Mono ADP-ribosylation inhibitors prevent inflammatory cytokine release in alveolar epithelial cells

ART1 knockdown decreases the IL-6-induced proliferation of colorectal cancer cells

Colorectal cancer (CRC) is a worldwide health concern. Chronic inflammation is a risk factor for CRC, and interleukin-6 (IL-6) plays a pivotal role in this process. Arginine-specific mono-ADP-ribosyltransferase-1 (ART1) positively regulates inflammatory cytokines. ART1 knockdown reduces the level of glycoprotein 130 (gp130), a key transducer in the IL-6 signalling pathway. However, the relationship between ART1 and IL-6 and the resulting effects on IL-6-induced proliferation in CRC cells remain unclear. The aims of this study were to investigate the effects of ART1 knockdown on IL-6-induced cell proliferation in vitro and use an in vivo murine model to observe the growth of transplanted tumours. The results showed that compared with the control, ART1-sh cancer cells induced by IL-6 exhibited reduced viability, a lower rate of colony formation, less DNA synthesis, decreased protein levels of gp130, c-Myc, cyclin D1, Bcl-xL, and a reduced p-STAT3/STAT3 ratio (P < 0.05). Moreover, mice transplanted with ART1-sh CT26 cells that had high levels of IL-6 displayed tumours with smaller volumes (P < 0.05). ART1 and gp130 were colocalized in CT26, LoVo and HCT116 cells, and their expression was positively correlated in human CRC tissues. Overall, ART1 may serve as a promising regulatory factor for IL-6 signalling and a potential therapeutic target for human CRC.

Mono-ADP-ribosylation sites of human CD73 inhibit its adenosine-generating enzymatic activity

CD73-derived adenosine plays a major role in damage-induced tissue responses by inhibiting inflammation. Damage-associated stimuli, such as hypoxia and mechanical stress, induce the cellular release of ATP and NAD⁺ and upregulate the expression of the nucleotide-degrading purinergic ectoenzyme cascade, including adenosine-generating CD73. Extracellular NAD⁺ also serves as substrate for mono-ADP-ribosylation of cell surface proteins, which in human cells is mediated by ecto-ADP-ribosyltransferase 1 (ARTC1). Here we explored, whether human CD73 enzymatic activity is regulated by mono-ADP-ribosylation, using recombinant human CD73 in the presence of ARTC1 with etheno-labelled NAD⁺ as substrate. Multi-colour immunoblotting with an anti-etheno-adenosine antibody showed ARTC1-mediated transfer of ADP-ribose together with the etheno label to CD73. HPLC analysis of the enzymatic activity of in vitro-ribosylated CD73 revealed strong inhibition of adenosine generation in comparison to non-ribosylated CD73. Mass spectrometry of in vitro-ribosylated CD73 identified six ribosylation sites. 3D model analysis indicated that three of them (R328, R354, R545) can interfere with CD73 enzymatic activity. Our study identifies human CD73 as target for ARTC1-mediated mono-ADP-ribosylation, which can profoundly modulate its adenosine-generating activity. Thus, in settings with enhanced release of NAD⁺ as substrate for ARTC1, assessment of CD73 protein expression in human tissues may not be predictive of adenosine formation resulting in anti-inflammatory activity.

TiPARP forms nuclear condensates to degrade HIF-1α and suppress tumorigenesis

Precisely controlling the activation of transcription factors is crucial for physiology. After a transcription factor is activated and carries out its transcriptional activity, it also needs to be properly deactivated. Here, we report a deactivation mechanism of HIF-1 and several other oncogenic transcription factors. HIF-1 promotes the transcription of an ADP ribosyltransferase, TiPARP, which serves to deactivate HIF-1. Mechanistically, TiPARP forms distinct nuclear condensates or nuclear bodies in an ADP ribosylation-dependent manner. The TiPARP nuclear bodies recruit both HIF-1α and an E3 ubiquitin ligase HUWE1, which promotes the ubiquitination and degradation of HIF-1α. Similarly, TiPARP promotes the degradation of c-Myc and estrogen receptor. By suppressing HIF-1α and other oncogenic transcription factors, TiPARP exerts strong antitumor effects both in cell culture and in mouse xenograft models. Our work reveals TiPARP as a negative-feedback regulator for multiple oncogenic transcription factors, provides insights into the functions of protein ADP-ribosylation, and suggests activating TiPARP as an anticancer strategy.

Arginine ADP-ribosyltransferase 1 promotes angiogenesis in colorectal cancer via the PI3K/Akt pathway

Arginine adenosine diphosphate (ADP)-ribosyl-transferase 1 (ART1) is known to play an important role in many physiological and pathological processes. Previous studies have demonstrated that ART1 promotes proliferation, invasion and metastasis in colon carcinoma. However, it was unclear whether ART1 is involved in angiogenesis in cases of colorectal cancer (CRC). In the present study, lentiviral vector‑mediated ART1‑cDNA or ART1-shRNA were transfected into LoVo cells, and the LoVo cells transfected with ART1-cDNA or ART1-shRNA were co-cultured with human umbilical vein endothelial cells (HUVECs) to determine the influence of ART1 on HUVECs. The proliferation, migration and angiogenesis of HUVECs were monitored using a cell counting kit-8 assay, a Transwell migration assay and immunohistochemical analysis in intrasplenic allograft tumors, respectively. Hypoxia‑inducible factor 1-α (HIF-1α), total (t-)Akt, phosphorylated (p-)Akt, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) expression levels were detected via western blot analysis. Our results revealed that HUVECs which were co-cultured with ART1-cDNA LoVo cells showed higher proliferation, migration and angiogenic abilities, but a reduction was noted in those cultured with ART1-shRNA LoVo cells; p-Akt, HIF-1α, VEGF and bFGF expression was increased in HUVECs cultured with ART1‑cDNA-transfected LoVo cells, but reduced in ART1-shRNA-transfected LoVo cells. In a mouse xenograft model, we noted that the tumor microvessel density (MVD) was significantly increased in intrasplenic transplanted ART1‑cDNA CT26 tumors but decreased in intrasplenic transplanted ART1‑shRNA tumors. These data suggest that ART1 promoted the expression of HIF-1α via the Akt pathway in tumor cells. It also upregulated VEGF and bFGF and enhanced angiogenesis in HUVECs. Thus, we suggest that ART1 plays an important role in the invasion of CRC cells and the metastasis of CRC.

Tubb3 regulation by the Erk and Akt signaling pathways: a mechanism involved in the effect of arginine ADP-ribosyltransferase 1 (Art1) on apoptosis of colon carcinoma CT26 cells

The influence of the most important classical mono-ADP-ribosyltransferase, arginine ADP-ribosyltransferase 1 (Art1), on survival and apoptosis of colon carcinoma cells and the potential mechanisms have been partly discussed in our previous study but still need to be further studied. In this present study, Art1 of colon carcinoma CT26 cells was silenced with lentiviral vector-mediated short hairpin RNA (shRNA) or overexpressed with lentiviral vector-mediated complementary DNA (cDNA) and allograft transplant tumors are established in Balb/c mice. We verified Art1 knockdown increases apoptosis of CT26 cells transplant tumor; Art1 overexpression acts oppositely. Accordingly, growth of transplant tumors is inhibited in Art1 knockdown transplant tumors and increases in Art1 overexpression transplant tumors. Furthermore, activity of Akt and Erk cell signal pathways and expression of an apoptosis biomarker, βIII-tubulin (Tubb3), decrease when Art1 was silenced and increase when Art1 was overexpressed. Inhibiting Akt pathway or Erk pathway both downregulates expression of Tubb3 on protein and messenger RNA (mRNA) level, indicating that Tubb3 could be regulated by both Akt and Erk pathways, and plays a role in the influence of Art1 on apoptosis of Balb/c mice allograft transplant tumor. We also demonstrated that Bcl-2 family is not the responsible downstream factor of the Erk pathway in colon carcinoma cells which is undergoing apoptosis. These findings enrich the molecular mechanism for the function of Art1 in colon carcinoma and provide a complementary support for Art1 to be a potential therapeutic target of the treatment of this kind of malignant tumor.

Evaluation of the expression and function of the P2X7 receptor and ART1 in human regulatory T-cell subsets

Regulatory T cells that express CD39 (CD39+ Treg) exhibit specific immunomodulatory properties. Ectonucleotidase CD39 hydrolyses ATP and ADP. ATP is a ligand of the P2X7 receptor and induces the shedding of CD62L and apoptosis. However, the role of ATP in CD39+ Treg cells has not been defined. Furthermore, NAD can activate the P2X7 receptor via ADP-ribosyltransferase (ART) enzymes and cause cell depletion in murine models. We evaluated the expression and function of P2X7 and ART1 in CD39+ Treg and CD39- Treg cells in the presence or absence of ATP and NAD. We isolated peripheral blood mononuclear cells from healthy subjects and purified CD4+ T cells, CD4+ CD25+ T cells and CD4+ CD25+ CD39+ T cells. P2X7 and ART1 expression was assessed by flow cytometry and real-time PCR. Our results showed low P2X7 expression on CD39+ Treg cells and higher levels of ART1 expression in CD4+ CD39+ T cells than the other subtypes studied. Neither shedding of CD62L nor cell death of CD39+ Treg or CD39- Treg cells was observed by 1mM ATP or 60μM NAD. In contrast, P2Xs receptor-dependent proliferation with 300μM ATP, was inhibited by NAD in the different cell types analysed. The NAD proliferation-inhibition was increased with P2Xs and A2a agonist and was reversed with P2Xs and A2a antagonist, therefore NAD inhibits P2Xs-dependent proliferation and A2a activation. In conclusion, our results suggest that the altered function and expression of P2X7 and ART1 in the human CD39+ Treg or CD39- Treg cells could participate in the resistance against cell death induced by ATP or NAD.

99mTc-Novobiocin: a~novel radiotracer for infection imaging

The radiosynthesis of 99mTc-Novobiocin (99mTc-NBN) complex and its suitability as a radiotracer for infection imaging was assessed. The radiochemical purity (RCP) of the 99mTc-NBN complex was determined using radio-TLC and radioactive HPLC and biodistribution was studied in artificially infected (A.I.) rats and rabbit, using single well gamma counter (SWGRC) interface with scalar count rate meter (SCRM) and Gamma Camera (γ-CM). The maximum RCP observed for the preparation having 2 mg of NBN, 111 MBq of sodium pertechnetate (Na99mTcO4) and 125 μL of SnF2 (1 μg/μL in 0.01 N HCl) at a pH 5.6 was 98.97±0.40% and remained stable >90% up to 120 min. The activity of the 99mTc-NBN in the infected muscle (TI) was significantly increased from 6.50±0.15 to 19.00±0.17% and decreased in the inflamed muscle (TII), normal muscle (NT), blood, liver, spleen, stomach and intestine within 120 min. The TI/NT and TII/NT ratios were 7.60±1.08 and 1.60±1.14. The Whole Body Static (WBS) images of A.I. rabbit were obtained at 30, 40, 50 and 60 min after the I.V. administration of 111 MBq of 99mTc-NBN to the A.I. rabbit. The stability in saline and serum, higher TI/NT, lower TII/NT ratios and WBS images confirmed the feasibility of the 99mTc-NBN complex as an infection imaging agent.

Side chain specificity of ADP-ribosylation by a sirtuin

Endogenous mono-ADP-ribosylation in eukaryotes is involved in regulating protein synthesis, signal transduction, cytoskeletal integrity, and cell proliferation, although few cellular ADP-ribosyltransferases have been identified. The sirtuins constitute a highly conserved family of protein deacetylases, and several family members have also been reported to perform protein ADP-ribosylation. We characterized the ADP-ribosylation reaction of the nuclear sirtuin homolog Trypanosoma brucei SIR2-related protein 1 (TbSIR2RP1) on both acetylated and unacetylated substrates. We demonstrated that an acetylated substrate is not required for ADP-ribosylation to occur, indicating that the reaction performed by TbSIR2RP1 is a genuine enzymatic reaction and not a side reaction of deacetylation. Biochemical and MS data showed that arginine is the major ADP-ribose acceptor for unacetylated substrates, whereas arginine does not appear to be the major ADP-ribose acceptor in reactions with acetylated histone H1.1. We performed combined ab initio quantum mechanical/molecular mechanical molecular dynamics simulations, which indicated that sirtuin ADP-ribosylation at arginine is energetically feasible, and involves a concerted mechanism with a highly dissociative transition state. In comparison with the corresponding nicotinamide cleavage in the deacetylation reaction, the simulations suggest that sirtuin ADP-ribosylation would be several orders slower but less sensitive to nicotinamide inhibition, which is consistent with experimental results. These results suggest that TbSIR2RP1 can perform ADP-ribosylation using two distinct mechanisms, depending on whether or not the substrate is acetylated.

Molecular mechanisms of the cytotoxicity of ADP-ribosylating toxins

Bacterial pathogens utilize toxins to modify or kill host cells. The bacterial ADP-ribosyltransferases are a family of protein toxins that covalently transfer the ADP-ribose portion of NAD to host proteins. Each bacterial ADP-ribosyltransferase toxin modifies a specific host protein(s) that yields a unique pathology. These toxins possess the capacity to enter a host cell or to use a bacterial Type III apparatus for delivery into the host cell. Advances in our understanding of bacterial toxin action parallel the development of biophysical and structural biology as well as our understanding of the mammalian cell. Bacterial toxins have been utilized as vaccines, as tools to dissect host cell physiology, and more recently for the development of novel therapies to treat human disease.