Oxidative Stress and ADP-ribosylation / László Virág

Personal data: 

László Virág
Full Professor

E-mail: lvirag[at]med.unideb.hu


László Virág, Full Professor
Péter Bai Ph.D., Senior lecturer
Edina Bakondi Ph.D., Assistant lecturer
Csaba Hegedűs Ph.D., Research fellow
Katalin Erdélyi M.Sc., Junior research fellow
Erzsébet Herbály, Laboratory assistant
Katalin Kovács M.Sc., Phd student
Attila Brunyánszki M.Sc., Phd student
István Kovács, Diploma student


Oxidative stress indicates an imbalance between the production and neutralization of reactive oxygen species (ROS). Various disease states ranging from ischemia-reperfusion injury, shock, diabetes, endothelial dysfunction to Parkinson’s disease and many others have been shown to be characterized by oxidative stress. Excessive production of ROS may cause various types of DNA damage. Recognition of DNA breakage requires the activation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1). Activated PARP-1 synthesizes a branching (ADP-ribose)n polymer from NAD+. The polymer serves as a recruitment signal for the effectors of the DNA repair machinery. Poly(ADP-ribose) is a transient signal which is quickly degraded by poly(ADP-ribose) glycohydrolase (PARG). In addition to its role in DNA repair, poly(ADP-ribosyl)ation has also been implicated in the regulation of the cell cycle, replication, transcription, protein degradation and retroviral integration. With recent discoveries of novel poly(ADP-ribosyl)ating enzymes, the diversity of biological processes regulated by poly(ADP-ribosyl)ation is likely to increase even further.
In severe oxidative stress situations, however, excessive PARP-1 activation consumes the cellular NAD+ and leads to depletion of NAD+ and ATP. The PARP-1-mediated cellular energetic crisis may culminate in cell dysfunction and cell death. Alternatively, poly(ADP-ribose) polymer may trigger caspase-independent cell death mediated by apoptosis-inducing factor (AIF). The mode of cell death (apoptosis versus necrosis) can be modified by inhibition or genetic ablation of PARP-1.





Figure 1. Intense poly(ADP-ribosyl)ation may cause cell death







Previous Results

Our previous work focused on the role of PARP-1 in the regulation of oxidative stress-induced cytotoxicity. We have demonstrated that the apoptosis-necrosis switch observed in severe oxidative stress is mediated by PARP-1 activation. We have also investigated the in vivo role played by PARP-1 in oxidative stress-related pathologies ranging from diabetes and asthma to contact dermatitis and shock.

Current research projects

PARG in cell death

Recently our interest slightly shifted from PARP-1 to PARG. Due to lack of specific, cell permeable inhibitors of PARG, using lentiviral siRNA constructs we generated cell lines with stable suppression of hPARG and hPARP1. We found that PARG acts in concert with PARP1 in facilitating DNA strand break repair. However, the apoptosis-necrosis switch observed after severe oxidative stress is also mediated by the concerted action of PARP1 and PARG. Besides oxidative stimuli such as hydrogen peroxide we are also investigating the role of poly(ADP-ribosyl)ation in the regulation of other models of DNA damage e.g. the ones caused by alkylating agents, adriamycin or cigarette smoke.

PARP2 in adipogenesis and regulation of metabolism

Dr. Bai has previously identified PARP2 as a coactivator of PPAR, the master regulator of lipid metabolism. Moreover, via modulating the cellular NAD+ level, PARPs may regulate the function of other NAD+-dependent enzymes such as the histone deacetylase SIRT1. Our project aims to dissect interactions between PARPs and SIRT1 in the regulation of catabolism and energy expenditure.




Figure 2. Altered adipose tissue in PARP2-deficient mice





PARylation in MSC differentiation

A new line of investigation focuses on the role played by poly(ADP-ribosyl)ation in mesenchymal stem cell (MSC) biology. MSCs are adherent multipotent cells that can be obtained from various tissues such as bone marrow, blood vessels and adipose tissue. MSCs can be induced to differentiate mainly to tissues of mesodermal origine (cartilage, fat, bone, stroma) but under specific conditions also to neurons and cardiomyocytes. An interesting property of MSCs is their strong immunosuppresive effect permitting even in allogenic cell therapy applications. The role of free radicals and poly(ADP-ribosyl)ation in MSC biology is mainly unexplored.




Figure 3. MSC cultures specifically stained to demonstrate adipogenic, osteogenic and chondrogenic differentiation potential











Representative publications:

1. Virág L, Salzman AL, Szabó C. Poly(ADP-ribose) synthetase activation mediates mitochondrial injury during oxidant-induced cell death. J Immunol. 1998;161(7):3753-9.

2. Soriano FG, Virág L, Jagtap P, Szabó É, Mabley JG, Liaudet L, Marton A, Hoyt DG, Murthy KGK, Salzman AL, Southan GJ, Szabó C: Diabetic endothelial dysfunction: the role of poly (ADP-ribose) polymerase activation. Nature Medicine, 7(1):108-113, 2001

3. Virág L, Szabó C: The therapeutic potential of poly(ADP-ribose) polymerase inhibitors. Pharmacological Reviews, 54(3):375-429., 2002.

4. Erdélyi K, Bakondi E, Gergely P, Szabó C and Virág L: Pathophysiologic role of oxidative stress-induced poly(ADP-ribose) polymerase-1 activation: focus on cell death and transcriptional regulation. Cell. Mol. Life. Sci. 2005 62(7-8):751-9.

5. Bakondi E, Gönczi M, Szabó É, Bai P, Pacher P, Gergely P, Kovács L, Hunyadi J, Szabó C, Csernoch L, Virág L: Role of intracellular calcium mobilization and cell density-dependent signaling in oxidative stress-induced cytotoxicity in HaCaT keratinocytes. J. Invest. Dermatol. 121(1):88-95, 2003.

Recent publications:

1. Erdélyi K, Bai P, Kovács I, Szabó E, Mocsár G, Kakuk A, Szabó C, Gergely P, Virág L. Dual role os poly(ADP-ribose) glycohydrolase in the regulation of cell death in oxidatively stressed A549 cells. FASEB J. 2009 Jul. 1.

2. Bai P, Hegedus C, Szabó E, Gyüre L, Bakondi E, Brunyánszki A, Gergely S, Szabó C, Virág L. Poly(ADP-ribose) polymerase mediates inflammation in a mouse model of contact hypersensitivity. J Invest Dermatol. 129(1):234-8. 2009

3. Hegedus C, Lakatos P, Oláh G, Tóth BI, Gergely S, Szabó E, Bíró T, Szabó C, Virág L. Protein kinase C protects from DNA damage-induced necrotic cell death by inhibiting poly(ADP-ribose) polymerase-1. FEBS Lett. 582(12):1672-8, 2008

4. Bai P, Houten SM, Huber A, Schreiber V, Watanabe M, Kiss B, de Murcia G, Auwerx J, Ménissier-de Murcia J. Poly(ADP-ribose) polymerase-2 controls adipocyte differentiation and adipose tissue function through the regulation of the activity of the retinoid X receptor/peroxisome proliferator-activated receptor-gamma heterodimer. J Biol Chem. 282(52):37738-46, 2007

5. Bai P, Hegedus C, Erdélyi K, Szabó E, Bakondi E, Gergely S, Szabó C, Virág L. Protein tyrosine nitration and poly(ADP-ribose) polymerase activation in N-methyl-N-nitro-N-nitrosoguanidine-treated thymocytes: implication for cytotoxicity. Toxicol Lett. 170(3):203-13, 2007

6. Erdèlyi K, Kiss A, Bakondi E, Bai P, Szabó C, Gergely P, Erdödi F, Virag L. Gallotannin inhibits the expression of chemokines and inflammatory cytokines in A549 cells. Mol Pharmacol. 68(3):895-904, 2005