CBASS Immunity Uses CARF-Related Effectors to Sense 3'-5'- and 2'-5'-Linked Cyclic Oligonucleotide Signals and Protect Bacteria from Phage Infection

cGAS/DncV-like nucleotidyltransferase (CD-NTase) enzymes are immune sensors that synthesize nucleotide second messengers and initiate antiviral responses in bacterial and animal cells. Here, we discover Enterobacter cloacae CD-NTase-associated protein 4 (Cap4) as a founding member of a diverse family of >2,000 bacterial receptors that respond to CD-NTase signals. Structures of Cap4 reveal a promiscuous DNA endonuclease domain activated through ligand-induced oligomerization. Oligonucleotide recognition occurs through an appended SAVED domain that is an unexpected fusion of two CRISPR-associated Rossman fold (CARF) subunits co-opted from type III CRISPR immunity. Like a lock and key, SAVED effectors exquisitely discriminate 2'-5'- and 3'-5'-linked bacterial cyclic oligonucleotide signals and enable specific recognition of at least 180 potential nucleotide second messenger species. Our results reveal SAVED CARF family proteins as major nucleotide second messenger receptors in CBASS and CRISPR immune defense and extend the importance of linkage specificity beyond mammalian cGAS-STING signaling.

The natural cytokinin 2OH3MeOBAR induces cell death by a mechanism that is different from that of the "classical" cytokinin ribosides

Cytokinin ribosides (N⁶-substituted adenosines) have demonstrated anticancer activity in various cultured cell lines, several xenografts and even a small clinical trial. Effects of kinetin riboside, N⁶-benzyladenosine (BAR) and N⁶-isopentenyladenosine on various parameters related to apoptosis have also been reported, but not directly compared with those of the highly active naturally occurring aromatic cytokinins oTR (ortho-topolin riboside) and 2OH3MeOBAR (N⁶-(2-hydroxy-3-methoxybenzyl)adenosine). Here we show that 2OH3MeOBAR is the most active cytokinin riboside studied to date (median, 1st quartile, 3rd quartile and range of GI50 in tests with the NCI60 cell panel: 0.19, 0.10, 0.43 and 0.02 to 15.7 μM, respectively) and it differs from other cytokinins by inducing cell death without causing pronounced ATP depletion. Analysis of NCI60 test data suggests that its activity is independent of p53 status. Further we demonstrate that its 5'-monophosphate, the dominant cancer cell metabolite, inhibits the candidate oncogene DNPH1. Synthesis, purification, HPLC-MS identification and HPLC-UV quantification of 2OH3MeOBAR metabolites are also reported.

Tandem mass spectrometry identification and LC-MS quantification of intact cytokinin nucleotides in K-562 human leukemia cells

We describe here a new reversed-phase high-performance liquid chromatography with mass spectrometry detection method for quantifying intact cytokinin nucleotides in human K-562 leukemia cells. Tandem mass spectrometry was used to identify the intracellular metabolites (cytokinin monophosphorylated, diphosphorylated, and triphosphorylated nucleotides) in riboside-treated cells. For the protein precipitation and sample preparation, a trichloroacetic acid extraction method is used. Samples are then back-extracted with diethyl ether, lyophilized, reconstituted, and injected into the LC system. Analytes were quantified in negative selected ion monitoring mode using a single quadrupole mass spectrometer. The method was validated in terms of retention time stabilities, limits of detection, linearity, recovery, and analytical accuracy. The developed method was linear in the range of 1-1,000 pmol for all studied compounds. The limits of detection for the analytes vary from 0.2 to 0.6 pmol.

Anticancer activity of natural cytokinins: a structure-activity relationship study

Cytokinin ribosides (N(6)-substituted adenosine derivatives) have been shown to have anticancer activity both in vitro and in vivo. This study presents the first systematic analysis of the relationship between the chemical structure of cytokinins and their cytotoxic effects against a panel of human cancer cell lines with diverse histopathological origins. The results confirm the cytotoxic activity of N(6)-isopentenyladenosine, kinetin riboside, and N(6)-benzyladenosine and show that the spectrum of cell lines that are sensitive to these compounds and their tissues of origin are wider than previously reported. The first evidence that the hydroxylated aromatic cytokinins (ortho-, meta-, para-topolin riboside) and the isoprenoid cytokinin cis-zeatin riboside have cytotoxic activities is presented. Most cell lines in the panel showed greatest sensitivity to ortho-topolin riboside (IC(50)=0.5-11.6 microM). Cytokinin nucleotides, some synthesized for the first time in this study, were usually active in a similar concentration range to the corresponding ribosides. However, cytokinin free bases, 2-methylthio derivatives and both O- and N-glucosides showed little or no toxicity. Overall the study shows that structural requirements for cytotoxic activity of cytokinins against human cancer cell lines differ from the requirements for their activity in plant bioassays. The potent anticancer activity of ortho-topolin riboside (GI(50)=0.07-84.60 microM, 1st quartile=0.33 microM, median=0.65 microM, 3rd quartile=1.94 microM) was confirmed using NCI(60), a standard panel of 59 cell lines, originating from nine different tissues. Further, the activity pattern of oTR was distinctly different from those of standard anticancer drugs, suggesting that it has a unique mechanism of activity. In comparison with standard drugs, oTR showed exceptional cytotoxic activity against NCI(60) cell lines with a mutated p53 tumour suppressor gene. oTR also exhibited significant anticancer activity against several tumour models in in vivo hollow fibre assays.

Severe exacerbation of chronic hepatitis B after emergence of lamivudine resistance in a cirrhotic patient: immediate switch to adefovir dipivoxil appears to be indicated

INTRODUCTION

Lamivudine is a treatment option for the therapy of chronic hepatitis B with an excellent safety profile. Unfortunately, viral resistance to lamivudine is common in the course of therapy. The lamivudine resistant mutants are usually less pathogenic than the wild type, but development of viral resistance can also lead to acute exacerbation of the underlying hepatitis. The recently FDA approved nucleoside analogue adefovir dipivoxil has potent antiviral activity against lamivudine-resistant mutants and can prevent viral replication effectively.

CASE REPORT

A 31-year-old man with pre-existing compensated liver cirrhosis developed resistance to lamivudine therapy leading to subacute liver failure. After referral adefovir dipivoxil 10 mg daily was initiated within an early access protocol. Since initiating therapy with adefovir dipivoxil progression of the subacute liver failure was delayed accompanied by a rapid decrease of ALT and decline of HBV viral load. Even so, the clinical course was not reverted but showed slower deterioration. This enabled the patient to undergo living-related liver transplantation. Adefovir dipivoxil was well tolerated in the acute phase of the disease and did not cause nephrotoxicity or favour the development of hepatorenal syndrome.

CONCLUSION

Adefovir dipivoxil resulted in a delay of hepatic decompensation and enabled liver transplantation as final treatment option for this patient. Earlier initiation might even have prevented the need of liver transplantation. Thus, in patients with pre-existing liver cirrhosis an early switch to adefovir dipivoxil appears indicated after emergence of lamivudine resistance.

Direct comparison of the potency of three novel cAMP analogs to induce CREB-phophorylation in rat pinealocytes

A modified analog of cyclic adenosine 3',5'-monophosphate (cAMP), Sp-adenosine-3',5'-monophosphorothioate, designed to be highly membrane-permeable and resistant towards phosphodiesterases was found to induce the phosphorylation of the cAMP-regulated transcription factor cyclic AMP-responsive element binding protein in cultured rat pinealocytes more efficiently than previously described cAMP analogs.

(Rp)- and (Sp)-8-piperidino-adenosine 3',5'-(cyclic)thiophosphates discriminate completely between site A and B of the regulatory subunits of cAMP-dependent protein kinase type I and II

8-Piperidino-cAMP has been shown to bind with high affinity to site A of the regulatory subunit of cAMP-dependent protein kinase type I (AI) whereas it is partially excluded from the homologous site (AII) of isozyme II [Ogreid, D., Ekanger, R., Suva, R. H., Miller, J. P., and Døskeland, S. O. (1989), Eur. J. Biochem. 181, 19-31]. To further increase this selectivity, the (Rp)- and (Sp)-diastereoisomers of 8-piperidino-cAMP[S] were synthesized and analyzed for their potency to inhibit binding of [3H]cAMP to site A and site B from type I (rabbit skeletal muscle) and type II (bovine myocardium) cAMP-dependent protein kinases. (Sp)-8-Piperidino-cAMP[S] showed an enhanced relative affinity for site AI, thus being by far the best A-selective compound (more than 100-fold) tested for this isozyme. In contrast, the (Rp)-isomer was less selective for AI than 8-Piperidino-cAMP itself. The reduction in affinities for BII, compared to 8-piperidino-cAMP, were 10-fold and 50-fold for the (Sp)- and (Rp)-isomer, respectively. Both isomers were almost completely excluded from AII, with affinities about 1000-fold lower than 8-piperidino-cAMP itself. The (Rp)-isomer selected BII with an affinity about 10,000 times higher than for AII, whereas the (Sp)-isomer showed a preference of about 70,000-fold in favour of BII. 8-Piperidino-cAMP as well as its (Sp)-isomer activated both types of holoenzyme protein kinases whereas the (Rp)-isomer acted as an antagonist of cAMP-induced activation. The study concludes that the combination of piperidino- and exocyclic sulfur substitutions generate cAMP analogs that completely discriminate between site A and B of cAMP-dependent protein kinases.

Chloramine-T effect on sodium conductance of neuroblastoma cells as studied by whole-cell clamp and single-channel analysis

Patch-clamp experiments were done on sodium channels of neuroblastoma cells (N1E-115) in the presence of tetraethylammonium ions to block potassium channels. In Ringer solution whole-cell records revealed a diphasic INa inactivation with the fast (tau 0) component. being clearly larger than the slow (tau 1 approximately 3 tau 0) component. In single-channel studies on inside-out patches the mean open time, to, turned out to be only a fraction of tau 0 and almost independent of membrane potential. After external application of chloramine-T INa inactivation of whole cells was delayed with both tau 0 and tau 1 increased, and incomplete, i.e. a persistent current component emerged. The latter was maximal at a more positive membrane potential than the peak current. Also, after chloramine-T treatment the peak INa increased, particularly at weak depolarizations. In inside-out patches the equally effective internal application of chloramine-T led to bursting channel openings with mean burst times (tb) approximately 6 ms, and gap times (tg) approximately 20 ms, where gap is defined as a closure of greater than or equal to 1.5 ms. Within the bursts to was approximately 2 ms, again clearly shorter than tau 0; the mean close time, tc was approximately 0.5 ms. The single-channel conductance was approximately 13 pS and unaffected by chloramine-T. Diphasic INa inactivation and the fact that to less than tau 0 led to an extension of the model of Aldrich and Stevens [J Neurosci 7:418-431 (1987)], in which overall kinetics is determined by the openings rather than closures of the sodium channels.(ABSTRACT TRUNCATED AT 250 WORDS)