Cytoplasmic PARP-1 promotes pancreatic cancer tumorigenesis and resistance

PARP-1 selectively impairs KRAS-driven phenotypic and molecular features in intrahepatic cholangiocarcinoma

OBJECTIVE

Intrahepatic cholangiocarcinoma (iCCA) is the second most common primary liver cancer with limited therapeutic options. KRAS mutations are among the most abundant genetic alterations in iCCA associated with poor clinical outcome and treatment response. Recent findings indicate that Poly(ADP-ribose)polymerase1 (PARP-1) is implicated in KRAS-driven cancers, but its exact role in cholangiocarcinogenesis remains undefined.

DESIGN

PARP-1 inhibition was performed in patient-derived and established iCCA cells using RNAi, CRISPR/Cas9 and pharmacological inhibition in KRAS-mutant, non-mutant cells. In addition, Parp-1 knockout mice were combined with iCCA induction by hydrodynamic tail vein injection to evaluate an impact on phenotypic and molecular features of Kras-driven and Kras-wildtype iCCA. Clinical implications were confirmed in authentic human iCCA.

RESULTS

PARP-1 was significantly enhanced in KRAS-mutant human iCCA. PARP-1-based interventions preferentially impaired cell viability and tumourigenicity in human KRAS-mutant cell lines. Consistently, loss of Parp-1 provoked distinct phenotype in Kras/Tp53-induced versus Akt/Nicd-induced iCCA and abolished Kras-dependent cholangiocarcinogenesis. Transcriptome analyses confirmed preferential impairment of DNA damage response pathways and replicative stress response mediated by CHK1. Consistently, inhibition of CHK1 effectively reversed PARP-1 mediated effects. Finally, Parp-1 depletion induced molecular switch of KRAS-mutant iCCA recapitulating good prognostic human iCCA patients.

CONCLUSION

Our findings identify the novel prognostic and therapeutic role of PARP-1 in iCCA patients with activation of oncogenic KRAS signalling.

Vesicular translocation of PARP-1 to cytoplasm causes ADP-ribosylation and disassembly of vimentin filaments during microglia activation induced by LPS

ADP-ribosylation plays a significant role in various biological processes including genomic stability maintenance, transcriptional regulation, energy metabolism, and cell death. Using macrodomain pull-down assay with microglia lysates and MALDI-TOF-MS analysis, we identified vimentin as a major protein highly ADP-ribosylated by the poly(ADP-ribose) polymerases-1 (PARP-1) in response to LPS. ABT-888, a potent inhibitor of PARP-1/2 blocks the disassembly and ADP-ribosylation of vimentin. PARP-1 is a highly abundant nuclear protein. Its nuclear functions in repairing DNA damages induced by various stress signals, such as inflammatory stresses, have been well studied. In contrast, limited studies have been done on the cytoplasmic role(s) of PARP-1. Our study focuses on the cytoplasmic role of PARP-1 during microglia activation. Using immunofluorescence microscopy and Western blotting, we showed that a significant amount of PARP-1 is present in the cytosol of microglia cells stimulated and activated by LPS. Live cell imaging showed the translocation of nuclear PARP-1-EGFP to the cytoplasm in vesicular structures upon LPS stimulation. ABT-888 and U0126 can block this translocation. Immunofluorescence staining with various organelle marker antibodies revealed that PARP-1 vesicles show colocalization with Lamin A/C, suggesting they might be derived from the nuclear envelope through nuclear envelope budding. In conclusion, we demonstrated that PARP-1 is translocated from the nucleus to cytoplasm via vesicles upon LPS stimulation and that cytoplasmic PARP-1 causes ADP-ribosylation and disassembly of vimentin filaments during microglia activation induced by LPS.

Poly-(ADP-ribose) polymerases inhibition by olaparib attenuates activities of the NLRP3 inflammasome and of NF-κB in THP-1 monocytes

Poly-(ADP-ribose) polymerases (PARPs) are a protein family that make ADP-ribose modifications on target genes and proteins. PARP family members contribute to the pathogenesis of chronic inflammatory diseases, including atherosclerosis, in which monocytes/macrophages play important roles. PARP inhibition is protective against atherosclerosis. However, the mechanisms by which PARP inhibition exerts this beneficial effect are not well understood. Here we show that in THP-1 monocytes, inhibition of PARP by olaparib attenuated oxidized low-density lipoprotein (oxLDL)-induced protein expressions of nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing-3 (NLRP3) inflammasome components: NLRP3, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), and caspase-1. Consistent with this effect, olaparib decreased oxLDL-enhanced interleukin (IL)-1β and IL-18 protein expression. Olaparib also decreased the oxLDL-mediated increase in mitochondrial reactive oxygen species. Similar to the effects of the NLRP3 inhibitor, MCC950, olaparib attenuated oxLDL-induced adhesion of monocytes to cultured human umbilical vein endothelial cells and reduced foam cell formation. Furthermore, olaparib attenuated the oxLDL-mediated activation of nuclear factor (NF)-κB through the oxLDL-mediated increase in IκBα phosphorylation and assembly of NF-κB subunits, demonstrated by co-immunoprecipitation of IκBα with RelA/p50 and RelB/p52 subunits. Moreover, PARP inhibition decreased oxLDL-mediated protein expression of a NF-κB target gene, VCAM1, encoding vascular cell adhesion molecule-1. This finding indicates an important role for NF-κB activity in PARP-mediated activation of the NLRP3 inflammasome. Thus, PARP inhibition by olaparib attenuates NF-κB and NLRP3 inflammasome activities, lessening monocyte cell adhesion and macrophage foam cell formation. These inhibitory effects of olaparib on NLRP3 activity potentially protect against atherosclerosis.

Time-resolved proteomic profiling reveals compositional and functional transitions across the stress granule life cycle

Stress granules (SGs) are dynamic, membrane-less organelles. With their formation and disassembly processes characterized, it remains elusive how compositional transitions are coordinated during prolonged stress to meet changing functional needs. Here, using time-resolved proteomic profiling of the acute to prolonged heat-shock SG life cycle, we identify dynamic SG proteins, further segregated into early and late proteins. Comparison of different groups of SG proteins suggests that their biochemical properties help coordinate SG compositional and functional transitions. In particular, early proteins, with high phase-separation-propensity, drive the rapid formation of the initial SG platform, while late proteins are subsequently recruited as discrete modules to further functionalize SGs. This model, supported by immunoblotting and immunofluorescence imaging, provides a conceptual framework for the compositional transitions throughout the acute to prolonged SG life cycle. Additionally, an early SG constituent, non-muscle myosin II, is shown to promote SG formation by increasing SG fusion, underscoring the strength of this dataset in revealing the complexity of SG regulation.

Identifying the personalized driver gene sets maximally contributing to abnormality of transcriptome phenotype in glioblastoma multiforme individuals

High heterogeneity in genome and phenotype of cancer populations made it difficult to apply population-based common driver genes to the diagnosis and treatment of cancer individuals. Characterizing and identifying the personalized driver mechanism for glioblastoma multiforme (GBM) individuals were pivotal for the realization of precision medicine. We proposed an integrative method to identify the personalized driver gene sets by integrating the profiles of gene expression and genetic alterations in cancer individuals. This method coupled genetic algorithm and random walk to identify the optimal gene sets that could explain abnormality of transcriptome phenotype to the maximum extent. The personalized driver gene sets were identified for 99 GBM individuals using our method. We found that genomic alterations in between one and seven driver genes could maximally and cumulatively explain the dysfunction of cancer hallmarks across GBM individuals. The driver gene sets were distinct even in GBM individuals with significantly similar transcriptomic phenotypes. Our method identified MCM4 with rare genetic alterations as previously unknown oncogenic genes, the high expression of which were significantly associated with poor GBM prognosis. The functional experiments confirmed that knockdown of MCM4 could significantly inhibit proliferation, invasion, migration, and clone formation of the GBM cell lines U251 and U118MG, and overexpression of MCM4 significantly promoted the proliferation, invasion, migration, and clone formation of the GBM cell line U87MG. Our method could dissect the personalized driver genetic alteration sets that are pivotal for developing targeted therapy strategies and precision medicine. Our method could be extended to identify key drivers from other levels and could be applied to more cancer types.

Regulation of Biomolecular Condensates by Poly(ADP-ribose)

Biomolecular condensates are reversible compartments that form through a process called phase separation. Post-translational modifications like ADP-ribosylation can nucleate the formation of these condensates by accelerating the self-association of proteins. Poly(ADP-ribose) (PAR) chains are remarkably transient modifications with turnover rates on the order of minutes, yet they can be required for the formation of granules in response to oxidative stress, DNA damage, and other stimuli. Moreover, accumulation of PAR is linked with adverse phase transitions in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In this review, we provide a primer on how PAR is synthesized and regulated, the diverse structures and chemistries of ADP-ribosylation modifications, and protein-PAR interactions. We review substantial progress in recent efforts to determine the molecular mechanism of PAR-mediated phase separation, and we further delineate how inhibitors of PAR polymerases may be effective treatments for neurodegenerative pathologies. Finally, we highlight the need for rigorous biochemical interrogation of ADP-ribosylation in vivo and in vitro to clarify the exact pathway from PARylation to condensate formation.

The potential of PARP inhibitors in targeted cancer therapy and immunotherapy

DNA damage response (DDR) deficiencies result in genome instability, which is one of the hallmarks of cancer. Poly (ADP-ribose) polymerase (PARP) enzymes take part in various DDR pathways, determining cell fate in the wake of DNA damage. PARPs are readily druggable and PARP inhibitors (PARPi) against the main DDR-associated PARPs, PARP1 and PARP2, are currently approved for the treatment of a range of tumor types. Inhibition of efficient PARP1/2-dependent DDR is fatal for tumor cells with homologous recombination deficiencies (HRD), especially defects in breast cancer type 1 susceptibility protein 1 or 2 (BRCA1/2)-dependent pathway, while allowing healthy cells to survive. Moreover, PARPi indirectly influence the tumor microenvironment by increasing genomic instability, immune pathway activation and PD-L1 expression on cancer cells. For this reason, PARPi might enhance sensitivity to immune checkpoint inhibitors (ICIs), such as anti-PD-(L)1 or anti-CTLA4, providing a rationale for PARPi-ICI combination therapies. In this review, we discuss the complex background of the different roles of PARP1/2 in the cell and summarize the basics of how PARPi work from bench to bedside. Furthermore, we detail the early data of ongoing clinical trials indicating the synergistic effect of PARPi and ICIs. We also introduce the diagnostic tools for therapy development and discuss the future perspectives and limitations of this approach.

PARP1 inhibition by Olaparib reduces the lethality of pancreatic cancer cells and increases their sensitivity to Gemcitabine

Pancreatic cancer (PC) is one of the tumors with the lowest survival rates due to the poor efficacy of the treatments currently used. Gemcitabine (GMZ), one of the chemotherapeutic agents employed when the tumor is unresectable, frequently fails due to the development of drug resistance. PARP1 is a relevant protein in this phenomenon and appears to be related to cancer progression in several types of tumors, including PC. To determine the relevance of PARP1 in the development and treatment of PC, we used the Panc02 cell line to generate modified PC cells with stably inhibited PARP1 expression (Panc02-L) and used GMZ, Olaparib (OLA) and GMZ+OLA as therapeutic strategies. Viability, radiosensitization, angiogenesis, migration, colony formation, TUNEL, cell cycle, multicellular tumorsphere induction and in vivo assays were performed to test the influence of PARP1 inhibition on resistance phenomena and tumor progression. We demonstrated that stable inhibition or pharmacological blockade of PARP1 using OLA-sensitized Panc02 cells against GMZ significantly decreased their IC₅₀, reducing colony formation capacity, cell migration and vessel formation (angiogenesis) in vitro. Furthermore, in vivo analyses revealed that Panc02-L-derived (PARP1-inhibited) tumors showed less growth and lethality, and that GMZ+OLA treatment significantly reduced tumor growth. In conclusion, PARP1 inhibition, both alone and in combination with GMZ, enhances the effectiveness of this chemotherapeutic agent and represents a promising strategy for the treatment of PC.

Mechanistic and functional extrapolation of SET and MYND domain-containing protein 2 to pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal neoplasms worldwide and represents the vast majority of pancreatic cancer cases. Understanding the molecular pathogenesis and the underlying mechanisms involved in the initiation, maintenance, and progression of PDAC is an urgent need, which may lead to the development of novel therapeutic strategies against this deadly cancer. Here, we review the role of SET and MYND domain-containing protein 2 (SMYD2) in initiating and maintaining PDAC development through methylating multiple tumor suppressors and oncogenic proteins. Given the broad substrate specificity of SMYD2 and its involvement in diverse oncogenic signaling pathways in many other cancers, the mechanistic extrapolation of SMYD2 from these cancers to PDAC may allow for developing new hypotheses about the mechanisms driving PDAC tumor growth and metastasis, supporting a proposition that targeting SMYD2 could be a powerful strategy for the prevention and treatment of PDAC.

High Expression of PARP1 in Tumor and Stroma Cells Predicts Different Prognosis and Platinum Resistance in Patients With Advanced Epithelial Ovarian Cancer

Objective

This study aimed to explore the roles of PARP1 mRNA and protein expression in platinum resistance and prognosis of EOC patients, and reveal the different roles of PARP1 protein in epithelial tumor and stroma cells.

Methods

The PARP1 mRNA expression of the EOC tissues was examined by RT-qPCR. The impacts of PARP1 expression on prognosis were measured by Kaplan-Meier and Cox regression. Receiver operating characteristic (ROC) curve analysis was employed for calculating the diagnostic value of PARP1 on platinum resistance. The microarray of formalin-fixed, paraffin-embedded (FFPE) tissues was processed for multiplex immunofluorescence to detect the protein levels of PARP1 and cytokeratin (CK).

Results

The PARP1mRNA expression of EOC patients was higher in the platinum-resistant group compared with the sensitive group (P<0.01). Kaplan-Meier analysis demonstrated that high PARP1 mRNA expression was associated with poor survival of EOC patients. In Cox regression analyses, high PARP1 mRNA expression independently predicted poor prognosis (P=0.001, HR=2.076, 95%CI=1.373-3.140). The area under the ROC curve of PARP1 mRNA for predicting the platinum resistance in EOC patients was 0.649, with a sensitivity of 0.607 and specificity of 0.668. Furthermore, the protein expression of PARP1 was higher in the platinum-resistant group than in the sensitive group (P<0.01) and associated with a worse prognosis. Additionally, according to CK labeling, we observed that enhanced expression of PARP1 in the CK+ region was associated with platinum resistance and lower survival, but in CK- region, it predicted a good prognosis and platinum sensitivity.

Conclusion

PARP1 may be a potential biomarker to predict platinum resistance and prognosis for EOC patients, exerting different roles on epithelial tumor and stromal cells.

Oxidative Stress Markers Are Associated with a Poor Prognosis in Patients with Pancreatic Cancer

Pancreatic cancer is a malignancy of rising prevalence, especially in developed countries where dietary patterns and sedentariness favor its onset. This malady ranks seventh in cancer-related deaths in the world, although it is expected to rank second in the coming years, behind lung cancer. The low survival rate is due to the asymptomatic course of the early stages, which in many cases leads to metastases when becoming evident in advanced stages. In this context, molecular pathology is on the way towards finding new approaches with biomarkers that allow a better prognosis and monitoring of patients. So the present study aims to evaluate a series of molecular biomarkers, PARP1, NOX1, NOX2, eNOS and iNOS, as promising candidates for prognosis and survival by using immunohistochemistry. The analysis performed in 41 patients with pancreatic cancer showed a correlation between a high expression of all these components with a low survival rate, with high statistical power for all. In addition, a 60-month longitudinal surveillance program was managed, accompanied by several clinical parameters. The derivative Kaplan–Meier curves indicated a low cumulative survival rate as well. Ultimately, our research emphasized the value of these molecules as survival-associated biomarkers in pancreatic cancer, offering new gates for clinical management.

Warangalone Induces Apoptosis in HeLa Cells via Mitochondria-Mediated Endogenous Pathway

Cervical cancer as one of the major malignant tumors seriously threatens women's health. More than 270,000 women die of cervical cancer each year. Warangalone is an isoflavone compound isolated from Cudrania tricuspidata with excellent antitumor activity. In this research, we investigated the molecular mechanism of warangalone-induced apoptosis in HeLa cells. The results show that warangalone can selectively and effectively inhibit HeLa cells proliferation. Warangalone can effectively inhibit the invasion and migration of HeLa cells. Furthermore, warangalone was confirmed to activate p53 and mitogen-activated protein kinase (MAPK) family signaling pathways to cause apoptosis. In this case, the expression of the B-cell lymphoma-2 (Bcl-2) family is regulated, and caspase-3 is eventually cleaved, finally triggering the mitochondrial apoptosis. In conclusion, warangalone can induce HeLa cells apoptosis via a mitochondria-mediated endogenous pathway, which represented the potential therapeutic effect of warangalone on cervical cancer.

Therapeutic Potential of PARP Inhibitors in the Treatment of Gastrointestinal Cancers

Gastrointestinal (GI) malignancies are a major global health burden, with high mortality rates. The identification of novel therapeutic strategies is crucial to improve treatment and survival of patients. The poly (ADP-ribose) polymerase (PARP) enzymes involved in the DNA damage response (DDR) play major roles in the development, progression and treatment response of cancer, with PARP inhibitors (PARPi) currently used in the clinic for breast, ovarian, fallopian, primary peritoneal, pancreatic and prostate cancers with deficiencies in homologous recombination (HR) DNA repair. This article examines the current evidence for the role of the DDR PARP enzymes (PARP1, 2, 3 and 4) in the development, progression and treatment response of GI cancers. Furthermore, we discuss the role of HR status as a predictive biomarker of PARPi efficacy in GI cancer patients and examine the pre-clinical and clinical evidence for PARPi and cytotoxic therapy combination strategies in GI cancer. We also include an analysis of the genomic and transcriptomic landscape of the DDR PARP genes and key HR genes (BRCA1, BRCA2, ATM, RAD51, MRE11, PALB2) in GI patient tumours (n = 1744) using publicly available datasets to identify patients that may benefit from PARPi therapeutic approaches.

The PARP Enzyme Family and the Hallmarks of Cancer Part 2: Hallmarks Related to Cancer Host Interactions

Poly (ADP-ribose) polymerases (PARPs) modify target proteins with a single ADP-ribose unit or with a poly (ADP-ribose) (PAR) polymer. PARP inhibitors (PARPis) recently became clinically available for the treatment of BRCA1/2 deficient tumors via the synthetic lethality paradigm. This personalized treatment primarily targets DNA damage-responsive PARPs (PARP1-3). However, the biological roles of PARP family member enzymes are broad; therefore, the effects of PARPis should be viewed in a much wider context, which includes complex effects on all known hallmarks of cancer. In the companion paper (part 1) to this review, we presented the fundamental roles of PARPs in intrinsic cancer cell hallmarks, such as uncontrolled proliferation, evasion of growth suppressors, cell death resistance, genome instability, replicative immortality, and reprogrammed metabolism. In the second part of this review, we present evidence linking PARPs to cancer-associated inflammation, anti-cancer immune response, invasion, and metastasis. A comprehensive overview of the roles of PARPs can facilitate the identification of novel cancer treatment opportunities and barriers limiting the efficacy of PARPi compounds.

The PARP Enzyme Family and the Hallmarks of Cancer Part 1. Cell Intrinsic Hallmarks

The 17-member poly (ADP-ribose) polymerase enzyme family, also known as the ADP-ribosyl transferase diphtheria toxin-like (ARTD) enzyme family, contains DNA damage-responsive and nonresponsive members. Only PARP1, 2, 5a, and 5b are capable of modifying their targets with poly ADP-ribose (PAR) polymers; the other PARP family members function as mono-ADP-ribosyl transferases. In the last decade, PARP1 has taken center stage in oncology treatments. New PARP inhibitors (PARPi) have been introduced for the targeted treatment of breast cancer 1 or 2 (BRCA1/2)-deficient ovarian and breast cancers, and this novel therapy represents the prototype of the synthetic lethality paradigm. Much less attention has been paid to other PARPs and their potential roles in cancer biology. In this review, we summarize the roles played by all PARP enzyme family members in six intrinsic hallmarks of cancer: uncontrolled proliferation, evasion of growth suppressors, cell death resistance, genome instability, reprogrammed energy metabolism, and escape from replicative senescence. In a companion paper, we will discuss the roles of PARP enzymes in cancer hallmarks related to cancer-host interactions, including angiogenesis, invasion and metastasis, evasion of the anticancer immune response, and tumor-promoting inflammation. While PARP1 is clearly involved in all ten cancer hallmarks, an increasing body of evidence supports the role of other PARPs in modifying these cancer hallmarks (e.g., PARP5a and 5b in replicative immortality and PARP2 in cancer metabolism). We also highlight controversies, open questions, and discuss prospects of recent developments related to the wide range of roles played by PARPs in cancer biology. Some of the summarized findings may explain resistance to PARPi therapy or highlight novel biological roles of PARPs that can be therapeutically exploited in novel anticancer treatment paradigms.

Recombinant protein TRAIL-Mu3 enhances the antitumor effects in pancreatic cancer cells by strengthening the apoptotic signaling pathway

Pancreatic cancer is a highly malignant type of cancer and its treatment remains a major challenge. The novel recombinant protein TNF-related apoptosis-inducing ligand (TRAIL)-Mu3 has been shown to exert stronger tumor inhibitory effects in colon cancer in vitro and in vivo compared with TRAIL. The present study investigated the antitumor effects of TRAIL-Mu3 on pancreatic cancer cells, and the possible mechanisms were further examined. Compared with TRAIL, TRAIL-Mu3 exhibited significantly higher cytotoxic effects on pancreatic cancer cell lines. The inhibitory effect of TRAIL-Mu3 on the viability of PANC-1 cells was shown to be a caspase-dependent process. The affinity of TRAIL-Mu3 to PANC-1 cell membranes was significantly enhanced compared with TRAIL. In addition, TRAIL-Mu3 upregulated death receptor (DR) expression in PANC-1 cells and promoted the redistribution of DR5 in lipid rafts. Western blotting results demonstrated that TRAIL-Mu3 activated the caspase cascade in a faster and more efficient manner compared with TRAIL in PANC-1 cells. Therefore, TRAIL-Mu3 enhanced the antitumor effects in pancreatic cancer cells by strengthening the apoptotic signaling pathway. The present study indicated the potential of TRAIL-Mu3 for the treatment of pancreatic cancer.

A 14-gene gemcitabine resistance gene signature is significantly associated with the prognosis of pancreatic cancer patients

To identify a gemcitabine resistance-associated gene signature for risk stratification and prognosis prediction in pancreatic cancer. Pearson correlation analysis was performed with gemcitabine half maximal inhibitory concentration (IC50) data of 17 primary pancreatic cancer lines from Genomics of Drug Sensitivity in Cancer (GDSC) and the transcriptomic data from GDSC and Broad Institute Cancer Cell Line Encyclopedia, followed by risk stratification, expression evaluation, overall survival (OS) prediction, clinical data validation and nomogram establishment. Our biomarker discovery effort identified a 14-gene signature, most of which featured differential expression. The 14-gene signature was associated with poor OS in E-MTAB-6134 (HR 2.37; 95% CI 1.75–3.2; p < 0.0001), pancreatic cancer-Canada (PACA-CA) (HR 1.76; 95% CI 1.31–2.37; p = 0.00015), and 4 other independent validation cohorts: pancreatic cancer-Australia (PACA-AU) (HR 1.9; 95% CI 1.38–2.61; p < 0.0001), The Cancer Genome Atlas (TCGA) (HR 1.73; 95% CI 1.11–2.69; p = 0.014), GSE85916 (HR 1.97; 95% CI 1.14–3.42; p = 0.014) and GSE62452 (HR 1.82; 95% CI 1.02–3.24; p = 0.039). Multivariate analysis revealed that the 14-gene risk score was an independent pancreatic cancer outcome predictor in E-MTAB-6134 (p < 0.001) and TCGA (p = 0.006). A nomogram including the 14-gene was established for eventual clinical translation. We identified a novel gemcitabine resistance gene signature for risk stratification and robust categorization of pancreatic cancer patients with poor prognosis.

Pancreatic Adenocarcinoma: Unconventional Approaches for an Unconventional Disease

This review highlights current treatments, limitations, and pitfalls in the management of pancreatic cancer and discusses current research in novel targets and drug development to overcome these clinical challenges. We begin with a review of the clinical landscape of pancreatic cancer, including genetic and environmental risk factors, as well as limitations in disease diagnosis and prevention. We next discuss current treatment paradigms for pancreatic cancer and the shortcomings of targeted therapy in this disease. Targeting major driver mutations in pancreatic cancer, such as dysregulation in the KRAS and TGFβ signaling pathways, have failed to improve survival outcomes compared with nontargeted chemotherapy; thus, we describe new advances in therapy such as Ras-binding pocket inhibitors. We then review next-generation approaches in nanomedicine and drug delivery, focusing on preclinical advancements in novel optical probes, antibodies, small-molecule agents, and nucleic acids to improve surgical outcomes in resectable disease, augment current therapies, expand druggable targets, and minimize morbidity. We conclude by summarizing progress in current research, identifying areas for future exploration in drug development and nanotechnology, and discussing future prospects for management of this disease.

Regulation of pancreatic cancer TRAIL resistance by protein O-GlcNAcylation

TRAIL-activating therapy is promising in treating various cancers, including pancreatic cancer, a highly malignant neoplasm with poor prognosis. However, many pancreatic cancer cells are resistant to TRAIL-induced apoptosis despite their expression of intact death receptors (DRs). Protein O-GlcNAcylation is a versatile posttranslational modification that regulates various biological processes. Elevated protein O-GlcNAcylation has been recently linked to cancer cell growth and survival. In this study, we evaluated the role of protein O-GlcNAcylation in pancreatic cancer TRAIL resistance, and identified higher levels of O-GlcNAcylation in TRAIL-resistant pancreatic cancer cells. With gain- and loss-of-function of the O-GlcNAc-adding enzyme, O-GlcNActransferase (OGT), we determined that increasing O-GlcNAcylation rendered TRAIL-sensitive cells more resistant to TRA-8-induced apoptosis, while inhibiting O-GlcNAcylation promoted TRA-8-induced apoptosis in TRAIL-resistance cells. Furthermore, we demonstrated that OGT knockdown sensitized TRAIL-resistant cells to TRA-8 therapy in a mouse model in vivo. Mechanistic studies revealed direct O-GlcNAc modifications of DR5, which regulated TRA-8-induced DR5 oligomerization. We further defined that DR5 O-GlcNAcylation was independent of FADD, the adapter protein for the downstream death-inducing signaling. These studies have demonstrated an important role of protein O-GlcNAcylation in regulating TRAIL resistance of pancreatic cancer cells; and uncovered the contribution of O-GlcNAcylation to DR5 oligomerization and thus mediating DR-inducing signaling.

PARP1 Enhances Influenza A Virus Propagation by Facilitating Degradation of Host Type I Interferon Receptor

Influenza A virus (IAV) utilizes multiple strategies to confront or evade host type I interferon (IFN)-mediated antiviral responses in order to enhance its own propagation within the host. One such strategy is to induce the degradation of type I IFN receptor 1 (IFNAR1) by utilizing viral hemagglutinin (HA). However, the molecular mechanism behind this process is poorly understood. Here, we report that a cellular protein, poly(ADP-ribose) polymerase 1 (PARP1), plays a critical role in mediating IAV HA-induced degradation of IFNAR1. We identified PARP1 as an interacting partner for IAV HA through mass spectrometry analysis. This interaction was confirmed by coimmunoprecipitation analyses. Furthermore, confocal fluorescence microscopy showed altered localization of endogenous PARP1 upon transient IAV HA expression or during IAV infection. Knockdown or inhibition of PARP1 rescued IFNAR1 levels upon IAV infection or HA expression, exemplifying the importance of PARP1 for IAV-induced reduction of IFNAR1. Notably, PARP1 was crucial for the robust replication of IAV, which was associated with regulation of the type I IFN receptor signaling pathway. These results indicate that PARP1 promotes IAV replication by controlling viral HA-induced degradation of host type I IFN receptor. Altogether, these findings provide novel insight into interactions between influenza virus and the host innate immune response and reveal a new function for PARP1 during influenza virus infection.IMPORTANCE Influenza A virus (IAV) infections cause seasonal and pandemic influenza outbreaks, which pose a devastating global health concern. Despite the availability of antivirals against influenza, new IAV strains continue to persist by overcoming the therapeutics. Therefore, much emphasis in the field is placed on identifying new therapeutic targets that can more effectively control influenza. IAV utilizes several tactics to evade host innate immunity, which include the evasion of antiviral type I interferon (IFN) responses. Degradation of type I IFN receptor (IFNAR) is one known method of subversion, but the molecular mechanism for IFNAR downregulation during IAV infection remains unclear. Here, we have found that a host protein, poly(ADP-ribose) polymerase 1 (PARP1), facilitates IFNAR degradation and accelerates IAV replication. The findings reveal a novel cellular target for the potential development of antivirals against influenza, as well as expand our base of knowledge regarding interactions between influenza and the host innate immunity.

Toxicoproteomic Analysis of Poly(ADP-ribose)-associated Proteins Induced by Oxidative Stress in Human Proximal Tubule Cells

2,3,5-Tris-(glutathion-S-yl)hydroquinone (TGHQ) is a nephrotoxic and nephrocarcinogenic metabolite of hydroquinone. TGHQ generates ROS, causing DNA strand breaks, hyperactivation of PARP-1, increases in intracellular calcium ([Ca2+]i), and cell death. PARP-1 catalyzes the attachment of ADP-ribose polymers (PAR) to target proteins. In human kidney proximal tubule cells (HK-2), ROS-mediated PARP-1 hyperactivation and elevations in [Ca2+]i are reciprocally coupled. The molecular mechanism of this interaction is unclear. The aim of the present study was to identify ROS-induced PAR-associated proteins to further understand their potential role in cell death. PAR-associated proteins were enriched by immunoprecipitation, identified by LC-MS/MS, and relative abundance was obtained by spectral counting. 356 proteins were PAR-modified following TGHQ treatment. 13 proteins exhibited gene ontology annotations related to calcium. Among these proteins, the general transcription factor II-I (TFII-I) is directly involved in the modulation of [Ca2+]i. TFII-I binding to phospholipase C (PLC) leads to calcium influx via the TRPC3 channel. However, inhibition of TRPC3 or PLC had no effect on TGHQ-mediated cell death, suggesting that their loss of function may be necessary but insufficient to cause cell death. Nevertheless, TGHQ promoted a time-dependent translocation of TFII-I from the nucleus to the cytosol concomitant with a decrease in tyrosine phosphorylation in α/β-TFII-I. Therefore it is likely that ROS have an important impact on the function of TFII-I, such as regulation of transcription, and DNA translesion synthesis. Our data also sheds light on PAR mediated signaling during oxidative stress, and contributes to the development of strategies to prevent PAR-dependent cell death.

Natural Product Mediated Regulation of Death Receptors and Intracellular Machinery: Fresh from the Pipeline about TRAIL-Mediated Signaling and Natural TRAIL Sensitizers

Rapidly developing resistance against different therapeutics is a major stumbling block in the standardization of therapy. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated signaling has emerged as one of the most highly and extensively studied signal transduction cascade that induces apoptosis in cancer cells. Rapidly emerging cutting-edge research has helped us to develop a better understanding of the signaling machinery involved in inducing apoptotic cell death. However, excitingly, cancer cells develop resistance against TRAIL-induced apoptosis through different modes. Loss of cell surface expression of TRAIL receptors and imbalance of stoichiometric ratios of pro- and anti-apoptotic proteins play instrumental roles in rewiring the machinery of cancer cells to develop resistance against TRAIL-based therapeutics. Natural products have shown excellent potential to restore apoptosis in TRAIL-resistant cancer cell lines and in mice xenografted with TRAIL-resistant cancer cells. Significantly refined information has previously been added and continues to enrich the existing pool of knowledge related to the natural-product-mediated upregulation of death receptors, rebalancing of pro- and anti-apoptotic proteins in different cancers. In this mini review, we will set spotlight on the most recently published high-impact research related to underlying mechanisms of TRAIL resistance and how these deregulations can be targeted by natural products to restore TRAIL-mediated apoptosis in different cancers.