose gradient analysis revealed that the distribution of GluR2 mRNA was shifted from heavy-sedimenting to much lighter fractions, and also to SG-containing non-polysomal fractions. Conversely, HSP70 mRNA was shifted from the non-polysomal to polysome fractions. YB-1 depletion abrogated the arsenite-responsive activation of HSP70 synthesis, but SGs harboring both mRNAs were still assembled. The number of SGs was increased by YB-1 depletion and decreased by its overexpression.


CONCLUSIONS
In arsenite-treated cells, YB-1 mediates the translational activation of HSP70 mRNA and also controls the number of SGs through inhibition of their assembly.


CONCLUSIONS
Under stress conditions, YB-1 exerts simultaneous but opposing actions on the regulation of translation via SGs and polysomes.
Department of Biochemistry, School of Pharmacy, Nihon University, 7-7-1, Narashinodai, Funabashi, Chiba 274-8555, Japan.
Toru
T
Tanaka
Department of Biochemistry, School of Pharmacy, Nihon University, 7-7-1, Narashinodai, Funabashi, Chiba 274-8555, Japan.
Sachiyo
S
Ohashi
Department of Biochemistry, School of Pharmacy, Nihon University, 7-7-1, Narashinodai, Funabashi, Chiba 274-8555, Japan. Electronic address: kobayashi.shunsuke@nihon-u-ac.jp.
Shunsuke
S
Kobayashi
D000818:Animals; D018053:Arsenites / Q000633:toxicity*; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics*; D051379:Mice; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D018091:Receptors, AMPA / Q000235:genetics; D013312:Stress, Physiological / Q000187:drug effects; D014157:Transcription Factors / Q000502:physiology*
D018053:Arsenites; D018840:HSP70 Heat-Shock Proteins; D012333:RNA, Messenger; D018091:Receptors, AMPA; D014157:Transcription Factors; C541744:Ybx1 protein, mouse; C015001:arsenite; C104722:glutamate receptor ionotropic, AMPA 2
GluR2 mRNA; HSP70 mRNA; Stress granule assembly; Translational regulation; YB-1