Poly(ADP-ribosyl)ation (PARylation) is a complex and reversible posttranslational modification catalyzed by
poly(ADP-ribose)polymerases (PARPs), which orchestrates
protein function and subcellular localization. The function of PARP1 in genotoxic stress response upon induction of oxidative DNA lesions and strand breaks is firmly established, but its role in the response to chemical-induced, bulky
DNA adducts is understood incompletely. To address the role of PARP1 in the response to bulky
DNA adducts, we treated human
cancer cells with
benzo[a]pyrene 7,8-dihydrodiol-9,10-epoxide (
BPDE), which represents the active metabolite of the environmental
carcinogen benzo[a]pyrene [B(a)P], in nanomolar to low micromolar concentrations. Using a highly sensitive LC-MS/MS method, we revealed that
BPDE induces cellular PAR formation in a time- and dose-dependent manner. Consistently, PARP1 activity significantly contributed to
BPDE-induced genotoxic stress response. On one hand, PARP1 ablation rescued
BPDE-induced NAD+ depletion and protected cells from
BPDE-induced short-term toxicity. On the other hand, strong sensitization effects of PARP inhibition and PARP1 ablation were observed in long-term clonogenic survival assays. Furthermore, PARP1 ablation significantly affected
BPDE-induced S- and G2-phase transitions. Together, these results point towards unresolved
BPDE-DNA lesions triggering replicative stress. In line with this,
BPDE exposure resulted in enhanced formation and persistence of
DNA double-strand breaks in PARP1-deficient cells as evaluated by microscopic co-localization studies of 53BP1 and γH2A.X foci. Consistently, an
HPRT mutation assay revealed that PARP inhibition potentiated the mutagenicity of
BPDE. In conclusion, this study demonstrates a profound role of PARylation in
BPDE-induced genotoxic stress response with significant functional consequences and potential relevance with regard to B[a]P-induced
cancer risks.