PIP2 and ATP cooperatively prevent cytosolic Ca2+-induced modification of ATP-sensitive K+ channels in rat pancreatic beta-cells

The factors that influence functional coupling between the sulfonylurea receptor (SUR1) and Kir6.2 subunits of ATP-sensitive K+ (K+(ATP)) channels were studied in rat pancreatic beta-cells using patch clamp and microfluorometric techniques. Tolbutamide at 10 micromol/l inhibited K+(ATP) channels in association with occurrence of action currents, but further exposure of beta-cells to the drug for 30 min or longer resulted in reappearance of K+(ATP) channel events. Half-maximal inhibition concentration (IC50) for tolbutamide was 1.5 microl/mol in 2.8 mmol/l glucose, and it was increased to 13.3 micromol/l when the cellular metabolism was inhibited by 0.5 mmol/l 2,4-dinitrophenol (DNP) for 5 min. Tolbutamide at 10 micromol/l induced an increase in cytosolic Ca2+ concentration ([Ca2+]i), and its amplitude was markedly reduced following exposure to 0.5 mmol/l DNP or long-term (30 min) exposure to 10 micromol/l tolbutamide. This tolbutamide insensitivity, as assessed by the [Ca2+]i response, was not observed when the external Ca2+ was omitted during the long-term exposure to tolbutamide. In cell-attached membrane patches, the tolbutamide insensitivity was also produced by treatment of cells with 150 micromol/l diazoxide and 25 mmol/l KCl in the presence, but not absence, of 2 mmol/l Ca2+ in the external solution. When the cytoplasmic face of inside-out membrane patches was treated with higher Ca2+ concentrations (2 micromol/l), both ADP-evoked activation and tolbutamide-induced inhibition of K+ ATP channels were attenuated with retaining ATP-induced inhibition, indicating the modification of K+(ATP) channels. The Ca2+-induced channel modification was prevented partially by phosphatidylinositol 4,5-bisphosphate (PIP2) and completely by ATP and PIP2 together, but not by ATP alone. Treatment of the channel with cytochalasin D, a disrupter of F-actin, evoked channel modification similar to that induced by Ca2+. The modification was prevented completely by phalloidin, a stabilizer of F-actin. In conclusion, long-term exposure to tolbutamide or metabolic inhibition causes modification of K+ ATP channels via mechanisms involving Ca2+-dependent reaction. The modification, which may reflect functional disconnection between SUR1 and Kir6.2, is prevented by ATP and PIP2, which may act cooperatively to stabilize membrane cytoskeletons (F-actin structures).

[The effect of whole pleural cavity irradiation with combined 60Co and electron beam plus local biological agents on malignant pleural effusion]

BACKGROUND

To study the effect and complications of combined 60Co γ ray and electron beam irradiation to malignant pleural effusion.

METHODS

From January,1996 to December,1998,55 patients with malignant pleural effusion (unilateral; 49 cases of primary lung cancer,4 breast cancer and 2 thymic tumor) received whole pleural cavity irradiation of 60Co γ ray with centrally placed lead blocks to protect the vital organs and normal lung tissue,and the electron beam irradiation at the area which was covered by lead blocks in 60Co γ ray irradiation.The pleural effusion was completely drained before radiotherapy,and dose distribution of middle level was calculated by TPS using EXT 2.4 version software (Multidata Co.USA).The 100% isodose curve was 2Gy,15 fractions were given and another 20Gy/10Fx irradiation was added to the visible tumor.All patients received sequential chemotherapy for 3-6 cycles (cisplatin-based regimens for lung cancer and thymic tumor,cyclophosphamide and adriamycin and fluoracil for breast cancer).Kaplan-Meier curve was used to evaluate the pleural effusion control rate and survival rate of patients.

RESULTS

Complete remission of the malignant pleural effusion was seen in 9 patients and partial in 46 when treatment completed.The 6-,12-,18-month pleural effusion control rate and survival rate of the patients were 76%,53%,44% and 64%,34%,26%,respectively.The median control time of effusion and survival time were 14 months (2-32 months) and 9 months (4-32 months) respectively.We did not find any abnormality in liver function as well as in kidney function before and after treatment.Myelosuppression was the main side effect after combined chemotherapy and radiotherapy.Nineteen patients suffered from acute oesophagitis in grade 1-2,and 3 serious pleural fibrosis.There was no acute irradiation pneumonitis.

CONCLUSIONS

The treatment for malignant pleural effusion with combined 60Co γ ray and electron beam irradiation is tolerable and effective in clinical use.

P2Y-purinoceptor mediated inhibition of L-type Ca2+ channels in rat pancreatic beta-cells

We used the patch-clamp technique to study the effects of extracellular ATP on the activity of ion channels recorded in rat pancreatic beta-cells. In cell-attached membrane patches, action currents induced by 8.3 mM glucose were inhibited by 0.1 mM ATP, 0.1 mM ADP or 15 microM ADPbetaS but not by 0.1 mM AMP or 0.1 mM adenosine. In perforated membrane patches, action potentials were measured in current clamp, induced by 8.3 mM glucose, and were also inhibited by 0.1 mM ATP with a modest hyperpolarization to -43 mV. In whole-cell clamp experiments, ATP dose-dependently decreased the amplitudes of L-type Ca2+ channel currents (ICa) to 56.7+/-4.0% (p<0.001) of the control, but did not influence ATP-sensitive K+ channel currents observed in the presence of 0.1 mM ATP and 0.1 mM ADP in the pipette. Agonists of P2Y purinoceptors, 2-methylthio ATP (0.1 mM) or ADPbetaS (15 microM) mimicked the inhibitory effect of ATP on ICa, but PPADS (0.1 mM) and suramin (0.2 mM), antagonists of P2 purinoceptors, counteracted this effect. When we used 0.1 mM GTPgammaS in the pipette solution, ATP irreversibly reduced ICa to 58.4+/-6.6% of the control (p<0.001). In contrast, no inhibitory effect of ATP was observed when 0.2 mM GDPbetaS was used in the pipette solution. The use of either 20 mM BAPTA instead of 10 mM EGTA, or 0.1 mM compound 48/80, a blocker of phospholipase C (PLC), in the pipette solution abolished the inhibitory effect of ATP on ICa, but 1 microM staurosporine, a blocker of protein kinase C (PKC), did not. When the beta-cells were pretreated with 0.4 microM thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca2+ pump, ATP lost the inhibitory effect on ICa. These results suggest that extracellular ATP inhibits action potentials by Ca2+-induced ICa inhibition in which an increase in cytosolic Ca2+ released from thapsigargin-sensitive store sites was brought about by a P2Y purinoceptor-coupled G-protein, PI-PLC and IP3 pathway.

[Study on the determination of free iron oxide in soil extract by FIA-ICP-AES]

Free iron oxide in soil extract is determined by flow injection analysis-inductively coupled plasma-atomic emission spectrometry. The effects of the volume of the loading sample and the concentration of the extractants(NH2OH.HCl,H2C2O4) were investigated. When 50 microL sampling ring is selected and the concentration of two extractants is controlled under 10 mg.mL-1, sprayer nozzle is not blocked and feeding is smooth, the background interference is checked effectively as well. The recoveries of standard addition are 97.6%-100% with precision 2.3%-3.5% RSD(n = 5).

[Combined five tumor markers in detecting primary hepatic carcinoma]

OBJECTIVE

To increase the detection rate of primary hepatic carcinoma (PHC) and to diagnose PHC earlier.

METHODS

AFP was combined with r-glutamyle transpeptidase (r-GT), alpha-fucosidase (AFU), tumor necrosis factor-alpha (TNF-alpha) and DR-70.

RESULTS

The positive detection rate of PHC negative AFP with combined four markers was 9.4%. The total positive detection rate of PHC with combined five tumor markers reached 98.0% which was significantly higher than that with AFP (P < 0.01).

CONCLUSIONS

The positive detection rate of PHC can be increased by combined five tumor markers. It is helpful in diagnosing PHC earlier and can differentiate PHC from liver cirrhosis.

Requirement for B cell linker protein (BLNK) in B cell development

Linker proteins function as molecular scaffolds to localize enzymes with substrates. In B cells, B cell linker protein (BLNK) links the B cell receptor (BCR)-activated Syk kinase to the phosphoinositide and mitogen-activated kinase pathways. To examine the in vivo role of BLNK, mice deficient in BLNK were generated. B cell development in BLNK-/- mice was blocked at the transition from B220+CD43+ progenitor B to B220+CD43- precursor B cells. Only a small percentage of immunoglobulin M++ (IgM++), but not mature IgMloIgDhi, B cells were detected in the periphery. Hence, BLNK is an essential component of BCR signaling pathways and is required to promote B cell development.

Correction of defective protein trafficking of a mutant HERG potassium channel in human long QT syndrome. Pharmacological and temperature effects

The chromosome 7-linked form of congenital long QT syndrome (LQT2) is caused by mutations in the human ether-a-go-go-related gene (HERG) that encodes the rapidly activating delayed rectifier potassium channel. One mechanism for the loss of normal channel function in LQT2 is defective protein trafficking, which results in the failure of the channel protein to reach the plasma membrane. Here we show that the N470D LQT2 mutant protein is trafficking-deficient when expressed at 37 degrees C in HEK293 cells, whereas at 27 degrees C its trafficking to the plasma membrane and channel function are markedly improved. We further show that the antiarrhythmic drug E-4031, which selectively blocks HERG channels, also corrects defective protein trafficking of the N470D mutant and can restore the generation of HERG current. Similar findings were obtained with the drugs astemizole and cisapride, as well as with high concentrations of glycerol. The effect of E-4031 on HERG protein trafficking was concentration-dependent and required low drug concentrations (saturation present at 5 microM), developed rapidly with drug exposure, and occurred post-translationally. These findings suggest that protein misfolding leading to defective trafficking of some HERG LQT mutations may be corrected by specific pharmacological strategies.

[Experimental study on stimulation of guided bone regeneration by acid fibroblast growth factor]

OBJECTIVE

To investigate the effect of acid fibroblast growth factor (aFGF) on guided bone regeneration (GBR), to study whether aFGF can promote the repairing ability of GBR in bone defect.

METHODS

10 mm long segmental defects were created in the diaphyses of both radii in 16 New Zealand rabbits. The defect was bridged with a silicon tube. Human recombinant aFGF was instilled into the tube on the experimental side, while the contralateral tube was instilled with saline as control group. The radiographic, gross and histologic examination of the samples were analyzed at 2, 4, 6 and 8 weeks after operation.

RESULTS

On the experimental side, there was new bone formation in the bone medullary cavity, the endosteum and the section surface of the cortex at 2 weeks. At 4 weeks, at the center of the blood clot in the tube there was new bone formation and bone defect was completely healed at 8 weeks. On the control side, new bone formation was less in every period compared with that of the experimental side. At 8 weeks, there was only partial healing of the bone defect.

CONCLUSION

It can be concluded that aFGF can promote new bone formation and facilitate GBR in bone defect.

Migration and function of glia in the developing Drosophila eye

Although glial cells have been implicated widely in the formation of axon tracts in both insects and vertebrates, their specific function appears to be context-dependent, ranging from providing essential guidance cues to playing a merely facilitory role. Here we examine the role of the retinal basal glia (RBG) in photoreceptor axon guidance in Drosophila. The RBG originate in the optic stalk and have been thought to migrate into the eye disc along photoreceptor axons, thus precluding any role in axon guidance. Here we show the following. (1) The RBG can, in fact, migrate into the eye disc even in the absence of photoreceptor axons in the optic stalk; they also migrate to ectopic patches of differentiating photoreceptors without axons providing a continuous physical substratum. This suggests that glial cells are attracted into the eye disc not through haptotaxis along established axons, but through another mechanism, possibly chemotaxis. (2) If no glial cells are present in the eye disc, photoreceptor axons are able to grow and direct their growth posteriorly as in wild type, but are unable to enter the optic stalk. This indicates that the RBG have a crucial role in axon guidance, but not in axonal outgrowth per se. (3) A few glia close to the entry of the optic stalk suffice to guide the axons into the stalk, suggesting that glia instruct axons by local interaction.

Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole

INTRODUCTION

The selective H1-receptor antagonist astemizole (Hismanal) causes acquired long QT syndrome. Astemizole blocks the rapidly activating delayed rectifier K+ current I(Kr) and the human ether-a go-go-related gene (HERG) K+ channels that underlie it. Astemizole also is rapidly metabolized. The principal metabolite is desmethylastemizole, which retains H1-receptor antagonist properties, has a long elimination time of 9 to 13 days, and its steady-state serum concentration exceeds that of astemizole by more than 30-fold. A second metabolite is norastemizole, which appears in serum in low concentrations following astemizole ingestion and has undergone development as a new antihistamine drug. Our objective in the present work was to study the effects of desmethylastemizole, norastemizole, and astemizole on HERG K+ channels.

METHODS AND RESULTS

HERG channels were expressed in a mammalian (HEK 293) cell line and studied using the patch clamp technique. Desmethylastemizole and astemizole blocked HERG current with similar concentration dependence (half-maximal block of 1.0 and 0.9 nM, respectively) and block was use dependent. Norastemizole also blocked HERG current; however, block was incomplete and required higher drug concentrations (half-maximal block of 27.7 nM).

CONCLUSIONS

Desmethylastemizole and astemizole cause equipotent block of HERG channels, and these are among the most potent HERG channel antagonists yet studied. Because desmethylastemizole becomes the dominant compound in serum, these findings support the postulate that it becomes the principal cause of long QT syndrome observed in patients following astemizole ingestion. Norastemizole block of HERG channels is weaker; thus, the risk of producing ventricular arrhythmias may be lower. These findings underscore the potential roles of some H1-receptor antagonist metabolites as K+ channel antagonists.

Mechanism of block and identification of the verapamil binding domain to HERG potassium channels

Calcium channel antagonists have diverse effects on cardiac electrophysiology. We studied the effects of verapamil, diltiazem, and nifedipine on HERG K+ channels that encode IKr in native heart cells. In our experiments, verapamil caused high-affinity block of HERG current (IC50=143.0 nmol/L), a value close to those reported for verapamil block of L-type Ca2+ channels, whereas diltiazem weakly blocked HERG current (IC50=17.3 micromol/L), and nifedipine did not block HERG current. Verapamil block of HERG channels was use and frequency dependent, and verapamil unbound from HERG channels at voltages near the normal cardiac cell resting potential or with drug washout. Block of HERG current by verapamil was reduced by lowering pHO, which decreases the proportion of drug in the membrane-permeable neutral form. N-methyl-verapamil, a membrane-impermeable, permanently charged verapamil analogue, blocked HERG channels only when applied intracellularly. Verapamil antagonized dofetilide block of HERG channels, which suggests that they may share a common binding site. The C-type inactivation-deficient mutations, Ser620Thr and Ser631Ala, reduced verapamil block, which is consistent with a role for C-type inactivation in high-affinity drug block, although the Ser620Thr mutation decreased verapamil block 20-fold more than the Ser631Ala mutation. Our findings suggest that verapamil enters the cell membrane in the neutral form to act at a site within the pore accessible from the intracellular side of the cell membrane, possibly involving the serine at position 620. Thus, verapamil shares high-affinity HERG channel blocking properties with other class III antiarrhythmic drugs, and this may contribute to its antiarrhythmic mechanism.

Novel mechanism associated with an inherited cardiac arrhythmia: defective protein trafficking by the mutant HERG (G601S) potassium channel

BACKGROUND

The congenital long-QT syndrome (LQTS) is an inherited disorder characterized by a prolonged cardiac action potential and a QT interval that leads to arrhythmia. Mutations in the human ether-a-go-go-related gene (HERG), which encodes the rapidly activating component of the delayed rectifier current (IKr), cause chromosome 7-linked LQTS (LQT2). Studies of mutant HERG channels in heterologous systems indicate that the mechanisms mediating LQT2 are varied and include mutant subunits that form channels with altered kinetic properties or nonfunctional mutant subunits. We recently reported a novel missense mutation of HERG (G601S) in an LQTS family that we have characterized in the present work.

METHODS AND RESULTS

To elucidate the electrophysiological properties of the G601S mutant channels, we expressed these channels in mammalian cells and Xenopus oocytes. The G601S mutant produced less current than wild-type channels but exhibited no change in kinetic properties or dominant-negative suppression when coexpressed with wild-type subunits. To examine the cellular trafficking of mutant HERG channel subunits, enhanced green fluorescent protein tagging and Western blot analyses were performed. These showed deficient protein trafficking of the G601S mutant to the plasma membrane.

CONCLUSIONS

Our results from both the Xenopus oocyte and HEK293 cell expression systems and green fluorescent protein tagging and Western blot analyses support the conclusion that the G601S mutant is a hypomorphic mutation, resulting in a reduced current amplitude. Thus, it represents a novel mechanism underlying LQT2.

The netrin receptor frazzled is required in the target for establishment of retinal projections in the Drosophila visual system

Retinal axons in Drosophila make precise topographic connections with their target cells in the optic lobe. Here we investigate the role of the Netrins and their receptor Frazzled in the establishment of retinal projections. We find that the Netrins, although expressed in the target, are not required for retinal projections. Surprisingly, Frazzled, found on both retinal fibers and target cells, is required in the target for attracting retinal fibers, while playing at best a redundant role in the retinal fibers themselves; this finding demonstrates that target attraction is necessary for topographic map formation. Finally, we show that Frazzled is not required for the differentiation of cells in the target. Our data suggest that Frazzled does not function as a Netrin receptor in attracting retinal fibers to the target; nor does it seem to act as a homotypic cell adhesion molecule. We favor the possibility that Frazzled in the target interacts with a component on the surface of retinal fibers, possibly another Netrin receptor.

[An experimental investigation of inhibition of interferon on lens epithelial cell growth in vitro]

OBJECTIVE

To investigate the inhibition of alpha-interferon (alpha-IFN) and gamma-interferon (gamma-IFN) on rabbit lens epithelial cell (RLEC) proliferation in vitro and their effective concentrations.

METHODS

The second and third passage of RLEC were used for assay. Various concentrations of alpha-IFN or gamma-IFN were added into the culture medium and RLECs were exposed to these drugs. After 24 and 72 hours, the inhibition of RLECs was determined by counting the RLEC numbers on a counting plate and MTT colorimetric assay.

RESULTS

Alpha-IFN and gamma-IFN may reduce the proliferation of RLECs at the concentration of 10(3) - 10(4) IU/ml. The inhibition of gamma-IFN was a little stronger than that of alpha-IFN.

CONCLUSION

The experiment provides a scientific basis for selection of drugs to prevent after cataract.

Three dimensional MRI estimates of brain and spinal cord atrophy in multiple sclerosis

OBJECTIVE

The association between brain atrophy and permanent functional deficits in multiple sclerosis and the temporal relation between atrophy and the clinical disease course have seldom been investigated. This study aims to determine the amount of infratentorial and supratentorial atrophy in patients by comparison with healthy controls, to establish the relation between atrophy and disability, and to derive the rates of volume loss in individual patients from their estimated disease durations.

METHODS

Three dimensional acquired MRI was performed on 20 relapsing-remitting and 20 secondary progressive multiple sclerosis patients and 10 control subjects. Volume data on infratentorial and supratentorial structures were obtained using the Cavalieri method of modern design stereology in combination with point counting. Corpus callosal sectional area and "T2 lesion load" were also determined.

RESULTS

Significantly reduced infratentorial and cerebral white matter volumes and corpus callosal sectional areas occurred in all patients compared with controls (p=0.0001-0.004). Mean estimates of volume loss in the cohort were -21%, -19%, -46%, and -12% for the brain stem, cerebellum, upper cervical cord and white matter, respectively, and -21% for the corpus callosal sectional area. Analysis of the amount of atrophy (volume differences between patients and controls) showed that upper cervical cord and cerebral white matter atrophy correlated with the expanded disability status scale (r=-0.37 and -0.37, p=0.018-0.023) and the Scripps neurologic rating scale scores (r=+0.49 and +0.43, p=0.002-0.007). There was no relation between estimated volume loss in the supratentorial and infratentorial compartments. The "T2 lesion load" was associated with ventricular enlargement and corpus callosal atrophy (r=+0.50 and -0.55, p=0.0003-0.0012). Infratentorial atrophy rates correlated with baseline exacerbation rates (r=-0.50 to -0.48, p=0.0016-0.0021) and were higher in relapsing-remitting than secondary progressive patients (p=0.009-0.02).

CONCLUSIONS

Significant cerebral and spinal cord volume reductions occurred in both patient subgroups compared with controls. Functional correlates were found with estimated volume loss in the upper cervical cord and cerebral white matter. Particularly for infratentorial structures, estimated rates of atrophy were higher in relapsing-remitting than secondary progressive patients, suggesting that atrophy, perhaps mainly due to tract degeneration, begins early in multiple sclerosis and may relate predominantly to acute inflammatory events, with or without other gradual non-inflammatory processes later in the disease course.

Regulation of rat pyruvate carboxylase gene expression by alternate promoters during development, in genetically obese rats and in insulin-secreting cells. Multiple transcripts with 5'-end heterogeneity modulate translation

A previous study on the gene structure of rat pyruvate carboxylase revealed that two tissue-specific promoters are responsible for the production of multiple transcripts with 5'-end heterogeneity (Jitrapakdee, S., Booker, G. W., Cassady, A. I., and Wallace, J. C. (1997) J. Biol. Chem. 272, 20522-20530). Here we report transcription and translation regulation of pyruvate carboxylase (PC) expression during development and in genetically obese rats. The abundance of PC mRNAs was low in fetal liver but increased by 2-4-fold within 7 days after birth, concomitant with an 8-fold increase in the amount of immunoreactive PC and its activity and then decreased during the weaning period. Reverse transcriptase polymerase chain reaction analysis indicated that the proximal promoter was activated during the suckling period and reduced in activity at weaning. In genetically obese Zucker rats, adipose PC was 4-5-fold increased, concomitant with a 5-6-fold increase in mRNA level. Reverse transcriptase-polymerase chain reaction analysis also showed that the proximal promoter was activated in the hyperlipogenic condition. Conversely, transcription of the proximal promoter was not detectable in various liver cell lines, suggesting that this promoter was not functional under cell culture conditions. In rat pancreatic islets and insulinoma cells, only transcripts D and E, generated from the distal promoter of the PC gene, were expressed. Glucose increased PC transcripts from the distal promoter when the insulinoma cells were maintained in 10 mM glucose. We conclude that the proximal promoter of the rat PC gene plays a major role in gluconeogenesis and lipogenesis, whereas the distal promoter is necessary for anaplerosis. In vitro translation and in vivo polysome profile analysis indicated that transcripts C and E were translated with similar translational efficiencies that are substantially greater than that of transcript D, suggesting that 5'-untranslated regions play a role in translational control.

Solution structure of N-terminal segment of hepatitis B virus surface antigen Pre-S1

A synthetic peptide, the N-terminus of hepatitis B virus surface antigen Pre-S1, was studied by two-dimensional NMR techniques. A series of(1)H nuclear magnetic resonance experiments were used to complete the identification of spin systems and sequential assignments of this 28-residue peptide. 157 distance constraints and 55 dihedral angle constraints were obtained. 20 structures with the lowest target function were selected by the distance geometry program DIANA. Energy minimization and the following 100 ps time-averaged restrained molecular dynamics (TR-MD) simulation in aqueous solution were performed for each conformer. After TRMD simulation, three locally convergent regions corresponding to residues 22-31, 36-40, 41-46 were found. The averaged pairwise root-mean-square deviation (RMSD) of backbone atoms for them were (1.71+/-0.49)A, (0.76 +/-0.31)A, (1.05 +/- 0.52)A, respectively. Four reverse turns found in these regions, residues 22-25, 37-40, 41-44 and 43-46, correspond to several important antibody binding sites revealed in relevant immunological research.

HERG channel dysfunction in human long QT syndrome. Intracellular transport and functional defects

Mutations in HERG are associated with human chromosome 7-linked congenital long QT (LQT-2) syndrome. We used electrophysiological, biochemical, and immunohistochemical methods to study the molecular mechanisms of HERG channel dysfunction caused by LQT-2 mutations. Wild type HERG and LQT-2 mutations were studied by stable and transient expression in HEK 293 cells. We found that some mutations (Y611H and V822M) caused defects in biosynthetic processing of HERG channels with the protein retained in the endoplasmic reticulum. Other mutations (I593R and G628S) were processed similarly to wild type HERG protein, but these mutations did not produce functional channels. In contrast, the T474I mutation expressed HERG current but with altered gating properties. These findings suggest that the loss of HERG channel function in LQT-2 mutations is caused by multiple mechanisms including abnormal channel processing, the generation of nonfunctional channels, and altered channel gating.

In vivo expression of an alternatively spliced human tumor message that encodes a truncated form of cathepsin B. Subcellular distribution of the truncated enzyme in COS cells

Cathepsin B is a lysosomal cysteine protease whose increased expression is believed to be linked to the malignant progression of tumors. Alternative splicing and the use of alternative transcription initiation sites in humans produce cathepsin B mRNAs that differ in their 5'- and 3'-untranslated ends. Some human tumors also contain cathepsin B-related transcripts that lack exon 3 which encodes the N-terminal signal peptide and 34 of the 62-amino acid inhibitory propeptide. In this study we show that one such transcript, CB(-2,3), which is missing exons 2 and 3, is likely to be a functional message in tumors. Thus, CB(-2,3) was found to be otherwise complete, containing the remainder of the cathepsin B coding sequence and the part of the 3'-untranslated region that is common to all previously characterized cathepsin B mRNAs in humans. Its in vitro translation product can be folded to produce enzymatic activity against the cathepsin B-specific substrate, Nalpha-benzyloxycarbonyl-L-Arg-L-Arg-4-methylcoumaryl-7-amide. Endogenous CB(-2,3) from the metastatic human melanoma cell line, A375M, co-sediments with polysomes, indicating that it engages the eukaryotic translation machinery in these cells. Epitope-tagged forms of the truncated cathepsin B from CB(-2,3) are produced in amounts comparable to the normal protein after transient transfection into COS cells. Immunofluorescence microscopy and subcellular fractionation show this novel tumor form of cathepsin B to be associated with nuclei and other membranous organelles, where it is likely to be bound to the cytoplasmic face of the membranes. This subcellular distribution was different from the lysosomal pattern shown by the epitope-tagged, full-length cathepsin B in COS cells. These results indicate that the message missing exons 2 and 3 is likely to be translated into a catalytically active enzyme, and that alternative splicing (exon skipping) could contribute to the aberrant intracellular trafficking of cathepsin B that is observed in some human cancers.

[The processing of Gekko gecko and the pharmacological action of its different parts]

Both pharmacologic and toxic experiments are made on different parts of Gekko gecko Linnaeus. The results show that Gekko gecko Linnaeus' heads and its feet have obvious pharmacological action without any toxic or side effects, which provides a sound basis for the increase in its clinical utilization and the expansion of its medicinal parts as well as guarantee of safety and effectiveness after taking the medicine.

[Mechanism and treatment of malignant glaucoma]

OBJECTIVE

To investigate the possible mechanism and the treatment of malignant glaucoma.

METHODS

The onsets of 34 eyes in 23 cases of malignant glaucoma were analyzed and the patients were treated with medicine, lens extraction, vitrectomy, anterior chamber plastic operation or combined procedures.

RESULTS

The effective rate in medical treatment was 35.3%. Combined procedures (lens extraction associated with vitrectomy and anterior chamber plastic operation) were all successful.

CONCLUSIONS

The possible mechanism of malignant glaucoma may be concerned with the formation of membranoid substance among vitreous face, ciliary body and posterior iris. Those who failured to medical therapy and were treated with combined operations may have good effect.

Properties of HERG channels stably expressed in HEK 293 cells studied at physiological temperature

We have established stably transfected HEK 293 cell lines expressing high levels of functional human ether-a go-go-related gene (HERG) channels. We used these cells to study biochemical characteristics of HERG protein, and to study electrophysiological and pharmacological properties of HERG channel current at 35 degrees C. HERG-transfected cells expressed an mRNA band at 4.0 kb. Western blot analysis showed two protein bands (155 and 135 kDa) slightly larger than the predicted molecular mass (127 kDa). Treatment with N-glycosidase F converted both bands to smaller molecular mass, suggesting that both are glycosylated, but at different levels. HERG current activated at voltages positive to -50 mV, maximum current was reached with depolarizing steps to -10 mV, and the current amplitude declined at more positive voltages, similar to HERG channel current expressed in other heterologous systems. Current density at 35 degrees C, compared with 23 degrees C, was increased by more than twofold to a maximum of 53.4 +/- 6.5 pA/pF. Activation, inactivation, recovery from inactivation, and deactivation kinetics were rapid at 35 degrees C, and more closely resemble values reported for the rapidly activating delayed rectifier K+ current (I(Kr)) at physiological temperatures. HERG channels were highly selective for K+. When we used an action potential clamp technique, HERG current activation began shortly after the upstroke of the action potential waveform. HERG current increased during repolarization to reach a maximum amplitude during phases 2 and 3 of the cardiac action potential. HERG contributed current throughout the return of the membrane to the resting potential, and deactivation of HERG current could participate in phase 4 depolarization. HERG current was blocked by low concentrations of E-4031 (IC50 7.7 nM), a value close to that reported for I(Kr) in native cardiac myocytes. Our data support the postulate that HERG encodes a major constituent of I(Kr) and suggest that at physiological temperatures HERG contributes current throughout most of the action potential and into the postrepolarization period.

Blockage of the HERG human cardiac K+ channel by the gastrointestinal prokinetic agent cisapride

Cisapride, a gastrointestinal prokinetic agent, is known to cause long Q-T syndrome and ventricular arrhythmias. The cellular mechanism is not known. The human ether-á-go-go-related gene (HERG), which encodes the rapidly activating delayed rectifier K+ current and is important in cardiac repolarization, may serve as a target for the action of cisapride. We tested the hypothesis that cisapride blocks HERG. The whole cell patch-clamp recording technique was used to study HERG channels stably expressed heterologously in HEK293 cells. Under voltage-clamp conditions, cisapride block of HERG is dose dependent with a half-maximal inhibitory concentration of 6.5 nM at 22 degrees C (n = 25 cells). Currents rapidly recovered with drug washout. The onset of block by cisapride required channel activation indicative of open or inactivated state blockage. Block of HERG with cisapride after channel activation was voltage dependent. At -20 mV, 10 nM cisapride reduced HERG tail-current amplitude by 5%, whereas, at + 20 mV, the tail-current amplitude was reduced by 45% (n = 4 cells). At -20 and + 20 mV, 100 nM cisapride reduced tail-current amplitude by 66 and 90%, respectively. We conclude that cisapride is a potent blocker of HERG channels expressed in HEK293 cells. This effect may account for the clinical occurrence of Q-T prolongation and ventricular arrhythmias observed with cisapride.

Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase

The Syk family of protein tyrosine kinases, consisting of ZAP-70 and Syk, associate with the pre- and alphabeta T cell antigen receptors (TCRs) and undergo tyrosine phosphorylation and activation following receptor engagement. Thymocyte development in zap-70-/- mice is blocked at the CD4+CD8+ TCR(lo) stage. The presence of Syk in the thymus has raised the possibility that Syk may be able to mediate TCR function. To determine if Syk can play a role in thymocyte development, we generated zap-70-/- mice expressing a human syk cDNA. Syk expression restored both thymocyte development and function. In addition, Syk function required the CD45 transmembrane protein tyrosine phosphatase. Hence, ZAP-70 and Syk can play overlapping functions and exhibit similar regulatory mechanisms in mediating alphabeta T cell development.

Effect of thiols on cadmium-induced expression of metallothionein and other oxidant stress genes in rat lung epithelial cells

This study examined cadmium-induced alterations in metallothionein-1 (MT), glutathione-S-transferase Ya (GST), and heme oxygenase-1 (HO) gene expression in an adult rat lung epithelial cell line. Elevations in MT mRNA and HO mRNA occurred as early as 1 h after exposure to a sub-toxic concentration of CdCl(2) (10 microM) whereas GST expression did not increase significantly until 4 h after Cd addition. At t = 8 h, levels of GST, MT, and HO mRNA were elevated 9-fold, 27-fold, and 44-fold, respectively, over basal expression. By 24 h, MT expression was almost back to baseline levels. GST mRNA and HO mRNA were also reduced, compared to 8 h, but to a lesser extent than MT expression. The MT gene was more responsive to low Cd concentrations (5 microM) than the genes for HO or GST whereas HO was induced more than the others at higher Cd doses (10-20 microM). Pro-oxidant conditions play a role in Cd-induced gene expression, as suggested by the rapid decline (15-30 min) in glutathione (GSH), amounting to 25-30% of baseline, that occurred after exposure to 10 microM CdCl(2). This was followed by resynthesis of GSH to a concentration higher than the initial. Depleting GSH by treatment of cells with buthionine sulfoximine (BSO) enhanced Cd-induced expression of MT, GST, and HO whereas thiol supplementation, by treatment with N-acetyl cysteine (NAC), had an attenuating effect. BSO and NAC pretreatment had no effect on basal gene expression or Cd uptake. In summary, this study has shown that: (1) Cd increases MT, GST, and HO gene expression in a time- and dose-dependent fashion: (2) MT gene expression appears to be most sensitive to Cd whereas the HO gene is most inducible at higher Cd concentrations; (3) Cd-induced expression is enhanced by GSH depletion and suppressed by thiol supplementation.

Olfactory epithelial organotypic slice cultures: a useful tool for investigating olfactory neural development

An in vitro slice culture was established for investigating olfactory neural development. The olfactory epithelium was dissected from embryonic day 13 rats; 400 microns slices were cultured for 5 days in serum-free medium on Millicell-CM membranes coated with different substrates. The slices were grown in the absence of their appropriate target, the olfactory bulb, or CNS derived glia. The cultures mimic many features of in vivo development. Cells in the olfactory epithelium slices differentiate into neurons that express olfactory marker protein (OMP). OMP-positive cells have the characteristic morphology of olfactory receptor neurons: a short dendrite and a single thin axon. The slices support robust axon outgrowth. In single-label experiments, many axons expressed neural specific tubulin, growth-associated protein 43 and OMP. Axons appeared to grow equally well on membranes coated with type I rat tail collagen, laminin or fibronectin. The cultures exhibit organotypic polarity with an apical side rich in olfactory neurons and a basal side supporting axon outgrowth. Numerous cells migrate out of the slices, of which a small minority was identified as neurons based on the expression of neural specific tubulin and HuD, a nuclear antigen, expressed exclusively in differentiated neurons. Most of the migrating cells, however, were positive for glial fibrillary acidic protein and S-100, indicating that they are differentiated glia. A subpopulation of these glial cells also expressed low-affinity nerve growth factor receptors, indicating that they are olfactory Schwann cells. Both migrating neurons and glia were frequently associated with axons growing out of the slice. In some cases, axons extended in advance of migrating cells. This suggests that olfactory receptor neurons in organotypic cultures require neither a pre-established glial/neuronal cellular terrain nor any target tissue for successful axon outgrowth. Organotypic olfactory epithelial slice cultures may be useful for investigating cellular and molecular mechanisms that regulate early olfactory development and function.

Pulmonary metallothionein expression in rats following single and repeated exposure to cadmium aerosols

This study examined the expression of metallothionein (MT) isoforms in the lungs of Lewis rats exposed to Cadmium (Cd) aerosols. With the use of isoform-specific oligonucleotide probes and Northern hybridization analysis, we demonstrated that a dramatic, rapid, and coordinate increase occurred in pulmonary MT-1 mRNA and MT-2 mRNA following Cd inhalation exposure. MT mRNAs levels reached a maximum at 2 h post-exposure and remained above control levels at 96 h after exposure. A considerable lag between the time of maximal elevations in MT mRNAs and MT protein accumulation was observed and suggested that regulatory mechanisms in addition to transcriptional control could be involved. MT expression (protein and mRNA) and Cd lung burden were directly related to aerosol Cd concentration. In situ hybridization and immunohistochemistry studies showed good correlation between the localization of MT protein and MT mRNAs. However, staining for MT protein and MT mRNA was not uniformly distributed in the lung. MT was particularly prominent within the alveolar compartment. Even within this area, however, heterogeneity of MT expression was evident. Experiments were subsequently conducted to determine whether prior exposure to Cd modulates the transcriptional activity of MT genes such that there is a greater elevation in gene expression upon reexposure to Cd. Surprisingly, animals pretreated with Cd exhibited a smaller incremental increase in MT mRNA levels in response to subsequent Cd exposure than controls with no prior treatment. Moreover, MT mRNA levels were elevated to a similar extent regardless of whether animals were exposed to Cd aerosols for 1, 2, or 3 weeks (3 h/day; 5 days/week). MT protein and lung Cd burden, on the other hand, exhibited an increasing linear trend as a function of exposure number. In summary, this study has demonstrated that: (1) the lung responds to Cd inhalation exposure by increasing MT mRNA and MT protein levels; (2) MT expression is prominent within alveolar cells but not all cells are MT positive; and (3) Cd-pretreatment does not increase the transcriptional potential of MT genes when the animal is subsequently reexposed to Cd.

Modulation of human muscle sodium channels by intracellular fatty acids is dependent on the channel isoform

Free fatty acids (FFAs), including arachidonic acid (AA), are implicated in the direct and indirect modulation of a spectrum of voltage-gated ion channels. Skeletal muscle sodium channels can be either activated or inhibited by FFA exposure; the response is dependent on both FFA structure and site of exposure. Recombinant human skeletal muscle sodium channels (hSkM1) were transfected into heterologous human renal epithelium HEK293t cells. Cytoplasmic delivery of 5 microM AA augmented the voltage-activated sodium current of hSkM1 channels by 190% (+/-54 S.E., n = 7) over a 20-min period. Similar results were seen with 5 microM oleic acid. Sodium currents in HEK293t cells transfected with human cardiac muscle sodium channels (hH1) were insensitive to AA treatment, and exposure to oleic acid inhibited the hH1 currents over a 20-min period by 29% (+/-13 S.E., n = 5). The increase in hSkM1 current was not accompanied by shifts in voltage dependence of activation, steady-state inactivation, or markedly altered kinetics of inactivation of the macroscopic current. The FFA-induced increase in sodium currents was not dependent on protein kinase C activity. In contrast, both isoforms were reversibly inhibited by external application of unsaturated FFA. Thus, the differential effects of FFA on skeletal muscle sodium channels first noted in cultured muscle cells can be reproduced by expressing recombinant sodium channels in epithelial cells. Although the responses to applied FFAs could be direct or indirect, we suggest that: 1) SkM1 has two classes of response to FFA, one which produces augmentation of macroscopic currents with intracellular FFA, and a second which produces inhibition with extracellular FFA; 2) H1 has only one class of response, which produces inhibition with extracellular FFA. A testable hypothesis is that the presence or absence of each response is due to a specific structure in SkM1 or H1. These specific structures may directly interact with FFA or may interact with intermediate components.

The role of prohormone convertases in insulin biosynthesis: evidence for inherited defects in their action in man and experimental animals

The hormone insulin remains the cornerstone of diabetic therapy since it is required for almost all cases of Type 1 and many cases of Type 2 diabetes. Since the discovery of insulin in 1921, much has been learned about its chemistry, structure and action as well as its production in the beta cell. Insulin is formed through a series of precursors, beginning with preproinsulin, the protein encoded in the insulin gene. These precursors direct the prohormone into the secretory pathway and ultimately into the secretory granules where it is converted into insulin and C-peptide. These products are stored and secreted together in a highly regulated manner in response to glucose and other stimuli. This review focuses on the recently discovered prohormone convertases, PC2 and PC3 (PC1), the enzymes responsible for the endoproteolytic processing of proinsulin to insulin and C-peptide in the beta cell as well as for the selective processing of proglucagon to glucagon in the alpha cell or GLP1 in intestinal L-cells. PC2 and PC3 are calcium-dependent serine proteases related to the bacterial enzyme subtilisin. They cleave selectively at Lys-Arg or Arg-Arg sites in precursors, generating products with C-terminal basic residues that are then removed by carboxypeptidase E, an exopeptidase. All 3 enzymes are expressed mainly in secretory granules of neuroendocrine cells throughout the body and in the brain. Inherited defects affecting the prohormone-processing enzymes have recently been found in association with unusual syndromes of obesity and other metabolic disorders.

Increased oxidant resistance of alveolar macrophages isolated from rats repeatedly exposed to cadmium aerosols

This study investigated potential mechanisms of oxidant resistance in alveolar macrophages (AM) isolated from Lewis rats exposed repeatedly to cadmium aerosols. Macrophages from Cd-adapted animals significantly greater resistance to oxidant-induced cytotoxicity than control cells when challenged with hydrogen peroxide in vitro. Elevations in glutathione peroxidase and glutathione reductase activities were associated with increased oxidant tolerance but catalase activity was unchanged. Metallothionein (MT) expression (protein and mRNA) was dramatically up-regulated in response to in vivo Cd exposure. A study using immunocytochemistry and in situ hybridization techniques revealed significantly heterogeneity in the expression of metallothionein by AMs. The percentage of AMs positive for MT (protein and mRNA) and the degree of MT expression within individual cells increased in response to additional Cd exposures. A putative state of activation was suggested by differences in size and number of inclusion bodies in macrophages from Cd-adapted animals and by secretion of a cytokine with interleukin-1-like characteristics. In summary, AMs from Cd-adapted animals are distinguished from control cells with respect to: (1) increased oxidant resistance, (2) secretion of cytokines, (3) elevations in enzymes associated with glutathione metabolism, and (4) up-regulation in metallothionein expression.

Expression of extracellular matrix molecules and cell surface molecules in the olfactory nerve pathway during early development

The spatial and temporal expression patterns of several extracellular matrix molecules--laminin and fibronectin and cell surface molecules, neural cell adhesion molecule (NCAM), L1, tenascin, chondroitin sulfate proteoglycan, and peanut agglutinin (PNA) binding sites--were investigated during early olfactory nerve development. NCAM and L1 have similar patterns: They are expressed in the olfactory nerve and on the olfactory receptor neurons (ORNs) commencing with the earliest olfactory axon outgrowth (E12-E15). Their expression patterns suggest that both NCAM and L1 are associated with extension and fasciculation of olfactory axons. A comparison of L1 and olfactory marker protein suggests that L1 is expressed predominantly on immature ORNs. Laminin has an unique punctate staining pattern in the developing olfactory pathway as early as E12. These laminin puncta might play a role in olfactory neurite outgrowth and guidance. At E14, when pioneer olfactory axons enter the brain, the laminin-positive meninges on the surface of the olfactory bulb primordium break down but remain intact in the rest of the telencephalon. This suggests a functional interaction between the olfactory axons and the glial-pial barrier. Fibronectin staining is diffuse throughout the cranial mesenchyme but is absent from the olfactory nerve pathway. No specific patterns of tenascin or chondroitin sulfate, were observed during early olfactory development. PNA binding sites were associated with olfactory axon fasciculation. The expression of several extracellular matrix molecules and cell surface molecules is spatially and temporally regulated in the developing olfactory system. These molecules, thus, may play functional roles in olfactory axon outgrowth, fasciculation, and/or guidance.

Increased oxidant resistance of alveolar epithelial type II cells. Isolated from rats following repeated exposure to cadmium aerosols

Alveolar epithelial type II cells (AEIIC) were isolated from male Lewis rats following repeated in vivo cadmium aerosol exposure and were subsequently evaluated for their oxidant resistance in vitro. AEIIC from Cd-adapted animals removed a greater proportion of hydrogen peroxide from the extracellular milieu and incurred less oxidant-induced cytotoxicity than AEIIC from air controls. This altered response to oxidants occurred coincident with changes in cellular resistance factors. A two-fold increase in glutathione peroxidase activity and a 1.5-fold increase in the activities of glutathione reductase and catalase were observed in Cd-adapted AEIIC compared to control cells. These cells also exhibited a dramatic induction of metallothionein (MT), a thiol-rich protein known to scavenge free radicals in vitro. MT concentration increased as a function of exposure number. MT was localized within the nucleus and cytoplasm of AEIIC by immunocytochemical techniques. MT positive cells showed a wide variation of MT content, particularly in the nucleus. The biochemical and physiological features of these AEIIC may explain, in part, why animals pretreated with Cd aerosols develop cross-tolerance to hyperoxia.

Proteolytic processing mechanisms in the biosynthesis of neuroendocrine peptides: the subtilisin-like proprotein convertases

The recent discovery of a novel family of precursor processing endoproteases has greatly accelerated progress in understanding the complex mechanisms underlying the maturation of prohormones, neuropeptides, and many other precursor-derived proteins. At least six members of this family have been found thus far in mammalian species, several having alternatively spliced isoforms, and related enzymes have been identified in many invertebrates, including molluscs, insects, nematodes, and coelenterates. The proprotein convertases are all dependent on calcium for activity and all possess highly conserved subtilisin-like domains with the characteristic catalytic triad of this serine protease (ordered Asp, His, and Ser along the polypeptide chain). Two members of this family, PC2 (SPC2) and PC1/PC3 (SPC3), appear to play a preeminent role in neuroendocrine precursor processing. Both convertases are expressed only in the brain and in the extended neuroendocrine system, while another important family member--furin/PACE (SPC1)--is expressed more ubiquitously, in almost all tissues, and at high levels in liver. SPC2 and SPC3 exhibit acidic pH optima and other properties which enhance their activity in the acidic, calcium-enriched environment of the dense-core secretory granules of the regulated pathway in neuroendocrine cells, while furin has a neutral pH optimum and is localized predominantly to the trans Golgi network where it is retained by a C-terminal transmembrane domain. Furin processes a wide variety of precursors in the constitutive pathway, such as those of growth factors, receptors, coagulation factors, and viral glycoproteins. Recent findings on the processing of proopiomelanocortin, proinsulin, proglucagon, and several other neuroendocrine precursors by SPC2 and SPC3 are discussed, along with information on the structure, properties, evolution, developmental expression, and regulation of the convertases. An inherited defect in the fat/fat mouse which affects the processing of proinsulin, and probably also many other prohormones, due to a point mutation in carboxypeptidase E has recently been identified and has begun to provide new insights into the functional integration of the individual processing steps.

Synergistic effects of growth factors on the regulation of smooth muscle cell scavenger receptor activity

Rabbit smooth muscle cells (SMC) express types I and II scavenger receptors (ScR) that are up-regulated by platelet secretion products. In the current studies we investigated the effect of growth factors secreted by platelets on ScR activity in rabbit and human SMC. Platelet-derived growth factor (PDGF BB) and transforming growth factor beta 1 (TGF-beta 1) at 10 ng/ml increased ScR activity in rabbit SMC (by approximately 4- and 2-fold, respectively) but not in human SMC. Epidermal growth factor (EGF) or insulin-like growth factor I (IGF-I) alone had little effect on SMC ScR activity. The growth factors had synergistic effects on ScR activity and on types I and II ScR mRNA expression. In rabbit SMC, PDGF BB, EGF, and TGF-beta 1 together stimulated ScR activity 12-fold. In human SMC, EGF and TGF-beta 1, together with either IGF-I or PDGF BB, stimulated receptor activity approximately 7-fold. Growth factor-mediated induction of ScR activity in rabbit and human SMC was blocked by the tyrosine kinase inhibitor tyrphostin 47, whereas the induction of ScR activity in rabbit but not human SMC was blocked by the protein kinase C inhibitor MDL.29,152. Studies using neutralizing antibodies demonstrated that TGF-beta 1 is the predominant factor in in vitro preparations of platelet secretory products which regulates ScR activity. The growth factors that act synergistically in regulating ScR activity in vitro are all present in atherosclerotic lesions, where they are produced by macrophages, endothelial cells, SMC, and platelets. The data suggest that these growth factors may regulate ScR activity in SMC in vivo and contribute to foam cell formation.

In vivo expression of metallothionein in rat alveolar macrophages and type II epithelial cells following repeated cadmium aerosol exposures

This study examined the ability of alveolar macrophages and alveolar type II epithelial cells to accumulate cadmium (Cd) and to express metallothionein (MT). Lung cells were isolated from Lewis rats repeatedly exposed to a Cd aerosol (1.6 mg Cd/m3). Intracellular Cd concentration rose following Cd exposure and showed an increasing rend as a function of exposure number. Alveolar macrophages accrued approximately four times more Cd than type II epithelial cells similarly exposed. Macrophages and type II cells responded to the presence of intracellular Cd by increasing MT protein levels. MT concentration was highly correlated with intracellular Cd. Immunocytochemical studies revealed that not all macrophages and type II cells from Cd-exposed animals were immunopositive for MT and that the intensity of immunostaining varied within each cell population. Although a greater percentage of macrophages were immunopositive for MT than type II cells, a greater proportion of type II cells showed moderate and dark MT staining patterns. Oligonucleotide probes, shown to distinguish between MT-1 and MT-2 mRNA isoforms, were used to test for cell-specific differences in MT isoform gene expression. The basal level of MT-1 mRNA was greater in macrophages than in type II cells. Following Cd administration, the level of MT-1 mRNA and MT-2 mRNA increased in each cell class but the response to Cd was three times greater in alveolar macrophages. Neither macrophages nor type II cells expressed MT mRNA isoforms in equal proportions. Macrophages expressed more MT-1 mRNA when exposed to air and more MT-2 mRNA in response to Cd exposure. Type II cells, on the other hand, expressed more MT-2 mRNA than MT-1 mRNA regardless of whether the cells were exposed to air or Cd. In conclusion, the present study has demonstrated that (1) alveolar macrophages and type II cells respond to in vivo Cd exposure by increasing MT protein and mRNA levels; (2) MT expression is greater in macrophages than in type II cells and correlates well with intracellular Cd concentration; and (3) the MT-2 mRNA to MT-1 mRNA ratio is cell and treatment specific.

Molecular modeling of the substrate specificity of prohormone convertases SPC2 and SPC3

In this paper we describe the results of molecular modeling of the structures of the active sites of two subtilisin-like prohormone convertases (SPCs), SPC2 (PC2) and SPC3 (PC1/PC3). These enzymes are members of a recently discovered family of cellular proteases involved in the processing of precursor proteins. Although these proteases all possess catalytic domains similar to the bacterial subtilisins no tertiary structural data from x-ray analysis are yet available. We have shown that despite the high structural homology of the subtilisins and the SPCs, the structure of the loop which lies immediately below the active sites differs due to the presence of a cis-peptide bond (Tyr167-Pro168) in this loop in the subtilisins and its absence in the SPCs. Accordingly, we have proposed a new alignment for the amino acid sequences of the SPCs in this region. Both SPC2 and SPC3 participate in the processing of prohormones at dibasic cleavage sites, typically Lys-Arg or Arg-Arg. To investigate the structural basis of the substrate specificity of these SPCs, we have carried out molecular mechanic calculations of the optimal arrangement and interactions of peptide substrates containing several residues of arginine or lysine, i.e. Arg, Ala-Ala-Ala-Arg, Arg-Ala-Ala-Arg, Arg-Ala-Arg-Arg, Arg-Ala-Lys-Arg, in the putative active sites. Such subtilisin-based modeling has allowed us to identify those negatively charged residues, Asp and Glu, in the S1, S2, and S4 subsites, which can directly interact with basic residues in the substrates via formation of salt bridges and thereby contribute to the substrate selectivity of the SPCs.

Interaction of retinoblastoma gene product with transcription factors ATFa and ATF2

Two highly related transcription factors, activating transcription factors a and 2 (ATFa and ATF2) are able to activate expression in CHO cells of a reporter gene driven by the human transforming growth factor beta 2 gene promoter. This action is dependent on the intact motif CGTCA which is found as part of the cAMP responsive element in a number of promoters and to which both factors can bind in vitro. The retinoblastoma gene product also weakly stimulates expression of this reporter gene but, in combination with the factors, it exhibits a differential action: additive or greater stimulatory effects with ATF2 but strong inhibition of the actions of ATFa. Thus, although both of these two related factors are able to exert the same apparent effect on this promoter, coexpression of the retinoblastoma gene product reveals at least one significant difference in their actions.

Evidence that pioneer olfactory axons regulate telencephalon cell cycle kinetics to induce the formation of the olfactory bulb

Early olfactory axons follow a specific pathway to reach the developing telencephalon. We observed that a subpopulation of these axons, the pioneer olfactory axons, penetrate into the ventricular zone of a highly restricted region of the telencephalon at E13 and E14. At E15, this same telencephalic region evaginates to form the olfactory bulb. To investigate the possibility that the pioneer olfactory axons induce the olfactory bulb by influencing precursor cell populations, we compared cell cycle kinetics and differentiation in the olfactory bulb primordium and the adjacent neocortex using cumulative bromdeoxyuridine labeling. The results showed that, 24 hr after the arrival of the first pioneer axons, the duration of the cell cycle is prolonged significantly in the olfactory bulb primordium. In addition, twice as many cells have exited the mitotic cycle in the olfactory bulb primordium versus the adjacent cortex. These findings suggest that pioneer olfactory axons play a role in the induction of the olfactory bulb by selectively modulating cell cycle kinetics in the olfactory bulb primordium. Afferent axons may influence target morphogenesis by modulating target precursor cell proliferation in other developing neural structures.

Localization and regulation of low affinity nerve growth factor receptor expression in the rat olfactory system during development and regeneration

Nerve growth factor (NGF), a classic neurotrophic factor, promotes neuronal survival, maintenance, regeneration and differentiation in the peripheral nervous system and parts of the central nervous system. NGF activity is mediated by cell surface bound receptors including the low affinity NGF receptor (LNGFr) which is expressed by some peripheral and central neurons and is present on peripheral nerve Schwann cells during development and regeneration. The olfactory system is a useful model for the study of the role of LNGFr in neuronal development and regeneration. The growth of olfactory axons into the brain begins in the embryo and continues through the first few postnatal weeks. In mature animals there is persistent turnover and generation of olfactory receptor neurons (ORNs) and continuous growth of new axons into the olfactory bulb. These new axons grow along the preexisting olfactory pathway. In the mature olfactory system, LNGFr has been observed in the glomerular layer of the olfactory bulb, the target of ORNs. However, neither the cellular localization nor the developmental expression of LNGFr has been characterized. Here, we tested the hypothesis that LNGFr expression is developmentally regulated in the olfactory nerve and is reinduced following injury to the mature olfactory nerve. LNGFr-immunoreactivity (IR) was first observed in the olfactory mucosa at embryonic day (E)13 and in the olfactory nerve at E14. LNGFr-IR increased in the nerve during embryonic development, began to decrease at around postnatal day (P)5 and was scarcely detectable in normal adults. The staining pattern suggests that LNGFr is located on the olfactory nerve Schwann cells. Streaks of LNGFr-IR were present in the adult olfactory nerve. We reasoned that these streaks might represent transient reexpression of LNGFr associated with normal olfactory neuron turnover and replacement. Consistent with this hypothesis, LNGFr was robustly reexpressed in the adult olfactory nerve following lesion of the olfactory epithelium. Starting late in development (E21) and in the adult, LNGFr-IR was also observed on fibers in deep layers of the olfactory bulb. LNGFr-IR was also observed in neurons of the nucleus of the diagonal band (NDB) in the basal forebrain. NDB is the sole source of cholinergic afferents of the olfactory bulb. Thus, we tested the hypothesis that LNGFr in the deep layers of the olfactory bulb is located on NDB axons by making lesions of NDB. Following the lesion, LNGFr-IR disappeared in the deep layers of the olfactory bulb but remained in the glomerular layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Single- and double-label immunocytochemical study of the ovine suprachiasmatic nucleus (SCN): GABAergic and peptidergic relationships

This study evaluated the neuropeptide and neurotransmitter content of the ovine suprachiasmatic nucleus (SCN) using both single- and double-label immunocytochemical methods. Single-label immunocytochemistry identified a few lightly labeled gamma aminobutyric acid (GABA) cells within the SCN as well as a dense plexus of fibers staining positive for the GABA biosynthetic enzyme, glutamic acid decarboxylase (GAD). Vasoactive intestinal polypeptide (VIP) fibers exhibited a similar distribution to GAD fibers; VIP cells were found throughout the SCN, as well as in the paraventricular (PVN) and supraoptic nuclei. Both GAD and VIP fibers exited dorsally from the SCN towards the PVN. Neurophysin (NP) and neuropeptide-Y (NPY) fibers were sparsely distributed throughout the SCN. Double-label immunocytochemistry revealed that GAD varicosities were often in close apposition to VIP cells. These results confirm the presence of GABAergic elements within the sheep SCN. Furthermore, they raise the possibility of a GABAergic modulation of VIP neuronal activity within the ovine SCN.

[Effect of arginine on lymphocyte responses to ConA in burned mice]

It is well accepted that nutritional support improves the immunologic functions in burned patients. Arginine has been demonstrated to have tissue-specific properties which induce beneficial effects upon the immune system. A series of experiments are carried out, in order to evaluate the immune effect of arginine on burned mice. 1. Lymphocytes from both burned and unburned mice are harvested and incubated in various concentrations of arginine solution for 72 hours, and ConA-stimulating lymphocyte transformation is determined after incubation. 2. Burned animals are divided into four groups. Standard diets for nutritional support are formulated. These formulas contain an identical carbohydrate and lipid (61% and 15% of total energy respectively) intake with varied proportions of protein for each group (24%, 23%, 22%, and 20% of total energy, respectively), in addition. 0%, 1%, 2% and 4% of protein energy is supplied by arginine for different groups. Lymphocyte proliferations in responses to ConA stimulation are determined on the 7th postburn day. The data shows that, in vitro study, increasing arginine concentrations enhanced lymphocyte responses to ConA. The arginine needed level for optimal lymphocyte responses is 1.8 mmol/L in burned mice and 0.9 mmol/L in unburned controls. This difference indicates that in burned mice, a higher arginine concentration is required for better lymphocyte responses. On the contrary, further increase of arginine concentration do not give better response. When varied amounts of arginine are given in the diet to the burned mice, the degree of lymphocyte response to ConA is different. The amount of arginine which supplies 2% of total energy is found to be optimal.

Mitogen-activated Ca++ channels in human B lymphocytes

Two complementary experimental methods have been used to examine mitogen-induced transmembrane conductances in human B cells using the Daudi cell line as a model for human B cell activation. Spectrofluorometry was used to investigate mitogen-induced changes in [Ca++]i and transmembrane potential. Activation of human B cells with anti-mu antibodies resulted in a biphasic rise in [Ca++]i, the second phase being mediated by the influx of extracellular Ca++. Ca++ influx was inhibited by high [K+]e, suggesting that this influx was transmembrane potential sensitive. Membrane currents of Daudi cells were investigated using voltage clamp techniques. Before mitogenic stimulation, the cells were electrically quiet. Within several minutes of the addition of anti-mu antibodies to the bath solution, inward currents were observed at negative voltages. Whole-cell currents changed instantly with voltage steps and were transmembrane potential sensitive in that at potentials more positive than -40 mV no currents were detectable. A similar conductance was also activated by the introduction of IP3 into the intracellular solution, suggesting that IP3 generation after surface IgM crosslinking is involved in the activation of this conductance. Both anti-mu and IP3 induced currents were blocked by 1 mM La , which is known to block Ca++ channels. These results strongly support the presence of membrane Ca++ channels in human B cells that function in the early stages of activation. Changes in transmembrane potential appear to be important in regulating Ca++ influx. These mechanisms work in concert to regulate the level of [Ca++]i during the early phases of human B cell activation.

Characterization of the cathepsin B gene and multiple mRNAs in human tissues: evidence for alternative splicing of cathepsin B pre-mRNA

We have cloned and characterized multiple messages for cathepsin B that differ in their 5' and 3' untranslated regions (UTRs) from human kidney and the hepatoma cell line HepG2. A comparison of these messages with the cloned human cathepsin B gene reveals that they arise by alternative splicing of a single gene. Processing at a cryptic intron donor site in exon 11 and splicing to exon 12 produces a 4.0-kb message with an alternate 3' UTR in addition to the 2.3-kb message described previously by Chan et al. (1986). Variable removal of exon 2 produces cathepsin B mRNAs which differ by 88 nucleotides in their 5'-UTRs. The ratio of the 2.3-kb to 4.0-kb transcript is about 2:1 in most of the tissues examined, but the ratio of mRNAs with variant 5' UTRs differs widely. Cathepsin B mRNAs lacking exon 2 are predominant in human tumors. In addition, human breast and colon carcinomas and a human melanoma contain a cathepsin B transcript that is also missing exon 3 encoding the signal peptide and 7 residues of the activation propeptide. An in vitro transcription/translation assay was used to demonstrate that this message could be translated from an internal methionine codon (residue 52), producing a 32-kD product lacking the signal peptide and more than half the propeptide. The transcription/translation assay also demonstrated that the variant messages differ in their rates of translation. The relative rates are about 8:2:1 for mRNA lacking exons 2 and 3 compared to mRNA lacking exon 2 and mRNA containing the full-length 5' end, respectively. These results suggest that the expression of cathepsin B in human tissues may be regulated in part at the level of mRNA processing.

Enhancer-dependent transcription of the epsilon-globin promoter requires promoter-bound GATA-1 and enhancer-bound AP-1/NF-E2

We analyzed epsilon-globin transcription in erythroid cells and in erythroid extracts to determine the requirements for enhancer-dependent expression of this gene. Mutations that abolished GATA-1 binding at a single position in the promoter prevented interaction with enhancers, whereas elimination of a second more distal promoter GATA-1 site had no effect. Deletion or mutation of the GATA-1 sites in either the human beta-globin locus control region DNase-hypersensitive site II enhancer or the chicken beta A/epsilon-globin enhancer did not diminish the ability of the enhancers to interact with the promoter. In contrast, mutation of the AP-1/NF-E2 sites in these enhancers resulted in elimination of enhancement. In vitro transcription of these constructs was promoter dependent and was not sensitive to abolition of GATA-1 binding in the promoter, consistent with the role of GATA-1 solely as a mediator of the enhancer effect. Thus, GATA-1 regulates the response of the epsilon-globin gene to enhancers through a specific site in the promoter and requires enhancer AP-1/NF-E2 binding to transduce the enhancer effect on transcription.

Polarization properties of planar dielectric waveguide gratings

An experimental and theoretical study of polarization properties of planar dielectric waveguide gratings operating at general (oblique) inicidence is reported. The radiation modes coupled out by a surface-relief waveguide grating, when the incident light is not normal to the grating rulings, are linearly polarized for TE excitation and are elliptically polarized for TM excitation. The polarization states of the radiation modes are determined primarily by the polarization state of the principal guided wave in the grating region and by the propagation directions of the radiation modes with respect to the plane of the principal guided wave. Experimental data and numerical results based on three physical models are presented.

[Change of T lymphocyte subsets in peripherial blood of children with malnutrition and zinc deficiency]

Sixty children with malnutrition were investigated in this study. The results showed a reduction of serum zinc in moderate and severe cases compared with the mild and normal groups. OKT3+, OKT4+ and OKT8+ cells in peripheral blood of mild malnutrition were significantly decreased in contrast to normal control. The reductive degree of OKT8+ and OKT4+ cells correlated with the severity of malnutrition. OKT8+, OKT4+ and OKT4+/OKT8+ ratio of moderate and severe malnutrition with infection were much lower than those without infection. Our findings suggested that main effective and regulative cells of cell-mediated immunity were impaired. OKT3+ and OKT4+ cells might be used as a sensitive index for early assessment of the immune function in malnutrition children.