Elevated AKT activity protects the prostate cancer cell line LNCaP from TRAIL-induced apoptosis.
We find that the prostate cancer cell lines ALVA-31, PC-3, and DU 145 are highly sensitive to apoptosis induced by TRAIL (tumor-necrosis factor-related apoptosis-inducing ligand), while the cell lines TSU-Pr1 and JCA-1 are moderately sensitive, and the LNCaP cell line is resistant. LNCaP cells lack active lipid phosphatase PTEN, a negative regulator of the phosphatidylinositol (PI) 3-kinase/Akt pathway, and demonstrate a high constitutive Akt activity. Inhibition of PI 3-kinase using wortmannin and LY-294002 suppressed constitutive Akt activity and sensitized LNCaP cells to TRAIL. Treatment of LNCaP cells with TRAIL alone induced cleavage of the caspase 8 and XIAP proteins. However, processing of BID, mitochondrial release of cytochrome c, activation of caspases 7 and 9, and apoptosis did not occur unless TRAIL was combined with either wortmannin, LY-294002, or cycloheximide. Blocking cytochrome c release by Bcl-2 overexpression rendered LNCaP cells resistant to TRAIL plus wortmannin treatment but did not affect caspase 8 or BID processing. This indicates that in these cells mitochondria are required for the propagation rather than the initiation of the apoptotic cascade. Infection of LNCaP cells with an adenovirus expressing a constitutively active Akt reversed the ability of wortmannin to potentiate TRAIL-induced BID cleavage. Thus, the PI 3-kinase-dependent blockage of TRAIL-induced apoptosis in LNCaP cells appears to be mediated by Akt through the inhibition of BID cleavage.
Nesterov
A
A
Division of Medical Oncology, Department of Pathology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
Lu
X
X
Johnson
M
M
Miller
G J
GJ
Ivashchenko
Y
Y
Kraft
A S
AS
D017209:Apoptosis / Q000187:drug effects*; D006801:Humans; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology*
D014409:Tumor Necrosis Factor-alpha; D019869:Phosphatidylinositol 3-Kinases