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To study the ability of Streptomyces to utilize environmental nucleotides, we screened for strains exhibiting extracellular 5′-inosine monophosphate (IMP)-dephosphorylating activity in our collection of soil isolates and obtained two producers: NE5-10 and Y2F8-2. The enzyme responsible for the activity was purified from the culture supernatant of each strain, and its mass spectral data were used to identify the coding sequence. The gene was successfully identified in the whole genome sequence of each strain; it was located in a conserved gene cluster of phosphate-related functions and encoded an approximately 600-amino acid long protein containing an N-terminal secretion signal. The mature part of the protein exhibited similarity to a known bacterial 5′-nucleotidase. The locus of the 5′-nucleotidase gene contained genes encoding proteins involved in phosphate utilization. The conserved gene arrangement of the locus in various Streptomyces genomes suggested the genetic region to be involved in phosphate-scavenging in this group of bacteria. Phylogenetic analysis demonstrated that the isolated Streptomyces enzymes represent an uncharacterized group of bacterial 5′-nucleotidases. Enzymatic characterization of the two Streptomyces enzymes demonstrated that both enzymes exhibited 5′-nucleotidase activity but differed in terms of optimal temperature and pH, dependence on divalent cations, and substrate specificity. The Km and Vmax values of the 5′-IMP-dephosphorylating activity were 0.239 mM and 9.47 U/mg, respectively, for NE5-10 and 0.221 mM and 38.17 U/mg, respectively, for Y2F8-2. Enzyme activity in the culture broth of the two Streptomyces producers occurred in a phosphate-limitation-dependent manner, supporting their involvement in the acquisition of phosphorus.Key points• We purified and characterized nucleotidases from two Streptomyces.• Two nucleotidases were presumed to be involved in phosphate acquisition.• It showed diversity in phosphate acquisition among microorganisms.

5′-Nucleotidases (EC 3.1.3.5) are enzymes that catalyze the hydrolytic dephosphorylation of 5′-ribonucleotides and 5′-deoxyribonucleotides to their respective nucleosides and phosphate. Most 5′-nucleotidases have broad substrate specificity and are multifunctional enzymes capable of cleaving phosphorus from not only mononucleotide phosphate molecules but also a variety of other phosphorylated metabolites. 5′-Nucleotidases are widely distributed throughout all kingdoms of life and found in different cellular locations. The well-studied vertebrate 5′-nucleotidases play an important role in cellular metabolism. These enzymes are involved in purine and pyrimidine salvage pathways, nucleic acid repair, cell-to-cell communication, signal transduction, control of the ribo- and deoxyribonucleotide pools, etc. Although the first evidence of microbial 5′-nucleotidases was obtained almost 60 years ago, active studies of genetic control and the functions of microbial 5′-nucleotidases started relatively recently. The present review summarizes the current knowledge about microbial 5′-nucleotidases with a focus on their diversity, cellular localizations, molecular structures, mechanisms of catalysis, physiological roles, and activity regulation and approaches to identify new 5′-nucleotidases. The possible applications of these enzymes in biotechnology are also discussed.Key points• Microbial 5′-nucleotidases differ in molecular structure, hydrolytic mechanism, and cellular localization.• 5′-Nucleotidases play important and multifaceted roles in microbial cells.• Microbial 5′-nucleotidases have wide range of practical applications.

Changes in nicotinamide adenine dinucleotide (NAD + ) levels that compromise mitochondrial function trigger release of DNA damaging reactive oxygen species. NAD + levels also affect DNA repair capacity as NAD + is a substrate for PARP-enzymes (mono/poly-ADP-ribosylation) and sirtuins (deacetylation). The ecto-5′-nucleotidase CD73, an ectoenzyme highly expressed in cancer, is suggested to regulate intracellular NAD + levels by processing NAD + and its bio-precursor, nicotinamide mononucleotide (NMN), from tumor microenvironments, thereby enhancing tumor DNA repair capacity and chemotherapy resistance. We therefore investigated whether expression of CD73 impacts intracellular NAD + content and NAD + -dependent DNA repair capacity. Reduced intracellular NAD + levels suppressed recruitment of the DNA repair protein XRCC1 to sites of genomic DNA damage and impacted the amount of accumulated DNA damage. Further, decreased NAD + reduced the capacity to repair DNA damage induced by DNA alkylating agents. Overall, reversal of these outcomes through NAD + or NMN supplementation was independent of CD73. In opposition to its proposed role in extracellular NAD + bioprocessing, we found that recombinant human CD73 only poorly processes NMN but not NAD + . A positive correlation between CD73 expression and intracellular NAD + content could not be made as CD73 knockout human cells were efficient in generating intracellular NAD + when supplemented with NAD + or NMN.

Background and purpose: ARL 67156, 6‐N,N‐Diethyl‐D‐β‐γ‐dibromomethylene adenosine triphosphate, originally named FPL 67156, is the only commercially available inhibitor of ecto‐ATPases. Since the first report on this molecule, various ectonucleotidases responsible for the hydrolysis of ATP at the cell surface have been cloned and characterized. In this work, we identified the ectonucleotidases inhibited by ARL 67156. Experimental approach: The effect of ARL 67156 on recombinant NTPDase1, 2, 3 & 8 (mouse and human), NPP1, NPP3 and ecto‐5′‐nucleotidase (human) have been evaluated. The inhibition of the activity of NTPDases (using the following substrates: ATP, ADP, UTP), NPPs (pnp‐TMP, Ap3A) and ecto‐5′‐nucleotidase (AMP) was measured by colorimetric or HPLC assays. Key results: ARL 67156 was a weak competitive inhibitor of human NTPDase1, NTPDase3 and NPP1 with Ki of 11±3, 18±4 and 12±3 μM, respectively. At concentrations used in the literature (50–100 μM), ARL 67156 partially but significantly inhibited the mouse and human forms of these enzymes. NTPDase2, NTPDase8, NPP3 and ecto‐5′‐nucleotidase activities were less affected. Importantly, ARL 67156 was not hydrolysed by either human NTPDase1, 2, 3, 8, NPP1 or NPP3. Conclusions and implications: In cell environments where NTPDase1, NTPDase3, NPP1 or mouse NTPDase8 are present, ARL 67156 would prolong the effect of endogenously released ATP on P2 receptors. However, it does not block any ectonucleotidases efficiently when high concentrations of substrates are present, such as in biochemical, pharmacological or P2X7 assays. In addition, ARL 67156 is not an effective inhibitor of NTPDase2, human NTPDase8, NPP3 and ecto‐5′‐nucleotidase. British Journal of Pharmacology (2007) 152, 141–150; doi:10.1038/sj.bjp.0707361

High levels of ecto-5'-nucleotidase (CD73) have been implicated in immune suppression and tumor progression, and have also been observed in cancer patients who progress on anti-PD-1 immunotherapy. Although regulatory T cells can express CD73 and inhibit T cell responses via the production of adenosine, less is known about CD73 expression in other immune cell populations. We found that tumor-infiltrating NK cells upregulate CD73 expression and the frequency of these CD73-positive NK cells correlated with larger tumor size in breast cancer patients. In addition, the expression of multiple alternative immune checkpoint receptors including LAG-3, VISTA, PD-1, and PD-L1 was significantly higher in CD73-positive NK cells than in CD73-negative NK cells. Mechanistically, NK cells transport CD73 in intracellular vesicles to the cell surface and the extracellular space via actin polymerization-dependent exocytosis upon engagement of 4-1BBL on tumor cells. These CD73-positive NK cells undergo transcriptional reprogramming and upregulate IL-10 production via STAT3 transcriptional activity, suppressing CD4-positive T cell proliferation and IFN-γ production. Taken together, our results support the notion that tumors can hijack NK cells as a means to escape immunity and that CD73 expression defines an inducible population of NK cells with immunoregulatory properties within the tumor microenvironment.

ATP and adenosine have emerged as important signaling molecules involved in vascular remodeling, retinal functioning and neurovascular coupling in the mammalian eye. However, little is known about the regulatory mechanisms of purinergic signaling in the eye. Here, we used three-dimensional multiplexed imaging, in situ enzyme histochemistry, flow cytometric analysis, and single cell transcriptomics to characterize the whole pattern of purine metabolism in mouse and human eyes. This study identified ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39), NTPDase2, and ecto-5′-nucleotidase/CD73 as major ocular ecto-nucleotidases, which are selectively expressed in the photoreceptor layer (CD73), optic nerve head, retinal vasculature and microglia (CD39), as well as in neuronal processes and cornea (CD39, NTPDase2). Specifically, microglial cells can create a spatially arranged network in the retinal parenchyma by extending and retracting their branched CD39 high /CD73 low processes and forming local “purinergic junctions” with CD39 low /CD73 − neuronal cell bodies and CD39 high /CD73 − retinal blood vessels. The relevance of the CD73–adenosine pathway was confirmed by flash electroretinography showing that pharmacological inhibition of adenosine production by injection of highly selective CD73 inhibitor PSB-12489 in the vitreous cavity of dark-adapted mouse eyes rendered the animals hypersensitive to prolonged bright light, manifested as decreased a-wave and b-wave amplitudes. The impaired electrical responses of retinal cells in PSB-12489-treated mice were not accompanied by decrease in total thickness of the retina or death of photoreceptors and retinal ganglion cells. Our study thus defines ocular adenosine metabolism as a complex and spatially integrated network and further characterizes the critical role of CD73 in maintaining the functional activity of retinal cells.

Purpose. Increased CD73 expression has been associated with progression in various cancer types. Results of the AZURE and other trials suggest that, in postmenopausal breast cancer patients, adjuvant bisphosphonates inhibit bone relapses and prolong overall survival. Based on these findings, adjuvant bisphosphonates (typically zoledronic acid) are standard-of-care in postmenopausal patients with high-risk early breast cancer. However, biomarkers are needed for improved patient selection. The aim of this study was to investigate the association of primary tumor CD73 expression with later development of bone metastases. Methods. To determine whether CD73 levels correlated with tumor parameters (hormone receptor status, tumor stage and grade), patient outcomes (bone metastases and survival) or other patient characteristics (menopausal status, chemotherapy or statin use), we analyzed primary breast tumor CD73 expression immunohistochemically in tumor microarray samples from the AZURE (BIG01/04) trial. Results. In the AZURE control arm, high CD73 score are significantly prognostic for overall survival (p-value = 0.03, HR = 1.87, 95% CI = 1.06–3.29), disease-free survival (p-value = 0.06, HR = 1.66, 95% CI = 0.982–2.8) and time to first metastasis to bone (p-value = 0.04, HR = 2.23, 95% CI = 1.04–4.81), as compared with low CD73 scores. However, high CD73 score did not display an association with time to non-bone metastasis or first recurrence to a non-skeletal site. In the zoledronate arm, high CD73 score did not have association with patient outcomes, first metastasis to bone, nor with bone recurrence at any time (distant recurrence, including skeletal) or first non-skeletal recurrence. In multivariate testing, CD73 had no significant association with age, ER status, tumor stage, histological grade, menopausal status, chemotherapy or statin use in either arm. Conclusions. High CD73 expression is associated with development of bone metastases. Zoledronate counteracts this effect. These results suggest that CD73 expression might serve as a biomarker for adjuvant zoledronic acid use.

Adenosine is a potent anticonvulsant acting on excitatory synapses through A1 receptors. Cellular release of ATP, and its subsequent extracellular enzymatic degradation to adenosine, could provide a powerful mechanism for astrocytes to control the activity of neural networks during high-intensity activity. Despite adenosine's importance, the cellular source of adenosine remains unclear. We report here that multiple enzymes degrade extracellular ATP in brain tissue, whereas only Nt5e degrades AMP to adenosine. However, endogenous A1 receptor activation during cortical seizures in vivo or heterosynaptic depression in situ is independent of Nt5e activity, and activation of astrocytic ATP release via Ca2+ photolysis does not trigger synaptic depression. In contrast, selective activation of postsynaptic CA1 neurons leads to release of adenosine and synaptic depression. This study shows that adenosine-mediated synaptic depression is not a consequence of astrocytic ATP release, but is instead an autonomic feedback mechanism that suppresses excitatory transmission during prolonged activity.

To investigate the function of the gene penF in the pentostatin and vidarabine (Ara-A) biosynthetic gene cluster in Streptomyces antibioticus NRRL 3238, PenF was recombinantly expressed and characterized. Enzymatic characterization of the enzyme demonstrated that PenF exhibited metal-dependent nucleoside 5ʹ-monophosphatase activity, showing a substrate preference for arabinose nucleoside 5ʹ-monophosphate over 2ʹ-deoxyribonucleoside 5ʹ-monophosphate and ribonucleoside 5ʹ-monophosphate. Metal ions such as Mg2+ and Mn2+ significantly enhanced enzyme activity, whereas Zn2+, Cu2+, and Ca2+ inhibited it. For vidarabine 5′-monophosphate, the Km and kcat values were determined to be 71.5 μM and 33.9 min−1, respectively. The kcat/Km value was 474.1 mM−1·min−1 for vidarabine 5-monophosphate and was 68-fold higher than that for 2′-deoxyadenosine 5′-monophosphate. Comparative sequence alignment and structural studies suggested that residues outside the primary substrate-binding site are responsible for this substrate specificity. In conclusion, PenF’s activity toward vidarabine 5ʹ-monophosphate likely plays a role in the dephosphorylation of precursors during Ara-A biosynthesis.

CD73 is overexpressed in many types of human and mouse cancers and is implicated in the control of tumor progression. However, the specific contribution from tumor or host CD73 expression to tumor growth remains unknown to date. Here, we show that host CD73 promotes tumor growth in a T cell-dependent manner and that the optimal antitumor effect of CD73 blockade requires inhibiting both tumor and host CD73. Notably, enzymatic activity of CD73 on nonhematopoietic cells limited tumor-infiltrating T cells by controlling antitumor T cell homing to tumors in multiple mouse tumor models. In contrast, CD73 on hematopoietic cells (including CD4⁺CD25⁺ Tregs) inhibited systemic antitumor T cell expansion and effector functions. Thus, CD73 on hematopoietic and nonhematopoietic cells has distinct adenosinergic effects in regulating systemic and local antitumor T cell responses. Importantly, pharmacological blockade of CD73 using its selective inhibitor or an anti-CD73 mAb inhibited tumor growth and completely restored efficacy of adoptive T cell therapy in mice. These findings suggest that both tumor and host CD73 cooperatively protect tumors from incoming antitumor T cells and show the potential of targeting CD73 as a cancer immunotherapy strategy.