ARTD1 regulates cyclin E expression and consequently cell-cycle re-entry and G1/S progression in T24 bladder carcinoma cells

Physiological levels of poly(ADP-ribose) during the cell cycle regulate HeLa cell proliferation

Protein targets of polyADP-ribosylation undergo covalent modification with high-molecular-weight, branched poly(ADP-ribose) (PAR) of lengths up to 200 or more ADP-ribose residues derived from NAD⁺. PAR polymerase 1 (PARP1) is the most abundant and well-characterized enzyme involved in PAR biosynthesis. Extensive studies have been carried out to determine how polyADP-ribosylation (PARylation) regulates cell proliferation during cell cycle, with conflicting conclusions. Since significant activation of PARP1 occurs during cell lysis in vitro, we changed the standard method for cell lysis, and using our sensitive ELISA system, quantified without addition of a PAR glycohydrolase inhibitor and clarified that the PAR level is significantly higher in S phase than that in G1. Under normal condition in the absence of exogenous DNA-damaging agent, PAR turns over with a half-life of <40 s; consistent with significant decrease of NAD⁺ levels in S phase, which is rescued by PARP inhibitors, in line with the observed rapid turnover of PAR. PARP inhibitors delayed cell cycle in S phase and decreased cell proliferation. Our results underscore the importance of a suitable assay system to measure rapid PAR chain dynamics in living cells and aid our understanding of the function of PARylation during the cell cycle.

The CD38 glycohydrolase and the NAD sink: implications for pathological conditions

Nicotinamide adenine dinucleotide (NAD) acts as a cofactor in several oxidation-reduction (redox) reactions and is a substrate for a number of nonredox enzymes. NAD is fundamental to a variety of cellular processes including energy metabolism, cell signaling, and epigenetics. NAD homeostasis appears to be of paramount importance to health span and longevity, and its dysregulation is associated with multiple diseases. NAD metabolism is dynamic and maintained by synthesis and degradation. The enzyme CD38, one of the main NAD-consuming enzymes, is a key component of NAD homeostasis. The majority of CD38 is localized in the plasma membrane with its catalytic domain facing the extracellular environment, likely for the purpose of controlling systemic levels of NAD. Several cell types express CD38, but its expression predominates on endothelial cells and immune cells capable of infiltrating organs and tissues. Here we review potential roles of CD38 in health and disease and postulate ways in which CD38 dysregulation causes changes in NAD homeostasis and contributes to the pathophysiology of multiple conditions. Indeed, in animal models the development of infectious diseases, autoimmune disorders, fibrosis, metabolic diseases, and age-associated diseases including cancer, heart disease, and neurodegeneration are associated with altered CD38 enzymatic activity. Many of these conditions are modified in CD38-deficient mice or by blocking CD38 NADase activity. In diseases in which CD38 appears to play a role, CD38-dependent NAD decline is often a common denominator of pathophysiology. Thus, understanding dysregulation of NAD homeostasis by CD38 may open new avenues for the treatment of human diseases.

Canine parvovirus induces G1/S cell cycle arrest that involves EGFR Tyr1086 phosphorylation

Canine parvovirus (CPV) has been used in cancer control as a drug delivery vehicle or anti-tumor reagent due to its multiple natural advantages. However, potential host cell cycle arrest induced by virus infection may impose a big challenge to CPV associated cancer control as it could prevent host cancer cells from undergoing cell lysis and foster them regain viability once the virotherapy was ceased. To explore CPV-induced cell cycle arrest and the underlying mechanism toward improved virotherapeutic design, we focus on epidermal growth factor receptor (EGFR), a cellular receptor interacting with TfR that mediates CPV-host interactions, and alterations on its tyrosine phosphorylation sites in response to CPV infection. We found that CPV could trigger host G1/S cell cycle arrest via the EGFR (Y1086)/p27 and EGFR (Y1068)/STAT3/cyclin D1 axes, and EGFR inhibitor could not reverse this process. Our results contribute to our understandings on the mechanism of CPV-induced host cellular response and can be used in the onco-therapeutic design utilizing CPV by preventing host cancer cells from entering cell cycle arrest.

Long non-coding RNA GAS5 inhibits DDP-resistance and tumor progression of epithelial ovarian cancer via GAS5-E2F4-PARP1-MAPK axis

Background

Epithelial ovarian cancer (EOC) is the malignant tumor of the female reproductive system with the highest fatality rate. Tolerance of chemotherapeutic drugs like cisplatin (DDP) occurring in very early stage is one of the important factors of the poor prognosis of epithelial ovarian cancer. Here we aim to study the dysregulation of a particular long noncoding RNA, lncRNA GAS5, and its role in EOC progression.

Methods

The low expression of lncRNA GAS5 in EOC tissues and OC cell lines was determined by microarray analyses and Real-Time qPCR. Flow cytometer assays were used to detect cell cycle and apoptosis of OC cells. CCK8 assay were performed to investigate the DDP sensitivity of OC cells. Western blot was carried out to detect cell growth markers, apoptotic markers, PARP1, E2F4, MAPK pathway protein expression and other protein expression in OC cell lines. The binding of GAS5 and E2F4 were proved by RNA pull-down and RIP assay. The effect of E2F4 on PARP1 were determined by CHIP-qPCR assay and luciferase reporter assay. The effect of lncRNA GAS5 on OC cells was assessed in vitro and in vivo.

Results

By microarray (3 EOC tissues νs. 3 normal ovary tissues) and RT- qPCR (53 EOC tissues νs. 10 normal ovary tissues) we identified lncRNA GAS5 to be dramatically low expressed in EOC samples and correlated with prognosis. Compared with sensitive cell lines, GAS5 was also low expressed in DDP resistant OC cell lines, and over-expression of GAS5 significantly enhanced the sensitivity of OC cells to DDP in vivo and in vitro. Meanwhile the over-expression of GAS5 also caused OC cells G0/G1 arrest and apoptosis increase. Mechanistically, GAS5 might regulate PARP1 expression by recruiting the transcription factor E2F4 to its promoter, and then affect the MAPK pathway activity. Due to the 5’TOP structure, GAS5 could be regulated by transcription inhibitor rapamycin in OC cells.

Conclusion

Here we explored the specific mechanisms of EOC cisplatin resistance and tumor progress due to lncRNA-GAS5, presented the GAS5-E2F4-PARP1-MAPK axis and its role in OC drug-sensitivity and progression for the first time, and the results may provide experimental basis for clinical application.

PARP-1 regulates DNA repair factor availability

PARP-1 holds major functions on chromatin, DNA damage repair and transcriptional regulation, both of which are relevant in the context of cancer. Here, unbiased transcriptional profiling revealed the downstream transcriptional profile of PARP-1 enzymatic activity. Further investigation of the PARP-1-regulated transcriptome and secondary strategies for assessing PARP-1 activity in patient tissues revealed that PARP-1 activity was unexpectedly enriched as a function of disease progression and was associated with poor outcome independent of DNA double-strand breaks, suggesting that enhanced PARP-1 activity may promote aggressive phenotypes. Mechanistic investigation revealed that active PARP-1 served to enhance E2F1 transcription factor activity, and specifically promoted E2F1-mediated induction of DNA repair factors involved in homologous recombination (HR). Conversely, PARP-1 inhibition reduced HR factor availability and thus acted to induce or enhance "BRCA-ness". These observations bring new understanding of PARP-1 function in cancer and have significant ramifications on predicting PARP-1 inhibitor function in the clinical setting.

PARP1 promoter links cell cycle progression with adaptation to oxidative environment

Although electrophiles are considered as detrimental to cells, accumulating recent evidence indicates that proliferating non-cancerous and particularly cancerous cells utilize these agents for pro-survival and cell cycle promoting signaling. Hence, the redox shift to mild oxidant release must be balanced by multiple defense mechanisms. Our latest findings demonstrate that cell cycle progression, which dictates oxidant level in stress-free conditions, determines PARP1 transcription. Growth modulating factors regulate CDK4/6-RBs-E2Fs axis. In cells arrested in G1 and G0, RB1-E2F1 and RBL2-E2F4 dimers recruit chromatin remodelers such as HDAC1, SWI/SNF and PRC2 to condense chromatin and turn off transcription. Release of retinoblastoma-based repressive complexes from E2F-dependent gene promoters in response to cell transition to S phase enables transcription of PARP1. This enzyme contributes to repair of oxidative DNA damage by supporting several strand break repair pathways and nucleotide or base excision repair pathways, as well as acting as a co-activator of transcription factors such as NRF2 and HIF1a, which control expression of antioxidant enzymes involved in removal of electrophiles and secondary metabolites. Furthermore, PARP1 is indispensible for transcription of the pro-survival kinases MAP2K6, ERK1/2 and AKT1, and for maintaining MAPK activity by suppressing transcription of the MAPK inhibitor, MPK1. In summary, cell cycle controlled PARP1 transcription helps cells to adapt to a pro-oxidant redox shift.

Cell Synchronization by Double Thymidine Block

Cell synchronization is widely used in studying mechanisms involves in regulation of cell cycle progression. Through synchronization, cells at distinct cell cycle stage could be obtained. Thymidine is a DNA synthesis inhibitor that can arrest cell at G1/S boundary, prior to DNA replication. Here, we present the protocol to synchronize cells at G1/S boundary by using double thymidine block. After release into normal medium, cell population at distinct cell cycle phase could be collected at different time points.

Effects of three IL-15 variants on NCI-H446 cell proliferation and expression of cell cycle regulatory molecules

Interleukin 15 (IL-15) is a cytokine exhibiting antitumor characteristic similar to that of IL-2. However, in human tissues and cells, IL-15 expression and secretion is very limited, suggesting IL-15 functions mainly intracellularly. In the present study, we assessed the effects of transfecting NCI-H446 small cell lung cancer cells with genes encoding three IL-15 variants: prototypical IL-15, mature IL-15 peptide, and modified IL-15 in which the IL-2 signal peptide is substituted for the native signal peptide. NCI-H446 cells transfected with empty plasmid served as the control group. We found that IL-15 transfection effectively inhibited NCI-H446 cell proliferation and arrested cell cycle progression, with the modified IL-15 carrying the IL-2 signal peptide exerting the greatest effect. Consistent with those findings, expression each of the three IL-15 variants reduced growth of NCI-H446 xenograph tumors, and the modified IL-15 again showed the greatest effect. In addition, IL-15 expression led to down-regulation of the positive cell cycle regulators cyclin E and CDK2 and up-regulation of the negative cycle regulators p21 and Rb. These findings suggest IL-15 acts as a tumor suppressor that inhibits tumor cell proliferation by inducing cell cycle arrest.