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Inactivation of DNA-dependent protein kinase by protein kinase Cdelta: implications for apoptosis
A Bharti1, S K Kraeft, M Gounder
1Cancer Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
Protein kinase Cdelta (PKCdelta) is proteolytically cleaved and activated at the onset of apoptosis induced by DNA-damaging agents, tumor necrosis factor, and anti-Fas antibody. A role for PKCdelta in apoptosis is supported by the finding that overexpression of the catalytic fragment of PKCdelta (PKCdelta CF) in cells is associated with the appearance of certain characteristics of apoptosis. However, the functional relationship between PKCdelta cleavage and induction of apoptosis is unknown. The present studies demonstrate that PKCdelta associates constitutively with the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). The results show that PKCdelta CF phosphorylates DNA-PKcs in vitro. Interaction of DNA-PKcs with PKCdelta CF inhibits the function of DNA-PKcs to form complexes with DNA and to phosphorylate its downstream target, p53. The results also demonstrate that cells deficient in DNA-PK are resistant to apoptosis induced by overexpressing PKCdelta CF. These findings support the hypothesis that functional interactions between PKCdelta and DNA-PK contribute to DNA damage-induced apoptosis.
Insights
Protein kinase Cdelta (PKCdelta) activation during apoptosis involves its interaction with DNA-dependent protein kinase (DNA-PK). This interaction inhibits DNA-PK, suggesting a role in DNA damage-induced cell death.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Protein kinase Cdelta (PKCdelta) is activated during apoptosis induced by various stimuli, including DNA damage.
- Overexpression of the active PKCdelta catalytic fragment (PKCdelta CF) mimics apoptotic features, but its precise role remains unclear.
Purpose of the Study:
- To elucidate the functional relationship between PKCdelta activation and the induction of apoptosis.
- To investigate the molecular interactions of PKCdelta during DNA damage-induced apoptosis.
Main Methods:
- Investigated the association between PKCdelta and DNA-dependent protein kinase catalytic subunit (DNA-PKcs).
- Assessed the phosphorylation of DNA-PKcs by PKCdelta CF in vitro.
- Evaluated the impact of PKCdelta CF on DNA-PKcs function and complex formation with DNA.
- Examined apoptosis induction in DNA-PK deficient cells overexpressing PKCdelta CF.
Main Results:
- PKCdelta constitutively associates with DNA-PKcs.
- PKCdelta CF phosphorylates DNA-PKcs, inhibiting its DNA binding and p53 phosphorylation.
- Cells lacking DNA-PK are resistant to apoptosis induced by PKCdelta CF overexpression.
Conclusions:
- Functional interactions between PKCdelta and DNA-PKcs are crucial for DNA damage-induced apoptosis.
- PKCdelta-mediated inhibition of DNA-PKcs contributes to the apoptotic process.