PKR activity is required for acute leukemic cell maintenance and growth

TY - JOUR

T1 - PKR activity is required for acute leukemic cell maintenance and growth

T2 - a role for PKR-mediated phosphatase activity to regulate GSK-3 phosphorylation

AU - Blalock, William L

AU - Grimaldi, Cecilia

AU - Fala, Federica

AU - Follo, Matilde

AU - Horn, Stefan

AU - Basecke, Jorg

AU - Martinelli, Giovanni

AU - Cocco, Lucio

AU - Martelli, Alberto M

N1 - Copyright 2009 Wiley-Liss, Inc.

PY - 2009/10/1

Y1 - 2009/10/1

N2 - Recent reports demonstrate that PKR is constitutively active in a variety of tumors and is required for tumor maintenance and growth. Here we report acute leukemia cell lines contain elevated levels of p-T451 PKR and PKR activity as compared to normal controls. Inhibition of PKR with a specific inhibitor, as well as overexpression of a dominant-negative PKR, inhibited cell proliferation and induced cell death. Interestingly, PKR inhibition using the specific inhibitor resulted in a time-dependent augmentation of AKT S473 and GSK-3alpha S21 phosphorylation, which was confirmed in patient samples. Increased phosphorylation of AKT and GSK-3alpha was not dependent on PI3K activity. PKR inhibition augmented levels of p-S473 AKT and p-S21/9 GSK-3alpha/beta in the presence of the PI3K inhibitor, LY294002, but was unable to augment GSK-3alpha or beta phosphorylation in the presence of the AKT inhibitor, A443654. Pre-treatment with the PKR inhibitor blocked the ability of A443654 and LY294002 to promote phosphorylation of eIF2alpha, indicating the mechanism leading to AKT phosphorylation and activation did not require eIF2alpha phosphorylation. The effects of PKR inhibition on AKT and GSK-3 phosphorylation were found to be, in part, PP2A-dependent. These data indicate that, in acute leukemia cell lines, constitutive basal activity of PKR is required for leukemic cell homeostasis and growth and functions as a negative regulator of AKT, thereby increasing the pool of potentially active GSK-3.

AB - Recent reports demonstrate that PKR is constitutively active in a variety of tumors and is required for tumor maintenance and growth. Here we report acute leukemia cell lines contain elevated levels of p-T451 PKR and PKR activity as compared to normal controls. Inhibition of PKR with a specific inhibitor, as well as overexpression of a dominant-negative PKR, inhibited cell proliferation and induced cell death. Interestingly, PKR inhibition using the specific inhibitor resulted in a time-dependent augmentation of AKT S473 and GSK-3alpha S21 phosphorylation, which was confirmed in patient samples. Increased phosphorylation of AKT and GSK-3alpha was not dependent on PI3K activity. PKR inhibition augmented levels of p-S473 AKT and p-S21/9 GSK-3alpha/beta in the presence of the PI3K inhibitor, LY294002, but was unable to augment GSK-3alpha or beta phosphorylation in the presence of the AKT inhibitor, A443654. Pre-treatment with the PKR inhibitor blocked the ability of A443654 and LY294002 to promote phosphorylation of eIF2alpha, indicating the mechanism leading to AKT phosphorylation and activation did not require eIF2alpha phosphorylation. The effects of PKR inhibition on AKT and GSK-3 phosphorylation were found to be, in part, PP2A-dependent. These data indicate that, in acute leukemia cell lines, constitutive basal activity of PKR is required for leukemic cell homeostasis and growth and functions as a negative regulator of AKT, thereby increasing the pool of potentially active GSK-3.

KW - Cell Line, Tumor

KW - Cell Proliferation

KW - Cell Survival

KW - Enzyme Activation

KW - Glycogen Synthase Kinase 3

KW - Humans

KW - Leukemia

KW - Phosphatidylinositol 3-Kinases

KW - Phosphorylation

KW - Protein Kinase Inhibitors

KW - Protein Phosphatase 2

KW - Proto-Oncogene Proteins c-akt

KW - eIF-2 Kinase

U2 - 10.1002/jcp.21848

DO - 10.1002/jcp.21848

M3 - SCORING: Journal article

C2 - 19507191

VL - 221

SP - 232

EP - 241

JO - J CELL PHYSIOL

JF - J CELL PHYSIOL

SN - 0021-9541

IS - 1

ER -