Control of HIF-1alpha expression by eIF2 alpha phosphorylation-mediated translational repression

Area of Science:

• Molecular Biology
• Cancer Research
• Cell Biology

Background:

• Hypoxia-inducible factor 1-alpha (HIF-1alpha) is crucial for tumor angiogenesis, regulating vascular endothelial growth factor (VEGF).
• Proteasome inhibitors (PI) are known to block tumor angiogenesis by reducing VEGF, but the underlying mechanisms remain unclear.

Purpose of the Study:

• To elucidate the mechanism by which proteasome inhibitors (PI) down-regulate HIF-1alpha expression and activity in prostate cancer cells.
• To investigate the role of translation initiation factor 2-alpha (eIF2alpha) phosphorylation in PI-mediated HIF-1alpha regulation.

Main Methods:

• Utilized human prostate cancer cell lines (LNCaP-Pro5, DU145, 253JB-V) and mouse embryonic fibroblasts (MEFs).
• Employed siRNA to deplete eIF2alpha and used a phosphorylation-deficient eIF2alpha mutant.
• Assessed HIF-1alpha protein levels, transcriptional activity, and eIF2alpha phosphorylation status.

Main Results:

• Proteasome inhibitors (PI) reduced HIF-1alpha protein levels and transcriptional activity in prostate cancer cells.
• PI induced eIF2alpha phosphorylation, leading to general translational repression and decreased HIF-1alpha expression.
• HIF-1alpha accumulated in cells with depleted eIF2alpha or a non-phosphorylatable eIF2alpha mutant, and in cells lacking eIF2alpha phosphorylation response to PIs.

Conclusions:

• Proteasome inhibitors down-regulate HIF-1alpha expression by inducing eIF2alpha phosphorylation and inhibiting HIF-1alpha translation in cancer cells exhibiting unfolded protein response activation.
• This mechanism provides insight into how PIs affect tumor angiogenesis and offers potential therapeutic targets.