CCK-B/Gastrin receptor transmembrane domain mutations selectively alter synthetic agonist efficacy without affecting the activity of endogenous peptides

Recent efforts have focused on identifying small nonpeptide molecules that can mimic the activity of endogenous peptide hormones. Understanding the molecular basis of ligand-induced receptor activation by these divergent classes of ligands should expedite the process of drug development. Using the cholecystokinin-B/gastrin receptor (CCK-BR) as a model system, we have recently shown that both affinity and efficacy of nonpeptide ligands are markedly affected by amino acid alterations within a putative transmembrane domain (TMD) ligand pocket. In this report, we examine whether residues projecting into the TMD pocket determine the pharmacologic properties of structurally diverse CCK-BR ligands, including peptides and synthetic peptide-derived partial agonists (peptoids). Nineteen mutant human CCK-BRs, each including a single TMD amino acid substitution, were transiently expressed in COS-7 cells and characterized. Binding affinities as well as ligand-induced inositol phosphate production at the mutant CCK-BRs were assessed for peptides (CCK-8 and CCK-4) and for peptoids (PD-135,158 and PD-136, 450). Distinct as well as overlapping determinants of peptide and peptoid binding affinity were identified, supporting that both classes of ligands, at least in part, interact with the CCK-BR TMD ligand pocket. Eight point mutations resulted in marked increases or decreases in the functional activity of the synthetic peptoid ligands. In contrast, the functional activity of both peptides, CCK-8 and CCK-4, was not affected by any of the CCK-BR mutations. These findings suggest that the mechanisms underlying activation of G-protein-coupled receptors by endogenous peptide hormones versus synthetic ligands may markedly differ.

Prediction on the binding domain between human interleukin-6 and its receptor

Based on the spatial conformations of human interleukin-6 (hIL-6) derived from nuclear magnetic resonance analysis and human interleukin-6 receptor (hIL-6R) modeled with homology modeling method using human growth hormone receptor as template, the interaction between hIL-6 and its receptor (hIL-6R) is studied with docking program according to the surface electrostatic potential analysis and spatial conformation complement. The stable region structure composed of hIL-6 and hIL-6R is obtained on the basis of molecular mechanism optimization and molecular dynamics simulation. The binding domain between hIL-6 and hIL-6R is predicted theoretically. Furthermore, the especial binding sites that influence the interaction between hIL-6 and hIL-6R are confirmed. The results lay a theoretical foundation for confirming the active regions of hIL-6 and designing novel antagonist with computer-guided techniques.

Three-dimensional structure and function study on the active region in the extracellular ligand-binding domain of human IL-6 receptor

In this study the three-dimensional (3-D) model of the ligand-binding domain (V106-P322) of human interleukin-6 receptor (hIL-6 R) was constructed by computer-guided homology modeling technique using the crystal structure of the ligand-binding domain (K52-L251) of human growth hormone receptor (hGHR) as templet. Furthermore, the active binding region of the 3-D model of hIL-6R with the ligand (hIL-6) was predicted. In light of the structural characteristics of the active region, a hydrophobic pocket shielded by two hydrophilic residues (E115 and E505) of the region was identified by a combination of molecular modelling and the site-directed or double-site mutation of the twelve crucial residues in the ligand-binding domain of hIL-6R (V106-P322). We observed and analyzed the effects of these mutants on the spatial conformation of the pocket-like region of hIL-6 R. The results indicated that any site-directed mutation of the five Cys residues (four conservative Cys residues: Cys121, Cys132, Cys165, Cys176; near membrane Cys residue: Cys193) or each double-site mutation of the five residues in WSEWS motif of hIL-6R (V106-P322) makes the corresponding spatial conformation of the pocket region block the linkage between hIL-6 R and hIL-6. However, the influence of the site-directed mutation of Cys211 and Cys277 individually on the conformation of the pocket region benefits the interaction between hIL-6R and hIL-6. Our study suggests that the predicted hydrophobic pocket in the 3-D model of hIL-6R (V106-P322) is the critical molecular basis for the binding of hIL-6R with its ligand, and the active pocket may be used as a target for designing small hIL-6R-inhibiting molecules in our further study.

Specific structural motifs determine TRAP220 interactions with nuclear hormone receptors

The TRAP coactivator complex is a large, multisubunit complex of nuclear proteins which associates with nuclear hormone receptors (NRs) in the presence of cognate ligand and stimulates NR-mediated transcription. A single subunit, TRAP220, is thought to target the entire complex to a liganded receptor through a domain containing two of the signature LXXLL motifs shown previously in other types of coactivator proteins to be essential for mediating NR binding. In this work, we demonstrate that each of the two LXXLL-containing regions, termed receptor binding domains 1 and 2 (RBD-1 and RBD-2), is differentially preferred by specific NRs. The retinoid X receptor (RXR) displays a weak yet specific activation function 2 (AF2)-dependent preference for RBD-1, while the thyroid hormone receptor (TR), vitamin D(3) receptor (VDR), and peroxisome proliferator-activated receptor all exhibit a strong AF2-dependent preference for RBD-2. Using site-directed mutagenesis, we show that preference for RBD-2 is due to the presence of basic-polar residues on the amino-terminal end of the core LXXLL motif. Furthermore, we show that the presence and proper spacing of both RBD-1 and RBD-2 are required for an optimal association of TRAP220 with RXR-TR or RXR-VDR heterodimers bound to DNA and for TRAP220 coactivator function. On the basis of these results, we suggest that a single molecule of TRAP220 can interact with both subunits of a DNA-bound NR heterodimer.

[Primary study on the life of Liu Chun, a famous Ming physician]

Liu Chun, a famous physician of the Ming dynasty, born in a prestigious family in Wuling (Tai County, Jiangsu Province). He studied medicine from his father Liu Juquan and Mr. Feng Tinggan in his early years. It was said Liu Chun moved to Chang'an (now Xi'an, Shaanxi Province) in 1368 and lived there for about twenty years, then moved to Liangzhou along with the army (Wuwei County, Gansu Province) before 1395 and resided in Ganzhou (Zhangye County, Gansu Province). He wrote many medical books, including Yi jing xiao xue, Yu ji wei yi, Za bing zhi li and Shang han zhi li, all published after his death. His other two books Tai su mai jue and Shou qin yang lao bu yi could not be found. It was inferred that Liu Chun who lived for about seventy years might be born in 1340 and died in 1412.

Antineutrophil cytoplasmic antibodies induce reactive oxygen-dependent dysregulation of primed neutrophil apoptosis and clearance by macrophages

This study assessed whether anti-neutrophil cytoplasmic antibodies (ANCAs) interfere with the safe deletion of neutrophils by apoptosis and phagocytic clearance. Tumor necrosis factor (TNF)-primed neutrophils were incubated with normal IgG (N IgG) or ANCA IgG for up to 36 hours. Compared with N IgG, ANCAs accelerated constitutive apoptosis of TNF-alpha primed neutrophils, as assessed by morphology and confirmed by DNA laddering pattern on gel electrophoresis, and accelerated progression to secondary necrosis. The accelerated apoptosis induced by ANCA was dependent on reactive oxygen species generation, as primed neutrophils from patients with chronic granulomatous disease failed to show an effect of ANCAs on apoptosis. However, there was no change in the rate at which neutrophils exhibited annexin V binding, indicating that externalization of phosphatidylserine was not accelerated by ANCAs. Furthermore, when ANCA-treated primed neutrophils were interacted with human or murine peritoneal macrophages after 12 hours there was significantly less phagocytosis by human macrophages and no difference in phagocytosis by murine peritoneal-derived macrophages when compared with N IgG-treated controls. In conclusion, ANCAs accelerate apoptosis and secondary necrosis in TNF-primed neutrophils by a mechanism dependent on the generation of reactive oxygen species, with uncoupling of nuclear and surface membrane changes, resulting in a "reduced window of opportunity" for phagocytic recognition and engulfment before disintegration.

Waveguide photodegradation of nonlinear optical organic chromophores in polymeric films

Waveguide photodegradation studies have been carried out to investigate the photostabilities of a series of nonlinear optical chromophores doped into poly(methyl methacrylate) waveguide films. The films were exposed to optical wavelengths lying either within these materials' main absorption bands or in the near-infrared region. Degradation studies were carried out in air, vacuum, and nitrogen environments at room temperature. Experimental results indicate that the principal photodegradation mechanism in operation is photo-oxidation. A simple analytical model indicated the relative sensitivity to photo-oxidation of the materials studied.

Studies on production of pullulan by the feed batch fermentation

The feed-batch fermentation of pullulan was investigated based on the conditions of batch fermentation. The optimal conditions of pullulan fermentation were determined by the investigation on the effect of feed mode, initial feed time, intermittent time, and composition of the feed solution on parameters such as productivity, conversion yield, biomass, dissolved oxygen (DO), pH of the fermentation broth, viscosity of the fermentation broth and molecular weight of the product. Above 70% of conversion yield and 100 kD of average molecular weight of the product was obtained at the optimal conditions.

cDNA cloning of an alternative splicing variant of protein kinase C delta (PKC deltaIII), a new truncated form of PKCdelta, in rats

Recently, an alternative splicing variant of mouse protein kinase C delta (PKC deltaII, GenBank Accession No. AB011812) has been reported which has a 78 bp (26 amino acid) insertion at the caspase-3 recognition sequence in the V3 region of PKC delta (PKC deltaI). We isolated a cDNA encoding a new variant of PKC delta (PKC deltaIII, AF219629), which has a 83 bp insertion at the same site in the V3 region, by RT-PCR using rat testis RNA as a template. In rats, the 83 bp insertion causes inframe termination, and rat PKC deltaIII protein is expressed as a truncated form, having only the regulatory domain without a catalytic domain. Genomic DNA analysis revealed that the difference between mouse PKC deltaII and rat PKC deltaIII is derived from the different sequence at the 5'-splicing donor sites. To investigate the potential functions of the truncated form of PKC delta, rat PKC deltaIII fused to green fluorescent protein (GFP) was expressed in CHO-K1 cells. PKC deltaIII-GFP was localized in the cytoplasm with dot-like accumulation and highly expressed on the plasma membrane, whereas PKC deltaI-GFP is localized homogeneously throughout the cytoplasm, including the nucleoplasm. Stimulation by phorbol ester caused weak translocation of deltaIII-GFP from the cytosol to the plasma membrane. These results suggest that PKC deltaIII may show a dominant negative effect against PKC deltaI, and that the modulation of signal transduction by alternative splicing variant may play a crucial role in the physiological and/or pathological conditions, and the pathogenesis of disease.

Deficiency of current methods in assaying endochitinase activity

Since chitin is degraded by a combination of both endo- and exochitinases, it is likely that both enzymes will be present in a crude extract. Currently used substrates for detecting endochitinase activity suffer from the fact that they could easily be digested by the contaminating exochitinase, thus giving either a false-positive or an inaccurate reading of the endochitinase activity. Using Photorhabdus luminescens, a bacterium symbiotically associated with insect-parasitic nematode Heterorhabditis bacteriophora as an exemplary system, we have identified these two chitinases by a simple "fluorimetric zymography" procedure. The exochitinase is a metalloenzyme and its activity is inhibited by 1,10-phenanthroline. Once the exochitinase activity is detected in a crude extract, its contribution must be eliminated before accurate determination of the endochitinase activity can be carried out. Specific properties of these enzymes including the pH activity profile, the requirement of metal ions for activity, and the molecular weight of the enzymes are among the factors to be considered in developing assaying procedures for endochitinase.

Replication protein A interactions with DNA. III. Molecular basis of recognition of damaged DNA

Human replication protein A (RPA) is a heterotrimeric single-stranded DNA-binding protein (subunits of 70, 32, and 14 kDa) that is required for cellular DNA metabolism. RPA has been reported to interact specifically with damaged double-stranded DNA and to participate in multiple steps of nucleotide excision repair (NER) including the damage recognition step. We have examined the mechanism of RPA binding to both single-stranded and double-stranded DNA (ssDNA and dsDNA, respectively) containing damage. We show that the affinity of RPA for damaged dsDNA correlated with disruption of the double helix by the damaged bases and required RPAs ssDNA-binding activity. We conclude that RPA is recognizing single-stranded character caused by the damaged nucleotides. We also show that RPA binds specifically to damaged ssDNA. The specificity of binding varies with the type of damage with RPA having up to a 60-fold preference for a pyrimidine(6-4)pyrimidone photoproduct. We show that this specific binding was absolutely dependent on the zinc-finger domain in the C-terminus of the 70-kDa subunit. The affinity of RPA for damaged ssDNA was 5 orders of magnitude higher than that of the damage recognition protein XPA (xeroderma pigmentosum group A protein). These findings suggest that RPA probably binds to both damaged and undamaged strands in the NER excision complex. RPA binding may be important for efficient excision of damaged DNA in NER.

Self-organized criticality in a computer network model

We study the collective behavior of computer network nodes by using a cellular automaton model. The results show that when the load of network is constant, the throughputs and buffer contents of nodes are power-law distributed in both space and time. Also the feature of 1/f noise appears in the power spectrum of the change of the number of nodes that bear a fixed part of the system load. It can be seen as yet another example of self-organized criticality. Power-law decay in the distribution of buffer contents implies that heavy network congestion occurs with small probability. The temporal power-law distribution for throughput might be a reasonable explanation for the observed self-similarity in computer network traffic.

Purification and identification of a tissue-specific repressor involved in serum amyloid A1 gene expression

We have previously demonstrated that the 5'-flanking regions from the rat serum amyloid A1 (SAA1) promoter are necessary and sufficient to confer specific cytokine-induced expression in cultured hepatoma cells. Deletion analysis identified a tissue-specific repressor (TSR) regulatory element, located between bp -289 and -256, that functioned as a silencer, contributing to the transcription repression on SAA1 promoter in nonliver cells. When this 34-base pair TSR-binding element was used as a probe in electrophoretic mobility shift assays, an intense DNA-protein complex was detected in nuclear extracts from HeLa and several other nonliver tissues. This TSR binding activity, however, was undetectable in extracts from liver or liver-derived cells. The distribution of TSR binding activity is therefore consistent with its regulatory role in repressing SAA1 expression in a tissue-specific manner. In this study, we purified TSR protein from HeLa nuclear extracts and showed that it has a molecular mass of approximately 50 kDa. Surprisingly, protein sequencing and antibody supershift experiments identified TSR as transcription factor AP-2. Subsequent functional analysis showed that forced expression of AP-2 in HepG2 cells could indeed inhibit conditioned medium-induced SAA1 promoter activation. Moreover, expression of a dominant-negative mutant of AP-2 in HeLa cells or mutation of the AP-2-binding site led to derepression of the SAA1 promoter, presumably by neutralizing the inhibitory effects of the endogenous wild-type AP-2. Our results therefore demonstrate a novel function for AP-2 in the transcriptional repression of SAA1 promoter. Together with its tissue distribution, AP-2 may contribute to SAA1's highly liver-specific expression pattern by restricting its expression in nonliver cells.

Immunocytochemical localization of serotonin and serotonin transporter (SET) in taste buds of rat

We used an immunocytochemical approach to study the localization of serotonin and its termination system, serotonin transporter (SET), in the taste buds of rats using specific antibodies against serotonin and SET. Under confocal laser scanning microscopy, both serotonin and SET immunoreactivity were detected in the taste buds of rat vallate papillae. Serotonin immunoreactivity was seen in the spindle-shaped cells with apical processes that seemed to be light (Type II) taste cells. SET-immunoreactivity was mainly localized in the periphery or interfaces between the taste cells. Double staining studies revealed that all serotonin-containing taste cells were immunoreactive for SET, while a subclass of SET-positive cells showed serotonin immunoreactivity. These data support the hypothesis that serotonin plays a transmitter role in taste receptor cells and suggest that the serotonin-induced sensation of taste is terminated by serotonin uptake through serotonin transporter.

High level of adenosine A1 receptor-like immunoreactivity in the CA2/CA3a region of the adult rat hippocampus

We describe the immunocytochemical distribution of adenosine A1 receptors in the rat hippocampus. Adenosine A1 receptor-like immunoreactivity was seen on the cell soma and dendrites of pyramidal cells and the cell soma and proximal part of dendrites of granule cells, but not on glial cells. Developmentally, adenosine A1 receptor-like immunoreactivity was diffuse on postnatal day 7 and increased in intensity in individual cells by day 21. In the CA2/CA3a region, the adult pattern of A1 receptor distribution was established by day 28. In the adult rat hippocampus, rostrocaudal inspection revealed that immunoreactivity in CA2/CA3a was greatest. Confocal microscopy revealed differences in the staining patterns for the adenosine A receptor and synaptophysin, a marker of presynaptic terminals. This result suggests that the adenosine A1 receptor might have postsynaptic physiological functions. Double-labeling of adenosine A1 receptors and anterogradely-labeled fibers from the supramammillary nucleus showed that the fibers from the supramammillary nucleus terminate directly on the cell soma of the A1 receptor-immunopositive neurons in CA2/CA3a and the dentate gyrus. These results indicate that the adenosine A 1 receptor in CA2/CA3a and the dentate gyrus are in a position to regulate hippocampal theta activity and that resultant strong synaptic depression in CA2/CA3a could play a role in regulating the intrinsic signal flow between CA3 and CA1.

[Correlation between the expression of vascular endothelial growth factor and prognosis of lung cancinoma]

OBJECTIVE

To determine the association between the expression of vascular endothelial growth factor (VEGF) and prognosis of lung cancer.

METHODS

Apply the SP immunohistochemistry stain method to investigate the expression of VEGF in 60 specimens of patients with lung cancer, who had undergone curative resection more than 36 months before.

RESULTS

The VEGF stain positive rate is 60% in 60 cases of lung cancer specimens; The immunoreactivity of VEGF was almost exclusively restricted to the tumor cells, the positive expression of VEGF showed significantly higher in the patients with lymph node metastasis and/or relapse. The positive rates of VEGF were higher in N1, N2 groups (53%, 80%) than in No group (23%, P < 0.01), and in relapse group (80%) than in non-relapse group (53%, P < 0.05). Postoperative survival time was shorter in VEGF(+) group (31 +/- 7 months) than in VEGF(-) group (64 +/- 7 months, P < 0.05). The 3, 5 year survival rates showed significant difference between VEGF(+) (31%, 11%) and VEGF(-) (88%, 50%) groups.

CONCLUSIONS

The results suggest VEGF is a reliable prognostic parameter and antiangiogenesis therapy will be a useful strategy in treatment of the human lung cancer.

Purification and characterization of the serum amyloid A3 enhancer factor

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to acute inflammation, its expression may be induced up to 1000-fold, primarily as a result of a 200-fold increase in the rate of SAA gene transcription. We showed previously that cytokine-induced transcription of the SAA3 gene promoter requires a transcriptional enhancer that contains three functional elements: two CCAAT/enhancer-binding protein (C/EBP)-binding sites and a third site that interacts with a constitutively expressed transcription factor, SAA3 enhancer factor (SEF). Each of these binding sites as well as cooperation among their binding factors is necessary for maximum transcription activation by inflammatory cytokines. Deletion or site-specific mutations in the SEF-binding site drastically reduced SAA3 promoter activity, strongly suggesting that SEF is important in SAA3 promoter function. To further elucidate its role in the regulation of the SAA3 gene, we purified SEF from HeLa nuclear extracts to near homogeneity by using conventional liquid chromatography and DNA affinity chromatography. Ultraviolet cross-linking and Southwestern experiments indicated that SEF consisted of a single polypeptide with an apparent molecular mass of 65 kDa. Protein sequencing and antibody supershift experiments identified SEF as transcription factor LBP-1c/CP2/LSF. Cotransfection of SEF expression vector with SAA3-luciferase reporter resulted in approximately a 5-fold increase in luciferase activity. Interestingly, interleukin-1 treatment of SEF-transfected cells caused dramatic synergistic activation (31-fold) of the SAA3 promoter. In addition to its role in regulating SAA3 gene expression, we provide evidence that SEF could also bind in a sequence-specific manner to the promoters of the alpha(2)-macroglobulin and Aalpha-fibrinogen genes and to an intronic enhancer of the human Wilm's tumor 1 gene, suggesting a functional role in the regulation of these genes.

Neurophysiological changes associated with selective neuronal damage in hippocampus following transient forebrain ischemia

Neurophysiological changes of hippocampal neurons were compared before and after transient forebrain ischemia using intracellular recording and staining techniques in vivo. Ischemic depolarization (ID) was used as an indication of severe ischemia. Under halothane anesthesia, approximately 13 min of ID consistently produced severe neuronal damage in the CA1 region of rat hippocampus, while CA3 pyramidal neurons and dentate granule cells remained intact. After such severe ischemia, approximately 60% of the CA1 neurons exhibited a synaptic potentiation. The excitability of these neurons progressively decreased following reperfusion. Approximately 30% of the CA1 neurons showed a synaptic depression following ischemia. The excitability of these neurons transiently decreased following reperfusion. After ischemia of the same severity, both synaptic transmission and excitability of CA3 and granule cells transiently depressed. These data suggest that ischemia-induced synaptic potentiation may be associated with the pathogenesis of neuronal damage following ischemia, and that the synaptic depression may have protective effects on hippocampal neurons after ischemic insult.

Is carbonyl sulfide a precursor for carbon disulfide in vegetation and soil? Interconversion of carbonyl sulfide and carbon disulfide in fresh grain tissues in vitro

The interconversion of carbonyl sulfide (COS) and carbon disulfide (CS(2)) was studied in the roots and shoots of barley and chickpeas. Ratios of conversion gases, K, 40 h after the addition of COS or CS(2) are recorded. The proportion of COS converted to each of CS(2), CO, and H(2)S and the proportion of CS(2) converted to COS were greater in roots than in shoots. More COS was converted to CS(2) than CS(2) to COS in roots and shoots of barley and chickpeas. The amount of COS converted to H(2)S and CO was 8 times the amount converted to CS(2) in barley and 3-4 times the amount in chickpeas. Carbonyl sulfide may be a precursor for CS(2) in vegetation and soil, just as the reverse is true in the atmosphere. These two different results might form a cycle of COS and CS(2).

[Histology and physiological function of dogs after extirpation of bronchi]

OBJECTIVE

To investigate the effect of extirpation of bronchi on histology and physiological function.

METHODS

21 dogs were divided in to two groups: control (3) and experimental (18). After bronchi extirpation one week, two weeks, one month, three months, six months, and twelve months, we used specimens to test the pulmonary surfactant (PS) and to observe the morphological changes.

RESULTS

After the operation, the residual lung nearby the operative area had traumatic changes. Around the aforementioned area, the structure of lung was normal. Specially after six months, the lung returned to good status. We found that two weeks after operation, the contents of PS increased remarkably (P < 0.05). After one month the parameter returned to normal (P > 0.05).

CONCLUSIONS

The residual lung after bronchi extirpation had ventilation and air-exchange functions. The lung function was preserved directly.