PHLPP-1 negatively regulates Akt activity and survival in the heart.
BACKGROUND
The recently discovered PHLPP-1 (PH domain leucine-rich repeat protein phosphatase-1) selectively dephosphorylates Akt at Ser473 and terminates Akt signaling in cancer cells. The regulatory role of PHLPP-1 in the heart has not been considered.


OBJECTIVE
To test the hypothesis that blockade/inhibition of PHLPP-1 could constitute a novel way to enhance Akt signals and provide cardioprotection.


RESULTS
PHLPP-1 is expressed in neonatal rat ventricular myocytes (NRVMs) and in adult mouse ventricular myocytes (AMVMs). PHLPP-1 knockdown by small interfering RNA significantly enhances phosphorylation of Akt (p-Akt) at Ser473, but not at Thr308, in NRVMs stimulated with leukemia inhibitory factor (LIF). The increased phosphorylation is accompanied by greater Akt catalytic activity. PHLPP-1 knockdown enhances LIF-mediated cardioprotection against doxorubicin and also protects cardiomyocytes against H(2)O(2). Direct Akt effects at mitochondria have been implicated in cardioprotection and mitochondria/cytosol fractionation revealed a significant enrichment of PHLPP-1 at mitochondria. The ability of PHLPP-1 knockdown to potentiate LIF-mediated increases in p-Akt at mitochondria and an accompanying increase in mitochondrial hexokinase-II was demonstrated. We generated PHLPP-1 knockout (KO) mice and demonstrate that AMVMs isolated from KO mice show potentiated p-Akt at Ser473 in response to agonists. When isolated perfused hearts are subjected to ischemia/reperfusion, p-Akt in whole-heart homogenates and in the mitochondrial fraction is significantly increased. Additionally in PHLPP-1 KO hearts, the increase in p-Akt elicited by ischemia/reperfusion is potentiated and, concomitantly, infarct size is significantly reduced.


CONCLUSIONS
These results implicate PHLPP-1 as an endogenous negative regulator of Akt activity and cell survival in the heart.
Miyamoto
Shigeki
S
Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, USA. smiyamoto@ucsd.edu
Purcell
Nicole H
NH
Smith
Jeffrey M
JM
Gao
Tianyan
T
Whittaker
Ross
R
Huang
Katherine
K
Castillo
Rene
R
Glembotski
Chris C
CC
Sussman
Mark A
MA
Newton
Alexandra C
AC
Brown
Joan Heller
JH
D000818:Animals; D002470:Cell Survival / Q000502:physiology; D015536:Down-Regulation / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D006321:Heart / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009687:Nuclear Proteins / Q000172:deficiency / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000172:deficiency / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats
D009687:Nuclear Proteins; D051057:Proto-Oncogene Proteins c-akt; C519282:PHLPP1 protein, mouse; D010749:Phosphoprotein Phosphatases