Search

DNA strand breaks activate Poly(ADP-ribose) polymerase (PARP) 1 and 2, which use NAD+ as the substrate to covalently conjugate ADP-ribose on themselves and other proteins (e.g., Histone) to promote chromatin relaxation and recruit additional DNA repair factors. Enzymatic inhibitors of PARP1 and PARP2 (PARPi) are promising cancer therapy agents that selectively target BRCA1- or BRCA2- deficient cancers. As immediate early responders to DNA strand breaks with robust activities, PARP1 and PARP2 normally form transient foci (<10 minutes) at the micro-irradiation-induced DNA lesions. In addition to enzymatic inhibition, PARPi also extend the presence of PARP1 and PARP2 at DNA lesions, including at replication forks, where they may post a physical block for subsequent repair and DNA replication. The dynamic nature of PARP1 and PARP2 foci made live cell imaging a unique platform to detect subtle changes and the functional interaction among PARP1, PARP2, and their regulators. Recent imaging studies have provided new understandings of the biological consequence of PARP inhibition and uncovered functional interactions between PARP1 and PARP2 and new regulators (e.g. , histone poly(ADP-ribosylation) factor). Here, we review recent advances in dissecting the temporal and spatial Regulation of PARP1 and PARP2 at DNA lesions and discuss their physiological implications on both cancer and normal cells. [ABSTRACT FROM AUTHOR]

To maintain tissue homeostasis, cell proliferation is balanced by cell death. PARP1 is an important protein involved in both processes. Upon sensing DNA damage, PARP1 forms poly(ADP-ribose) (PAR) chains to recruit the repair proteins, ensuring genome integrity and faithful cell proliferation. In addition, PAR also regulates the activity of PARP1. Persistent DNA damage can signal the cell to progress toward programmed cell death, apoptosis. During apoptosis, proteolytic cleavage of PARP1 generates an N-terminal, ZnF1–2 PARP1 (DNA binding or regulatory fragment), and C-terminal, PARP1 ΔZnF1–2 (catalytic or PAR carrier fragment), which exhibits a basal activity. Regulation of the apoptotic fragments by PAR has not been studied. Here, we report that PAR inhibits the basal level activity of PARP1 ΔZnF1–2 , and ZnF1–2 PARP1 interacts with PARP1 ΔZnF1–2 to exhibit DNA-dependent stimulation and partially restores the PAR-dependent stimulation. Interestingly, along with the auto-modification domain of PARP1, the DNA-binding domains, ZnF1–2 PARP1 , also acts as an acceptor of PARylation; therefore, ZnF1–2 PARP1 exhibits a reduced affinity for DNA upon PARylation. Furthermore, we show that ZnF1–2 PARP1 shows trans-dominant inhibition of DNA-dependent stimulation of PARP2. Altogether, our study explores the regulation of the catalytic activity of PARP1 ΔZnF1–2 and PARP2 by the regulatory apoptotic fragment of PARP1. • PAR acts as an inhibitor of the catalytic apoptotic fragment of PARP1 PARP1 ΔZnF1-2. • Regulatory fragment (ZnF1-2 PARP1) and PARP1 ΔZnF1-2 can assemble independent of DNA. • ZnF1-2 PARP1 complements PARP1 ΔZnF1-2 for DNA-dependent activation. • ZnF1 is necessary for PAR-dependent stimulation of PARP1. • ZnF1-2 PARP1 trans-dominantly inhibits the DNA-dependent stimulation of PARP2. [ABSTRACT FROM AUTHOR]

In mammalian cells, chromatin poly(ADP-ribos)ylation (PARylation) at sites of DNA Double-Strand Breaks (DSBs) is mediated by two highly related enzymes, PARP1 and PARP2. However, enzyme-specific genetic interactions with other DSB repair factors remain largely undefined. In this context, it was previously shown that mice lacking PARP1 and H2AX, a histone variant that promotes DSB repair throughout the cell cycle, or the core nonhomologous end-joining (NHEJ) factor Ku80 are not viable, while mice lacking PARP1 and the noncore NHEJ factor DNA-PKcs are severely growth retarded and markedly lymphoma-prone. Here, we have examined the requirement for PARP2 in these backgrounds. We find that, like PARP1, PARP2 is essential for viability in mice lacking H2AX. Moreover, treatment of H2AX-deficient primary fibroblasts or B lymphocytes with PARP inhibitors leads to activation of the G2/M checkpoint and accumulation of chromatid-type breaks in a lineage- and gene-dose dependent manner. In marked contrast to PARP1, loss of PARP2 does not result in additional phenotypes in growth, development or tumorigenesis in mice lacking either Ku80 or DNA-PKcs. Altogether these findings highlight specific nonoverlapping functions of PARP1 and PARP2 at H2AX-deficient chromatin during replicative phases of the cell cycle and uncover a unique requirement for PARP1 in NHEJ-deficient cells. [ABSTRACT FROM AUTHOR]

Poly(ADP-ribose) polymerase 1 (PARP1) and PARP2 are DNA-dependent poly(ADP-ribose)transferases localized in nucleus. They have a significant homology in the C-terminal catalytic domain structure but differ in their N-terminal DNA-binding parts. The structural difference has an impact on the interaction of PARP1 and PARP2 with DNA and their DNA-dependent activation. Here, we compare the interaction of PARP1 and PARP2 with free 147 bp nucleosomal DNA and its nucleosome-associated variant (NCP) that contain in one strand a 1-nucleotide gap with 5'-dRP (imitating the intermediate of Base Excision Repair) or no specific damage. The affinity of PARP2 for the DNA strongly depends on the gap presence and to a lesser extent on the association with nucleosomes, while PARP1 interacts primarily with blunt ends of all DNAs and with a lower affinity with the single-strand break. The activities of PARP1 and PARP2 in the autoPARylation reaction and heteromodification of histones are distinctly stimulated by HPF1, depending on the gap presence in activating DNA. The most significant HPF1-induced stimulation of the histone modification in the presence of gapped NCP is a peculiar feature of PARP2. We propose a specific regulatory role of PARP2 in the process of DNA repair in the context of chromatin. • The activities of PARP1 and PARP2 are distinctly stimulated by HPF1. • The stimulatory action of HPF1 on PARP1/PARP2 automodification depends on the DNA gap presence. • The most significant stimulation of histone modification in the presence of gapped NCP is specific for PARP2. [ABSTRACT FROM AUTHOR]

Poly(ADP-ribosyl)ation is one of immediate cellular responses to DNA damage and is catalyzed by poly(ADP-ribose) polymerases (PARPs). PARP1 is a well-known regulator of DNA repair. Another member of this family, PARP2, was discovered later. The study of PARP1 and PARP2 functions started a long time ago, and special attention has been given to the role of these enzymes in base excision repair. This review summarizes my lab's data on the functions of PARP1 and PARP2 in base excision repair as well as the results obtained in the course of our collaboration with Dr. Samuel H. Wilson., (Copyright © 2020 Elsevier B.V. All rights reserved.)