The PARP inhibitor ABT-888 potentiates dacarbazine-induced cell death in carcinoids

Activation of proline metabolism maintains ATP levels during cocaine-induced polyADP-ribosylation

Cocaine is a commonly abused drug worldwide. Acute as well as repeated exposure to cocaine activates persistent cellular and molecular changes in the brain reward regions. The effects of cocaine are predominantly mediated via alterations in neuronal gene expression by chromatin remodeling. Poly(ADP-ribose) polymerase-1 (PARP-1) catalyzed PARylation of chromatin has been reported as an important regulator of cocaine-mediated gene expression. PARP-1 dependent ADP-ribosylation is an energy-dependent process. In this study, we investigated the cellular energy response to cocaine-induced upregulation of PARP-1 expression. Exposure of differentiated SH-SY5Y cells to varying concentrations of cocaine resulted in the induction of PARP-1 dependent PARylation of p53 tumor suppressor. Further analysis revealed that PARylation of p53 by cocaine treatment resulted in nuclear accumulation of p53. However, induction and nuclear accumulation of p53 did not correlate with neuronal apoptosis/cell death upon cocaine exposure. Interestingly, cocaine-induced p53 PARylation resulted in the induction of proline oxidase (POX)—a p53 responsive gene involved in cellular metabolism. Given that cocaine-induced p53 PARylation is an energy-dependent process, we observed that cocaine-induced PARP-1/p53/POX axes alters cellular energy metabolism. Accordingly, using pharmacological and genetic studies of PARP-1, p53, and POX, we demonstrated the contribution of POX in maintaining cellular energy during neuronal function. Collectively, these studies highlight activation of a novel metabolic pathway in response to cocaine treatment.

Inhibition of topoisomerase IIA (Top2α) induces telomeric DNA damage and T cell dysfunction during chronic viral infection

T cells play a critical role in controlling viral infection; however, the mechanisms regulating their responses remain incompletely understood. Here, we investigated the role of topoisomerase IIA (Top2α, an enzyme that is essential in resolving entangled DNA strands during replication) in telomeric DNA damage and T cell dysfunction during viral infection. We demonstrated that T cells derived from patients with chronic viral (HBV, HCV, and HIV) infection had lower Top2α protein levels and enzymatic activity, along with an accumulation of the Top2α cleavage complex (Top2cc) in genomic DNA. In addition, T cells from virally infected subjects with lower Top2α levels were vulnerable to Top2α inhibitor-induced cell apoptosis, indicating an important role for Top2α in preventing DNA topological disruption and cell death. Using Top2α inhibitor (ICRF193 or Etoposide)-treated primary T cells as a model, we demonstrated that disrupting the DNA topology promoted DNA damage and T cell apoptosis via Top2cc accumulation that is associated with protein-DNA breaks (PDB) at genomic DNA. Disruption of the DNA topology was likely due to diminished expression of tyrosyl-DNA phosphodiesterase 2 (TDP2), which was inhibited in T cells in vitro by Top2α inhibitor and in vivo by chronic viral infection. These results suggest that immune-evasive viruses (HBV, HCV, and HIV) can disrupt T cell DNA topology as a mechanism of dysregulating host immunity and establishing chronic infection. Thus, restoring the DNA topologic machinery may serve as a novel strategy to protect T cells from unwanted DNA damage and to maintain immune competence.

Topological DNA damage, telomere attrition and T cell senescence during chronic viral infections

BACKGROUND

T cells play a key role in controlling viral infections; however, the underlying mechanisms regulating their functions during human viral infections remain incompletely understood. Here, we used CD4 T cells derived from individuals with chronic viral infections or healthy T cells treated with camptothecin (CPT) - a topoisomerase I (Top 1) inhibitor - as a model to investigate the role of DNA topology in reprogramming telomeric DNA damage responses (DDR) and remodeling T cell functions.

RESULTS

We demonstrated that Top 1 protein expression and enzyme activity were significantly inhibited, while the Top 1 cleavage complex (TOP1cc) was trapped in genomic DNA, in T cells derived from individuals with chronic viral (HCV, HBV, or HIV) infections. Top 1 inhibition by CPT treatment of healthy CD4 T cells caused topological DNA damage, telomere attrition, and T cell apoptosis or dysfunction via inducing Top1cc accumulation, PARP1 cleavage, and failure in DNA repair, thus recapitulating T cell dysregulation in the setting of chronic viral infections. Moreover, T cells from virally infected subjects with inhibited Top 1 activity were more vulnerable to CPT-induced topological DNA damage and cell apoptosis, indicating an important role for Top 1 in securing DNA integrity and cell survival.

CONCLUSION

These findings provide novel insights into the molecular mechanisms for immunomodulation by chronic viral infections via disrupting DNA topology to induce telomeric DNA damage, T cell senescence, apoptosis and dysfunction. As such, restoring the impaired DNA topologic machinery may offer a new strategy for maintaining T cell function against human viral diseases.

VRK1 promotes cisplatin resistance by up-regulating c-MYC via c-Jun activation and serves as a therapeutic target in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a common malignant disease characterized by poor prognosis. Chemoresistance remains a major cause of ESCC relapse. Vaccinia-related kinase 1 (VRK1) has previously been identified as a cancer-related gene. However, there is little research demonstrating an association between VRK1 and ESCC. In this study, we show that VRK1 is overexpressed in ESCC primary tumor samples and cell lines. VRK1 expression was significantly correlated with clinical characteristics and predicted poor outcomes in ESCC patients. Functionally, knockdown of VRK1 inhibited ESCC cell proliferation, survival, migration and invasion; conversely, VRK1 overexpression produced the opposite effects. Furthermore, we found that up-regulation of VRK1 promoted cisplatin (CDDP) resistance in ESCC both in vitro and in vivo, whereas knockdown of VRK1 reduced this resistance. Further studies verified that VRK1 phosphorylated c-Jun and that the VRK1/c-Jun pathway contributed to CDDP resistance in ESCC. Mechanistically, a dual luciferase reporter assay revealed that c-Jun transcriptionally activated the expression of c-MYC. Silencing c-MYC abolished the c-Jun-mediated CDDP resistance of ESCC cells. A Kaplan-Meier analysis indicated that c-MYC is a potential prognostic factor in ESCC. Finally, luteolin, a VRK1 inhibitor, attenuated the malignant biological behaviors and CDDP resistance in ESCC cells. Collectively, we conclude that VRK1 promotes CDDP resistance through c-MYC by activating c-Jun and potentiating a malignant phenotype in ESCC. Our studies provide novel insight into the role of VRK1 in carcinogenesis and indicate that VRK1 can serve as a potential therapeutic target in ESCC.