The role of polar interactions in the molecular recognition of CD40L with its receptor CD40

CD40 Ligand (CD40L) is transiently expressed on the surface of T-cells and binds to CD40, which is expressed on the surface of B-cells. This binding event leads to the differentiation, proliferation, and isotype switching of the B-cells. The physiological importance of CD40L has been demonstrated by the fact that expression of defective CD40L protein causes an immunodeficiency state characterized by high IgM and low IgG serum levels, indicating faulty T-cell dependent B-cell activation. To understand the structural basis for CD40L/CD40 association, we have used a combination of molecular modeling, mutagenesis, and X-ray crystallography. The structure of the extracellular region of CD40L was determined by protein crystallography, while the CD40 receptor was built using homology modeling based upon a novel alignment of the TNF receptor superfamily, and using the X-ray structure of the TNF receptor as a template. The model shows that the interface of the complex is composed of charged residues, with CD40L presenting basic side chains (K143, R203, R207), and CD40 presenting acidic side chains (D84, E114, E117). These residues were studied experimentally through site-directed mutagenesis, and also theoretically using electrostatic calculations with the program Delphi. The mutagenesis data explored the role of the charged residues in both CD40L and CD40 by switching to Ala (K143A, R203A, R207A of CD40L, and E74A, D84A, E114A, E117A of CD40), charge reversal (K143E, R203E, R207E of CD40L, and D84R, E114R, E117R of CD40), mutation to a polar residue (K143N, R207N, R207Q of CD40L, and D84N, E117N of CD40), and for the basic side chains in CD40L, isosteric substitution to a hydrophobic side chain (R203M, R207M). All the charge-reversal mutants and the majority of the Met and Ala substitutions led to loss of binding, suggesting that charged interactions stabilize the complex. This was supported by the Delphi calculations which confirmed that the CD40/CD40L residue pairs E74-R203, D84-R207, and E117-R207 had a net stabilizing effect on the complex. However, the substitution of hydrophilic side chains at several of the positions was tolerated, which suggests that although charged interactions stabilize the complex, charge per se is not crucial at all positions. Finally, we compared the electrostatic surface of TNF/TNFR with CD40L/CD40 and have identified a set of polar interactions surrounded by a wall of hydrophobic residues that appear to be similar but inverted between the two complexes.

In vivo functional discrimination between plant thioredoxins by heterologous expression in the yeast Saccharomyces cerevisiae

Whereas vertebrates possess only two thioredoxin genes, higher plants present a much greater diversity of thioredoxins. For example, Arabidopsis thaliana has five cytoplasmic thioredoxins (type h) and at least as many chloroplastic thioredoxins. The abundance of plant thioredoxins leads to the question whether the various plant thioredoxins play a similar role or have specific functions. Because most of these proteins display very similar activities on artificial or biological substrates in vitro, we developed an in vivo approach to answer this question. The disruption of both of the two Saccharomyces cerevisiae thioredoxin genes leads to pleiotropic effects including methionine auxotrophy, H2O2 hypersensitivity, altered cell cycle characteristics, and a limited ability to use methionine sulfoxide as source of methionine. We expressed eight plant thioredoxins (six cytoplasmic and two chloroplastic) in yeast trx1, trx2 double mutant cells and analyzed the different phenotypes. Arabidopsis type h thioredoxin 2 efficiently restored sulfate assimilation whereas Arabidopsis type h thioredoxin 3 conferred H2O2 tolerance. All thioredoxins tested could complement for reduction of methionine sulfoxide, whereas only type h thioredoxins were able to complement the cell cycle defect. These findings clearly indicate that specific interactions between plant thioredoxins and their targets occur in vivo.

Transgenic nematodes as biomonitors of microwave-induced stress

Transgenic nematodes (Caenorhabditis elegans strain PC72), carrying a stress-inducible reporter gene (Escherichia coli beta-galactosidase) under the control of a C. elegans hsp16 heat-shock promoter, have been used to monitor toxicant responses both in water and soil. Because these transgenic nematodes respond both to heat and toxic chemicals by synthesising an easily detectable reporter product, they afford a useful preliminary screen for stress responses (whether thermal or non-thermal) induced by microwave radiation or other electromagnetic fields. We have used a transverse electromagnetic (TEM) cell fed from one end by a source and terminated at the other end by a matched load. Most studies were conducted using a frequency of 750 MHz, at a nominal power setting of 27 dBm. The TEM cell was held in an incubator at 25 degrees C inside a shielded room; corresponding controls were shielded and placed in the same 25 degrees C incubator; additional baseline controls were held at 15 degrees C (worm growth temperature). Stress responses were measured in terms of beta-galactosidase (reporter) induction above control levels. The time-course of response to continuous microwave radiation showed significant differences from 25 degrees C controls both at 2 and 16 h, but not at 4 or 8 h. Using a 5 x 5 multiwell plate array exposed for 2 h, the 25 microwaved samples showed highly significant responses compared with a similar control array. The wells most strongly affected were those in the rows closest to the source, whereas the most distant row did not rise above control levels, suggesting a shadow effect. These differential responses are difficult to reconcile with general heating effects, although localised power absorption affords a possible explanation. Experiments in which the frequency and/or power settings were varied suggested a greater response at 21 than at 27 dBm, both at 750 and 300 MHz, although extremely variable responses were observed at 24 dBm and 750 MHz. Thus, lower power levels tended, if anything, to induce larger responses (with the above-mentioned exception), which is opposite to the trend anticipated for any simple heating effect. These results are reproducible and data acquisition is both rapid and simple. The evidence accrued to date suggests that microwave radiation causes measurable stress to transgenic nematodes, presumably reflecting increased levels of protein damage within cells (the common signal thought to trigger hsp gene induction). The response levels observed are comparable to those observed with moderate concentrations (ppm) of metal ions such as Zn2+ and Cu2+. We conclude that this approach deserves further and more detailed investigation, but that it has already demonstrated clear biological effects of microwave radiation in terms of the activation of cellular stress responses (hsp gene induction).

A novel human WD protein, h-beta TrCp, that interacts with HIV-1 Vpu connects CD4 to the ER degradation pathway through an F-box motif

HIV-1 Vpu interacts with CD4 in the endoplasmic reticulum and triggers CD4 degradation, presumably by proteasomes. Human beta TrCP identified by interaction with Vpu connects CD4 to this proteolytic machinery, and CD4-Vpu-beta TrCP ternary complexes have been detected by coimmunoprecipitation. beta TrCP binding to Vpu and its recruitment to membranes require two phosphoserine residues in Vpu essential for CD4 degradation. In beta TrCP, WD repeats at the C terminus mediate binding to Vpu, and an F box near the N terminus is involved in interaction with Skp1p, a targeting factor for ubiquitin-mediated proteolysis. An F-box deletion mutant of beta TrCP had a dominant-negative effect on Vpu-mediated CD4 degradation. These data suggest that beta TrCP and Skp1p represent components of a novel ER-associated protein degradation pathway that mediates CD4 proteolysis.

Tonoplast intrinsic proteins from cauliflower (Brassica oleracea L. var. botrytis): immunological analysis, cDNA cloning and evidence for expression in meristematic tissues

The vacuolar membrane (tonoplast) of plant cells contains aquaporins, protein channels that facilitate the selective transport of water. These tonoplast intrinsic proteins (TIPs) of 23-29 kDa belong to the ancient major intrinsic protein (MIP) family. A monospecific polyclonal antiserum directed against a 26 kDa intrinsic protein from the tonoplast of meristematic cells from cauliflower (Brassica oleracea L. var. botrytis) was used to screen a cDNA library. Two distinct cDNAs have been isolated. Both clones, c26-1 and c26-2, encode closely related TIPs. The c26-1 insert, consisting of 933 bp upstream of the poly(A) tail, is a full-length cDNA with an open reading frame encoding a protein of 251 amino acids with a calculated M(r) of 25,500. The c26-2 insert is a 5' truncated cDNA. The two cDNAs share 90.5% sequence identity within their overlapping coding regions but only 35% sequence identity in the 3' untranslated regions, indicating that highly related TIP-encoding genes are expressed in meristematic cells. Although TIPs have previously been found in a variety of cell types, they have not been found in meristems. The derived amino acid sequences (BobTIP26-1 and BobTIP26-2, respectively) closely resemble the aquaporin gamma-TIP from Arabidopsis thaliana. Northern blot analysis and in situ hybridization show that BobTIP26 mRNAs preferentially accumulate in highly meristematic cells, mostly before and during cell enlargement, and in the living cells of the xylem. This differential pattern of expression is also found by immunodetection of BobTIP26 polypeptides. The gene expression patterns are discussed with respect to the probable function of the gene products.

Double-stranded-RNA-activated protein kinase (PKR) regulates Ca2+ stores in Xenopus oocytes

Expression of the double-stranded-RNA-dependent protein kinase (PKR) in Xenopus oocytes attenuated Ca2+ entry-dependent membrane currents activated by depletion of Ca2+ stores, whereas expression of a dominant-negative PKR mutant had the opposite effect. These results appeared to be due to perturbation of releasable Ca2+ stores, and not actions of PKR on protein synthesis. PKR may thus have novel protein substrates and cellular functions in Ca2+ storage and signalling.

Cdc53 is a scaffold protein for multiple Cdc34/Skp1/F-box proteincomplexes that regulate cell division and methionine biosynthesis in yeast

In budding yeast, ubiquitination of the cyclin-dependent kinase (Cdk) inhibitor Sic1 is catalyzed by the E2 ubiquitin conjugating enzyme Cdc34 in conjunction with an E3 ubiquitin ligase complex composed of Skp1, Cdc53 and the F-box protein, Cdc4 (the SCFCdc4 complex). Skp1 binds a motif called the F-box and in turn F-box proteins appear to recruit specific substrates for ubiquitination. We find that Skp1 interacts with Cdc53 in vivo, and that Skp1 bridges Cdc53 to three different F-box proteins, Cdc4, Met30, and Grr1. Cdc53 contains independent binding sites for Cdc34 and Skp1 suggesting it functions as a scaffold protein within an E2/E3 core complex. F-box proteins show remarkable functional specificity in vivo: Cdc4 is specific for degradation of Sic1, Grr1 is specific for degradation of the G1 cyclin Cln2, and Met30 is specific for repression of methionine biosynthesis genes. In contrast, the Cdc34-Cdc53-Skp1 E2/E3 core complex is required for all three functions. Combinatorial control of SCF complexes may provide a basis for the regulation of diverse cellular processes.

Roles of sphingosine-1-phosphate in cell growth, differentiation, and death

Recent evidence suggests that branching pathways of sphingolipid metabolism may mediate either apoptotic or mitogenic responses depending on the cell type and the nature of the stimulus. While ceramide has been shown to be an important regulatory component of apoptosis induced by tumor necrosis factor alpha and the Fas ligand, sphingosine-1-phosphate (SPP), a further metabolite of ceramide, has been implicated as a second messenger in cellular proliferation and survival induced by platelet-derived growth factor, neuronal growth factor, and serum. SPP protects cells from apoptosis resulting from elevations of ceramide. Inflammatory cytokines stimulate sphingomyelinase, but not ceramidase, leading to accumulation of ceramide, whereas growth signals also stimulate ceramidase and sphingosine kinase leading to increased SPP levels. We propose that the dynamic balance between levels of sphingolipid metabolites, ceramide, and SPP and consequent regulation of different members of the mitogen-activated protein kinases (JNK versus ERK) family is an important factor that determines whether a cell survives or dies.

Modifiable templates facilitate customization of physician order entry

Physician order entry is a key factor in improving the quality of healthcare, while simultaneously reducing its cost. This paper describes an editor, a database, and a run-time system for creating and executing highly customized, user modifiable, order entry templates. The system allows non-programmers to create new order entry templates rapidly. Over the past 18 months, the templates have been used on over 2500 patients to enter over 40,000 separate orders.

The hyper-CVAD regimen improves outcome in relapsed acute lymphoblastic leukemia

Sixty-six adults with refractory acute lymphocytic leukemia received salvage therapy with the 'hyper-CVAD' regimen, consisting of eight courses of alternating intensive chemotherapy with growth factor support, followed by oral maintenance chemotherapy. Their outcome was compared with 63 prognostically similar historical control patients treated with high-dose Ara-C plus mitoxantrone with or without GM-CSF. Overall, the complete response rates were similar in the treatment and control groups (29 of 66 (44%) vs 24 of 63 (38%)). There were more patients in the current study with primary resistant disease (10 of 66 (15%) vs one of 63 (2%), P = 0.006), and conversely fewer patients with secondary resistance (19 of 66 (29%) vs 28 of 63 (44%), P = 0.06). Recovery of granulocyte counts above 500/microl was significantly faster in the current study when compared to high-dose Ara-C-treated patients who were given GM-CSF (20 vs 25 days, P = 0.04). Survival was prolonged in the hyper-CVAD-treated patients, with most of the benefit seen in first salvage patients (42 vs 20 weeks, P = 0.016). When only first salvage patients were considered, there was a significant difference in disease-free survival in favor of hyper-CVAD (52 vs 20 weeks, P = 0.008). The hyper-CVAD regimen is a more effective and less toxic salvage regimen for relapsed acute lymphocytic leukemia than high-dose Ara-C-based regimens.

Cell salvage auto transfusion in total knee replacement surgery

We conducted a prospective, randomized study to assess the impact of cell salvage, auto transfusion on the requirements for allogeneic blood for patients undergoing a total knee replacement (TKR). One hundred consecutive TKR patients were randomly allocated to receive either autologous blood (using cell salvage) or an allogeneic blood transfusion as necessary. Patients allocated to the autologous group were rescued with allogeneic blood if the postoperative haemoglobin fell below 9 g dL-1. Forty-two (84%) of 50 patients in the autologous group required no supplementary blood transfusion. Forty (80%) of 50 patients allocated to receive allogeneic blood required transfusion. There were no detrimental effects of autologous blood transfusion. We conclude that autologous blood transfusion, using the cell saver system, is a safe and effective method of reducing the need for allogeneic blood transfusion and, in doing so, reduces the risk of transmission of infections associated with allogeneic blood transfusion, whilst decreasing demand on precious allogeneic blood reserves.

Nuclear calcium signalling by individual cytoplasmic calcium puffs

It is known that the nucleoplasmic ionised calcium concentration (Can) controls nuclear functions such as transcription, although the source and nature of the signals which modulate Can are unclear. Using confocal imaging, we investigated the subcellular origin of Can signals in Fluo-3-loaded HeLa cells. Our data indicate that all signals which increased Can were of cytoplasmic origin. Can was elevated during the propagation of global Ca waves within cells. More strikingly, we found that individual cytoplasmic elementary release events e.g. Ca puffs, evoked by physiological levels of stimulation, caused transient Can increases. Significantly, >70% of all Ca puffs originated within a 2-3 micron perinuclear zone and propagated anisotropically across the entire nucleus. Due to the relatively slow relaxation of Can transients compared with those in the cytoplasm, repetitive perinuclear Ca puffs were integrated into a 'staircase' of increasing Can. Due to the effective diffusion of Ca in the nucleoplasm, the nucleus served as a 'Ca tunnel', distributing Ca to parts of the cytosol which were otherwise not within the cytoplasmic diffusion radii of Ca puffs. Given the close proximity of the majority of puff sites to the nucleus, it seems that the elementary Ca release system is designed to facilitate nuclear Ca signalling. Consequently, Ca-dependent regulation of nuclear function must be considered at the microscopic elementary level.

[Use of abciximab during coronary angioplasty]

The IIb-IIIa glycoprotein is the platelet receptor of fibrinogen and the final common pathway of platelet activation and aggregation. Abciximab is a Fab fragment of the chimeric monoclonal antibody (c7E3) interfering with the glycoprotein receptor. It is the only anti IIb-IIIa currently available, commercialized under the name of Reopro. Preliminary clinical data has been obtained with its use in high risk coronary angioplasty. The EPIC trial showed a 35% relative reduction of the principal combined criterion of judgement of cardiac morbidity and mortality at 1 month, a benefit even greater in acute coronary syndromes (-72%) than in programmed procedures for complex type C lesions (-10%). The incidence of severe bleeding was high (14%). The results of the CAPTURE trial could widen the indications of abciximab to include the period surrounding angioplasty for unstable angina as the use of Reopro in the 24 hours before the procedure significantly reduced the risk of ischaemic events (10.8% versus 16.4%). In programmed angioplasty, the EPILOG trial investigated the effects of adapting the dose of heparin and an infusion of abciximab to body weight early (4th to 6th hour) withdrawal of the arterial introducer without continuing heparin. Using a 70 IU/Kg dosage modulated to algorithms taking into account the ACT, the incidence of bleeding complications was reduced to 1.8%, the same as the control group, and the benefits with regards to ischaemic events were not only maintained but increased (a 56% reduction at 1 months). Utilization of abciximab would be supported by the Cost saving approach of the EPIC trial 3-years follow-up which showed presentation of the initial benefits.

Metabolism of sulfur amino acids in Saccharomyces cerevisiae

Sulfur amino acid biosynthesis in Saccharomyces cerevisiae involves a large number of enzymes required for the de novo biosynthesis of methionine and cysteine and the recycling of organic sulfur metabolites. This review summarizes the details of these processes and analyzes the molecular data which have been acquired in this metabolic area. Sulfur biochemistry appears not to be unique through terrestrial life, and S. cerevisiae is one of the species of sulfate-assimilatory organisms possessing a larger set of enzymes for sulfur metabolism. The review also deals with several enzyme deficiencies that lead to a nutritional requirement for organic sulfur, although they do not correspond to defects within the biosynthetic pathway. In S. cerevisiae, the sulfur amino acid biosynthetic pathway is tightly controlled: in response to an increase in the amount of intracellular S-adenosylmethionine (AdoMet), transcription of the coregulated genes is turned off. The second part of the review is devoted to the molecular mechanisms underlying this regulation. The coordinated response to AdoMet requires two cis-acting promoter elements. One centers on the sequence TCACGTG, which also constitutes a component of all S. cerevisiae centromeres. Situated upstream of the sulfur genes, this element is the binding site of a transcription activation complex consisting of a basic helix-loop-helix factor, Cbf1p, and two basic leucine zipper factors, Met4p and Met28p. Molecular studies have unraveled the specific functions for each subunit of the Cbf1p-Met4p-Met28p complex as well as the modalities of its assembly on the DNA. The Cbf1p-Met4p-Met28p complex contains only one transcription activation module, the Met4p subunit. Detailed mutational analysis of Met4p has elucidated its functional organization. In addition to its activation and bZIP domains, Met4p contains two regulatory domains, called the inhibitory region and the auxiliary domain. When the level of intracellular AdoMet increases, the transcription activation function of Met4 is prevented by Met30p, which binds to the Met4 inhibitory region. In addition to the Cbf1p-Met4p-Met28p complex, transcriptional regulation involves two zinc finger-containing proteins, Met31p and Met32p. The AdoMet-mediated control of the sulfur amino acid pathway illustrates the molecular strategies used by eucaryotic cells to couple gene expression to metabolic changes.

Nuclear export signal of IkappaBalpha interferes with the Rev-dependent posttranscriptional regulation of human immunodeficiency virus type I

De novo synthesized IkappaBalpha accumulates transiently in the nucleus where it inhibits NF-kappaB-dependent transcription and reduces nuclear NF-kappaB content. A sequence present in the C-terminal domain of IkappaBalpha and homologous to the HIV-1 Rev nuclear export signal (NES) has been recently defined as a functional NES conferring on IkappaBalpha the ability to export IkappaBalpha/NF-kappaB complexes. Rev utilises its RNA-binding activity and NES sequence to promote specifically the transport of unspliced and monospliced viral RNAs to the cytoplasm. The object of this work was to determine if nuclear IkappaBalpha could interfere with Rev-dependent transport of viral RNA from the nucleus to the cytoplasm. We report that accumulation of IkappaBalpha in the cell nucleus blocks viral replication. This effect could be dissociated from the capacity of IkappaBalpha to inhibit NF-kappaB-DNA-binding activity and required a functional IkappaBalpha NES motif. Indeed, mutation of the NES abrogated the capacity of IkappaBalpha to inhibit Rev-dependent mechanisms involved in the replication of either wild-type or NF-kappaB-mutated HIV-1 molecular clones. Nuclear accumulation of a reporter protein tagged with a nuclear localization signal (NLS) and fused to the IkappaBalpha NES motif (NLS-PK-NES) was sufficient to inhibit HIV-1 replication at a post-transcriptional level by specifically blocking the expression of a Rev-dependent gene. Furthermore, in cells pulsed with TNF, a treatment which favors nuclear accumulation of newly synthesized IkappaBalpha, NLS-PK-NES expression promoted sustained accumulation of nuclear NF-kappaB lacking DNA-binding activity. This NES-mediated accumulation of inactive nuclear NF-kappaB is likely the consequence of interference in the IkappaBalpha-mediated export of NF-kappaB. These findings indicate that IkappaBalpha and Rev compete for the same nuclear export pathway and suggest that nuclear accumulation of IkappaBalpha, which would occur during normal physiological cell activation process, may interfere with the Rev-NES-mediated export pathway of viral RNAs, thus inhibiting HIV-1 replication.

Selective feticide by embolization in twin-twin transfusion syndrome. A report of two cases

BACKGROUND

The early development of complications in twin-twin transfusion syndrome is a poor prognostic sign. For this reason, new techniques for intrauterine therapy are being developed: invasive options, such as selective feticide of one of the twins, have been reported.

CASES

Two cases of twin-twin transfusion syndrome in the late second trimester were treated by selective feticide using vascular embolization to the more severely damaged fetus. In one case the embolized fetus was a hydropic recipient with a normal cotwin; in the other, the donor fetus was affected by bilateral hydrocephalus. These fetuses underwent ultrasound-guided embolization using a bolus of histoacryl injected into the umbilical vein and fetal heart. Both patients went on to deliver healthy singletons in the third trimester.

CONCLUSION

In twin-twin transfusion syndrome of early onset, embolization may help one of the twins survive. This technique is neither time-consuming nor expensive and does not require a general anesthetic.

Indium-111 antimyosin scintigraphy before and after coronary bypass surgery: unexpected preoperative myocardial uptakes

The present study was designed to evaluate 111In-antimyosin scintigraphy in detecting pre- and post-operative myocardial infarction in patients undergoing coronary artery bypass surgery. Fab antimyosin scintigraphy has been shown to be sensitive and specific in detecting myocardial necrosis and to be potentially valuable in situations where other criteria are not reliable. In a previous study, postoperative antimyosin uptakes occurred in 82% of the studied patients. Sixteen consecutive patients with an indication of coronary artery surgery were assessed by preoperative coronary angiography, serial electrocardiograms, and myocardial scanning with 111Indium-labeled antimyosin antibodies performed before and after operation. In four patients, a recent myocardial infarction (1 to 3 months) was detected with an accurate localization when compared to the classic criteria of myocardial infarction. One more patient with a 21-year old myocardial infarction showed an intense uptake whereas there was no recent acute coronary event. Four other patients had an unexpected preoperative uptake, since there were no acute coronary events in their medical history. All preoperative scintigraphic uptakes were still present on the second scan performed postoperatively in these nine patients. Only one patient showed a new postoperative uptake when compared to the preoperative scan which was normal; this postoperative septal infarct was confirmed by a postoperative coronary angiography. Extracardiac uptakes (sternum and ribs) were frequently observed after operation and might hamper the interpretation of postoperative scintigrams. Unexpected preoperative uptakes may be related to non diagnosed small necrosis. A preoperative reference scan is required for an accurate interpretation of a postoperative 111In-antimyosin uptake. Moreover, extracardiac uptakes may limit the interpretation of perioperative cardiac damage.

The carboxy-terminus of I kappaB alpha determines susceptibility to degradation by the catalytic core of the proteasome

The Rel/NF-kappaB family of transcription factors controls the expression of a wide variety of genes that are implicated in immune and inflammatory responses and cellular proliferation. Disregulation of NF-kappaB is associated with cellular transformation and the maintenance of a high anti-apoptotic threshold in transformed cells. NF-kappaB activity is in turn regulated by its sequestration in the cytoplasm by the inhibitor I kappaB. I kappaB alpha, the most abundant and well-characterized member of the I kappaB multiprotein family, is rapidly degraded in response to multiple physiologic stimuli. In the present study we show that not only the amino-terminus, but also the carboxy-terminus of I kappaB alpha contain transferable signals that must be simultaneously present in an unrelated protein to render it susceptible to activation-induced, proteasome-mediated degradation. We show here that I kappaB alpha amino-terminal modifications occur independently of the carboxy-terminus. Moreover, we present evidence indicating a critical role for the carboxy-terminal region in facilitating proteolysis by the catalytic core of the proteasome. When incubated with 20S proteasome extracted from rat liver, I kappaB alpha was quickly degraded while a deletion mutant lacking the carboxy-terminus was resistant to proteolysis. Likewise, chimeric proteins of beta-galactosidase with the I kappaB alpha carboxy-terminus were degraded in vitro independently of the presence of the I kappaB alpha amino-terminus, whereas chimeric proteins lacking the I kappaB alpha carboxy-terminus were stable. Our results identify the carboxy-terminus of I kappaB alpha as a domain critical for degradation through interaction with an as yet unidentified component of the proteasome.

Aquaporin-related proteins in the filter chamber of homopteran insects

In the Homopteran order of insects, the plant xylem feeders exhibit a highly differentiated part of their digestive tract known as the filter chamber. In this tissue, water crosses plasma membranes through a transepithelial osmotic gradient. In previous studies on the filter chamber of Cicadella viridis, we purified and characterized from the plasma membranes a 25 kDa protein that we demonstrated to be an aquaporin (or water channel, member of the major intrinsic protein family, a group of membrane channels for small solutes). We called this protein AQPcic for Cicadella aquaporin. In the present study, we used polyclonal antibody anti-AQPcic in Western blotting and immunocytochemical analysis of the intestinal tract of Cercopis sanguinolenta, Philaenus spumarius, Aphrophora alni (Cercopidae), Euscelidius variegatus, and Scaphoideus titanus (Jassidae). Western blotting experiments revealed that immunologically related AQPcic proteins are found in those species. The molecular weight of these proteins is 15-26 kDa. Immunocytochemical studies on ultrathin filter-chamber sections revealed that the anti-AQPcic antibody systematically labelled the membrane microvilli of epithelial cells. A good correlation thus exists between the physiology of these cells and the presence of aquaporin-related proteins in their membranes.