Stimulation of DNA synthesis by adenosine diphosphoribosylation of HeLa nuclear proteins during the cell cycle

Poly-ADP-ribose polymerase: machinery for nuclear processes

It is becoming increasingly clear that the nuclear protein, poly-ADP-ribose polymerase 1 (PARP1), plays essential roles in the cell, including DNA repair, translation, transcription, telomere maintenance, and chromatin remodeling. Despite the exciting progress made in understanding the ubiquitous role of poly-ADP-ribose metabolism, a basic mechanism of PARP's activity regulating multiple nuclear processes is yet to be outlined. This review offers a holistic perspective on activity of PARP1, based on empirically observable phenomena. Primary attention is given to mechanisms by which PARP1 regulates a broad range of essential nuclear events, including two complementary processes (1) regulation of protein-nucleic acid interactions by means of protein shuttling and (2) utilizing poly-ADP-ribose as an anionic matrix for trapping, recruiting, and scaffolding proteins.

Decreased poly(ADP-ribosyl)ation of CTCF, a transcription factor, is associated with breast cancer phenotype and cell proliferation

PURPOSE

There is compelling evidence of a relationship between poly(ADP-ribosyl)ation and tumorigenesis; however, much less is known about the role of specific targets of poly(ADP-ribosyl)ation in tumor development. Two forms of the multifunctional transcription factor, CTCF, were previously identified: a 130-kDa protein (CTCF-130), characteristic for cell lines, and a 180-kDa protein (CTCF-180), modified by poly(ADP-ribosyl)ation. This study was aimed to investigate differential poly(ADP-ribosyl)ation of CTCF in normal and tumor breast tissues.

EXPERIMENTAL DESIGN

Western blot analysis, mass spectrometry, and immunohistochemical and immunofluorescent stainings were used to characterize CTCF-130 and CTCF-180 in breast cell lines, primary cultures, and normal and tumor breast tissues. The immunoreactivity score was used for CTCF-130 quantification in tissues.

RESULTS

We discovered that only CTCF-180 is detected in the normal breast tissues, whereas both CTCF-130 and CTCF-180 are present in breast tumors. Using an antibody specific for CTCF-130, we observed that 87.7% of breast tumors were positive for CTCF-130. A negative correlation existed between the levels of CTCF-130, tumor stage, and tumor size. Significantly, a transition from CTCF-180 to CTCF-130 was discovered in primary cultures generated from normal breast tissues, indicating a link between CTCF-130 and proliferation. Conversely, the appearance of CTCF-180 was observed following growth arrest in breast cell lines.

CONCLUSIONS

Collectively, our data suggest that the loss of CTCF poly(ADP-ribosyl)ation is associated with cell proliferation and breast tumor development. We propose the use of CTCF-130 as a marker for tumor breast cells and lower levels of CTCF-130 as an indicator of unfavorable prognosis.

Poly(ADP-ribosyl)ation reactions in the regulation of nuclear functions

Poly(ADP-ribosyl)ation is a post-translational modification of proteins. During this process, molecules of ADP-ribose are added successively on to acceptor proteins to form branched polymers. This modification is transient but very extensive in vivo, as polymer chains can reach more than 200 units on protein acceptors. The existence of the poly(ADP-ribose) polymer was first reported nearly 40 years ago. Since then, the importance of poly(ADP-ribose) synthesis has been established in many cellular processes. However, a clear and unified picture of the physiological role of poly(ADP-ribosyl)ation still remains to be established. The total dependence of poly(ADP-ribose) synthesis on DNA strand breaks strongly suggests that this post-translational modification is involved in the metabolism of nucleic acids. This view is also supported by the identification of direct protein-protein interactions involving poly(ADP-ribose) polymerase (113 kDa PARP), an enzyme catalysing the formation of poly(ADP-ribose), and key effectors of DNA repair, replication and transcription reactions. The presence of PARP in these multiprotein complexes, in addition to the actual poly(ADP-ribosyl)ation of some components of these complexes, clearly supports an important role for poly(ADP-ribosyl)ation reactions in DNA transactions. Accordingly, inhibition of poly(ADP-ribose) synthesis by any of several approaches and the analysis of PARP-deficient cells has revealed that the absence of poly(ADP-ribosyl)ation strongly affects DNA metabolism, most notably DNA repair. The recent identification of new poly(ADP-ribosyl)ating enzymes with distinct (non-standard) structures in eukaryotes and archaea has revealed a novel level of complexity in the regulation of poly(ADP-ribose) metabolism.

Cell cycle regulation of poly(ADP-ribose) synthetase in FR3T3 cells

The properties of poly(ADP-ribose) synthetase were studied throughout the cell cycle progression of non-synchronized rat FR3T3 fibroblasts using an immunological and biochemical approach. Cells in the various phases of the cell cycle were sorted from an asynchronously growing population by using flow cytofluorometry. G1, S and G2 + M fractions were used for enzymatic assays in the presence of saturating concentrations of DNAase I for the analysis of total poly(ADP-ribose) synthetase; maximal enzyme activity was found in the G2 + M phase. Purified IgG, specific for the FR3T3 poly(ADP-ribose) synthetase were used for the labelling of endogenous synthetase in order to quantify the enzyme immunologically. Localization of nuclear immunofluorescence was observed and analysis of poly(ADP-ribose) synthetase content throughout the cell cycle were carried out using double fluorescent staining and cytofluorometry. Poly(ADP-ribose) synthetase content as measured immunologically was found to increase from G1 to S and G2 + M phases. Quiescent cells showed a lower content as measured immunologically of poly(ADP-ribose) synthetase than cells in the G1 phase. In exponentially growing cells, the ratio between enzyme activity of poly(ADP-ribose) synthetase over the amount of enzyme measured immunologically was found to be higher in the G2 + M phase. These results show that a cell-cycle specific event activates poly(ADP-ribose) synthetase in the G2 + M phase.

Retarded decline in poly-ADPR content and poly-ADPR synthetase activity in chicken dystrophic muscle

The activity of poly-ADPR synthetase declines just after hatching in normal chick muscle nuclei. However, in dystrophic chick muscle nuclei it decreases 5 weeks after hatching. A delayed decrease in the amount of poly-ADPR is also observed in dystrophic chick muscle nuclei. These observations suggest that dystrophic muscle follows an abnormal developmental program.

Poly ADP-ribosylation of DNA-dependent RNA polymerase I from quail oviduct. Dependence on progesterone stimulation

Progesterone causes in goblet cells of oviducts of estrogen hormone-stimulated immature quails selectively gene activation without affecting DNA synthesis. This biological model has been used to study the influence of poly ADP-ribosylation during the processes of DNA transcription. Administration of progesterone in vivo causes an increase of the activity of RNA polymerase I and II in isolated nuclei. This increase is accompanied by a marked decrease of the specific activity of poly (ADP-Rib) polymerase. After in vitro ADP-ribosylation of nuclear proteins the template capacity of chromatin for ""exogenous'' RNA synthesis (with E. coli DNA-dependent RNA polymerases) as well as for ""endogenous'' RNA synthesis with DNA dependent RNA polymerases II is not affected, whereas the data presented seem to indicate that the capacity for RNA synthesis mediated by ""endogenous'' DNA-dependent RNA polymerase I might be inhibited after ADP-ribosylation. Evidence is presented to show that a considerable amount of poly (ADP-Rib), synthesized by poly (ADP-Rib) polymerase in isolated nuclei, is linked with RNA polymerase I. The rate of synthesis of poly (ADP-Rib) is dependent on the incubation temperature (optimum at 25 degrees C) and it can be inhibited by the specific inhibitors of poly (ADP-Rib) polymerase nicotineamide, thymidine and formycin B. Poly (ADP-Rib) is probably associated with RNA polymerase I through a covalent linkage. ADP-ribosylated RNA polymerase I has been purified 550 fold with respect to the nuclear extract corresponding to a 4,000 fold purification from the whole cell homogenate. The ratio between poly (ADP-Rib), formed during preincubation of nuclei with NAD, and RNA polymerase I remains almost constant during the purification procedures. The extent of ADP-ribosylation of RNA polymerase I decreases during gene expression. Thus we conclude that poly ADP-ribosylation of this enzyme is one of the regulatory mechanisms by which specificity of DNA transcription is achieved.

Poly(ADP-ribose): release of template restriction in HeLa cells

Evidence is presented to show that ADP-ribosylation of nuclear proteins by poly(ADP-ribose) polymerase enhances template-primer activity of HeLa cell nuclear DNA. We used Escherichia coli DNA polymerase I (EC 2.7.7.7; DNA nucleotidyltransferase) as an exogenous probe of nuclear DNA status. Neither NAD nor free poly(ADP-ribose) acts directly on the bacterial enzyme. The stimulation is specific for formation of ADP-ribosylated proteins and is not a generalized polyanion or nucleotide effect on chromatin. The release of template restriction is proportional to the capacity of a given cell line to synthesize poly(ADP-ribose); both the stimulation and poly(ADP-ribose) formation are coordinately proportional to NAD concentration. Binding studies with DNA polymerase indicate exposure or generation of additional 3'-OH primer sites due to ADP-ribosylation in intact nuclei. With intact cells, there appears a correlation among growth, physiological template restriction, and the above effects of ADP-ribosylation.