Inhibition of integrin-linked kinase (ILK) suppresses activation of protein kinase B/Akt and induces cell cycle arrest and apoptosis of PTEN-mutant prostate cancer cells

Inhibition of integrin-linked kinase (ILK) suppresses activation of protein kinase B/Akt and induces cell cycle arrest and apoptosis of PTEN-mutant prostate cancer cells

^*British Columbia Cancer Agency and Jack Bell Research Centre, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada; ^‡Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; and ^†Kinetek Pharmaceuticals, 1779 West 75th Avenue, Vancouver, BC V6P 6P2, Canada

Communicated by Erkki Ruoslahti, The Burnham Institute, La Jolla, CA (received for review September 27, 1999)

Abstract

PTEN is a tumor suppressor gene located on chromosome 10q23 that encodes a protein and phospholipid phosphatase. Somatic mutations of PTEN are found in a number of human malignancies, and loss of expression, or mutational inactivation of PTEN, leads to the constitutive activation of protein kinase B (PKB)/Akt via enhanced phosphorylation of Thr-308 and Ser-473. We recently have demonstrated that the integrin-linked kinase (ILK) can phosphorylate PKB/Akt on Ser-473 in a phosphoinositide phospholipid-dependent manner. We now demonstrate that the activity of ILK is constitutively elevated in a serum- and anchorage-independent manner in PTEN-mutant cells, and transfection of wild-type (WT) PTEN into these cells inhibits ILK activity. Transfection of a kinase-deficient, dominant-negative form of ILK or exposure to a small molecule ILK inhibitor suppresses the constitutive phosphorylation of PKB/Akt on Ser-473, but not on Thr-308, in the PTEN-mutant prostate carcinoma cell lines PC-3 and LNCaP. Transfection of dominant-negative ILK and WT PTEN into these cells also results in the inhibition of PKB/Akt kinase activity. Furthermore, dominant-negative ILK or WT PTEN induces G₁ phase cycle arrest and enhanced apoptosis. Together, these data demonstrate a critical role for ILK in PTEN-dependent cell cycle regulation and survival and indicate that inhibition of ILK may be of significant value in PTEN-mutant tumor therapy.

Footnotes

↵ § To whom reprint requests should be addressed. E-mail: SDedhar{at}interchange.ubc.ca.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.060579697.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.060579697
Abbreviations:

PKB,

protein kinase B;

PI3-kinase,

phosphatidylinositol 3-kinase;

PI(3,4,5)P3,

phosphatidylinositol 3,4,5-trisphosphate;

FAK,

focal adhesion kinase;

ILK,

integrin-linked kinase;

GSK-3,

glycogen synthase kinase-3;

WT,

wild type;

KD,

kinase deficient;

MBP,

myelin basic protein;

GFP,

green fluorescent protein;

GST,

glutathione S-transferase