Mono(ADP-ribosyl)ation (MARylation) is a regulatory post-translational modification of proteins that controls their functions through a variety of mechanisms. MARylation is catalyzed by ...mono(ADP-ribosyl) transferase (MART) enzymes, a subclass of the poly(ADP-ribosyl) polymerase (PARP) family of enzymes. Although the role of PARPs and poly(ADP-ribosyl)ation (PARylation) in cellular pathways, such as DNA repair and transcription, is well studied, the role of MARylation and MARTs (i.e., the PARP 'monoenzymes') are not well understood. Moreover, compared to PARPs, the development of MART-targeted therapeutics is in its infancy. Recent studies are beginning to shed light on the structural features, catalytic targets, and biological functions of MARTs. The development of new technologies to study MARTs have uncovered essential roles for these enzymes in the regulation of cellular processes, such as RNA metabolism, cellular transport, focal adhesion, and stress responses. These insights have increased our understanding of the biological functions of MARTs in cancers, neuronal development, and immune responses. Furthermore, several novel inhibitors of MARTs have been developed and are nearing clinical utility. In this review, we summarize the biological functions and molecular mechanisms of MARTs and MARylation, as well as recent advances in technology that have enabled detection and inhibition of their activity. We emphasize PARP-7, which is at the forefront of the MART subfamily with respect to understanding its biological roles and the development of therapeutically useful inhibitors. Collectively, the available studies reveal a growing understanding of the biochemistry, chemical biology, physiology, and pathology of MARTs.
Poly-ADP-ribosylation (PARylation) is a fully reversible post-translational modification with key roles in cellular physiology. Due to the multi-domain structure of poly(ADP-ribose) polymerase-1 ...(PARP1) and the highly dynamic nature of the PARylation reaction, studies on the biochemical mechanism and structural dynamics remain challenging. Here, we report label-free, time-resolved monitoring of PARP1-dependent PARylation using ATR-FTIR spectroscopy. This includes PARP1 activation by binding to DNA strand break models, NAD
substrate binding, PAR formation, and dissociation of automodified PARP1 from DNA. Analyses of PARP1 activation at different DNA models demonstrate a strong positive correlation of PARylation and PARP1 dissociation, with the strongest effects observed for DNA nicks and 3' phosphorylated ends. Moreover, by examining dynamic structural changes of PARP1, we reveal changes in the secondary structure of PARP1 induced by NAD
and PARP inhibitor binding. In summary, this approach enables holistic and dynamic insights into PARP1-dependent PARylation with molecular and temporal resolution.
Cells have evolved a complex network of biochemical pathways, collectively known as the DNA damage response (DDR), to prevent detrimental mutations from being passed on to their progeny. The DDR ...coordinates DNA repair with cell-cycle checkpoint activation and other global cellular responses. Genes encoding DDR factors are frequently mutated in cancer, causing genomic instability, an intrinsic feature of many tumours that underlies their ability to grow, metastasize and respond to treatments that inflict DNA damage (such as radiotherapy). One instance where we have greater insight into how genetic DDR abrogation impacts on therapy responses is in tumours with mutated BRCA1 or BRCA2. Due to compromised homologous recombination DNA repair, these tumours rely on alternative repair mechanisms and are susceptible to chemical inhibitors of poly(ADP-ribose) polymerase (PARP), which specifically kill homologous recombination-deficient cancer cells, and have become a paradigm for targeted cancer therapy. It is now clear that many other synthetic-lethal relationships exist between DDR genes. Crucially, some of these interactions could be exploited in the clinic to target tumours that become resistant to PARP inhibition. In this Review, we discuss state-of-the-art strategies for DDR inactivation using small-molecule inhibitors and highlight those compounds currently being evaluated in the clinic.
Poly(ADP-ribosyl)ation (PARylation) is a posttranslational modification involved in multiple biological processes, including DNA damage repair. This modification is catalyzed by poly(ADP-ribose) ...polymerase (PARP) family of enzymes. PARylation is composed of both linear and branched polymers of poly(ADP-ribose) (PAR). However, the biochemical mechanism of polymerization and biological functions of branched PAR chains are elusive. Here we show that PARP2 is preferentially activated by PAR and subsequently catalyzes branched PAR chain synthesis. Notably, the direct binding to PAR by the N-terminus of PARP2 promotes the enzymatic activity of PARP2 toward the branched PAR chain synthesis. Moreover, the PBZ domain of APLF recognizes the branched PAR chain and regulates chromatin remodeling to DNA damage response. This unique feature of PAR-dependent PARP2 activation and subsequent PARylation mediates the participation of PARP2 in DNA damage repair. Thus, our results reveal an important molecular mechanism of branched PAR synthesis and a key biological function of branched PARylation.
During the development, progression and dissemination of neoplastic lesions, cancer cells can hijack normal pathways and mechanisms. This includes the control of the function of cellular proteins ...through reversible post‐translational modifications, such as ADP‐ribosylation, phosphorylation, and acetylation. In the case of mono‐ADP‐ribosylation and poly‐ADP‐ribosylation, the addition of one or several units of ADP‐ribose to target proteins occurs via two families of enzymes that can generate ADP‐ribosylated proteins: the diphtheria toxin‐like ADP‐ribosyltransferase (ARTD) family, comprising 17 different proteins that are either poly‐ADP‐ribosyltransferases or mono‐ADP‐ribosyltransferases or inactive enzymes; and the clostridial toxin‐like ADP‐ribosyltransferase family, with four human members, two of which are active mono‐ADP‐ribosyltransferases, and two of which are enzymatically inactive. In line with a central role for poly‐ADP‐ribose polymerase 1 in response to DNA damage, specific inhibitors of this enzyme have been developed as anticancer therapeutics and evaluated in several clinical trials. Recently, in combination with the discovery of a large number of enzymes that can catalyse mono‐ADP‐ribosylation, the role of this modification has been linked to human diseases, such as inflammation, diabetes, neurodegeneration, and cancer, thus revealing the need for the development of specific ARTD inhibitors. This will provide a better understanding of the roles of these enzymes in human physiology and pathology, so that they can be targeted in the future to generate new and efficacious drugs. This review summarizes our present knowledge of the ARTD enzymes that are involved in mono‐ADP‐ribosylation reactions and that have roles in cancer biology. In particular, the well‐documented role of macro‐containing ARTD8 in lymphoma and the putative role of ARTD15 in cancer are discussed.
A number of intracellular ARTD enzymes that are involved in the post‐translational modification, mono‐ADP‐ribosylation, can have roles in cancer biology. The connection between cancer and ARTD8/PARP14 is well established. ARTD8, a Stat6‐interacting protein, is associated with aggressiveness of B‐cell lymphomas. The endoplasmic reticulum ARTD15/PARP16 can play a role in the nucleo‐cytoplasmic trafficking. A dys‐regulation of this process leads to the mislocalisation of oncogenic and tumour‐suppressor proteins.
Poly(ADP-ribose) polymerase 1 (PARP1) and PARP2 are recruited and activated by DNA damage, resulting in ADP-ribosylation at numerous sites, both within PARP1 itself and in other proteins. Several ...PARP1 and PARP2 inhibitors are currently employed in the clinic or undergoing trials for treatment of various cancers. These drugs act primarily by trapping PARP1 on damaged chromatin, which can lead to cell death, especially in cells with DNA repair defects. Although PARP1 trapping is thought to be caused primarily by the catalytic inhibition of PARP-dependent modification, implying that ADP-ribosylation (ADPr) can counteract trapping, it is not known which exact sites are important for this process. Following recent findings that PARP1- or PARP2-mediated modification is predominantly serine-linked, we demonstrate here that serine ADPr plays a vital role in cellular responses to PARP1/PARP2 inhibitors. Specifically, we identify three serine residues within PARP1 (499, 507, and 519) as key sites whose efficient HPF1-dependent modification counters PARP1 trapping and contributes to inhibitor tolerance. Our data implicate genes that encode serine-specific ADPr regulators, HPF1 and ARH3, as potential PARP1/PARP2 inhibitor therapy biomarkers.
The anti-cancer drug target poly(ADP-ribose) polymerase 1 (PARP1) and its close homologue, PARP2, are early responders to DNA damage in human cells
. After binding to genomic lesions, these enzymes ...use NAD
to modify numerous proteins with mono- and poly(ADP-ribose) signals that are important for the subsequent decompaction of chromatin and the recruitment of repair factors
. These post-translational modifications are predominantly serine-linked and require the accessory factor HPF1, which is specific for the DNA damage response and switches the amino acid specificity of PARP1 and PARP2 from aspartate or glutamate to serine residues
. Here we report a co-structure of HPF1 bound to the catalytic domain of PARP2 that, in combination with NMR and biochemical data, reveals a composite active site formed by residues from HPF1 and PARP1 or PARP2 . The assembly of this catalytic centre is essential for the addition of ADP-ribose moieties after DNA damage in human cells. In response to DNA damage and occupancy of the NAD
-binding site, the interaction of HPF1 with PARP1 or PARP2 is enhanced by allosteric networks that operate within the PARP proteins, providing an additional level of regulation in the induction of the DNA damage response. As HPF1 forms a joint active site with PARP1 or PARP2, our data implicate HPF1 as an important determinant of the response to clinical PARP inhibitors.
ADP‐ribosylation is a conserved post‐translational protein modification that plays a role in all major cellular processes, particularly DNA repair, transcription, translation, stress response and ...cell death. Hence, dysregulation of ADP‐ribosylation is linked to the physiopathology of several human diseases including cancers, diabetes and neurodegenerative disorders. Protein ADP‐ribosylation can be reversed by the macrodomain‐containing proteins PARG, TARG1, MacroD1 and MacroD2, which hydrolyse the ester bond known to link proteins to ADP‐ribose as well as consecutive ADP‐ribose subunits; targeting this bond can thus result in the complete removal of the protein modification or the conversion of poly(ADP‐ribose) to mono(ADP‐ribose). Recently, proteins containing the NUDIX domain – namely human NUDT16 and bacterial RppH – have been shown to process in vitro protein ADP‐ribosylation through an alternative mechanism, converting it into protein‐conjugated ribose‐5′‐phosphate (R5P, also known as pR). Though this protein modification was recently identified in mammalian tissues, its physiological relevance and the mechanism of generating protein phosphoribosylation are currently unknown. Here, we identified ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) as the first known mammalian enzyme lacking a NUDIX domain to generate pR from ADP‐ribose on modified proteins in vitro. Thus, our data show that at least two enzyme families – Nudix and ENPP/NPP – are able to metabolize protein‐conjugated ADP‐ribose to pR in vitro, suggesting that pR exists and may be conserved from bacteria to mammals. We also demonstrate the utility of ENPP1 for converting protein‐conjugated mono(ADP‐ribose) and poly(ADP‐ribose) into mass spectrometry‐friendly pR tags, thus facilitating the identification of ADP‐ribosylation sites.
Mammalian membrane‐bound ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is able to hydrolyse protein ADP‐ribosylation to generate phosporibosylated proteins, implicating it as a new enzyme that can modulate protein ADP‐ribosylation. Furthermore, ENPP1 enzymatic activity can be used to process protein ADP‐ribosylation for the characterization of modification sites by mass spectrometry.
ADP-ribosylation is a post-translational modification of proteins catalyzed by ADP-ribosyltransferases. It comprises the transfer of the ADP-ribose moiety from NAD
+ to specific amino acid residues ...on substrate proteins or to ADP-ribose itself. Currently, 22 human genes encoding proteins that possess an ADP-ribosyltransferase catalytic domain are known. Recent structural and enzymological evidence of poly(ADP-ribose)polymerase (PARP) family members demonstrate that earlier proposed names and classifications of these proteins are no longer accurate. Here we summarize these new findings and propose a new consensus nomenclature for all ADP-ribosyltransferases (ARTs) based on the catalyzed reaction and on structural features. A unified nomenclature would facilitate communication between researchers both inside and outside the ADP-ribosylation field.
Protein ADP-ribosylation is essential for the regulation of several cellular pathways, enabling dynamic responses to diverse pathophysiological conditions. It is modulated through a dynamic interplay ...between ADP-ribose readers, writers and erasers. While ADP-ribose synthesis has been studied and reviewed extensively, ADP-ribose processing by erasing enzymes has received comparably less attention. However, major progress in the mass spectrometric identification of ADP-ribosylated residues and the biochemical characterization of ADP-ribose erasers has substantially expanded our knowledge of ADP-ribosylation dynamics. Herein, we describe recent insights into the biology of ADP-ribose erasers and discuss the intricately orchestrated cellular processes to switch off ADP-ribose-dependent mechanisms.
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