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.
Division of Medical Oncology, Department of Pathology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
A
A
Nesterov
X
X
Lu
M
M
Johnson
G J
GJ
Miller
Y
Y
Ivashchenko
A S
AS
Kraft
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