Modulation of Akt kinase activity by binding to Hsp90

Modulation of Akt kinase activity by binding to Hsp90

^*Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan; and ^†Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Tokyo 170-8455, Japan

Communicated by Satoshi Ōmura, The Kitasato Institute, Tokyo, Japan (received for review March 28, 2000)

Abstract

Serine/threonine kinase Akt/PKB is a downstream effector molecule of phosphoinositide 3-kinase and is thought to mediate many biological actions toward anti-apoptotic responses. We found that Akt formed a complex with a 90-kDa heat-shock protein (Hsp90) in vivo. By constructing deletion mutants, we identified that amino acid residues 229–309 of Akt were involved in the binding to Hsp90 and amino acid residues 327–340 of Hsp90β were involved in the binding to Akt. Inhibition of Akt-Hsp90 binding led to the dephosphorylation and inactivation of Akt, which increased sensitivity of the cells to apoptosis-inducing stimulus. The dephosphorylation of Akt was caused by an increase in protein phosphatase 2A (PP2A)-mediated dephosphorylation and not by a decrease in 3-phosphoinositide-dependent protein kinase-1-mediated phosphorylation. These results indicate that Hsp90 plays an important role in maintaining Akt kinase activity by preventing PP2A-mediated dephosphorylation.

Footnotes

↵ ‡ To whom reprint requests should be addressed. E-mail: ttsuruo{at}iam.u-tokyo.ac.jp.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.170276797.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.170276797
Abbreviations:

MAPK,

mitogen-activated protein kinase;

pAb,

polyclonal antibody;

PARP,

poly(ADP-ribose) polymerase;

PDK1,

3-phosphoinositide-dependent protein kinase-1;

PH,

pleckstrin homology;

PI(3)K,

phosphoinositide 3-kinase;

PP2A,

protein phosphatase 2A;

PtdIns(3,4,5)P3,

phosphatidylinositol 3,4,5-triphosphate;

Hsp90,

90-kDa heat shock protein;

WT,

wild type;

KD-akt,

kinase-dead form of akt cDNA