Related Experiment Videos
Role for the double-stranded RNA activated protein kinase PKR in E2F-1-induced apoptosis
Stephan A Vorburger1, Abujiang Pataer, Kazumi Yoshida
1Department of Surgical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA.
Abstract:
The transcription factor E2F-1 induces cell cycle progression at the G1/S checkpoint, and deregulation of E2F-1 provokes apoptosis in a wide variety of malignant cells. To date only p14(ARF) and p73, a p53 homologue, have been identified as E2F-1-inducible genes capable of mediating an apoptotic response. Here we show that adenovirus-mediated E2F-1 overexpression in cancer cells induces expression and autophosphorylation of the double-stranded RNA-dependent protein kinase PKR leading to phosphorylation of its downstream target, the alpha-subunit of the eukaryotic translation initiation factor 2 (eIF-2alpha) and to apoptotic cell death. This PKR-dependent apoptosis occurs in cell lines with mutated p53 and in cell lines with mutated p53 and p73, and is significantly reduced by the chemical inhibition of PKR activation. Further, PKR(-/-) mouse embryo fibroblasts, but not PKR(+/+) mouse embryo fibroblasts, demonstrate significant resistance to E2F-1-induced apoptosis. We conclude that an important pathway of E2F-1-mediated apoptosis is dependent on PKR activation and does not require p53 or p73.
Insights
The transcription factor E2F-1 triggers apoptosis in cancer cells via the protein kinase PKR pathway. This mechanism activates PKR-dependent apoptosis, independent of p53 or p73 tumor suppressors.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- The transcription factor E2F-1 promotes cell cycle progression and its deregulation can induce apoptosis in malignant cells.
- Previously identified E2F-1-inducible genes mediating apoptosis include p14(ARF) and p73.
Purpose of the Study:
- To investigate the role of the double-stranded RNA-dependent protein kinase PKR in E2F-1-induced apoptosis.
- To elucidate the signaling pathway downstream of E2F-1 that leads to programmed cell death.
Main Methods:
- Adenovirus-mediated overexpression of E2F-1 in various cancer cell lines.
- Assessment of PKR and eIF-2alpha phosphorylation levels.
- Inhibition of PKR activation using chemical inhibitors.
- Analysis of E2F-1-induced apoptosis in PKR-deficient (PKR-/-) and wild-type (PKR+/+) mouse embryo fibroblasts.
Main Results:
- Overexpression of E2F-1 induced expression and autophosphorylation of PKR.
- PKR activation led to phosphorylation of eIF-2alpha and subsequent apoptotic cell death.
- PKR-dependent apoptosis was observed in cell lines with mutated p53 and p73.
- Chemical inhibition of PKR significantly reduced E2F-1-induced apoptosis.
- PKR-/- mouse embryo fibroblasts exhibited resistance to E2F-1-induced apoptosis compared to PKR+/+ cells.
Conclusions:
- E2F-1-mediated apoptosis can occur through a pathway involving PKR activation.
- This PKR-dependent apoptotic pathway is independent of functional p53 or p73.
- PKR represents a critical mediator in E2F-1-induced programmed cell death in cancer cells.