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Poly ADP-ribosylation: a DNA break signal mechanism
F R Althaus1, H E Kleczkowska, M Malanga
1University of Zürich-Tierspital, Institute of Pharmacology and Toxicology, Switzerland.
Abstract:
Recent evidence obtained with transgenic knockout mice suggests that the enzyme poly(ADP-ribose)polymerase (PARP) does not play a direct role in DNA break processing. Nevertheless, inactivation of the catalytic or the DNA nick-binding functions of PARP affects cellular responses to genotoxins at the level of cell survival, sister chromatid exchanges and apoptosis. In the present report, we conceptualize the idea that PARP is part of a DNA break signal mechanism. In vitro screening studies revealed the existence of a protein family containing a polymer-binding motif of about 22 amino acids. This motif is present in p53 protein as well as in MARCKS, a protein involved in the regulation of the actin cytoskeleton. Biochemical analyses showed that these sequences are directly targeted by PARP-associated polymers in vitro, and this alters several molecular functions of p53- and MARCKS protein. PARP-deficient knockout mice from transgenic mice were found to exhibit several phenotypic features compatible with altered DNA damage signaling, such as downregulation and lack of responsiveness of p53 protein to genotoxins, and morphological changes compatible with MARCKS-related cytoskeletal dysfunction. The knockout phenotype could be rescued by stable expression of the PARP gene. We propose that PARP-associated polymers may recruit signal proteins to sites of DNA breakage and reprogram their functions.
Insights
Poly(ADP-ribose)polymerase (PARP) acts as a DNA damage signaling mechanism, not directly processing breaks. PARP-associated polymers recruit and reprogram signaling proteins at DNA break sites, influencing cell survival and apoptosis.
Area of Science:
- Molecular Biology
- Cellular Biology
- Genetics
Background:
- Recent evidence suggests poly(ADP-ribose)polymerase (PARP) is not directly involved in DNA break processing.
- However, PARP inactivation impacts cellular responses to genotoxins, affecting cell survival, sister chromatid exchanges, and apoptosis.
Purpose of the Study:
- To investigate the role of PARP in DNA damage signaling.
- To identify proteins interacting with PARP-associated polymers and their functional consequences.
Main Methods:
- In vitro screening to identify proteins with PARP polymer-binding motifs.
- Biochemical analyses of PARP polymer interactions with p53 and MARCKS proteins.
- Phenotypic analysis of PARP-deficient knockout mice.
Main Results:
- A protein family with a conserved polymer-binding motif, including p53 and MARCKS, was identified.
- PARP-associated polymers directly target these motifs, altering p53 and MARCKS protein functions in vitro.
- PARP-deficient mice showed impaired DNA damage signaling, including p53 hyporesponsiveness and cytoskeletal defects.
- The knockout phenotype was rescued by stable PARP gene expression.
Conclusions:
- PARP functions as a crucial component of a DNA break signaling mechanism.
- PARP-associated polymers may recruit and reprogram signaling proteins, such as p53 and MARCKS, at DNA break sites.
- This mechanism is vital for cellular responses to genotoxic stress and maintaining genomic stability.