Related Experiment Videos
Constitutively active Akt is an important regulator of TRAIL sensitivity in prostate cancer
1Department of Pharmaceutical Sciences, University of Maryland-School of Pharmacy, Greenebaum Cancer Center, 20 N Pine Street, Baltimore, MD 21201-1180, USA.
Abstract:
TRAIL/Apo-2L is a member of the tumor necrosis factor superfamily and has recently been shown to induce apoptosis in cancer cells, but not in normal cells. In nude mice injected with human tumors, TRAIL reduces the size of these tumors without side effects. Akt promotes cell survival and block apoptosis. Some prostate cancer cells express high levels of Akt due to lack of active lipid phosphatase PTEN, a negative regulator of PI-3 kinase pathway, which may be responsible for drug resistance. The objective of this paper is to investigate the intracellular molecules that regulate TRAIL resistance. We have examined caspase-8 activity, BID cleavage, Akt activity, mitochondrial membrane potential (DeltaPsi(m)) and apoptosis in prostate cancer (LNCap, PC-3, PC-3M and DU145) cells treated with or without TRAIL. PC-3, PC-3M and DU145 cells are sensitive to TRAIL, whereas LNCap cells are resistant. LNCap cells express the highest level of constitutively active Akt, which is directly correlated with TRAIL resistance. TRAIL activates caspase-8 in all the cell lines. Downregulation of constitutively active Akt by PI-3 kinase inhibitors (wortmannin and LY-294002), dominant negative Akt or PTEN, renders LNCap cells sensitive to TRAIL. Inhibition of TRAIL sensitivity occurs at the level of BID cleavage. Inhibition of protein synthesis by cycloheximide also causes LNCap cells sensitive to TRAIL. Overexpression of Bcl-2 or Bcl-X(L) inhibits TRAIL-induced DeltaPsi(m) and apoptosis. Overexpression of constitutively active Akt in PC-3M cells (express very low levels of constitutively active Akt) restores TRAIL resistance. These data suggest that elevated Akt activity protects LNCap cells from TRAIL-induced apoptosis, and the PI-3 kinase/Akt pathway may inhibit apoptotic signals by inhibiting processing of BID. Thus, constitutively active Akt is an important regulator of TRAIL sensitivity in prostate cancer.
Insights
High Akt activity in prostate cancer cells confers resistance to TRAIL-induced apoptosis. Inhibiting the PI-3 kinase/Akt pathway restores TRAIL sensitivity by affecting BID cleavage, suggesting Akt as a key regulator of this process.
Area of Science:
- Oncology
- Molecular Biology
- Cell Death Research
Background:
- TRAIL (TNF-related apoptosis-inducing ligand) induces apoptosis in cancer cells but not normal cells.
- Akt signaling promotes cell survival and inhibits apoptosis, potentially contributing to drug resistance in prostate cancer.
- PTEN, a negative regulator of the PI-3 kinase pathway, is often deficient in prostate cancer, leading to elevated Akt activity.
Purpose of the Study:
- To investigate intracellular molecules regulating TRAIL resistance in prostate cancer cells.
- To determine the role of Akt activity in mediating resistance to TRAIL-induced apoptosis.
- To explore potential therapeutic strategies targeting the PI-3 kinase/Akt pathway for overcoming TRAIL resistance.
Main Methods:
- Assessed caspase-8 activity, BID cleavage, Akt activity, and mitochondrial membrane potential (ΔΨm) in prostate cancer cell lines (LNCaP, PC-3, PC-3M, DU145) treated with TRAIL.
- Utilized PI-3 kinase inhibitors (wortmannin, LY-294002), dominant-negative Akt, PTEN, cycloheximide, Bcl-2, and Bcl-xL to modulate signaling pathways.
- Overexpressed constitutively active Akt in TRAIL-sensitive cells to assess its impact on resistance.
Main Results:
- LNCaP cells, expressing high Akt activity, were resistant to TRAIL, while PC-3, PC-3M, and DU145 cells were sensitive.
- Downregulation of Akt activity using inhibitors or genetic manipulation sensitized LNCaP cells to TRAIL.
- Akt inhibition affected TRAIL sensitivity at the level of BID cleavage, and overexpression of Akt in sensitive cells restored resistance.
- Bcl-2 and Bcl-xL overexpression inhibited TRAIL-induced mitochondrial membrane potential loss and apoptosis.
Conclusions:
- Elevated Akt activity is a key mechanism protecting prostate cancer cells from TRAIL-induced apoptosis.
- The PI-3 kinase/Akt pathway inhibits TRAIL-induced apoptosis, potentially by interfering with BID processing.
- Targeting the PI-3 kinase/Akt pathway represents a promising strategy to enhance TRAIL efficacy in prostate cancer treatment.