A microfluidic electroporation device for cell lysis

We demonstrate a micro-electroporation device for cell lysis prior to subcellular analysis. Simple circuit models show that electrical lysis method is advantageous because it is selective towards plasma membrane while leaving organelle membrane undamaged. In addition, miniaturization of this concept leads to negligible heat generation and bubble formation. The designed microdevices were fabricated using a combination of photolithography, metal-film deposition, and electroplating. We demonstrate the electro-lysis of human carcinoma cells in these devices to release the subcellular materials.

Memory consolidation induces N-methyl-d-aspartic acid-receptor- and Ca2+/calmodulin-dependent protein kinase II-dependent modifications in α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor properties

The N-methyl-D-aspartic acid (NMDA) receptor-dependent activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) is necessary for induction of the long-term potentiation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor-mediated responses in the CA1 region of the hippocampus, a putative model for learning and memory. We analyzed the interplay among NMDA receptor, CaMKII and AMPA receptor during consolidation of the memory for an inhibitory avoidance learning task in the rat. Bilateral intra-CA1 infusion of the NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoic acid (AP5) or of the CaMKII inhibitor 2-[N-(2-hydroxyethyl)]-N-(4-methoxybenzenesulfonyl)] amino-N-(4-chlorocinnamyl)-N-methylbenzylamine) (KN-93) immediately after step-down inhibitory avoidance training hindered memory consolidation. Learning of the avoidance response induced the NMDA receptor-dependent translocation of alphaCaMKII to a postsynaptic density-enriched fraction isolated from dorsal CA1 and the autophosphorylation of this kinase at Thr-286. Step-down inhibitory avoidance training increased the quantity of GluR1 and GluR2/3 AMPA receptor subunits and the phosphorylation of GluR1 at Ser-831 but not at Ser-845 in CA1 postsynaptic densities. The intra-CA1 infusion of KN-93 and AP5 blocked the increases in GluR1 and GluR2/3 levels and the phosphorylation of GluR1 brought on by step-down inhibitory avoidance training. Our data suggest that step-down inhibitory avoidance learning promotes the learning-specific and NMDA receptor-dependent activation of CaMKII in the CA1 region of the dorsal hippocampus and that this activation is necessary for phosphorylation and translocation of AMPA receptor to the postsynaptic densities, similarly to what happens during long-term potentiation.

Subcellular localization and trafficking of kainate receptors

Glutamate receptors of the kainate type have been identified recently as key players in the modulation of neuronal-network activity. The role of kainate receptors depends on their precise subcellular localization in presynaptic, postsynaptic and extrasynaptic domains. Subcellular localization of kainate receptors has been inferred mainly from electrophysiological studies with the help of selective pharmacological tools and kainate receptor mutant mice. These studies, combined with recent ultrastructural data, highlight the diversity of subcellular localizations of kainate receptors. It is important to understand the molecular mechanisms that underlie the polarized trafficking of kainate receptors in distinct neuronal domains. In this article, we review recent data that shed light on the trafficking and membrane delivery of kainate receptor isoforms, and on the identification of proteins that interact with kainate receptors and might regulate this trafficking.

A subcellular distribution of estrogen receptor-alpha is changed during artificially induced senescence of PC12 pheochromocytoma cells

Although estrogen has been considered as a sex hormone for decades, recent reports suggest that estrogen might modulate the development and physiological function of the brain. In addition, the subcellular localization of estrogen receptors (ERs) has shown their presence within both the perinuclear cytoplasm and nuclei, suggesting that these ERs may differ functionally. We, therefore, assayed changes in the subcellular localization of ER-alpha immunoreactivity (IR) in rat pheochromocytoma PC12 cells during the artificial senescence induced by the telomerase inhibitor, 3'-azido-3'-deoxythymidine (AZT). After 2 months of culture with AZT, PC12 cells showed morphological and biochemical characteristics of cellular senescence. In the cells showing artificial senescence, the ER-alpha IR was mainly localized within the cytoplasm, whereas in control cells, ER-alpha IR was found only in the nuclei. Since senescence was induced by AZT, which inhibits the action of telomerase whenever the cells divide, the change in subcellular distribution of ER-alpha IR may be correlated with the length of the telomere.

Root phloem-specific expression of the plasma membrane amino acid proton co-transporter AAP3

Amino acids are regarded as the nitrogen 'currency' of plants. Amino acids can be taken up from the soil directly or synthesized from inorganic nitrogen, and then circulated in the plant via phloem and xylem. AtAAP3, a member of the Amino Acid Permease (AAP) family, is mainly expressed in root tissue, suggesting a potential role in the uptake and distribution of amino acids. To determine the spatial expression pattern of AAP3, promoter-reporter gene fusions were introduced into Arabidopsis. Histochemical analysis of AAP3 promoter-GUS expressing plants revealed that AAP3 is preferentially expressed in root phloem. Expression was also detected in stamens, in cotyledons, and in major veins of some mature leaves. GFP-AAP3 fusions and epitope-tagged AAP3 were used to confirm the tissue specificity and to determine the subcellular localization of AtAAP3. When overexpressed in yeast or plant protoplasts, the functional GFP-AAP3 fusion was localized in subcellular organelle-like structures, nuclear membrane, and plasma membrane. Epitope-tagged AAP3 confirmed its localization to the plasma membrane and nuclear membrane of the phloem, consistent with the promoter-GUS study. In addition, epitope-tagged AAP3 protein was localized in endodermal cells in root tips. The intracellular localization suggests trafficking or cycling of the transporter, similar to many metabolite transporters in yeast or mammals, for example, yeast amino acid permease GAP1. Despite the specific expression pattern, knock-out mutants did not show altered phenotypes under various conditions including N-starvation. Microarray analyses revealed that the expression profile of genes involved in amino acid metabolism did not change drastically, indicating potential compensation by other amino acid transporters.

An efficient method for flow cytometric analysis of pollen and detection of 2n nuclei in Brassica napus pollen

A simple and reliable method was developed for isolating pollen nuclei from Brassica napus and Triticum aestivum for DNA analysis using flow cytometry. The nuclei were released from pollen by ultrasonic treatment. The isolated nuclei following filtration through nylon mesh and a purification procedure were suitable for flow cytometric analysis as well as for isolating genomic DNA. Ultrasonic treatment time was optimized for B. napus pollen at different developmental stages. The method is effective and suitable for the preparation of many samples. We analyzed the nuclear DNA levels in pollen of B. napus at three major developmental stages as well as in mature wheat pollen. Only a single 1C peak representing the haploid DNA level was detected in the nuclei isolated from Brassica uninucleate microspores as well as in mature Triticum pollen. Interestingly, diploid nuclei were detected in both binucleate and mature pollen of B. napus. The possible origins of the diploid nuclei are discussed.

Exploring the use of soft X-ray microscopy for imaging subcellular structures of the inner ear1

The soft X-ray microscope at the Lawrence Berkeley National Laboratory was developed for visualization of biological tissue. Soft X-ray microscopy provides high-resolution visualization of hydrated, non-embedded and non-sectioned cells and is thus potentially an alternative to transmission electron microscopy. Here we show for the first time soft X-ray micrographs of structures isolated from the guinea-pig inner ear. Sensory outer hair cells and supporting pillar cells are readily visualized. In the hair cells, individual stereocilia can easily be identified within the apical hair bundle. The underlying cuticular plate is, however, too densely composed or too thick to be clearly visualized, and thus appears very dark. The cytoplasmic structures protruding from the cuticular plates as well as the fibrillar material surrounding and projecting from the cell nuclei can be seen. In the pillar cells the images reveal individual microtubule bundles. Soft X-ray images of the acellular tectorial membrane and thin two-layered Reissner's membrane display a level of resolution comparable to low-power electron microscopy.

Differential distribution of the KCl cotransporter KCC2 in thalamic relay and reticular nuclei

In the thalamus of the rat the reversal potential of GABA-induced anion currents is more negative in relay cells than in neurones of the reticular nucleus (nRt) due to different chloride extrusion mechanisms operating in these cells. The distribution of KCl cotransporter type 2 (KCC2), the major neuronal chloride transporter that may underlie this effect, is unknown in the thalamus. In this study the precise regional and ultrastructural localization of KCC2 was examined in the thalamus using immunocytochemical methods. The neuropil of all relay nuclei was found to display intense KCC2 immunostaining to varying degrees. In sharp contrast, the majority of the nRt was negative for KCC2. In the anterior and dorsal part of the nRt, however, KCC2 immunostaining was similar to relay nuclei and parvalbumin and calretinin were found to colocalize with KCC2. At the ultrastructural level, KCC2 immunoreactivity was mainly located in the extrasynaptic membranes of thick and thin dendrites and the somata of relay cells but was also found in close association with asymmetrical synapses formed by cortical afferents. Quantitative evaluation of KCC2 distribution at the electron microscopic level demonstrated that the density of KCC2 did not correlate with dendritic diameter or synaptic coverage but is 1.7 times higher on perisynaptic membrane surfaces than on extrasynaptic membranes. Our data demonstrate that the regional distribution of KCC2 is compatible with the difference in GABA-A reversal potential between relay and reticular nuclei. At the ultrastructural level, abundant extrasynaptic KCC2 expression will probably play a role in the regulation of extrasynaptic GABA-A receptor-mediated inhibition.

Applications of an efficient method for comparing immunogold labelling patterns in the same sets of compartments in different groups of cells

Quantitative immunoelectron microscopy often involves determining the distributions of gold label in different intracellular compartments and then drawing comparisons between compartments in the same sample of cells or between experimental groups of cells. In the case of within-group comparisons, recent developments in the estimation of relative labelling index and labelling density make it possible to test whether or not particular compartments are preferentially labelled. These methods are ideally suited to analysing gold label restricted to volume (organelle) or surface (membrane) compartments but may be modified to analyse label localised in mixtures of both. Here, a simple and efficient approach to drawing between-group comparisons for label associated with organelles and/or membranes is presented. The method relies on multistage random sampling of specimens (via blocks and microscopic fields) followed by simply counting gold particles associated with different compartments. The distributions of raw gold counts in different groups are then compared by contingency table analysis with statistical degrees of freedom for chi-squared values being determined by the number of compartments and the number of experimental groups of cells. Compartmental chi-squared values making substantial contributions to the total chi-squared values then identify where the main between-group differences reside. The method requires no information about compartment size (for example, organelle profile area or membrane trace length) and does not even depend critically on standardising between-group magnification. Its application is illustrated using datasets from immunolabelling studies designed to localise the KDEL receptor, phosphatidyl-inositol 4,5-bisphosphate, GLUT4 and rab4 at the electron microscopic level.

Caveolar and lipid raft localization of the growth hormone receptor and its signaling elements: impact on growth hormone signaling

The growth hormone receptor (GHR) is a cell surface receptor that mediates the somatogenic and metabolic effects of the growth hormone (GH). GHR signaling is transduced via the receptor-associated cytoplasmic tyrosine kinase called Janus protein kinase 2 (JAK2). The major intracellular signaling systems activated by JAK2 in response to GH include the signal transducer and activator of transcription (STAT) 5 and extracellular signal-regulated kinase (ERK)-1 and -2 pathways. In this report, we investigate the role of cholesterol-rich plasma membrane microdomains (caveolae and lipid rafts) in GH signaling. By subcellular fractionation of the GH-responsive 3T3-F442A murine preadipocyte, we found dramatic enrichment (6.7-fold) of plasma membrane GHR in the caveolae membranes (CM). JAK2 was also represented in the CM fraction, but was less enriched (2.5-fold) than GHR. ERK1/2 and the important ERK pathway upstream small adaptor protein, Grb2 (growth factor receptor-bound protein 2), were also enriched in caveolae (2.3- and 8.3-fold, respectively), but STAT5 was barely detected in the same fraction. Correspondingly, GH-induced tyrosine-phosphorylated GHR, JAK2, and ERK1/2 were highly represented in the CM fraction, whereas tyrosine-phosphorylated STAT5 was enriched in the non-membranous fraction of the post-nuclear supernatant. Additionally, GH induced further accumulation of GHR, Grb2, and SHC proteins in the CM fraction. Interestingly, treatment of the cells with the caveolae-disrupting agent, methyl-beta-cyclodextrin (mbetaCD), selectively inhibited GH-induced ERK1/2 activation but not STAT5 phosphorylation; repletion of cholesterol in mbetaCD-treated cells restored GH-induced ERK activation. Comparison of 3T3-F442A cells with the GHR-expressing human IM-9 lymphoblasts revealed similar enrichment of GHR in the lipid raft fraction of IM-9 as in the CM fraction of 3T3-F442A, but there were dramatic differences in the ERKs and Grb2. The IM-9 cell, in which ERKs are not activated by GH, displayed no enrichment of ERKs and Grb2 in the lipid raft fraction. Our results suggest that localization of GHRs in the CM fraction of the plasma membrane plays important roles in signaling.

Pituitary adenylate cyclase activating polypeptide-mediated intracrine signaling in the testicular germ cells

Pituitary adenylate cyclase activating polypeptide (PACAP) is found not only in the brain, but is also abundantly expressed in the testicular germ cells. However, the physiological role of testicular PACAP remains unknown. Autoradiographic studies showed a considerable number of PACAP-specific binding sites in the seminiferous tubules. Immunohistochemistry demonstrated PAC1-receptor (R)-like immunoreactivity (li) in the cytoplasm of round spermatids, aggregated in the acrosome and coexpressed with PACAP-li. Spermatid-enriched fractions were examined for the subcellular localization of PACAP binding sites and PAC1-R-li. The highest levels of PACAP binding sites and PAC1-R-li were found in the cytosolic, followed by the nuclear, and the lowest levels in the membrane fraction. The testicular cytosolic PAC1-R-like protein showed a specific competitive inhibition in the radio-receptor assay for PACAP38 and 27, with a Ki of 0.069 nM and 0.179 nM, respectively. The addition of PACAP to the cytosol of spermatids only slightly activated adenylate cyclase, while it markedly stimulated the expression and activation of ERK-type mitogen-activated protein kinase (MAPK). In the PAC1-R-like protein-depleted cytosol, a PAC1-R-specific agonist, maxadilan, did not activate MAPK, but PACAP and VIP still did. Because VPAC2-R, which binds both PACAP and VIP, is expressed in the testis, the findings suggest that cytosolic VPAC2-R-like proteins are also present and coupled to MAPK. The MAPK activation does not seem to require a heterotrimeric G-protein. Because PACAP and its receptors are coexpressed in the cytoplasm of spermatids, endogenous PACAP may directly interact with the cytosolic PAC1-R-like protein without the ligand being released into the extracellular space. This possibility is supported by the observation that cytosolic endogenous PACAP in spermatids was co-immunoprecipitated with the cytosolic PAC1-R. This mechanism may be called "intracrine," and its physiological significance is discussed.

Cell signal control of the G protein-gated potassium channel and its subcellular localization

G protein-gated inward rectifier K(+) (K(G)) channels are directly activated by the betagamma subunits released from pertussis toxin-sensitive G proteins, and contribute to neurotransmitter-induced deceleration of heart beat, formation of slow inhibitory postsynaptic potentials in neurones and inhibition of hormone release in endocrine cells. The physiological roles of K(G) channels are critically determined by mechanisms which regulate their activity and their subcellular localization. K(G) channels are tetramers of inward rectifier K(+) (Kir) channel subunits, Kir3.x. The combination of Kir3.x subunits in each K(G) channel varies among tissues and cell types. Each subunit of the channel possesses one Gbetagamma binding site. The binding of Gbetagamma increases the number of functional K(G) channels via a mechanism that can be described by the Monod-Wyman-Changeux allosteric model. During voltage pulses K(G) channel current alters time dependently. The K(G) current exhibits inward rectification due to blockade of outward-going current by intracellular Mg(2+) and polyamines. Upon repolarization, this blockade is relieved practically instantaneously and then the current slowly increases further. This slow current alteration is called 'relaxation'. Relaxation is caused by the voltage-dependent behaviour of regulators of G protein signalling (RGS proteins), which accelerate intrinsic GTP hydrolysis mediated by the Galpha subunit. Thus, the relaxation behaviour of K(G) channels reflects the time course with which the G protein cycle is altered by RGS protein activity at each membrane potential. Subcellular localization of K(G) channels is controlled by several distinct mechanisms, some of which have been recently clarified. The neuronal K(G) channel, which contains Kir3.2c, is localized in the postsynaptic density (PSD) of various neurones including dopaminergic neurones in substantia nigra. Its localization at PSD may be controlled by PDZ domain-containing anchoring proteins. The K(G) channel in thyrotrophs is localized exclusively on secretary vesicles, which upon stimulation are rapidly inserted into the plasma membrane and causes hyperpolarization of the cell. This mechanism indicates a novel negative feedback regulation of exocytosis. In conclusion, K(G) channels are under the control of a variety of signalling molecules which regulate channel activity, subcellular localization and thus their physiological roles in myocytes, neurones and endocrine cells.

Resolution of cAMP signals in three-dimensional microdomains using novel, real-time sensors

A large number of hormones, neurotransmitters, and odorants alter cellular behavior by triggering changes in intracellular levels of cAMP. Although the effector proteins that bind cAMP have been identified, it is not known how this one messenger can differentially regulate the activities of hundreds of cellular proteins. The spatial and temporal nature of cAMP signals and, thus, their information content remain largely unknown. We present here a high-resolution method for measuring cAMP signals near the plasma membrane in single cells. Cyclic nucleotide-gated (CNG) ion channels from olfactory receptor neurons have been genetically modified to improve their cAMP-sensing properties. We show how these channels can be used in electrophysiological experiments to accurately measure changes in cAMP concentration near the membrane, where most adenylyl cyclases reside. We have found in several cell types (both excitable and nonexcitable) that cAMP is produced in subcellular compartments near the plasma membrane, and that diffusion of cAMP from these compartments to the bulk cytosol is severely hindered. We also show that a uniform extracellular stimulus can initiate very distinct cAMP signals within different compartments of a simple, nonexcitable cell. Analysis of compartmental models indicates that diffusional restrictions between microdomains (near the membrane) and the cytosol, as well as differential regulation of phosphodiesterase activity, are necessary to explain such distinct signals. Using modified CNG channels as sensors has much greater spatial and temporal resolution than other methods for measuring cAMP, and should help to unravel the complexities of signaling by this ubiquitous messenger. Cyclic AMP (cAMP), the prototypical second messenger, regulates a wide variety of cellular processes. Changes in cAMP concentration transmit information to downstream effectors including protein kinase A (PKA), cyclic nucleotide-gated (CNG) channels, hyperpolarization activated (Ih) channels, and Epac. However, it is largely unclear how differential regulation of cellular targets occurs. The concept of compartmentation emerged over 20 years ago in studies of cardiac myocytes, to help explain how a variety of extracellular stimuli that primarily act through cAMP can have very different downstream effects on the cell. The basis for compartmentation, and indeed, the nature of cAMP signals themselves, have remained mysteries. To understand how these signals function within the cell it is important to answer the following questions: (i) How are cAMP signals localized? (ii) What are the kinetics of cAMP signals in localized domains? and (iii) What information is contained in the amplitude and frequency of cAMP signals? We describe here a high-resolution method for measuring cAMP signals near the plasma membrane, using modified cyclic nucleotide-gated ion channels. This approach was inspired by the field of retinal phototransduction, the best-studied second messenger signaling system, in which elegant biochemical studies have been complemented by real-time measurements of cGMP signals using endogenous cyclic nucleotide-gated (CNG) channels. CNG channels are directly opened by the binding of cyclic nucleotides. They were discovered in retinal photoreceptor cells and olfactory receptor neurons, where they generate the electrical response to light and odorants. The native retinal channel is cGMP specific, while the native olfactory channel is equally sensitive to cAMP and cGMP. Native CNG channels consist of A and B subunits, both of which bind cyclic nucleotides, although most A subunits form functional channels on their own. We have modified an olfactory channel A subunit (CNGA2) to improve its sensitivity and selectivity for cAMP. Two of the findings with this approach, summarized here, are: (i) cAMP in several cell types is produced in subcellular compartments under the plasma membrane with restricted diffusional access to the bulk cytosol; and (ii) the amplitude and kinetics of cAMP signals within these compartments are distinct from those in the remainder of the cell.

α1-Adrenergic receptor subtypes: non-identical triplets with different dancing partners?

Alpha(1)-adrenergic receptors are one of the three subfamilies of G protein coupled receptors activated by epinephrine and norepinephrine to control important functions in many target organs. Three human subtypes (alpha(1A), alpha(1B), alpha(1D)) are derived from separate genes and are highly homologous in their transmembrane domains but not in their amino or carboxyl termini. Recent advances in our understanding of these "non-identical triplets" include development of knockout mice lacking single or multiple subtypes, new insights into subcellular localization and trafficking, identification of allosteric modulators, and increasing evidence for an important role in brain function. Although all three subtypes activate the same G(q/11) signaling pathway, they also appear to interact with different protein binding partners. Recent evidence suggests they may also form dimers, and may initiate independent signals through pathways yet to be clearly elucidated. Thus, this subfamily represents a common phenomenon of a group of similar but non-identical receptor subtypes activated by the same neurotransmitter, whose individual functional roles remain to be clearly established.

Role of PKCα and PKCι in phenylephrine-induced contraction of rat corpora cavernosa

Constriction of the penile vasculature prevents erection and is largely mediated by physiological agonists. We hypothesized that protein kinase C (PKC) may act as a regulator of penile vascular tone. Studies were designed to identify PKC isoforms present and to investigate their roles in phenylephrine-induced muscle contraction in the isolated rat corpora cavernosa. We demonstrated the presence of PKCalpha, beta, gamma, epsilon, delta, eta, and iota in rat corpora cavernosa and a subcellular distribution, which favored a membrane association for PKCalpha, beta, delta, and iota. Phenylephrine (3 microM) generated an active stress of 9.6 +/- 1.5 mN/mm2 and was associated with a significant increase of PKCalpha and PKCiota immunoreactivity in the particulate fraction. The amount of PKCalpha and PKCiota in the particulate fraction rose by 36 +/- 4.4 and 51 +/- 2.2% with phenylephrine stimulation. Furthermore, the phenylephrine concentration-response curve was potentiated in the presence of phorbol 12-myristate13-acetate (PMA) (0.1 microM), a PKC activator (EC50: phenylephrine 1.0 +/- 0.8 microM vs phenylephrine + PMA 0.3 +/- 0.1 microM) and inhibited in the presence of chelerythrine chloride (30 microM), a PKC inhibitor (EC50: phenylephrine 1.0 +/- 0.8 microM vs phenylephrine + chelerythrine chloride 5.7 +/- 2.4 microM). Based on these results, we suggest a potential role for PKCalpha and PKCiota in phenylephrine-induced smooth muscle tone of the rat cavernosum.

Role of the LXXLL-motif and activation function 2 domain in subcellular localization of Dax-1 (dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1)

Dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (Dax-1, NR0B1) is an orphan nuclear receptor that represses transcription by Ad4 binding protein/steroidogenic factor 1 (Ad4BP/SF-1, NR5A1). Observations on human diseases and the phenotypes of mice, in which the corresponding genes have been disrupted, have elucidated essential roles of these two nuclear receptors in differentiation of steroidogenic tissues. However, little is known about how the functions of these factors are regulated. Here we have examined their subcellular localization and have clarified the molecular mechanisms regulating subcellular localization of Dax-1. Prompted by the finding that nuclear localization of Dax-1 correlates with the presence of Ad4BP/SF-1 in the early stages of pituitary development, we have tested the possibility that interaction between the two factors is essential for the nuclear localization of Dax-1. In vitro studies with cultured cells demonstrated that an interaction involving the LXXLL motifs in the N-terminal repeat region of Dax-1 plays a key role in its subcellular localization. In addition, we found that a mutant form of DAX-1 (L466R), from a patient with adrenal hypoplasia congenita, was defective in nuclear localization in spite of having an intact N terminus. Taken together, the results reveal that the subcellular localization of Dax-1 is influenced by the presence of Ad4BP/SF-1, and that two regions of Dax-1 have important roles for this process.

Porcine spermadhesin PSP-I/PSP-II stimulates macrophages to release a neutrophil chemotactic substance: modulation by mast cells

The complex of porcine seminal plasma heterodimers I and II (PSP-I/PSP-II), which are heterodimers of glycosylated spermadhesins, is the major component of porcine seminal fluid. The proinflammatory and immunostimulatory activities of this spermadhesin complex suggest its participation in modulation of the uterine immune activity that may ensure reproductive success. Spermadhesin PSP-I/PSP-II induced the migration of neutrophils into the peritoneal cavity of rats via activation of resident cells. In the present study, we have investigated the involvement of macrophages and mast cells in the neutrophil chemotactic activity of PSP-I/PSP-II and the underlying mechanism. Macrophages and mast cells were isolated, cultured, and stimulated with purified PSP-I/PSP-II. Pharmacological modulation was performed using the glucocorticoid dexamethasone, indomethacin (cyclooxygenase inhibitor), MK886 (leukotriene inhibitor), and the supernatant of spermadhesin-stimulated mast cells. Macrophages stimulated with PSP-I/PSP-II released into the culture supernatant a neutrophil chemotactic substance. This activity was partly inhibited by both dexamethasone (85%) and the supernatant of spermadhesin-stimulated mast cells (74%) but not by indomethacin and MK886. An anti-tumor necrosis factor (TNF) alpha antibody neutralized (by 68%) the neutrophil chemotactic activity of PSP-I/PSP-II-stimulated macrophages. An anti-interleukin (IL)-4 antibody blocked the inhibitory activity of spermadhesin-stimulated mast cells on release of a neutrophil chemotactic substance by PSP-I/PSP-II-stimulated macrophages. As a whole, these data indicate that the neutrophil migration-inducing ability of spermadhesin PSP-I/PSP-II involves the release of the inflammatory cytokine TNFalpha by stimulated macrophages and that this activity is modulated by the lymphokine IL-4 liberated by mast cells. The balance between these two cytokines may control onset of the local inflammatory reaction, avoiding excessive neutrophil recruitment that would lead to tissue damage.

Correlation of subcellular compartmentalization of HPMA copolymer-Mce6 conjugates with chemotherapeutic activity in human ovarian carcinoma cells

PURPOSE

Intracellular targets sensitive to oxidized damage generated by photodynamic therapy (PDT) utilizing N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-mesochlorin e6 monoethylenediamine (Mce6) conjugates was explored to aid in the design of second generation PDT delivery systems.

METHODS

Low temperature, metabolic inhibitor, and nuclear localization sequences (NLS(FITC)) were used to achieve desired subcellular localization that was evaluated by confocal analysis and subcellular fractionation. Mce6 was bound to HPMA copolymer conjugates via non-degradable dipeptide linkers (P-GG-Mce6, P-NLS(FITC)-GG-Mce6) or lysosomally degradable tetrapeptide spacers (P-GFLG-Mce6, P-NLS(FITC)-GFLG-Mce6). Chemotherapeutic efficacy was assessed by the concentration that inhibited growth by 50% (IC50), cell associated drug concentration (CAD) and confocal microscopy.

RESULTS

P-GFLG-Mce6 possessed enhanced chemotherapeutic activ ity compared to P-GG-Mce6 indicating enzymatically released Mce6 was more active than copolymer-bound Mce6. Lysosomes appeared less sensitive to photodamage as observed by a higher IC50. Nuclear-directed HPMA copolymer-Mce6 conjugates (P-NLS(FITC)-GG-Mce6, P-NLS(FITC)-GFLG-Mce6) possessed enhanced chemotherapeutic activity. However, control cationic HPMA copolymer-Mce6 conjugates containing a scrambled NLS (P-scNLS(FITC)-GG-Mce6) or amino groups (P-NH2-GG-Mce6) also displayed increased chemotherapeutic activity.

CONCLUSIONS

Nuclear delivery was observed for P-NLS(FITC)-GG-Mce6 and P-NLS(FITC)-GFLG-Mce6 indicating NLS was a feasible approach for nuclear delivery. Due to the cationic nature of NLS, increased membrane binding of PDT systems incorporating cationic nuclear targeting moieties must be addressed.

Macrophages induce apoptosis in proximal tubule cells

Macrophages play important roles during renal inflammation. Infiltrating macrophages produce proinflammatory mediators and induce apoptosis in a variety of target cells. Because proximal tubules are frequently damaged in inflammatory processes, we investigated murine macrophages (J774) in the induction of apoptosis in murine PKSV-PR proximal tubule cells. PKSV-PR cells were co-cultured with activated or non-activated macrophages. Apoptosis was assessed by Annexin-V-FITC/propidium iodide staining and analyzed by fluorescence-activated cell sorting. Macrophages were separated from tubule cells with transwell membranes to distinguish soluble factor-mediated from direct cell-to-cell contact-mediated apoptosis. Cell supernatants from activated and non-activated macrophages were analyzed for induction of apoptosis. Activated (but not non-activated) macrophages induced tubule cell apoptosis in co-culture. Soluble factors were mainly responsible for induction of apoptosis; membrane separation and transfer of cell supernatant from activated macrophages showed similar levels of apoptosis induction. Although tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta(1), measured by ELISA, increased significantly in supernatants from activated macrophages, blocking TNF-alpha and TGF-beta did not decrease apoptosis in PKSV-PR cells co-cultured with macrophages. Moreover, exogenous addition of TNF-alpha, TGF-beta, anti-Fas antibody, or TRAIL failed to induce apoptosis in tubule cells. We conclude that inflammatory macrophages mediate proximal tubule cell death, directing apoptosis mainly via release of unidentified soluble factors.

Presence and functional significance of presynaptic ryanodine receptors

Ca(2+)-induced Ca(2+) release (CICR) mediated by sarcoplasmic reticulum resident ryanodine receptors (RyRs) has been well described in cardiac, skeletal and smooth muscle. In brain, RyRs are localised primarily to endoplasmic reticulum (ER) and have been demonstrated in postsynaptic entities, astrocytes and oligodendrocytes where they regulate intracellular Ca(2+) concentration ([Ca(2+)](i)), membrane potential and the activity of a variety of second messenger systems. Recently, the contribution of presynaptic RyRs and CICR to functions of central and peripheral presynaptic terminals, including neurotransmitter release, has received increased attention. However, there is no general agreement that RyRs are localised to presynaptic terminals, nor is it clear that RyRs regulate a large enough pool of intracellular Ca(2+) to be physiologically significant. Here, we review direct and indirect evidence that on balance favours the notion that ER and RyRs are found in presynaptic terminals and are physiologically significant. In so doing, it became obvious that some of the controversy originates from issues related to (i) the ability to demonstrate conclusively the physical presence of ER and RyRs, (ii) whether the biophysical properties of RyRs are such that they can contribute physiologically to regulation of presynaptic [Ca(2+)](i), (iii) how ER Ca(2+) load and feedback gain of CICR contributes to the ability to detect functionally relevant RyRs, (iv) the distance that Ca(2+) diffuses from plasma membranes to RyRs to trigger CICR and from RyRs to the Active Zone to enhance vesicle release, and (v) the experimental conditions used. The recognition that ER Ca(2+) stores are able to modulate local Ca(2+) levels and neurotransmitter release in presynaptic terminals will aid in the understanding of the cellular mechanisms controlling neuronal function.

A mathematical model of single target site location by Brownian movement in subcellular compartments

The location of distinct sites is mandatory for many cellular processes. In the subcompartments of the cell nucleus, only very small numbers of diffusing macromolecules and specific target sites of some types may be present. In this case, we are faced with the Brownian movement of individual macromolecules and their "random search" for single/few specific target sites, rather than bulk-averaged diffusion and multiple sites. In this article, I consider the location of a distant central target site, e.g. a globular protein, by individual macromolecules executing unbiased (i.e. drift-free) random walks in a spherical compartment. For this walk-and-capture model, the closed-form analytic solution of the first passage time probability density function (p.d.f.) has been obtained as well as the first and second moment. In the limit of a large ratio of the radii of the spherical diffusion space and central target, well-known relations for the variance and the first two moments for the exponential p.d.f. were found to hold with high accuracy. These calculations reinforce earlier numerical results and Monte Carlo simulations. A major implication derivable from the model is that non-directed random movement is an effective means for locating single sites in submicron-sized compartments, even when the diffusion coefficients are comparatively small and the diffusing species are present in one copy only. These theoretical conclusions are underscored numerically for effective diffusion constants ranging from 0.5 to 10.0 microm(2) s(-1), which have been reported for a couple of nuclear proteins in their physiological environment. Spherical compartments of submicron size are, for example, the Cajal bodies (size: 0.1-1.0 microm), which are present in 1-5 copies in the cell nucleus. Within a small Cajal body of radius 0.1 microm a single diffusing protein molecule (with D=0.5 microm(2) s(-1)) would encounter a medium-sized protein of radius 2.5 nm within 1 s with a probability near certainty (p=0.98).

Characterization of ribosomal S6 protein kinase p90rsk during meiotic maturation and fertilization in pig oocytes: mitogen-activated protein kinase-associated activation and localization

Mitogen-activated protein kinase (MAPK) becomes activated during the meiotic maturation of pig oocytes, but its physiological substrate is unknown. The 90-kDa ribosome S6 protein kinase (p90rsk) is the best known MAPK substrate in Xenopus and mouse oocytes. The present study was designed to investigate the expression, phosphorylation, subcellular localization, and possible roles of p90rsk in porcine oocytes during meiotic maturation, fertilization, and parthenogenetic activation. This kinase was partially phosphorylated in oocytes at germinal vesicle (GV) stage through a MAPK-independent mechanism, but its full phosphorylation is dependent on MAPK activity. After fertilization or electrical activation, p90rsk was dephosphorylated shortly before pronucleus formation, which coincided with the inactivation of MAPK. A protein phosphatase inhibitor, okadaic acid, accelerated the phosphorylation of p90rsk during meiotic maturation and induced its rephosphorylation in activated eggs. MAPK kinase (MAPKK or MEK) inhibitor U0126 inhibited the activation of MAPK and p90rsk in both cumulus-enclosed and denuded pig oocytes, but prevented GV breakdown (GVBD) only in cumulus-enclosed oocytes. Active MAPK and p90rsk were detected in pig cumulus cells, and U0126 induced their dephosphorylation. In meiosis II arrested eggs, U0126 led to the inactivation of MAPK and p90rsk, as well as the interphase transition of the eggs. P90rsk was distributed evenly in GV oocytes, but it accumulated in the nucleus before GVBD. It was localized to the meiotic spindle after GVBD and concentrated in the spindle mid zone during emission of the polar bodies. All these results suggest that p90rsk is downstream of MAPK and plays functional roles in the regulation of nuclear status and microtubule organization. Although MAPK and p90rsk activity are not essential for the spontaneous meiotic resumption in denuded oocytes, activation of this cascade in cumulus cells is indispensable for the gonadotropin-induced meiotic resumption of pig oocytes.

Renal effects of supernatant from macrophages activated by Crotalus durissus cascavella venom: the role of phospholipase A2 and cyclooxygenase

In Brazil, the genus Crotalus is responsible for approximately 1500 cases of snakebite annually. The most common complication in the lethal cases is acute renal failure, although the mechanisms of the damaging effects are not totally understood. In this work, we have examined the renal effects caused by a supernatant of macrophages stimulated by Crotalus durissus cascavella venom as well the potential role of phospholipase A2 and cyclo-oxygenase. Rat peritoneal macrophages were collected and placed in a RPMI medium and stimulated by crude Crotalus durissus cascavella venom (1, 3 or 10 microg/ml) for 1 hr. They were then washed and kept in a culture for 2 hr. The supernatant (1 ml) was tested in an isolated perfused rat kidney. The first 30 min. of each experiment were used as an internal control, and the supernatant was added to the system after this period. All experiments lasted 120 min. A study of toxic effect on perfusion pressure, glomerular filtration rate, urinary flow percent of sodium tubular transport and percent of proximal tubular sodium transport was made. The lowest concentration of venom (1 microg/ml) was not statistically different from the control values. The most intense effects were seen at 10 microg/ml for all renal parameters. The infusion of the supernatant of macrophages stimulated with crude venom (3 or 10 microg/ml) increased the perfusion pressure, glomerular filtration rate and urinary flow, decreased the percent of sodium tubular transport and percent of proximal tubular sodium transport. Dexamethasone (10 microM) and quinacrine (10 microM) provided protection against the effect of the venom on glomerular filtration rate, urinary flow, percent of sodium tubular transport, percent of proximal tubular sodium transport and perfusion pressure. Indomethacin (10 microM) and nordiidroguaretic acid (1 microM) reversed almost all functional changes, except those of the perfusion pressure. These results suggest that macrophages stimulated with Crotalus durissus cascavella venom release mediators capable of promoting nephrotoxicity in vitro. Moreover, phospholipase A2 and cyclooxygenase products are involved in these biologic effects.

Isometric force kinetics upon rapid activation and relaxation of mouse, guinea pig and human heart muscle studied on the subcellular myofibrillar level

The kinetics of force development and relaxation upon rapid application and removal of Ca2+ was measured in bundles of few myofibrils isolated from triton X-100 skinned left ventricular trabeculae of mice (M), guinea pigs (G) and humans (H). Upon rapidly switching from relaxing solution (pCa 7.5) to activating solution (pCa 4.5) at 10 degrees C, force rose by a single exponential with a rate constant k(act) of 5.2 s(-1) (M), 1.7 s(-1) (G) and 0.3 s(-1) (H) to a plateau of 0.14 microN/microm2 (M), 0.16 microN/microm2 (G) and 0.15 microN/microm2 (H). A rapid release followed by a rapid restretch to the original length applied during steady-state Ca2+ activation at pCa 4.5 induced an exponential force redevelopment with a rate constant k(redev) that was indistinguishable from k(act), indicating that k(act) is limited by cross-bridge turnover kinetics rather than by the Ca2+-induced activation of the regulatory system. Upon rapidly switching from pCa 4.5 to pCa 7.5, force decayed in a pronounced biphasic manner. Thus a slow initial, almost linear decay with a rate constant k(lin) of 1.8 s(-1) (M), 0.6 s(-1) (G) and 0.15 s(-1) (H) and a duration t(lin) of 0.06 s (M), 0.11 s (G) and 0.3 s (H) was followed by a rapid exponential decay with a rate constant k(rel) of 18 s(-1) (M), 11 s(-1) (G) and 4.6 s(-1) (H). The pronounced biphasic shapes of the force decays determined here for the first time in cardiac myofibrils differs from the force decays that had been reported for multicellular skinned trabeculae in which relaxation was induced by rapid removal of Ca2+ by flash photolysis of caged Ca2+ chelators. In the skinned trabeculae, no pronounced initial slow phase was observed. The force decays shown here are much more similar to those reported for single skeletal myofibrils. The kinetics of isometric relaxation of skinned trabeculae (i.e., multicellular preparations), therefore, do not reflect the kinetics of force relaxation at the cardiac myofibrillar level.

Subcellular interactions between parallel fibre and climbing fibre signals in Purkinje cells predict sensitivity of classical conditioning to interstimulus interval

Classical conditioning of the nictitating membrane response requires a specific temporal interval between conditioned stimulus and unconditioned stimulus, and produces an increase in Protein Kinase C (PKC) activation in Purkinje cells. To evaluate whether biochemical interactions within the Purkinje cell may explain the temporal sensitivity, a model of PKC activation by Ca2+, diacylglycerol (DAG), and arachidonic acid (AA) is developed. Ca2+ elevation is due to CF stimulation and IP3 induced Ca2+ release (IICR). DAG and IP3 result from PF stimulation, while AA results from phospholipase A2 (PLA2). Simulations predict increased PKC activation when PF stimulation precedes CF stimulation by 0.1 to 3 s. The sensitivity of IICR to the temporal relation between PF and CF stimulation, together with the buffering system of Purkinje cells, significantly contribute to the temporal sensitivity.

Extinction antagonizes olfactory memory at the subcellular level

Memory loss occurs by diverse mechanisms, as different time constants of performance decrement and sensitivities to experimental manipulations suggest. While the phenomena of memory decay, interference, and extinction are well established behaviorally, little is known about them at the circuit or molecular level. In Drosophila, odorant memories lasting up to 3 hr can be localized to mushroom body Kenyon cells, a single neuronal level in the olfactory pathway. The plasticity underlying this memory trace can be induced without Kenyon cell synaptic output. Experimental extinction, i.e., presentation of the conditioned stimulus without the reinforcer, reduces memory performance and does so at the same circuit level as memory formation. Thus, unreinforced presentation of learned odorants antagonizes intracellularly the signaling cascade underlying memory formation.

Involvement of P2X7 receptors in the regulation of neurotransmitter release in the rat hippocampus

Although originally cloned from rat brain, the P2X7 receptor has only recently been localized in neurones, and functional responses mediated by these neuronal P2X7 receptors (P2X7 R) are largely unknown. Here we studied the effect of P2X7 R activation on the release of neurotransmitters from superfused rat hippocampal slices. ATP (1-30 mm) and other ATP analogues elicited concentration-dependent [3 H]GABA outflow, with the following rank order of potency: benzoylbenzoylATP (BzATP) > ATP > ADP. PPADS, the non-selective P2-receptor antagonist (3-30 microm), Brilliant blue G (1-100 nm) the P2X7 -selective antagonist and Zn2+ (0.1-30 microm) inhibited, whereas lack of Mg2+ potentiated the response by ATP. In situ hybridization revealed that P2X7 R mRNA is expressed in the neurones of the cell body layers in the hippocampus. P2X7 R immunoreactivity was found in excitatory synaptic terminals in CA1 and CA3 region targeting the dendrites of pyramidal cells and parvalbumin labelled structures. ATP (3-30 microm) and BzATP (0.6-6 microm) elicited concentration-dependent [14 C]glutamate efflux, and blockade of the kainate receptor-mediated transmission by CNQX (10-100 microm) and gadolinium (100 microm), decreased ATP evoked [3 H]GABA efflux. The Na+ channel blocker TTX (1 microm), low temperature (12 degrees C), and the GABA uptake blocker nipecotic acid (1 mm) prevented ATP-induced [3 H]GABA efflux. Brilliant blue G and PPADS also reduced electrical field stimulation-induced [3 H]GABA efflux. In conclusion, P2X7 Rs are localized to the excitatory terminals in the hippocampus, and their activation regulates the release of glutamate and GABA from themselves and from their target cells.

Activation of the p53 tumor suppressor protein

The p53 tumor suppressor gene plays an important role in preventing cancer development, by arresting or killing potential tumor cells. Mutations within the p53 gene, leading to the loss of p53 activity, are found in about half of all human cancers, while many of the tumors that retain wild type p53 carry mutations in the pathways that allow full activation of p53. In either case, the result is a defect in the ability to induce a p53 response in cells undergoing oncogenic stress. Significant advances have been made recently in our understanding of the molecular pathways through which p53 activity is regulated, bringing with them fresh possibilities for the design of cancer therapies based on reactivation of the p53 response.

Recruitment of activated G protein-coupled receptors to pre-existing clathrin-coated pits in living cells

The process of clathrin-mediated endocytosis tightly regulates signaling of the superfamily of seven-transmembrane G protein-coupled receptors (GPCRs). A fundamental question in the cell biology of membrane receptor endocytosis is whether activated receptors can initiate the formation of clathrin-coated pits (CPs) or whether they are simply mobilized to pre-existing CPs. Here, using various approaches, including a dynamic assay to monitor the distribution of CPs and GPCR-beta-arrestin complexes in live HeLa cells, we demonstrate for the first time that activated GPCRs do not initiate the de novo formation of CPs but instead are targeted to pre-existing CPs.

Disparate cell types use a shared complex of PDZ proteins for polarized protein localization

Based on their morphology and function, epithelial cells and neurons appear to have very little in common; however, growing evidence indicates that these two disparate cell types share an underlying polarization pathway responsible for sorting proteins to specific subcellular sites. An evolutionarily conserved complex of PDZ domain-containing proteins thought to be responsible for polarized protein localization has been identified from both brain and epithelial tissue, both from mammals and from the nematode C. elegans. Some of the most recent data on PDZ proteins and the proteins with which they interact are summarized. In particular, some of the more recently proposed models for their function in cells, and the in vivo and in vitro data that support these models are focussed upon.

Apical organelles of Apicomplexa: biology and isolation by subcellular fractionation

The apical organelles are characteristic secretory vesicles of Plasmodium, Toxoplasma, Cryptosporidium and other apicomplexan organisms. They consist of rhoptries, micronemes and dense granules. Recent research has provided much new data concerning their structure, contents, functions and development. All of these organelles contain complex mixtures of proteins, with broad homologies as well as differences in molecular structure between species and genera. Many of the proteins interact with host cell membranes, and are thought to mediate selective adhesion to host cells as well as membrane modification during intracellular invasion. Micronemal proteins are important in the initial selection of host cells, and in enabling gliding motility of the parasites, while rhoptries appear to be more important in parasitophorous vacuole formation. Dense granules are involved predominantly in modifying the host cell after invasion. Research into apical organellar composition and function depends on accurate assignment of molecular identity. This requires the simultaneous application of several complementary approaches including immunolocalisation by light- and electron-microscopy, subcellular fractionation, and transgene expression. The merits and limitations of these different types of approach are discussed, and the importance of cell fractionation methods in characterising apical organelle proteins is stressed.

S-Nitrosylation of mitochondrial caspases

Caspase-3 is a cysteine protease located in both the cytoplasm and mitochondrial intermembrane space that is a central effector of many apoptotic pathways. In resting cells, a subset of caspase-3 zymogens is S-nitrosylated at the active site cysteine, inhibiting enzyme activity. During Fas-induced apoptosis, caspases are denitrosylated, allowing the catalytic site to function. In the current studies, we sought to identify the subpopulation of caspases that is regulated by S-nitrosylation. We report that the majority of mitochondrial, but not cytoplasmic, caspase-3 zymogens contain this inhibitory modification. In addition, the majority of mitochondrial caspase-9 is S-nitrosylated. These studies suggest that S-nitrosylation plays an important role in regulating mitochondrial caspase function and that the S-nitrosylation state of a given protein depends on its subcellular localization.

The complete set of genes encoding major intrinsic proteins in Arabidopsis provides a framework for a new nomenclature for major intrinsic proteins in plants

Major intrinsic proteins (MIPs) facilitate the passive transport of small polar molecules across membranes. MIPs constitute a very old family of proteins and different forms have been found in all kinds of living organisms, including bacteria, fungi, animals, and plants. In the genomic sequence of Arabidopsis, we have identified 35 different MIP-encoding genes. Based on sequence similarity, these 35 proteins are divided into four different subfamilies: plasma membrane intrinsic proteins, tonoplast intrinsic proteins, NOD26-like intrinsic proteins also called NOD26-like MIPs, and the recently discovered small basic intrinsic proteins. In Arabidopsis, there are 13 plasma membrane intrinsic proteins, 10 tonoplast intrinsic proteins, nine NOD26-like intrinsic proteins, and three small basic intrinsic proteins. The gene structure in general is conserved within each subfamily, although there is a tendency to lose introns. Based on phylogenetic comparisons of maize (Zea mays) and Arabidopsis MIPs (AtMIPs), it is argued that the general intron patterns in the subfamilies were formed before the split of monocotyledons and dicotyledons. Although the gene structure is unique for each subfamily, there is a common pattern in how transmembrane helices are encoded on the exons in three of the subfamilies. The nomenclature for plant MIPs varies widely between different species but also between subfamilies in the same species. Based on the phylogeny of all AtMIPs, a new and more consistent nomenclature is proposed. The complete set of AtMIPs, together with the new nomenclature, will facilitate the isolation, classification, and labeling of plant MIPs from other species.

The complete set of genes encoding major intrinsic proteins in Arabidopsis provides a framework for a new nomenclature for major intrinsic proteins in plants

Major intrinsic proteins (MIPs) facilitate the passive transport of small polar molecules across membranes. MIPs constitute a very old family of proteins and different forms have been found in all kinds of living organisms, including bacteria, fungi, animals, and plants. In the genomic sequence of Arabidopsis, we have identified 35 different MIP-encoding genes. Based on sequence similarity, these 35 proteins are divided into four different subfamilies: plasma membrane intrinsic proteins, tonoplast intrinsic proteins, NOD26-like intrinsic proteins also called NOD26-like MIPs, and the recently discovered small basic intrinsic proteins. In Arabidopsis, there are 13 plasma membrane intrinsic proteins, 10 tonoplast intrinsic proteins, nine NOD26-like intrinsic proteins, and three small basic intrinsic proteins. The gene structure in general is conserved within each subfamily, although there is a tendency to lose introns. Based on phylogenetic comparisons of maize (Zea mays) and Arabidopsis MIPs (AtMIPs), it is argued that the general intron patterns in the subfamilies were formed before the split of monocotyledons and dicotyledons. Although the gene structure is unique for each subfamily, there is a common pattern in how transmembrane helices are encoded on the exons in three of the subfamilies. The nomenclature for plant MIPs varies widely between different species but also between subfamilies in the same species. Based on the phylogeny of all AtMIPs, a new and more consistent nomenclature is proposed. The complete set of AtMIPs, together with the new nomenclature, will facilitate the isolation, classification, and labeling of plant MIPs from other species.

Characterization of the manganese-containing superoxide dismutase and its gene regulation in stress response of Schizosaccharomyces pombe

Fission yeast Schizosaccharomyces pombe contains two superoxide dismutases (SODs), one in the cytosol and the other in mitochondria. The sod2+ gene encoding putative mitochondrial superoxide dismutase containing manganese (MnSOD) has been isolated. Purification and analysis of the sod2+ gene product revealed that it contained only manganese as a cofactor, thus verified to be a genuine MnSOD. It was localized in mitochondria as expected. Its N-terminal amino acid sequence indicated that the mitochondrial targeting sequence of 21 amino acids was removed. The native form consisted of two identical subunits. The sod2+ expression was induced by external stresses, such as treatments with superoxide generators, high osmolarity, and heat. The induction by these stress treatments depended on Wis1-Spc1 MAPK signal transduction pathway being independent of transcription factors Atf1 or Pap1. The sod2 disruption rendered cells sensitive to various superoxide-generators, heat, and high osmolarity, suggesting that the mitochondrial MnSOD acts as a general defense agent against multiple stresses.

Control of cell polarity and chemotaxis by Akt/PKB and PI3 kinase through the regulation of PAKa

We demonstrate that PI3 kinase and protein kinase B (PKB or Akt) control cell polarity and chemotaxis, in part, through the regulation of PAKa, which is required for myosin II assembly. We demonstrate that PI3K and PKB mediate PAKa's subcellular localization, PAKa's activation in response to chemoattractant stimulation, and chemoattractant-mediated myosin II assembly. Mutation of the PKB phosphorylation site in PAKa to Ala blocks PAKa's activation and inhibits PAKa redistribution in response to chemoattractant stimulation, whereas an Asp substitution leads to an activated protein. Addition of the PI3K inhibitor LY294002 results in a rapid loss of cell polarity and the axial distribution of actin, myosin, and PAKa. These results provide a mechanism by which PI3K regulates chemotaxis.

Assessment of prediction accuracy of protein function from protein--protein interaction data

Functional prediction of open reading frames coded in the genome is one of the most important tasks in yeast genomics. Among a number of large-scale experiments for assigning certain functional classes to proteins, experiments determining protein-protein interaction are especially important because interacting proteins usually have the same function. Thus, it seems possible to predict the function of a protein when the function of its interacting partner is known. However, in vitro experiments often suffer from artifacts and a protein can often have multiple binding partners with different functions. We developed an objective prediction method that can systematically include the information of indirect interaction. Our method can predict the subcellular localization, the cellular role and the biochemical function of yeast proteins with accuracies of 72.7%, 63.6% and 52.7%, respectively. The prediction accuracy rises for proteins with more than three binding partners and thus we present the open prediction results for 16 such proteins.

Regulation of the activities of multifunctional Ca2+/calmodulin-dependent protein kinases

Ca2+/calmodulin-dependent protein kinases (CaM-kinases) II, IV, and I play important roles as Ca2+ responsive multifunctional protein kinases in controlling a variety of cellular functions in response to an increase in intracellular Ca2+, and hence regulation of their activities is very important. CaM-kinase II is activated through autophosphorylation of threonine-286 (in the case of alpha isoform), and CaM-kinases IV and I are activated through phosphorylation of threonine-196 and 177, respectively, by CaM-kinase kinase. After activation, CaM-kinases II and IV lose their Ca2+/calmodulin-dependent activity upon autophosphorylation of threonine-305 and serine-332, respectively, in the absence of Ca2+, becoming Ca2+/calmodulin-independent forms. The activated CaM-kinases II, IV, and I are deactivated upon dephosphorylation of phosphothreonine-286, 196, and 177, respectively, by CaM-kinase phosphatase or other multifunctional protein phosphatases and restored to the original ground states. Thus, the activities of the three multifunctional CaM-kinases are regulated by phosphorylation and dephosphorylation.

Redundant and segregated functions of granule-associated heparin-binding group II subfamily of secretory phospholipases A2 in the regulation of degranulation and prostaglandin D2 synthesis in mast cells

We herein demonstrate that mast cells express all known members of the group II subfamily of secretory phospholipase A2 (sPLA2) isozymes, and those having heparin affinity markedly enhance the exocytotic response. Rat mastocytoma RBL-2H3 cells transfected with heparin-binding (sPLA2-IIA, -V, and -IID), but not heparin-nonbinding (sPLA2-IIC), enzymes released more granule-associated markers (beta-hexosaminidase and histamine) than mock- or cytosolic PLA2alpha (cPLA2alpha)-transfected cells after stimulation with IgE and Ag. Site-directed mutagenesis of sPLA2-IIA and -V revealed that both the catalytic and heparin-binding domains are essential for this function. Confocal laser and electron microscopic analyses revealed that sPLA2-IIA, which was stored in secretory granules in unstimulated cells, accumulated on the membranous sites where fusion between the plasma membrane and granule membranes occurred in activated cells. These results suggest that the heparin-binding sPLA2s bind to the perigranular membranes through their heparin-binding domain, and lysophospholipids produced in situ by their enzymatic action may facilitate the ongoing membrane fusion. In contrast to the redundant role of sPLA2-IIA, -IID, and -V in the regulation of degranulation, only sPLA2-V had the ability to markedly augment IgE/Ag-stimulated immediate PGD2 production, which reached a level comparable to that elicited by cPLA2alpha. The latter observation reveals an unexplored functional segregation among the three related isozymes expressed in the same cell population.

Identification of further important residues within the Glut4 carboxy-terminal tail which regulate subcellular trafficking

The insulin-responsive glucose transporter, Glut4, exhibits a unique subcellular distribution such that in the absence of insulin >95% of the protein is stored within intracellular membranes. In response to insulin, Glut4 exhibits a large mobilisation to the plasma membrane. Studies of the amino acid motifs which regulate the unique trafficking of Glut4 have identified several key residues within the soluble cytoplasmic N- and C-terminal domains of Glut4. Of particular note is a Leu-498Leu-499 motif within the C-terminal domain that has been proposed to regulate both internalisation from the plasma membrane and sorting to an insulin-sensitive compartment. In this study, we have examined the role of the adjacent amino acids (Glu-491, Gln-492 and Glu-493) by their sequential replacement with Ala. Our results are consistent with the notion that Glu-491 and Glu-493 play an important role in the sub-endosomal trafficking of Glut4, as substitution of these residues with Ala results in increased levels of these proteins at the cell surface, reduced insulin-stimulated translocation and increased susceptibility to endosomal ablation. These residues, together with other identified sequences within the C-terminus of Glut4, are likely to be crucial targeting elements that regulate Glut4 subcellular distribution.

Significance of platelet-derived microparticles and activated platelets in diabetic nephropathy

We measured levels of platelet-derived microparticles (PMP), which have coagulative activity and are produced by platelet activation or physical stimulation, and CD62P/CD63-positive platelets in patients with diabetes mellitus to determine their clinical significance and effects on complications of diabetes including diabetic nephropathy. We also compared these levels before and after administration of the antiplatelet drug cilostazol. Plasma PMP and CD62P/CD63-positive platelet levels were significantly higher in patients with diabetes mellitus than normal controls. CD62P-positive platelet levels were significantly higher in patients with nephropathy than in patients without complications. After administration of cilostazol, PMP and CD62P/CD63-positive platelet levels were significantly decreased. The increases in platelet activity and its related procoagulant activity appear to account in part for the hypercoagulability observed in diabetes mellitus. Our findings suggest that activated platelets might play a role in the development of diabetic nephropathy. Furthermore, antiplatelet therapy with cilostazol for diabetic patients may be useful as antithrombin therapy including antiplatelet therapy, since it suppresses the production of intrinsic coagulants produced by platelet activation.

Loose ligation of the rat sciatic nerve is accompanied by changes in the subcellular content of protein kinase C beta II and gamma in the spinal dorsal horn

This study examined whether loose ligation of the sciatic nerve was accompanied by specific changes in protein kinase C (PKC) betaII and gamma isozymes in the spinal dorsal horn. The isozyme staining pattern was visualized with immunocytochemistry. Their content in subcellular fractions was estimated from Western immunoblots. In control animals, PKC betaII immunoreactivity extended from lamina I into lamina III, while PKC gamma immunoreactivity was concentrated within laminae II and III. In ligated animals exhibiting thermal hyperalgesia, the content of both PKC betaII and gamma in the synaptosomal membrane fraction, but not crude cytosolic fraction, was significantly greater by an average of 40% from their respective controls. These data support suggestions that peripheral nerve injury engenders plastic changes in the dorsal horn to contribute to the development of persistent pain.

Effect of ticlopidine on platelet-derived microparticles in patients with connective tissue diseases

We evaluated the plasma concentrations of platelet activation markers and platelet-derived microparticles (PMP) in patients with connective tissue diseases complaining of peripheral circulation disorders (n = 16) and studied the effect of ticlopidine hydrochloride (ticlopidine) on PMP generation. There were significant differences in the levels of PMP and a platelet activation marker between before and after treatment with ticlopidine (PMP: 695 +/- 393 vs. 354 +/- 206/10(4) platelets, p < 0. 01; platelet CD63: 9.13 +/- 5.64 vs. 5.22 +/- 2.74%, p < 0.05). On the other hand, markers of vascular endothelium, such as vascular endothelium-derived small vesicles and serum thrombomodulin levels, were not affected by the administration of ticlopidine. Levels of cytokines and soluble adhesion molecules remained unchanged by ticlopidine administration. These findings suggest that ticlopidine may be useful for the inhibition of PMP-dependent vascular damage in patients with connective tissue diseases complaining of peripheral circulation disorders.

pH regulation in apoplastic and cytoplasmic cell compartments of leaves

The regulation of pH in the apoplast, cytosol and chloroplasts of intact leaves was studied by means of fluorescent pH indicators and as a response of photosynthesis to acid stress. The apoplastic pH increased under anaerobiosis. Aeration reversed this effect. Apoplastic responses to CO2, HCl or NH3 differed considerably. Whereas HCl and ammonia caused rapid acidification or alkalinization, the return to initial pH values was slow after cessation of fumigation. Addition of CO2 either did not produce the acidification expected on the basis of known apoplastic buffering or even caused some alkalinization. Removal of CO2 shifted the apoplastic pH into the alkaline range before the pH returned to initial steady-state levels. In the presence of vanadate, the alkaline shift was absent and the apoplastic pH returned slowly to the initial level when CO2 was removed from the atmosphere. In contrast to the response of the apoplast, anaerobiosis acidified the cytosol or, in some species, had little effect on its pH. Acidification was rapidly reversed upon re-admission of oxygen. The CO2-dependent pH changes were very fast in the cytosol. Considerable alkalinization was observed after removal of CO2 under aerobic, but not under anaerobic conditions. Rates of the re-entry of protons into the cytosol during recovery from CO2 stress increased in the presence of oxygen with the length of previous exposure to high CO2. Effective pH regulation in the chloroplasts was indicated by the recovery of photosynthesis after the transient inhibition of photosynthetic electron flow when CO2 was increased from 0.038% to 16% in air. As photosynthesis became inhibited under high CO2, reduction of the electron transport chain increased transiently. The time required for recovery of photosynthesis from inhibition during persistent CO2 stress was similar to the time required for establishing steady-state pH values in the cytosol under acid stress. The high capacity of leaf cells for the rapid re-attainment of pH homeostasis in the apoplast and the cytoplasm under acid or alkaline stress suggested the rapid activation or deactivation of membrane-localised proton-transporting enzymes and corresponding ion channel regulation for co-transport of anions or counter-transport of cations together with proton fluxes. Acidification of the cytoplasm appeared to activate energy-dependent proton export primarily into the vacuoles whereas apoplastic alkalinization resulted in the pumping of protons into the apoplast. Proton export rates from the cytosol into the apoplast after anaerobiosis were about 100 nmol (m2 leaf area)(-1) s(-1) or less. Proton export under acid stress into the vacuole was about 1200 nmol m(-2) s(-1). The kinetics of pH responses to the addition or withdrawal of CO2 indicated the presence of carbonic anhydrase in the cytosol, but not in the apoplast.

Platelet-derived microparticles stimulate coronary artery smooth muscle cell mitogenesis by a PDGF-independent mechanism

This study investigates the role of platelet-derived microparticles for vascular smooth muscle cell (SMC) proliferation. Microparticles concentration dependently stimulated p42/p44 MAP kinase phosphorylation, c-fos induction, DNA synthesis, and proliferation of cultured bovine coronary artery SMC. The maximum mitogenic effects of microparticles were significantly higher than those of platelet-derived growth factor (PDGF)-BB. Microparticle-induced SMC mitogenesis was heat sensitive, whereas the effects of PDGF were not. In addition, neutralizing anti-PDGF antibodies prevented PDGF-induced DNA synthesis but did not inhibit the effects of microparticles. In contrast to PDGF, which potently stimulated SMC migration, microparticles had only minor migratory activity. These results demonstrate a novel mechanism of SMC mitogenesis by platelet-derived microparticles that is probably independent of PDGF.

Structural transitions at microtubule ends correlate with their dynamic properties in Xenopus egg extracts

Microtubules are dynamically unstable polymers that interconvert stochastically between growing and shrinking states by the addition and loss of subunits from their ends. However, there is little experimental data on the relationship between microtubule end structure and the regulation of dynamic instability. To investigate this relationship, we have modulated dynamic instability in Xenopus egg extracts by adding a catastrophe-promoting factor, Op18/stathmin. Using electron cryomicroscopy, we find that microtubules in cytoplasmic extracts grow by the extension of a two- dimensional sheet of protofilaments, which later closes into a tube. Increasing the catastrophe frequency by the addition of Op18/stathmin decreases both the length and frequency of the occurrence of sheets and increases the number of frayed ends. Interestingly, we also find that more dynamic populations contain more blunt ends, suggesting that these are a metastable intermediate between shrinking and growing microtubules. Our results demonstrate for the first time that microtubule assembly in physiological conditions is a two-dimensional process, and they suggest that the two-dimensional sheets stabilize microtubules against catastrophes. We present a model in which the frequency of catastrophes is directly correlated with the structural state of microtubule ends.

Activation of human leukocytes by acute hypoxia

Exposure of human leukocytes to 12% and 6% O(2) in vitro resulted in striking ultrastructural and morphological changes. These changes included the appearance of crater-like holes, a reduction in granular size and disruption of the cellular membrane. The implications of these findings is discussed.