Genomic instability in a PARP-1(-/-) cell line expressing PARP-1 DNA-binding domain

Impact of PARP-1 and DNA-PK expression on survival in patients with glioblastoma multiforme

PURPOSE

To analyze, whether higher tumor levels of DNA repair enzymes contribute to worse treatment results of glioblastoma multiforme (GBM) patients after postoperative radiotherapy.

MATERIALS AND METHODS

Thirty four patients with GBM received postoperative radiotherapy. Tumor sections were examined for poly-ADP ribose polymerase-1 (PARP-1) and DNA protein kinase (DNA-PK) expression. Immunohistochemical staining intensities of PARP-1 and DNA-PK were determined (score 0-3) and expression levels were correlated with patients overall survival.

RESULTS

Median survival time of the whole study group was 10.0 months (95% CI 8.1-11.9). Median survival of patients with high and low (≥median and <median) tumor PARP-1 levels were 10.0 months (95% CI 7.9-12.1) and 12.0 months (95% CI 8.3-15.7), respectively (p=0.93). In contrast, median survival of patients with high and low tumor DNA-PK levels were 9.0 months (95% CI 7.2-10.8) and 13.0 months (95% CI 10.7-15.3), respectively (p=0.02). In multivariate analysis, DNA-PK expression emerged as a significant independent predictor for overall survival (HR 3.9, 95% CI 1.5-10.7, p=0.01).

CONCLUSION

This hypothesis generating study showed that high tumor levels of DNA-PK correlate with poor survival of GBM patients. Further studies are needed to confirm these results and to clarify whether DNA-PK inhibitors might have a potential to radiosensitize GBM and improve the treatment outcome of this devastating disease.

Differential regulation of CXC ligand 1 transcription in melanoma cell lines by poly(ADP-ribose) polymerase-1

The continuous production of the CXC ligand 1 (CXCL1) chemokine by melanoma cells is a major effector of tumor growth. We have previously shown that the constitutive expression of this chemokine is dependent upon transcription factors nuclear factor-kappa B (NF-kappaB), stimulating protein-1 (SP1), high-mobility group-I/Y (HMGI/Y), CAAT displacement protein (CDP) and poly(ADP-ribose) polymerase-1 (PARP-1). In this study, we demonstrate for the first time the mechanism of transcriptional regulation of CXCL1 through PARP-1 in melanoma cells. In its inactive state, PARP-1 binds to the CXCL1 promoter in a sequence-specific manner and prevents binding of NF-kappaB (p65/p50) to its element. However, activation of the PARP-1 enzymatic activity enhances CXCL1 expression, owing to the loss of PARP-1 binding to the CXCL1 promoter, accompanied by enhanced binding of p65 to the promoter. The delineation of the role of NF-kappaB-interacting factors in the putative CXCL1 enhanceosome will provide key information in developing strategies to block constitutive expression of this and other chemokines in cancer and to develop targeted therapy.

The emerging role of poly(ADP-ribose) polymerase-1 in longevity

In the present paper, the involvement of the family of poly(ADP-ribose) polymerases (PARPs), and especially of PARP-1, in mammalian longevity is reviewed. PARPs catalyse poly(ADP-ribosyl)ation, a covalent post-translational protein modification in eukaryotic cells. PARP-1 and PARP-2 are activated by DNA strand breaks, play a role in DNA base-excision repair (BER) and are survival factors for cells exposed to low doses of ionising radiation or alkylating agents. PARP-1 is the main catalyst of poly(ADP-ribosyl)ation in living cells under conditions of DNA breakage, accounting for about 90% of cellular poly(ADP-ribose). DNA-damage-induced poly(ADP-ribosyl)ation also functions as a negative regulator of DNA damage-induced genomic instability. Cellular poly(ADP-ribosyl)ation capacity in permeabilised mononuclear blood cells (MNC) is positively correlated with life span of mammalian species. Furthermore PARP-1 physically interacts with WRN, the protein deficient in Werner syndrome, a human progeroid disorder, and PARP-1 and WRN functionally cooperate in preventing carcinogenesis in vivo. Some of the other members of the PARP family have also been revealed as important regulators of cellular functions relating to ageing/longevity. In particular, tankyrase-1, tankyrase-2, PARP-2 as well as PARP-1 have been found in association with telomeric DNA and are able to poly(ADP-ribosyl)ate the telomere-binding proteins TRF-1 and TRF-2, thus blocking their DNA-binding activity and controlling telomere extension by telomerase.

Poly(ADP-ribose) polymerase (PARP-1) and p53 independently function in regulating double-strand break repair in primate cells

PARP-1 is rapidly activated by DNA strand breaks, which finally leads to the modulation of multiple protein activities in DNA replication, DNA repair and checkpoint control. PARP-1 may be involved in homologous recombination, and poly(ADP-ribosyl)ation of p53 represents one possible mechanism that activates p53 as a recombination surveillance factor. Here, we examined the influence of PARP-1 on homology-directed double-strand break (DSB) repair by use of a fluorescence- and I-SceI- meganuclease-based assay with either episomal or chromosomally integrated DNA substrates. Surprisingly, the transient expression of both full-length PARP-1 and of a dominant negative mutant, retaining the DNA-binding but lacking the catalytic domain, down-regulated DSB repair in a dose-dependent manner. This effect was seen regardless of p53 status, however, with enhanced inhibition in the presence of wild-type p53. Taken together, our data reveal that PARP-1 overexpression counteracts DSB repair independently of its enzymatic activity and of poly(ADP-ribosyl)ation of p53 in particular, but synergizes with p53 in suppressing chromosomal rearrangements.

Fine tuning the transcriptional regulation of the CXCL1 chemokine

Constitutive activation of the transcription factor nuclear factor-κB (NF-κB) plays a major role in inflammatory diseases as well as cancer by inducing the endogenous expression of many proinflammatory proteins such as chemokines, and facilitating escape from apoptosis. The constitutive expression of chemokines such as CXCL1 has been correlated with growth, angiogenesis, and metastasis of cancers such as melanoma. The transcription of CXCL1 is regulated through interactions of NF-κB with other transcriptional regulatory molecules such as poly(ADP-ribose) polymerase-1 (PARP-1) and cAMP response element binding protein (CREB)-binding protein (CBP). It has been proposed that these two proteins interact with NF-κB and other enhancers to form an enhanceosome at the promoter region of CXCL1 and modulate CXCL1 transcription. In addition to these positive cofactors, a negative regulator, CAAT displacement protein (CDP), may also be involved in the transcriptional regulation of CXCL1. It has been postulated that the elevated expression of CXCL1 in melanomas is due to altered interaction between these molecules. CDP interaction with the promoter down-regulates transcription, whereas PARP and/or CBP interactions enhance transcription. Thus, elucidation of the interplay between components of the enhanceosome of this gene is important in finding more efficient and new therapies for conditions such as cancer as well as acute and chronic inflammatory diseases.