Inhibition of cell death by a novel 16.2 kD heat shock protein predominantly via Hsp90 mediated lipid rafts stabilization and Akt activation pathway.
AlphaB-crystallin homology, heat stress induction and chaperone activity suggested that a previously encloned gene product is a novel small heat shock protein (Hsp16.2). Suppression of Hsp16.2 by siRNA sensitized cells to hydrogen peroxide or taxol induced cell-death. Over-expressing of Hsp16.2 protected cells against stress stimuli by inhibiting cytochrome c release from the mitochondria, nuclear translocation of AIF and endonuclease G, and caspase 3 activation. Recombinant Hsp16.2 protected mitochondrial membrane potential against calcium induced collapse in vitro indicating that Hsp16.2 stabilizes mitochondrial membrane systems. Hsp16.2 formed self-aggregates and bound to Hsp90. Inhibition of Hsp90 by geldanamycin diminished the cytoprotective effect of Hsp16.2 indicating that this effect was Hsp90-mediated. Hsp16.2 over-expression increased lipid rafts formation as demonstrated by increased cell surface labeling with fluorescent cholera toxin B, and increased Akt phosphorylation. The inhibition of PI-3-kinase-Akt pathway by LY-294002 or wortmannin significantly decreased the protective effect of the Hsp16.2. These data indicate that the over-expression of Hsp16.2 inhibits cell death via the stabilization of mitochondrial membrane system, activation of Hsp90, stabilization of lipid rafts and by the activation of PI-3-kinase-Akt cytoprotective pathway.
Bellyei
Szabolcs
S
Department of Biochemistry and Medical Chemistry, University of Pécs, 12 Szigeti Street, Pécs, H-7624, Hungary.
Szigeti
Andras
A
Boronkai
Arpad
A
Pozsgai
Eva
E
Gomori
Eva
E
Melegh
Bela
B
Janaky
Tamas
T
Bognar
Zita
Z
Hocsak
Eniko
E
Sumegi
Balazs
B
Gallyas
Ferenc
F
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D021962:Membrane Microdomains / Q000187:drug effects* / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D038203:alpha-Crystallin B Chain / Q000235:genetics
D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D038203:alpha-Crystallin B Chain; D051057:Proto-Oncogene Proteins c-akt