Susceptibility to seizure-induced injury and acquired microencephaly following intraventricular injection of saporin-conjugated 192 IgG in developing rat brain

To study the role of neurotrophin-responsive neurons in brain growth and developmental resistance to seizure-induced injury, we infused saporin-conjugated 192-IgG (192 IgG-saporin), a monoclonal antibody directed at the P75 neurotrophin receptors (p75(NTR)), into the ventricles of postnatal day 8 (P8) rat pups. 7-10 days after immunotoxin treatment, loss of p75(NTR) immunoreactivity was associated with depletion of basal forebrain cholinergic projection to the neocortex and hippocampus. Kainic acid (KA)-induced seizures on P15 resulted in hippocampal neuronal injury in the majority of toxin-treated animals (13/16), but only rarely in saline-injected controls (2/25) (P < 0.001). In addition, widespread cerebral atrophy and a significant decrease in brain weight with preserved body weight were observed. Volumetric analysis of the hippocampal hilar region revealed a 2-fold reduction in perikaryal size and a 1.7-fold increase in cell packing density after 192 IgG-saporin injection. These observations indicate that neurotrophin-responsive neurons including basal forebrain magnocellular cholinergic neurons may be critical for normal brain growth and play a protective role in preventing excitotoxic neuronal injury during development.

On the contentious sequence and glycosylation motif of the ribosome inactivating plant protein gelonin

The amino acid sequence and the glycosylation motif of the ribosome inactivating protein (RIP) gelonin are identified by Fourier transform ion cyclotron resonance mass spectrometry. Intact gelonin as isolated from the seeds of Gelonium multiflorum consists of at least three different post-translational modified forms: analysis of gelonin peptides as obtained by proteolytic digestion is consistent with the amino acid sequence published by Nolan et al. High resolution mass determination established a glycosylation pattern of GlcNAc2Man(3-5)Xyl. N189 was identified as glycosylation site. The proposed glycan structure is consistent with a standard plant N-glycosylation pattern as found in other RIP. Based on these results we suggest that gelonin is located in the vacuole of Gelonium multiflorum seeds.

Expression of a truncated form of ribosomal protein L3 confers resistance to pokeweed antiviral protein and the Fusarium mycotoxin deoxynivalenol

The contamination of important agricultural products such as wheat, barley, or maize with the trichothecene mycotoxin deoxynivalenol (DON) due to infection with Fusarium species is a worldwide problem. Trichothecenes inhibit protein synthesis by targeting ribosomal protein L3. Pokeweed antiviral protein (PAP), a ribosome-inactivating protein binds to L3 to depurinate the alpha-sarcin/loop of the large rRNA. Plants transformed with the wild-type PAP show lesions and express very low levels of PAP because PAP autoregulates its expression by destabilizing its own mRNA. We show here that transgenic tobacco plants expressing both the wild-type PAP and a truncated form of yeast L3 (L3delta) are phenotypically normal. PAP mRNA and protein levels are very high in these plants, indicating that L3delta suppresses the autoregulation of PAP mRNA expression. Ribosomes are not depurinated in the transgenic plants expressing PAP and L3delta, even though PAP is associated with ribosomes. The expression of the endogenous tobacco ribosomal protein L3 is up-regulated in these plants and they are resistant to the Fusarium mycotoxin DON. These results demonstrate that expression of an N-terminal fragment of yeast L3 leads to trans-dominant resistance to PAP and the trichothecene mycotoxin DON, providing evidence that both toxins target L3 by a common mechanism.

Enhanced photodynamic destruction of a transplantable fibrosarcoma using photochemical internalisation of gelonin

Photochemical internalisation (PCI) is a technique for releasing biologically active macromolecules from endocytic vesicles by light activation of a photosensitiser localised in the same vesicles of targeted cells. This study investigated the PCI of the toxin gelonin as a way of enhancing the effect of photodynamic therapy (PDT) on a human malignant fibrous histiocytoma transplanted into nude mice using the photosensitiser disulphonated aluminium phthalocyanine (AlPcS_2a). Pharmacokinetic studies after intraperitoneal administration showed that the serum level of AlPcS_2a fitted a biexponential model (half-lives of 1.8 and 26.7 h). The tumour concentration was roughly constant up to 48 h, although fluorescence microscopy showed that the drug location was initially mainly vascular, but became intracellular by 48 h. To compare PDT with PCI, 48 h after intraperitoneal injection of 10 mg kg⁻¹ AlPcS_2a, and 6 h after direct intratumour injection of 50 μg gelonin (PCI) or a similar volume of phosphate-buffered saline (PDT controls), tumour-bearing animals were exposed to red light (150 J cm⁻²). Complete response was observed for more than 100 days in 50% of the PCI tumours but only 10% of the PDT tumours (P<0.01). In tumours examined histologically 4 days after light delivery, the depth of necrosis was 3–4 mm after PDT, but 7 mm after PCI. The deeper effect after PCI demonstrates that the light fluence needed to kill tumour is less than with PDT. We conclude that PCI with gelonin can markedly enhance the effect of PDT on this type of tumour and may have a role clinically as an adjunct to surgery to control localised disease.

Nontoxic membrane translocation peptide from protamine, low molecular weight protamine (LMWP), for enhanced intracellular protein delivery: in vitro and in vivo study

Naturally derived, nontoxic peptides from protamine by the authors, termed low molecular weight protamines (LMWPs), possess high arginine content and carry significant sequence similarity to that of TAT, by far the most potent protein transduction domain peptide. Therefore, it was hypothesized that these LMWPs would also inherit the similar translocation activity across the cell membrane, which enables any impermeable species to be transduced into the cells. LMWPs were prepared by enzymatic digestion of protamine, examined their capability of transducing an impermeable protein toxin into the tumor cells by chemical conjugation, and determined cytotoxicity of transduced protein toxin (e.g., gelonin) against cancer cell lines and a tumor-bearing mouse. In vitro results showed that LMWPs could indeed translocate themselves into several mammalian cell lines as efficiently as TAT, thereby transducing impermeable gelonin into the cells by chemical conjugation. In vivo studies further confirmed that LMWP could carry an impermeable gelonin across the tumor mass and subsequently inhibit the tumor growth. In conclusion, the presence of equivalent cell translocation potency, absence of toxicity of peptide itself, and the suitability for low-cost production by simple enzymatic digestion could expand the range of clinical applications of LMWPs, including medical imaging and gene/protein therapies.

Selective cholinergic immunolesioning affects synaptic plasticity in developing visual cortex

Cholinergic neurotransmission is known to affect activity-dependent plasticity in various areas, including the visual cortex. However, relatively little is known about the exact role of subcortical cholinergic inputs in the regulation of plastic events in this region during early postnatal development. In the present study, synaptic transmission and plasticity in the developing visual cortex were studied following selective immunotoxic removal of the basal forebrain cholinergic afferents in 4-day-old rat pups. The lesion produced dramatic cholinergic neuronal and terminal fibre loss associated with decreased mRNA levels for the M1 and M2 muscarinic receptors, as well as clear-cut impairments of long-term potentiation (LTP) in visual cortex slices. Indeed, after theta burst stimulation of layer IV a long-term depression (LTD) instead of an LTP was induced in immunolesioned slices. This functional change appears to be due to the lack of cholinergic input as exogenous application of acetylcholine prevented the shift from LTP to LTD. In addition, lesioned rats showed an increased sensitivity to acetylcholine (ACh). While application of 20 microm ACh produced a depression of the field potential in immunolesioned rat slices, in order to observe the same effect in control slices we had to increase ACh concentration to up to 200 microm. Taken together, our results indicate that deprivation of cholinergic input affects synaptic transmission and plasticity in developing visual cortex, suggesting that the cholinergic system could play an active role in the refinement of the cortical circuitry during maturation.

Preparation and preliminary application of monoclonal antibodies against Trichokirin-S1, a small ribosome-inactivating peptide from the seeds of Trichosanthes kirilowii

Trichokirin-S1, a small ribosome-inactivating peptide recently purified from the seeds of Trichosanthes kirilowii, has potential clinical applications because of its small molecular mass. Two stable strains of hybridomas (1F11 and 2A5) that can secrete highly specific monoclonal antibodies (mAbs) against Trichokirin-S1 have been developed using the hybridoma technique. The isotypes of these two mAbs, 1F11 and 2A5, were determined to be IgG2a and IgG1, respectively. The affinity constants, which were measured by non-competitive ELISA, were found to be 2.3 x10(8) M(-1) and 2.8 x 10(8) M(-1), respectively. An immunoaffinity method using 2A5-coupled Sepharose 4B was successfully developed to purify Trichokirin-S1. These two antibodies have also been used to detect Trichokirin-S1 in Western blot.

Aging and cholinergic deafferentation alter GluR1 expression in rat frontal cortex

Previously, we demonstrated that plasticity of frontal cortex is altered in aging rats: lesions of the nucleus basalis magnocellularis (NBM) produce larger declines in dendritic morphology in frontal cortex of aged rats compared to young adults. Cholinergic afferents from the NBM modulate glutamatergic transmission in neocortex, and glutamate is known to be involved in dendritic plasticity. To begin to identify possible mechanisms underlying age-related differences in plasticity after NBM lesion, we assessed the effect of cholinergic deafferentation on expression of the AMPA receptor subunit GluR1 in frontal cortex of young adult and aging rats. Young adult, middle-aged, and aged rats received sham or 192 IgG-saporin lesions of the NBM, and an unbiased stereological technique was used to estimate the total number of intensely GluR1-immunopositive neurons in layer II-III of frontal cortex. While the number of GluR1-positive neurons was increased in both middle-aged and aged rats, lesions markedly increased the number of intensely GluR1-immunopositive neurons in frontal cortex of young adult rats only. This age-related difference in lesion-induced expression of AMPA receptor subunit protein could underlie the age-related differences in dendritic plasticity after NBM lesions.

CD38 as a target of IB4 mAb carrying saporin-S6: design of an immunotoxin for ex vivo depletion of hematological CD38+ neoplasia

An anti-CD38 mAb (IB4) coupled to saporin-S6, a type 1 ribosome-inactivating protein (RIP), was designed for ex vivo or loco-regional therapeutical applications in myeloma and lymphoma. The ability of this immunotoxin to eliminate CD38+ cells was studied in vitro on selected CD38+ human cell lines (Raji, HBL6, L540 and CEM) and on CD38+ neoplastic cells from a Non Hodgkin Lymphoma (NHL) patient. HBL6, Raji and L540 cells resulted very sensitive to the IB4/saporin-S6 conjugate, concentrations as low as 100 pM of the immunotoxin completely inhibited protein synthesis. CD38+ neoplastic cells from the NHL patient were completely eliminated after treatment with immunotoxin at 10 nM concentration. CFU-c rescue by bone marrow precursors was maintained after exposure to the immunotoxin. These results indicate that IB4/saporin-S6 is endowed with strong and specific cytotoxic effects on selected CD38+ tumor cells lineages. Consequently, it is reasonable to propose a clinical use of the IB4/saporin-S6 for ex vivo purging of unwanted cells (e.g. depletion of contaminating neoplastic cells in aphereses obtained from G-CSF-treated patients) or for loco-regional therapies of CD38+ tumors.

Pro- and anti-apoptotic evidence for cholinergic denervation and hippocampal sympathetic ingrowth in rat dorsal hippocampus

In rat, injection of the specific cholinotoxin, 192 IgG-saporin, into the medial septum results not only in a selective cholinergic denervation of hippocampus, but in an ingrowth of peripheral sympathetic fibers, originating from the superior cervical ganglion, into the hippocampus. A similar process, in which peripheral noradrenergic axons invade hippocampus, may also occur in Alzheimer's disease. Since apoptotic cell death has been demonstrated in the selective neuronal loss found in Alzheimer's disease, the aim of this study was to measure apoptotic protein expression and DNA fragmentation in hippocampal sympathetic ingrowth and cholinergic denervation. Western blot, TdT-mediated dUTP nick end labeling, and oligo ligation techniques were used. Choline acetyltransferase activity and norepinephrine concentrations were also measured. As seen in our previous results, an increase in apoptotic markers was induced by cholinergic denervation alone (medial septum lesion + ganglionectomy), while hippocampal sympathetic ingrowth (medial septum + sham ganglionectomy) reduced or normalized apoptotic effects to control group levels. A decrease in choline acetyltransferase activity was also found in the dorsal hippocampus of hippocampal sympathetic ingrowth and cholinergic denervation groups. An increase in norepinephrine concentration was found in hippocampal sympathetic ingrowth but not in cholinergic denervation group. Results of this study suggest that cholinergic denervation is responsible for most of the proapoptotic responses, while hippocampal sympathetic ingrowth produces a protective effect in the process of programmed cell death in rat dorsal hippocampus. This effect may be a secondary to an altered relationship between norepinephrine-acetylcholine.

Tumor-induced mechanical hyperalgesia involves CGRP receptors and altered innervation and vascularization of DsRed2 fluorescent hindpaw tumors

Functional and anatomical relationships among primary afferent fibers, blood vessels, and cancers are poorly understood. However, recent evidence suggests that physical and biochemical interactions between these peripheral components are important to both tumor biology and cancer-associated pain. To determine the role of these peripheral components in a mouse model of cancer pain, we quantified the change in nerve and blood vessel density within a fibrosarcoma tumor mass using stereological analysis of serial confocal optical sections of immunostained hind paw. To this end we introduced the Discoma coral-derived red fluorescent protein (DsRed2) into the NCTC 2472 fibrosarcoma line using the Sleeping Beauty transposon methodology, thus providing a unique opportunity to visualize tumor-nerve-vessel associations in context with behavioral assessment of tumor-associated hyperalgesia. Tumors from hyperalgesic mice are more densely innervated with calcitonin gene related peptide (CGRP)-immunoreactive nerve fibers and less densely vascularized than tumors from non-hyperalgesic mice. As hyperalgesia increased from Day 5 to 12 post-implantation, the density of protein gene product 9.5 (PGP9.5)-immunoreactive nerves and CD31-immunoreactive blood vessels in tumors decreased, whereas CGRP-immunoreactive nerve density remained unchanged. Importantly, intra-tumor injection of a CGRP1 receptor antagonist (CGRP 8-37) partially blocked the tumor-associated mechanical hyperalgesia, indicating that local production of CGRP may contribute to tumor-induced nociception through a receptor-mediated process. The results describe for the first time the interaction among sensory nerves, blood vessels and tumor cells in otherwise healthy tissue, and our assessment supports the hypothesis that direct tumor cell-axon communication may underlie, at least in part, the occurrence of cancer pain.

The 1.4 anstroms structure of dianthin 30 indicates a role of surface potential at the active site of type 1 ribosome inactivating proteins

Ribosome inactivating proteins (RIPs) are plant proteins with enzymatic activity identified as rRNA N-glycosidase (EC 3.2.2.22), which cleaves the N-glycosidic bond of a specific adenine on the ricin/sarcin region of rRNA, thus causing inhibition of protein synthesis. They also depurinate extensively DNA and other polynucleotides. The three-dimensional structure of dianthin 30, a type 1 (single-chain) RIP of Dianthus caryophyllus (leaves), is now described at 1.4 angstroms, a resolution never achieved before for any RIP. The fold typical of RIPs is conserved, despite some differences in the loop regions. The general structure comparison by superimposed alpha-carbon (249 atoms) and the sequence alignment by structure for dianthin 30 and saporin-S6 give a root mean square deviation of 0.625 angstroms. Despite the differences reported for the biological activities of the two RIPs, their structures fit quite well and both show a protein segment containing strands beta7, beta8, and beta9 shorter than other RIPs. However, the surface electrostatic potential in the active site region neatly distinguishes dianthin 30 from saporin-S6. The possible relationship between the charge distribution and the behavior of the proteins toward different substrates is discussed.

Forebrain acetylcholine regulates adult hippocampal neurogenesis and learning

Hippocampus-mediated learning enhances neurogenesis in the adult dentate gyrus (DG), and this process has been suggested to be involved in memory formation. The hippocampus receives abundant cholinergic innervation and acetylcholine (ACh) plays an important role in learning and Alzheimer's disease (AD) pathophysiology. Here, we show that a selective neurotoxic lesion of forebrain cholinergic input with 192 IgG-saporin reduces DG neurogenesis with a concurrent impairment in spatial memory. Conversely, systemic administration of the cholinergic agonist physostigmine increases DG neurogenesis. We find that changes of forebrain ACh levels primarily influence the proliferation and/or the short-term survival rather than the long-term survival or differentiation of the new neurons. We further demonstrate that these newly born cells express the muscarinic receptor subtypes M1 and M4. Our data provide evidence that forebrain ACh promotes neurogenesis, and suggest that the impaired cholinergic function in AD may in part contribute to deficits in learning and memory through reductions in the formation of new hippocampal neurons.

Basal forebrain cholinergic lesions in 7-day-old rats alter ultrasound vocalisations and homing behaviour

We analysed the effects of 192 IgG-saporin lesions on pnd 7 upon neonatal behavioural responses. Number of ultrasonic vocalisations (USVs) were recorded on pnds 9, 11 and 13. On pnd 13 rats underwent a homing test to measure olfactory orientation towards nest material. 192 IgG-saporin reduced the number of USVs at all ages considered while increasing number of entrancies into the nest area. These data suggest that early damage to the basal forebrain cholinergic nuclei induces significant changes in the rat behavioural repertoire as early as the second-postnatal week.

Acetylcholine in the orbitofrontal cortex is necessary for the acquisition of a socially transmitted food preference

The social transmission of food preference task (STFP) has been used to examine the involvement of the hippocampus in learning and memory for a natural odor-odor association. However, cortical involvement in STFP has not been extensively studied. The orbitofrontal cortex (OFC) is important in odor-guided learning, and cholinergic depletion of the entire neocortex results in impairments in STFP. Here we examined the specific role of cholinergic modulation in the OFC by assessing the effect of 192 immunoglobulin G-saporin infusion directly into OFC prior to training on STFP. Cholinergic depletion in the OFC impaired expression of the socially transmitted odor association measured 2 d after training, indicating that cholinergic function in the OFC is essential for this form of associative learning.

[Cloning and expression of luffin-a gene from the seeds of Luffa cylindrical]

OBJECTIVE

To clone luffin-a cDNA from the seeds of Luffa cylindrical, and to obtain bioactive recombinant luffin-a protein using the expression vector pET-44a (+) in E. coli.

METHODS

The cDNA sequence encoding luffin-a was cloned from the fresh seeds of Luffa cylindrical by RT-PCR. The target DNA fragments were sequenced after T-A cloning. The luffin-a expression plasmid was constructed by inserting the luffin-a cDNA fragment into vector pET-44a (+). Luffin-a was expressed in E. coli by addition of IPTG into final concentration 1.0 mmol/L. The recombinant luffin-a was identified by SDS-PAGE. The biological activity of luffin-a protein was evaluated by using the MTT assay in HepG2 cells following fluid-phase endocytosis.

RESULTS

In comparison with the reported luffin-a, the homology of nucleotide sequence of the cloned luffin-a gene was 99.73%, while their amino acid sequences were identical. The solubility of recombinant protein was analyzed by SDS-PAGE, and the luffin-a was mainly produced in inclusion bodies. The recombinant luffin-a, renatured by dialysis of the denatured products, showed a similar cytotoxicity to ricin A chain.

CONCLUSION

The cDNA of luffin-a has been successfully cloned. The recombinant luffin-a protein expressed by E. coli is bioactive.

Further analysis of the effects of immunotoxic lesions of the basal nucleus of Meynert reveals substantial impairment on visual discrimination learning in monkeys

In this paper we undertake a combined analysis of several studies in which marmoset monkeys received immunotoxic lesions of the cortical cholinergic projections from the basal nucleus of Meynert (NBM) bilaterally and/or in combination with immunotoxic lesions of other parts of the cholinergic system or ablations of the target inferotemporal neocortical area. Analysis of the mean learning scores across all visual discriminations learning tasks for each lesion combination revealed highly significant impairments where the NBM was lesioned bilaterally or where an NBM lesion in one hemisphere was crossed with an inferotemporal cortical ablation in the other hemisphere. This demonstrates that the cholinergic projection from the NBM to the major target area of neocortex involved in visual discrimination learning, i.e. the inferotemporal cortex, makes an important contribution to the perceptuo-mnemonic processes necessary for this type of learning. A new study demonstrates a significant effect of a subtotal bilateral cholinergic lesion confined to the NBM on a concurrent object-reward association task using black objects which is perceptually and mnemonically demanding. These results do not preclude the possibility that cholinergic projections from the NBM to other parts of the neocortex make a contribution to other cortical functions which are not mnemonic. It is well established that lesions of the cholinergic projection from the diagonal band of Broca disrupts the mnemonic functions of the hippocampus. The results described here suggest that degeneration of the cholinergic projections in Alzheimer's disease and other dementias will contribute to the loss of those mnemonic functions which are dependent on the neocortex.

Evidence for retro-translocation of pokeweed antiviral protein from endoplasmic reticulum into cytosol and separation of its activity on ribosomes from its activity on capped RNA

Pokeweed antiviral protein (PAP) is a single-chain ribosome inactivating protein (RIP) that binds to ribosomes and depurinates the highly conserved alpha-sarcin/ricin loop (SRL) of the large subunit rRNA. Catalytic depurination of a specific adenine has been proposed to result in translation arrest and cytotoxicity. Here, we show that both precursor and mature forms of PAP are localized in the endoplasmic reticulum (ER) in yeast. The mature form is retro-translocated from the ER into the cytosol where it escapes degradation unlike the other substrates of the retro-translocation pathway. A mutation of a highly conserved asparagine residue at position 70 (N70A) delays ribosome depurination and the onset of translation arrest. The ribosomes are eventually depurinated, yet cytotoxicity and loss of viability are markedly absent. Analysis of the variant protein, N70A, does not reveal any decrease in the rate of synthesis, subcellular localization, or the rate of transport into the cytosol. N70A destabilizes its own mRNA, binds to cap, and blocks cap dependent translation, as previously reported for the wild-type PAP. However, it cannot depurinate ribosomes in a translation-independent manner. These results demonstrate that N70 near the active-site pocket is required for depurination of cytosolic ribosomes but not for cap binding or mRNA destabilization, indicating that the activity of PAP on capped RNA can be uncoupled from its activity on rRNA. These findings suggest that the altered active site of PAP might accommodate a narrower range of substrates, thus reducing ribotoxicity while maintaining potential therapeutic benefits.

Removal of cholinergic input to perirhinal cortex disrupts object recognition but not spatial working memory in the rat

The perirhinal cortex of the temporal lobe has a crucial role in object recognition memory. Cholinergic transmission within perirhinal cortex also seems to be important for this function, as the muscarinic receptor antagonist scopolamine disrupts object recognition performance when administered systemically or directly into perirhinal cortex. In the present study, we directly assessed the contribution of cholinergic basal forebrain input to perirhinal cortex in object recognition. Selective bilateral removal of the cholinergic basal forebrain inputs to perirhinal cortex was accomplished by injecting the immunotoxin 192 IgG-saporin directly into perirhinal cortex in rats. These animals were significantly impaired relative to vehicle-injected controls in a spontaneous object recognition task despite intact spatial alternation performance. These results are consistent with recent reports of object recognition impairment following acute cholinergic receptor blockade and extend these findings by demonstrating that chronic removal of cholinergic basal forebrain input to an otherwise intact perirhinal cortex causes a severe object recognition deficit similar to that associated with more extensive cell body lesions of perirhinal cortex.

Pokeweed antiviral protein inhibits brome mosaic virus replication in plant cells

Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein isolated from the pokeweed plant (Phytolacca americana) that inhibits the proliferation of several plant and animal viruses. We have shown previously that PAP and nontoxic mutants of PAP can directly depurinate brome mosaic virus (BMV) RNA in vitro, resulting in reduced viral protein translation. Here we expand on these initial studies and, using a barley protoplast system, demonstrate that recombinant PAP and nontoxic mutants isolated from E. coli are able to reduce the accumulation of BMV RNAs in vivo. Pretreatment of only BMV RNA3 with PAP prior to transfection of barley protoplasts reduced the accumulation of all BMV RNAs, with a more severe effect on subgenomic RNA4 levels. Using in vitro RNA synthesis assays, we show that a depurinated template causes the BMV replicase to stall at the template nucleotide adjacent to the missing base. These results provide new insight into the antiviral mechanism of PAP, namely that PAP depurination of BMV RNA impedes both RNA replication and subgenomic RNA transcription. These novel activities are distinct from the PAP-induced reduction of viral RNA translation and represent new targets for the inhibition of viral infection.

Interactions between saporin, a ribosome-inactivating protein, and DNA: a study by atomic force microscopy

Saporins are enzymes belonging to the PNAG class (polynucleotide: adenosine glycosidase), plant enzymes commonly known as ribosome-inactivating proteins (RIP), as a result of their property of irreversibly damaging eukaryotic ribosomes. Direct imaging with tapping-mode atomic force microscopy (AFM) has been used to study pGEM-4Z plasmid DNA binding to the saporin-SO6 (isoform from Saponaria officinalis seeds). Saporin wrapped the plasmidic DNA, and distribution of the enzyme molecules along the DNA chain was markedly variable; plasmid digested with saporin-SO6 appeared fragmented or topologically modified. The supercoiled DNA strands were cleaved, giving rise to a linearized form and to relaxed forms. Electrophoretic analysis of the effect of standard preparations of saporin-SO6 on pGEM-4S confirmed the presence of DNA strand-cleaving activity.

Mitochondrial DNA D-loop as a new target of Saporin 6 nuclease activity

The single-chain ribosome-inactivating proteins (RIPs) from plant origin, including Saporin 6 from the seeds of Saponaria officinalis, are ribotoxins known to act as N-glycosidases which depurinate the conserved alpha sarcin loop of large rRNAs. As a consequence, the eukaryotic ribosomes become inactivated, thereby arresting the protein synthesis at the elongation step. RIPs are currently under study as antiviral and antiproliferative agents. Additional in vitro activities of RIPs against either RNA or DNA have been recently described. A specific nuclease activity on plasmidic DNA was demonstrated by either purified or bacterial-recombinant molecules. We report here that human mitochondrial DNA (mtDNA) is a new specific target of Saporin 6 nuclease activity. A unique site of cleavage has been identified and mapped within the most variable part of the D-loop region of the covalently closed circular mtDNA molecule.

Sexually dimorphic effects of hippocampal cholinergic deafferentation in rats

To determine whether the basal forebrain-hippocampal cholinergic system supports sexually dimorphic functionality, male and female Long-Evans rats were given either selective medial septum/vertical limb of the diagonal band (MS/VDB) cholinergic lesions using the neurotoxin 192 IgG-saporin or a control surgery and then postoperatively tested in a set of standard spatial learning tasks in the Morris water maze. Lesions were highly specific and effective as confirmed by both choline acetyltransferase/parvalbumin immunostaining and acetylcholinesterase histochemistry. Female controls performed worse than male controls in place learning and MS/VDB lesions failed to impair spatial learning in male rats, both consistent with previous findings. In female rats, MS/VDB cholinergic lesions facilitated spatial reference learning. A subsequent test of learning strategy in the water maze revealed a female bias for a response, relative to a spatial, strategy; MS/VDB cholinergic lesions enhanced the use of a spatial strategy in both sexes, but only significantly so in males. Together, these results indicate a sexually dimorphic function associated with MS/VDB-hippocampal cholinergic inputs. In female rats, these neurons appear to support sex-specific spatial learning processes.

CNS activity of Pokeweed anti-viral protein (PAP) in mice infected with lymphocytic choriomeningitis virus (LCMV)

Background

Others and we have previously described the potent in vivo and in vitro activity of the broad-spectrum antiviral agent PAP (Pokeweed antiviral protein) against a wide range of viruses. The purpose of the present study was to further elucidate the anti-viral spectrum of PAP by examining its effects on the survival of mice challenged with lymphocytic choriomeningitis virus (LCMV).

Methods

We examined the therapeutic effect of PAP in CBA mice inoculated with intracerebral injections of the WE54 strain of LCMV at a 1000 PFU dose level that is lethal to 100% of mice within 7–9 days. Mice were treated either with vehicle or PAP administered intraperitoneally 24 hours prior to, 1 hour prior to and 24 hours, 48 hours 72 hours and 96 hours after virus inoculation.

Results

PAP exhibits significant in vivo anti- LCMV activity in mice challenged intracerebrally with an otherwise invariably fatal dose of LCMV. At non-toxic dose levels, PAP significantly prolonged survival in the absence of the majority of disease-associated symptoms. The median survival time of PAP-treated mice was >21 days as opposed to 7 days median survival for the control (p = 0.0069).

Conclusion

Our results presented herein provide unprecedented experimental evidence that PAP exhibits antiviral activity in the CNS of LCMV-infected mice.

Construction of tumor-specific toxins using ubiquitin fusion technique

The use of cytotoxic agents to eliminate cancer cells is limited because of their nonselective toxicity and unwanted side effects. One of the strategies to overcome these limitations is to use latent prodrugs that become toxic in situ after being enzymatically activated in target cells. In this work we describe a method for producing tumor-specific toxins by using a ubiquitin fusion technique. The method is illustrated by the production of recombinant toxins by in-frame fusion of ubiquitin to saporin, a toxin from the plant Saponaria officinalis. Ubiquitin-fused toxins were rapidly degraded via the ubiquitin-proteasome system, significantly reducing their nonspecific toxicity. The insertion of the protease-cleavage sequence between ubiquitin and saporin led to the removal of ubiquitin by the protease and resulted in protease-dependent stabilization of the toxin. We engineered toxins that can be stabilized by specific proteases such as deubiquitinating enzymes and prostate-specific antigen (PSA). Both constructs were activated in vitro and in cultured cells by the appropriate enzyme. Processing by the protease resulted in a greater than 10-fold increase in the toxicity of these constructs. Importantly, the PSA-cleavable toxin was able to kill specifically the PSA-producing prostate cancer cells. The ubiquitin fusion technique is thus a versatile and reliable method for obtaining selective cytotoxic agents and can easily be adapted for different kinds of toxins and activating proteases.