Regulation of tissue inhibitor of metalloproteinases-1 in rat Sertoli cells: induction by germ cell residual bodies, interleukin-1alpha, and second messengers

In the testis, FSH has been shown to induce the expression and secretion of tissue inhibitor of metalloproteinases-1 (TIMP-1) from Sertoli cells in vitro. This study was performed to elucidate further the cellular origin of testicular TIMP-1 and its expression by hormonal and paracrine factors. This is the first report on the expression of testicular TIMP-1 in vivo. TIMP-1 mRNA in whole testis was decreased after hypophysectomy and strongly increased by the injection of FSH-S17 to hypophysectomized rats. Primary cultures of both peritubular and Sertoli cells showed basal expression of TIMP-1 mRNA. In contrast, we were unable to detect TIMP-1 mRNA in Leydig cells, freshly isolated immature germ cells (primary spermatocytes and spermatids), or residual bodies. We further show that treatment of Sertoli cells with 8-(4-chlorophenyl)thio-cAMP (8-CPTcAMP) in combination with 12-O-tetradecanoylphorbol 13-acetate (TPA) or Ca(2+) inducers (calcium ionophore A23187 or thapsigargin) had additive (TPA) and synergistic effects (Ca(2+)) on the level of TIMP-1 mRNA and secreted protein. We also show that both the level of TIMP-1 mRNA and secreted protein from Sertoli cells were strongly increased by residual bodies, as well as by the cytokine interleukin-1alpha. TIMP-1 was not up-regulated by either 8-CPTcAMP or interleukin-1alpha in peritubular cells. In contrast to the regulated secretory fraction of TIMP-1, we also detected constitutively expressed immunoreactive TIMP-1 in the nucleus of Sertoli cells, suggesting a role of nuclear TIMP-1 in these cells. In conclusion, our data show that secretion of TIMP-1 from Sertoli cells is highly regulated by hormonal and local processes in the testis, indicating that TIMP-1 is of physiological importance during both testicular development and spermatogenesis.

Subcellular compartmentalization of E2F family members is required for maintenance of the postmitotic state in terminally differentiated muscle

Maintenance of cells in a quiescent state after terminal differentiation occurs through a number of mechanisms that regulate the activity of the E2F family of transcription factors. We report here that changes in the subcellular compartmentalization of the E2F family proteins are required to prevent nuclei in terminally differentiated skeletal muscle from reentering S phase. In terminally differentiated L6 myotubes, E2F-1, E2F-3, and E2F-5 were primarily cytoplasmic, E2F-2 was nuclear, whereas E2F-4 became partitioned between both compartments. In these same cells, pRB family members, pRB, p107, and p130 were also nuclear. This compartmentalization of the E2F-1 and E2F-4 in differentiated muscle cells grown in vitro reflected their observed subcellular location in situ. We determined further that exogenous E2F-1 or E2F-4 expressed in myotubes at levels fourfold greater than endogenous proteins compartmentalized identically to their endogenous counterparts. Only when overexpressed at higher levels was inappropriate subcellular location for these proteins observed. At these levels, induction of the E2F-regulated genes, cyclins A and E, and suppression of factors associated with myogenesis, myogenin, and p21(Cip1) was observed. Only at these levels of E2F expression did nuclei in these terminally differentiated cells enter S phase. These data demonstrate that regulation of the subcellular compartmentalization of E2F-family members is required to maintain nuclei in a quiescent state in terminally differentiated cells.

Half a century of "the nuclear matrix"

A cell fraction that would today be termed "the nuclear matrix" was first described and patented in 1948 by Russian investigators. In 1974 this fraction was rediscovered and promoted as a fundamental organizing principle of eukaryotic gene expression. Yet, convincing evidence for this functional role of the nuclear matrix has been elusive and has recently been further challenged. What do we really know about the nonchromatin elements (if any) of internal nuclear structure? Are there objective reasons (as opposed to thinly veiled disdain) to question experiments that use harsh nuclear extraction steps and precipitation-prone conditions? Are the known biophysical properties of the nucleoplasm in vivo consistent with the existence of an extensive network of anastomosing filaments coursing dendritically throughout the interchromatin space? To what extent may the genome itself contribute information for its own quarternary structure in the interphase nucleus? These questions and recent work that bears on the mystique of the nuclear matrix are addressed in this essay. The degree to which gene expression literally depends on nonchromatin nuclear structure as a facilitating organizational format remains an intriguing but unsolved issue in eukaryotic cell biology, and considerable skepticism continues to surround the nuclear matrix fraction as an accurate representation of the in vivo situation.

Rabphilin knock-out mice reveal that rabphilin is not required for rab3 function in regulating neurotransmitter release

Rab3A and rab3C are GTP-binding proteins of synaptic vesicles that regulate vesicle exocytosis. Rabphilin is a candidate rab3 effector at the synapse because it binds to rab3s in a GTP-dependent manner, it is co-localized with rab3s on synaptic vesicles, and it dissociates with rab3s from the vesicles during exocytosis. Rabphilin contains two C(2) domains, which could function as Ca(2+) sensors in exocytosis and is phosphorylated as a function of stimulation. However, it is unknown what essential function, if any, rabphilin performs. One controversial question regards the respective roles of rab3s and rabphilin in localizing each other to synaptic vesicles: although rabphilin is mislocalized in rab3A knock-out mice, purified synaptic vesicles were shown to require rabphilin for binding of rab3A but not rab3A for binding of rabphilin. To test whether rabphilin is involved in localizing rab3s to synaptic vesicles and to explore the functions of rabphilin in regulating exocytosis, we have now analyzed knock-out mice for rabphilin. Mice that lack rabphilin are viable and fertile without obvious physiological impairments. In rabphilin-deficient mice, rab3A is targeted to synaptic vesicles normally, whereas in rab3A-deficient mice, rabphilin transport to synapses is impaired. These results show that rabphilin binds to vesicles via rab3s, consistent with an effector function of rabphilin for a synaptic rab3-signal. Surprisingly, however, no abnormalities in synaptic transmission or plasticity were observed in rabphilin-deficient mice; synaptic properties that are impaired in rab3A knock-out mice were unchanged in rabphilin knock-out mice. Our data thus demonstrate that rabphilin is endowed with the properties of a rab3 effector but is not essential for the regulatory functions of rab3 in synaptic transmission.

Role of myosin II tail sequences in its function and localization at the cleavage furrow in Dictyostelium

Cytoplasmic myosin II accumulates in the cleavage furrow and provides the force for cytokinesis in animal and amoeboid cells. One model proposes that a specific domain in the myosin II tail is responsible for its localization, possibly by interacting with a factor concentrated in the equatorial region. To test this possibility, we have expressed myosins carrying mutations in the tail domain in a strain of Dictyostelium cells from which the endogenous myosin heavy chain gene has been deleted. The mutations used in this study include four internal tail deletions: Mydelta824-941, Mydelta943-1464, Mydelta943-1194 and Mydelta1156-1464. Contrary to the prediction of the hypothesis, immunofluorescence staining demonstrated that all mutant myosins were able to move toward the furrow region. Chimeric myosins, which consisted of a Dictyostelium myosin head and chicken skeletal myosin tail, also efficiently localized to the cleavage furrow. All these deletion and chimeric mutant myosins, except for Mydelta943-1464, the largest deletion mutant, were able to support cytokinesis in suspension. Our data suggest that there is no single specific domain in the tail of Dictyostelium myosin II that is required for its functioning at and localization to the cleavage furrow.

Frequent colocalization of mu opioid and NMDA-type glutamate receptors at postsynaptic sites in periaqueductal gray neurons

In the ventrolateral periaqueductal gray (PAG), endogenous pathways which dampen pain transmission can be activated by either opioids or excitatory amino acids such as N-methyl D-aspartate (NMDA). The effects of these ligands may converge, because morphine-produced analgesia in the PAG can be blocked by NMDA receptor antagonists. To determine the relationship between the subcellular sites where opioid ligands of the mu opioid receptor (MOR) and NMDA receptor ligands may act, we studied the ultrastructural distribution of immunolabeling for MOR and the R1 subunit of the NMDA receptor (NR1) in the ventrolateral PAG. MOR labeling was most commonly distributed along extrasynaptic regions of the plasma membrane of neuronal dendrites (80% or 245/306). In addition, MOR labeling was found presynaptically in axon terminals (13% or 39/306) which preferentially formed symmetric (inhibitory-type) synapses. NR1 immunoreactivity was also prevalent in dendrites (72% or 242/335), but in contrast to MOR, was usually associated with a subset of postsynaptic densities. Axon terminals (5%, 17/335) and glial processes (18%, 61/335) comprised the remainder of NR1-labeled profiles. There was a striking colocalization of MOR and NR1 labeling within dendrites. The majority of NR1-labeled dendrites contained MOR labeling (72%, 176/242) and likewise, the majority of MOR-labeled dendrites contained NR1 labeling (72%, 176/245). Thus, mu opioid and NMDA receptor ligands may act at several overlapping subcellular sites to modulate behaviors subserved by the ventrolateral PAG, such as antinociception.

Effects of the central pair apparatus on microtubule sliding velocity in sea urchin sperm flagella

To produce oscillatory bending movement in cilia and flagella, the activity of dynein arms must be regulated. The central-pair microtubules, located at the centre of the axoneme, are often thought to be involved in the regulation, but this has not been demonstrated definitively. In order to determine whether the central-pair apparatus are directly involved in the regulation of the dynein arm activity, we analyzed the movement of singlet microtubules that were brought into contact with dynein arms on bundles of doublets obtained by sliding disintegration of elastase-treated flagellar axonemes. An advantage of this new assay system was that we could distinguish the bundles that contained the central pair apparatus from those that did not, the former being clearly thicker than the latter. We found that microtubule sliding occurred along both the thinner and the thicker bundles, but its velocity differed between the two kinds of bundles in an ATP concentration dependent manner. At high ATP concentrations, such as 0.1 and 1 mM, the sliding velocity on the thinner bundles was significantly higher than that on the thicker bundles, while at lower ATP concentrations the sliding velocity did not change between the thinner and the thicker bundles. We observed similar bundle width-related differences in sliding velocity after removal of the outer arms. These results provide first evidence suggesting that the central pair and its associated structures may directly regulate the activity of the inner (and probably also the outer) arm dynein.

Isoform sorting and the creation of intracellular compartments

The generation of isoforms via gene duplication and alternative splicing has been a valuable evolutionary tool for the creation of biological diversity. In addition to the formation of molecules with related but different functional characteristics, it is now apparent that isoforms can be segregated into different intracellular sites within the same cell. Sorting has been observed in a wide range of genes, including those encoding structural molecules, receptors, channels, enzymes, and signaling molecules. This results in the creation of intracellular compartments that (a) can be independently controlled and (b) have different functional properties. The sorting mechanisms are likely to operate at the level of both proteins and mRNAs. Isoform sorting may be an important consequence of the evolution of isoforms and is likely to have contributed to the diversity of functional properties within groups of isoforms.

Influence of SR Ca(2+)-ATPase and Na(+)-Ca(2+)-exchanger on the force-frequency relation

The data presented indicate that altered systolic and diastolic function in failing human hearts may result from altered expression of calcium cycling proteins. Decreased systolic force production and inversion of the force-frequency relation seem to be related to reduced protein levels of SR Ca2+ ATPase and/or to increased protein levels of the Na(+)-Ca2+ exchanger resulting in an increased ratio of Na(+)-Ca2+ exchanger to SR Ca2+ ATPase. Impaired diastolic function may result from reduced SR Ca2+ ATPase and is most pronounced in failing hearts with lack of upregulation of the Na(+)-Ca2+ exchanger. Thus, failing hearts with reduced SR Ca2+ ATPase protein levels and unchanged Na(+)-Ca2+ exchanger protein levels exhibit severe impairment of both systolic and diastolic function.

Effect of bafilomycin A1 and nocodazole on endocytic transport in HeLa cells: implications for viral uncoating and infection

Bafilomycin A1 (baf), a specific inhibitor of vacuolar proton ATPases, is commonly employed to demonstrate the requirement of low endosomal pH for viral uncoating. However, in certain cell types baf also affects the transport of endocytosed material from early to late endocytic compartments. To characterize the endocytic route in HeLa cells that are frequently used to study early events in viral infection, we used 35S-labeled human rhinovirus serotype 2 (HRV2) together with various fluid-phase markers. These virions are taken up via receptor-mediated endocytosis and undergo a conformational change to C-antigenic particles at a pH of <5.6, resulting in release of the genomic RNA and ultimately in infection (E. Prchla, E. Kuechler, D. Blaas, and R. Fuchs, J. Virol. 68:3713-3723, 1994). As revealed by fluorescence microscopy and subcellular fractionation of microsomes by free-flow electrophoresis (FFE), baf arrests the transport of all markers in early endosomes. In contrast, the microtubule-disrupting agent nocodazole was found to inhibit transport by accumulating marker in endosomal carrier vesicles (ECV), a compartment intermediate between early and late endosomes. Accordingly, lysosomal degradation of HRV2 was suppressed, whereas its conformational change and infectivity remained unaffected by this drug. Analysis of the subcellular distribution of HRV2 and fluid-phase markers in the presence of nocodazole by FFE revealed no difference from the control incubation in the absence of nocodazole. ECV and late endosomes thus have identical electrophoretic mobilities, and intraluminal pHs of <5.6 and allow uncoating of HRV2. As bafilomycin not only dissipates the low endosomal pH but also blocks transport from early to late endosomes in HeLa cells, its inhibitory effect on viral infection could in part also be attributed to trapping of virus in early endosomes which might lack components essential for uncoating. Consequently, inhibition of viral uncoating by bafilomycin cannot be taken to indicate a low pH requirement only.

Occurrence of a transcription factor, cAMP response element-binding protein (CREB), in the postsynaptic sites of the brain

The postsynaptic density (PSD) fraction prepared from the rat forebrain contained a transcription factor, cAMP response element-binding protein (CREB). The occurrence of CREB in the PSD was confirmed by immunoelectron microscopic examination. CREB in the PSD fraction was phosphorylated both by protein kinase A and Ca2+/calmodulin-dependent protein kinase II (CaMKII) endogenous to the fraction, and dissociated from the PSD after phosphorylation, especially under CaMKII-activated conditions. The fraction containing CREB that was released from PSD after phosphorylation possessed cAMP response element (CRE)-binding activity. Thus, PSD anchors functionally active CREB. These results suggest that CREB anchored to the PSD is liberated by phosphorylation upon specific synaptic stimulation, translocates into the nucleus, and then triggers synaptic activity-dependent changes in gene expression.

Involvement of PKC-alpha in regulatory volume decrease responses and activation of volume-sensitive chloride channels in human cervical cancer HT-3 cells

1. The present study was carried out to identify the specific protein kinase C (PKC) isoform involved in regulatory volume decrease (RVD) responses, and to investigate the signal transduction pathways underlying the activation of volume-sensitive chloride channels in human cervical cancer HT-3 cells. The role of Ca2+ in RVD and in the activation of chloride currents was also studied. 2. The time course of RVDs was prolonged by microinjection of PKC-alpha antibody but not by PKC-beta or PKC-gamma antibody, and also by exposure to Ca2+-free medium, in particular when combined with microinjection of EDTA. Immunofluorescence staining showed that hypotonic superfusion evoked the translocation of PKC-alpha to the cell membrane, whereas PKC-beta or PKC-gamma remained unaffected. The translocation of PKC-alpha was observed a few minutes after hypotonic stress, reaching peak intensity at 30 min, and returned to the cytoplasm 60 min after hypotonic exposure. Western blot analyses showed an increased PKC-alpha level in terms of intensity and phosphorylation in the cell membrane, while neither PKC-beta nor PKC-gamma was activated upon hyposmotic challenge. 3. Whole-cell patch-clamp studies demonstrated that neomycin and PKC blockers such as staurosporine and H7 inhibited volume-sensitive chloride currents. The inhibitory effect of neomycin on chloride currents can be reversed by the PKC activator phorbol 12-myristate, 13-acetate (PMA). Moreover, the PKC inhibitor and PKC-alpha antibody, but not PKC-beta or PKC-gamma antibody, significantly attenuated the chloride currents. The activation of volume-sensitive chloride currents were insensitive to the changes of intracellular Ca2+ but required the presence of extracellular Ca2+. 4. Our results suggest the involvement of PKC-alpha and extracellular Ca2+ in RVD responses and the activation of volume-sensitive chloride channels in HT-3 cells.

PAK promotes morphological changes by acting upstream of Rac

The serine/threonine kinase p21-activated kinase (PAK) has been implicated as a downstream effector of the small GTPases Rac and Cdc42. While these GTPases evidently induce a variety of morphological changes, the role(s) of PAK remains elusive. Here we report that overexpression of betaPAK in PC12 cells induces a Rac phenotype, including cell spreading/membrane ruffling, and increased lamellipodia formation at growth cones and shafts of nerve growth factor-induced neurites. These effects are still observed in cells expressing kinase-negative or Rac/Cdc42 binding-deficient PAK mutants, indicating that kinase- and p21-binding domains are not involved. Furthermore, lamellipodia formation in all cell lines, including those expressing Rac binding-deficient PAK, is inhibited significantly by dominant-negative RacN17. Equal inhibition is achieved by blocking PAK interaction with the guanine nucleotide exchange factor PIX using a specific N-terminal PAK fragment. We conclude that PAK, via its N-terminal non-catalytic domain, acts upstream of Rac mediating lamellipodia formation through interaction with PIX.

Prostasome-like particles in stallion semen

Human semen contains membranous vesicles called prostasomes. They are secreted by the prostate gland and contain large amounts of cholesterol, sphingomyelin, and Ca2+. Prostasomes enhance the motility of ejaculated spermatozoa and are involved in a number of additional biological functions. No prostasome-like vesicles have been described in horse semen up to now. We have demonstrated the presence of prostasome-like vesicles in the equine semen and characterized them as to size, morphology, and lipid composition; we have found that they are similar to human prostasomes in many respects. We propose that these vesicles might be important for the fecundity of horse semen. This is of interest since the success of artificial insemination is limited by the fact that stallion sperm barely survive cryopreservation.

Subcellular localization and possible function of actin, tropomyosin and actin-related protein 3 (Arp3) in the fission yeast Schizosaccharomyces pombe

We investigated subcellular localizations and interactions of actin and two actin cytoskeleton-related proteins, Cdc8 tropomyosin and actin-related protein 3, Arp3, in the fission yeast Schizosaccharomyces pombe, using specific antibodies and by gene disruption. Actin was localized to the medial microfilamentous ring in the region of the septum during cytokinesis and to cortical patches by immunoelectron microscopy. F-actin cables were detected throughout the cell cycle by fluorescent staining with Bodipy-phallacidin. Cables were often linked to the patches and to the medial ring during its formation. Tropomyosin was localized to the medial ring and the cables. It was also distributed in the cell as patches, although co-localization with F-actin was not frequent. In cdc8ts mutant cells, F-actin cables were not observed although the F-actin patches were detected and cell polarity was maintained. These observations suggest that the F-actin cables may be involved in the formation of the medial ring, and that tropomyosin plays an important role in organizing both the ring and the cable, but is not involved in the F-actin patch formation or maintenance of cell polarity. Binding of Arp3 to actin was revealed by immunoprecipitation as well as by DNase I column chromatography. Arp3 seemed to form a complex with several proteins in the cell extracts, as previously reported for other organisms. Contrary to a previous report (McCollum et al., EMBO J. 15, 6438-6446, 1996), Arp3 was found to be concentrated in the medial region from early anaphase to late cytokinesis. Following arp3 gene disruption, F-actin patches were delocalized throughout the cell and cells did not undergo polarized growth, suggesting that Arp3 influences the proper localization of the actin patches in the cell and thereby controls the polarized growth of the cell.

Role of tyrosine kinase in erythrocyte lysate-induced contraction in rabbit cerebral arteries

OBJECT

This study was undertaken to explore whether erythrocyte lysate, a proposed cause of vasospasm, produces vasoconstriction by activation of tyrosine kinase in rabbit cerebral arteries.

METHODS

Isometric tension was used to monitor contractions in rabbit basilar arteries induced by erythrocyte lysate, 5-hydroxytryptamine (5-HT), or KCl in the absence or presence of tyrosine kinase inhibitors. Erythrocyte lysate, 5-HT, or KCl produced concentration-dependent contractions in rabbit basilar arteries. Preincubation with the tyrosine kinase inhibitors tyrphostin A23 and genistein (30 and 100 microM), but not diadzein, an inactive analog of genistein, attenuated significantly the contraction induced by erythrocyte lysate (p < 0.05). Tyrphostin A23, genistein, and diadzein (30 microM) failed to reduce the contraction caused by 5-HT. Genistein, but not tyrphostin A23 or diadzein (30 microM), attenuated significantly the contraction induced by KCl (p < 0.05). In another series, arterial rings were initially contracted with erythrocyte lysate, 5-HT, or KCl and the relaxant effect of genistein was then tested. Genistein relaxed rabbit basilar arteries that had been contracted by exposure to erythrocyte lysate, 5-HT, or KCl (30-100 microM; p < 0.05).

CONCLUSIONS

These data indicate that tyrosine kinase may play a role in the regulation of cerebral arterial contraction and tyrosine kinase inhibitors may be useful in the management of cerebral vasospasm.

Quantitation of changes in P0 mRNA by polymerase chain reaction in primary cultured Schwann cells stimulated by axolemma-enriched fraction

A requirement for large numbers of primary culture cells has frequently restricted investigations of gene expression in glial cells. We have developed a non-radioactive method based on reverse transcription-polymerase chain reaction (RT-PCR) to accurately assess small changes in the expression of the myelin specific gene P0 in Schwann cells. Using axolemma-enriched fraction (AEF) as an inducing agent, we demonstrate that RT-PCR can be used to detect 4-8-fold increases in P0 mRNA levels occurring in a time and dose dependent manner, utilizing only 250000 cells per assay. Initial experiments used an in vitro transcribed RNA for P0 constructed with a 300 bp deletion for quantitation by competitive RT-PCR. Relative quantitation by co-amplification of the housekeeping gene glyceraldehyde-phosphate dehydrogenase was established and provided similar results. Product evaluation was enhanced 50-100-fold by the incorporation of primers labelled with biotin at the 5' end, allowing for the sensitive detection of PCR product by enhanced chemiluminescence and autoradiography. This technique provides sensitivity to detect and evaluate picogram amounts of DNA. Our results validate the assay for P0 gene expression and indicate that the technique should facilitate the study of multiple genes of interest in glial cell systems.

The impact of cellular fragmentation induced experimentally at different stages of mouse preimplantation development

It has been demonstrated previously that removal of acellular debris from the preimplantation mouse embryo is beneficial for subsequent development to the hatched blastocyst stage. We have studied the impact of cellular fragmentation induced in the mouse embryo during the late pronuclei and 8-cell stages on the hatching frequency and total cell number at the blastocyst stage. At the late pronuclei stage about one-quarter of the cytoplasm was removed from embryos in the experimental group, in four to six steps, thus creating four to six cytoplasts that were subsequently returned as anucleated fragments under the zona pellucida. Embryos with one-quarter of the cytoplasm removed and with intact cytoplasm after partial zona dissection (PZD) served as controls. At the 8-cell stage, embryos with their nucleoplast removed from two blastomeres served as an experimental group. Groups of embryos with part of the cytoplast removed from two blastomeres (nucleated fragments), embryos with two blastomeres removed and embryos after PZD alone served as controls. After manipulation all embryos were left in culture and analysed at about 100 h after human chorionic gonadotrophin administration. Fragments induced at the late pronuclei stage did not participate in compaction and were often spontaneously expelled from the embryo during hatching. Neither embryo hatching rate nor total cell number was affected when compared with zygotes with reduced cytoplasm. Although both nucleated and anucleated fragments induced at the 8-cell stage participated in recompaction, hatching was not compromised and there was no interference in further development as assessed by the cell number or hatching rate at the blastocyst stage, as compared with embryos with blastomeres removed. We conclude that anucleated cellular fragments formed in an otherwise healthy embryo, both before and after acquisition of the ability for compaction, are benign and that their removal provides no benefit for embryo development, at least to the hatched blastocyst stage.

Regulation of the insulin signalling pathway by cellular protein-tyrosine phosphatases

Protein-tyrosine phosphatases (PTPases) have been implicated in the physiological regulation of the insulin signalling pathway. In cellular and molecular studies, the transmembrane, receptor-type PTPase LAR and the intracellular, non-receptor enzyme PTP1B have been shown to have a direct impact on insulin action in intact cell models. Since insulin signalling can be enhanced by reducing the abundance or activity of specific PTPases, pharmaceutical agents directed at blocking the interaction between individual PTPases and the insulin receptor may have potential clinical relevance to the treatment of insulin-resistant states such as obesity and Type II diabetes mellitus.

Subcellular and submitochondrial mode of action of Bcl-2-like oncoproteins

Bcl-2 is the prototype of a class of oncogenes which regulates apoptosis. Bcl-2-related gene products with either death-promoting and death-inhibitory activity are critically involved in numerous disease states and thus constitute prime targets for therapeutic interventions. The relative amount of death agonists and antagonists from the Bcl-2 family constitutes a regulatory rheostat whose function is determined, at least in part, by selective protein-protein interactions. Bcl-2 and its homologs insert into intracellular membranes including mitochondria, the endoplasmatic reticulum and the nuclear envelope. Many of the molecular genetic, ultrastructural, crystallographic and functional studies suggest that Bcl-2-related molecules exert their apoptosis-regulatory effects via regulating mitochondrial alterations preceding the activation of apoptogenic proteases and nucleases. Via a direct effect on mitochondrial membranes, Bcl-2 prevents all hallmarks of the early stage of apoptosis including disruption of the inner mitochondrial transmembrane potential and the release of apoptogenic protease activators from mitochondria. The mitochondrial permeability transition (PT) pore, also called mitochondrial megachannel or multiple conductance channel, is a multiprotein complex formed at the contact site between the mitochondrial inner and outer membranes, exactly at the same localization at which Bax, Bcl-2, and Bcl-XL are particularly abundant. The PT pore participates in the regulation of matrix Ca2+, pH, deltapsim, and volume and functions as a Ca2+-, voltage-, pH-, and redox-gated channel with several levels of conductance and little if any ion selectivity. Experiments involving the purified PT pore complex indicate that Bax, Bcl-2, and Bcl-XL exert at least part of their apoptosis-regulatory function by facilitating (Bax) or inhibiting (Bcl-2, Bcl-XL) PT pore opening. These findings clarify the principal (but not exclusive) mechanism of Bcl-2-mediated cytoprotection.

Inhibitors of in vitro mineralization from rabbit aorta and their role in biomineralization

Mineralization of aorta is known to occur late in life and appears to be a pathological phenomenon. In vitro studies revealed that the matrix prepared from the thoracic aorta pieces after their extraction with 3% Na2HPO4 and 0.1 mM CaCl2 were mineralized under physiological conditions of temperature, pH, and ionic strength of the media to form matrix-bound mineral phase resembling hydroxyapatite in nature. However, the matrix identically prepared from the unextracted rabbits aortae failed to mineralize under identical assay conditions. The addition of the aorta extract in the assay system inhibited the above mineralization process. Standard biochemical techniques, e.g., dialysis, ion exchange, and molecular sieve chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and amino acid analysis by high-performance liquid chromatography were employed to isolate, purify, and characterize the potent inhibitory biomolecules from the aorta extract. The inhibitory activity of the aorta extract was found to be primarily due to the presence of three biomolecules having molecular weights of 66, 45, and 27-29 kDa. The above inhibitory biomolecules loosely associated with aorta may be involved in the control of calcification associated with arteriosclerosis.

Mechanism of the facilitation of PC2 maturation by 7B2: involvement in ProPC2 transport and activation but not folding

Among the members of the prohormone convertase (PC) family, PC2 has a unique maturation pattern: it is retained in the ER for a comparatively long time and its propeptide is cleaved in the TGN/ secretory granules rather than in the ER. It is also unique by its association with the neuroendocrine protein 7B2. This interaction results in the facilitation of proPC2 maturation and in the production of activatable proPC2 from CHO cells. In the present study, we have investigated the mechanism of this interaction. ProPC2 binds 7B2 in the ER, but exits this compartment much more slowly than 7B2. We found that proPC2 was also slow to acquire the capacity to bind 7B2, whereas 7B2 could bind proPC2 rapidly after synthesis. This indicated that proPC2 folding was the limiting step in the formation of the complex. Indeed, sensitivity of native proPC2 to N-glycanase F digestion and inhibition of proPC2 folding supported the notion that 7B2 is not involved in the early steps of proPC2 folding, and that proPC2 must fold before binding 7B2. Under experimental conditions that prevent propeptide cleavage, 7B2 expression increased proPC2 transport to the Golgi. This increase exhibited the same kinetics as the facilitation of the removal of the propeptide. Finally, proPC2 activation could be reconstituted in Golgi- enriched subcellular fractions. In vitro, 7B2 was required for proPC2 activation at an acidic pH. Taken together, our results demonstrate that rather than promoting proPC2 folding, 7B2 acts as a helper protein involved in proPC2 transport and is required in the proPC2 activation process. We propose, therefore, that 7B2 stabilizes proPC2 in a conformation already competent for these two events.

Mechanism of long-range Ca2+ signalling in the nucleus of isolated rat hepatocytes

Ca2+ regulates a wide range of cell proteins, in both the cytosol and nucleus. It enters the nucleus from stores along the nuclear envelope, but how it then spreads through the nuclear interior is unknown. Here we used high-speed confocal line-scanning microscopy to examine the propagation of Ca2+ waves across nuclei in isolated rat hepatocytes. Nuclear Ca2+ waves began at the nucleus/cytosol border as expected, then spread across the nucleus at less than half the speed of cytosolic Ca2+ waves. High concentrations of caffeine slowed Ca2+ waves in the cytosol but not in the nucleus. We developed a mathematical model based on diffusion to analyse these data, and the model was able to describe the nuclear but not cytosolic Ca2+ waves that were experimentally observed. These findings suggest that Ca2+ waves cross the nucleus by simple diffusion, which is distinct from the reaction-diffusion mechanism by which Ca2+ waves propagate across the cytosol. Since the range of messenger action for Ca2+ in the cytosol is much smaller than the distance across the nucleus, this also suggests that the unique environment and geometry of the nuclear interior may permit this simple mechanism of Ca2+ wave propagation to control Ca2+-mediated processes in a relatively large region despite Ca2+ release pools that are spatially limited.

An ATP-dependent inwardly rectifying potassium channel, KAB-2 (Kir4. 1), in cochlear stria vascularis of inner ear: its specific subcellular localization and correlation with the formation of endocochlear potential

Cochlear endolymph has a highly positive potential of approximately +80 mV. This so-called endocochlear potential (EP) is essential for hearing. Although pivotal roles of K+ channels in the formation of EP have been suggested, the types and distribution of K+ channels in cochlea have not been characterized. Because EP was depressed by vascular perfusion of Ba2+, an inhibitor of inwardly rectifying K+ (Kir) channels, but not by either 4-aminopyridine or tetraethylammonium, we examined the expression of Kir channel subunits in cochlear stria vascularis, the tissue that is supposed to play the central role in the generation of positive EP. Of 11 members of the Kir channel family examined with reverse transcription-PCR, we could detect only expression of KAB-2 (Kir4.1) mRNA in stria vascularis. KAB-2 immunoreactivity was specifically localized at the basolateral membrane of marginal cells but not in either basal or intermediate cells. Developmental expression of KAB-2 in marginal cells paralleled formation of EP. Furthermore, deaf mutant mice (viable dominant spotting; WV/WV) expressed no KAB-2 in their marginal cells. These results suggest that KAB-2 in marginal cells may be critically involved in the generation of positive EP.

Distinct processing of endogenous and overexpressed recombinant presenilin 1

The presenilin 1 (PS1) gene has been identified by positional cloning. More than 30 mutations were detected in this gene which cosegregate with Alzheimer's disease (AD). Understanding their role in disease pathogenesis requires a characterization of the PS1 protein. We have generated a set of antibodies against the three major hydrophilic domains of the deduced amino acid sequence. Analyzing cultured cells and brain samples, we identified the endogenous PS1 polypeptide as well as amino- and carboxy-terminal fragments. These metabolites were much more abundant than the full-length molecule, indicating substantial processing. Overexpression of human PS1 markedly increased the full-length polypeptide but hardly altered the amount of the metabolites. Instead, additional proteolytic fragments appeared suggesting a different metabolism of the excess PS1, which may impede studies in transfected cells. Our results indicate a tight regulation of the endogenous PS1 metabolites. PS1 and its fragments are shown to be integral membrane proteins of the endoplasmic reticulum. The mechanisms regulating the generation of the metabolites, their potential function, and role in AD remain to be studied.

Dynamic imaging of neutrophil migration in three dimensions: mechanical interactions between cells and matrix

Fluorescence confocal microscopy was used to obtain three-dimensional (3-D) images of human neutrophils migrating through a 3-D matrix of amniotic membrane with a temporal resolution of 30-60 s and a spatial resolution of approximately 2 microm in the z-dimension. Neutrophils migrating in response to a chemoattractant gradient within a 3-D matrix were apparently able to generate traction by use of lateral pseudopods inserted into footholds in the matrix as evidenced by matrix distortion. Similar anchored pseudopods were seen in cells migrating across polycarbonate membranes with 0.8-microm pores; the presence of these pores increased cell polarization and migration compared with cells on membranes without pores. Expansion of pseudopods distal to narrow constrictions in the matrix and porous filters was observed and appeared to be used to pull cells through the openings. Neutrophils deformed parts of the elastic amnion matrix during migration without permanently altering the substrate. Contact guidance of neutrophils crawling along matrix fibrils was also observed. These observations show that neutrophils migrating in 3-D are able to utilize mechanical structures in the matrix, not present on 2-D surfaces, to generate traction for locomotion.

Change of karyoskeleton during mammalian spermatogenesis: expression pattern of nuclear lamin C2 and its regulation

Nuclear lamins are a multigene family of major karyoskeletal proteins. The expression pattern of members of the lamin family has been shown to be developmentally regulated. Of particular interest have been the findings that mammalian spermatogenic cells express two small lamin isoforms (B3 and C2) which are shorter splicing variants of their somatic counterparts (the lamins B2 and C, respectively). Although lamins B3 and C2 appear to be specific for the germ line, the expression pattern and localization of these proteins is not known. In the present study, we present evidence that during rat spermatogenesis lamin C2 is selectively expressed in spermatocytes, i.e., the cells undergoing meiosis. As in the case of other members of the family, lamin C2 was detected at the nuclear periphery. Northern blotting and in situ hybridization indicate that meiotic expression of lamin C2 is regulated at the transcriptional level. This is in contrast to the situation during amphibian oogenesis, where lamin expression is largely posttrascriptionally regulated. Interestingly, the expression pattern of lamin C2 temporally coincides with that of structural protein components of another meiosis-specific karyoskeletal structure, the synaptonemal complex (SC). Taken together, we conclude that pairing and recombination of homologous chromosomes during meiotic prophase is accompanied by significant changes in the organization of the karyoskeleton which are accomplished by the expression of stage-specific proteins.

Localized calcium signalling and neuronal integration in cerebellar Purkinje neurones

The use of high resolution imaging techniques has revealed new forms of dendritic signal integration in neurones. In contrast to electrical signals that have a more widespread influence on the cell, brief Ca2+ transients resulting from synaptic activation are often restricted to a small part of the dendritic tree. In cerebellar Purkinje neurones, different levels of Ca2+ signalling have been observed that may involve the entire neurone or be spatially limited to fine dendritic structures. The Ca2+ signals accompanying subthreshold excitatory postsynaptic potentials resulting from stimulation of the excitatory parallel fibre input can be restricted to regions as small as a spiny dendrite or a single dendritic spine. With the recruitment of increasing numbers of inputs there is a summation of Ca2+ signals in highly restricted regions of the spiny dendrites that is independent of electrical summation at the soma. Of a number of potential sources that could provide the Ca2+ responsible for the postsynaptic changes, Ca2+ entry through voltage-gated Ca2+ channels has received the most support, although other sources like Ca2+ entry through ligand-gated channels and especially Ca2+ release from intracellular stores need to be considered.

Activation of aminoglycoside antibiotics to cytotoxins

We have previously postulated an enzymatic transformation of gentamicin (to a metabolite or an 'activated' molecule) as part of its ototoxic action. Here we test with eight aminoglycosides whether the proposed mechanism applies to these antibiotics as a group. Drugs were activated by incubation with a subcellular fraction from liver, and cytotoxicity was tested in a bioassay using isolated outer hair cells from guinea pig. None of the aminoglycosides compromised the viability of the cells when assayed directly, i.e. without a preceding activation. In contrast, all clinically ototoxic aminoglycosides tested were significantly cytotoxic following the incubation. Neamine, considered to be non-ototoxic, did not yield a cytotoxin. A subcellular fraction from cochlear lateral wall tissues also converted gentamicin to a cytotoxin. The results support the hypothesis that activation of aminoglycosides precedes their toxic actions and demonstrate that the capability for activation is not confined to liver.

Distribution and subcellular localization of a growth inhibitory factor in hamster liver and its intracellular partner(s)

The subcellular, intralobular distributions and intracellular partner(s) of a factor which inhibits the proliferation of cell growth (Hashimoto C. et al. (1994) Biochim. Biophys. Acta 1221, 107-117) were determined in hamster livers, using a combination of immunological and biochemical techniques. The IgG fraction from an antiserum raised against the growth inhibitory factor with 37 kDa was shown to be highly specific for the antigen. The nuclear and cytosolic fractions demonstrated inhibitory effects on cell growth and Western blot analysis revealed that both fractions contained the immunoreactive 37 kDa protein with the anti-inhibitory factor IgG but microsomal and mitochondrial fractions did not. The nuclear and cytoplasmic localization of the inhibitory factor were further confirmed by immunochemical staining mediated through the immune IgG and an avidin-biotinylated horseradish peroxidase complex, the parenchymal liver cells were clearly stained, but endothelial and connective tissue cells were not. Although some staining was evident throughout the liver parenchyma, the hepatocytes with most intensively stained nuclei were located in the periportal region. In the liver from hamsters 6 days old or the regenerating hamster livers 3 days after partial hepatectomy, the staining intensity was low and the number of hepatocytes with the inhibitory factor positive nuclei was very few compared with the adult hamster livers. In primary cultures of the isolated hepatocytes from adult hamster the inhibitory factor disappeared from nuclei after incubation for 24-48 h. The extracts of hepatic nuclei from adult hamsters were immunoprecipitated with either the anti-growth inhibitory factor IgG or a monoclonal antibody to the RM protein. The growth inhibitory factor and the RB protein coprecipitated in each case, implying that the proteins were complexed with each other in the nuclei. The RB protein family is composed of two sets of species, an un- or underphosphorylated species and a hyperphosphorylated one. It was suggested that the factor bound preferentially to the un- or underphosphorylated member of the family.

Cardiac alpha(1)-adrenoceptors that regulate contractile function: subtypes and subcellular signal transduction mechanisms

Activation of alpha(1)-adrenoceptors as well as endothelin (ET) and angiotensin II (Ang II) receptors in cardiac muscle is coupled to acceleration of the hydrolysis of phosphoinositide (PI), with resultant production of inositol 1,4,5-trisphosphate (IP(3)) and diacylglycerol. There is an excellent correlation between the extent of acceleration of the PI hydrolysis and the positive inotropic effect (PIE) under most experimental conditions after the administration of a-adrenoceptor agonists, ET and Ang II in the rabbit ventricular muscle. The PIE of the alpha-adrenoceptor agonists, ET and Ang II is associated with a negative lusitropic effect and an increase in the sensitivity of myofilaments to Ca(2)+ ions. The PIE can be selectively inhibited by inhibitors of protein kinase C (PKC) such as staurosporine, NA 0345 and H-7, with little effect on the PI hydrolysis and the PIE of isoproterenol and Bay k 8644. Surprisingly, an activator of PKC, phorbol 12,13-dibutyrate (PDBu), selectively and more completely inhibited the PIE and acceleration of PI hydrolysis induced by the alpha-adrenoceptor agonists as well as by ET and Ang II in the rabbit. These receptor agonists consistently cause intracellular alkalinization by activation of Na+-H+ exchange, while the effects on membrane ion channel activities are divergent. For example, alpha-adrenoceptor agonists cause monophasic prolongation of the action potential, the time course of which coincides well with that of the PIE, while ET and Ang II produce a biphasic change in action potential duration, i.e., the long-lasting prolongation preceded by a transient abbreviation. Alpha-adrenoceptor agonists scarcely affect I(ca), whereas ET elicits a biphasic alteration of the current. In addition, the potassium current, I(K1), is markedly suppressed by alpha-adrenoceptor agonists, but this effect is not revealed with Ang II under the same experimental condition. These results indicate that the effects of alpha(1)-adrenoceptor stimulation are partially shared by those of FT and Ang II receptor activation in the heart. Approximately 60% of the total population of alpha(1)-adrenoceptors in the rabbit ventricle are composed of alpha(1A) subtype, which is susceptible to chlorethylclonidine (CEC) and is predominantly responsible for the alpha(1)-mediated PIE and PI hydrolysis. The remaining fraction that belongs to alpha(1A) subtype is further subclassified into the WB 4101-sensitive (partly coupled to PI hydrolysis) and the niguldipine-sensitive (PI hydrolysis-unrelated) subtypes.

Exercise increases the plasma membrane content of the Na+ -K+ pump and its mRNA in rat skeletal muscles

Muscle fibers adapt to ionic challenges of exercise by increasing the plasma membrane Na+-K+ pump activity. Chronic exercise training has been shown to increase the total amount of Na+-K+ pumps present in skeletal muscle. However, the mechanism of adaptation of the Na+-K+ pump to an acute bout of exercise has not been determined, and it is not known whether it involves alterations in the content of plasma membrane pump subunits. Here we examine the effect of 1 h of treadmill running (20 m/min, 10% grade) on the subcellular distribution and expression of Na+-K+ pump subunits in rat skeletal muscles. Red type I and IIa (red-I/IIa) and white type IIa and IIb (white-IIa/IIb) hindlimb muscles from resting and exercised female Sprague-Dawley rats were removed for subcellular fractionation. By homogenization and gradient centrifugation, crude membranes and purified plasma membranes were isolated and subjected to gel electrophoresis and immunoblotting by using pump subunit-specific antibodies. Furthermore, mRNA was isolated from specific red type I (red-I) and white type IIb (white-IIb) muscles and subjected to Northern blotting by using subunit-specific probes. In both red-I/IIa and white-IIa/IIb muscles, exercise significantly raised the plasma membrane content of the alpha1-subunit of the pump by 64 +/- 24 and 55 +/- 22%, respectively (P < 0.05), and elevated the alpha2-polypeptide by 43 +/- 22 and 94 +/- 39%, respectively (P < 0.05). No significant effect of exercise could be detected on the amount of these subunits in an internal membrane fraction or in total membranes. In addition, exercise significantly increased the alpha1-subunit mRNA in red-I muscle (by 50 +/- 7%; P < 0.05) and the beta2-subunit mRNA in white-IIb muscles (by 64 +/- 19%; P < 0.01), but the alpha2- and beta1-mRNA levels were unaffected in this time period. We conclude that increased presence of alpha1- and alpha2-polypeptides at the plasma membrane and subsequent elevation of the alpha1- and beta2-subunit mRNAs may be mechanisms by which acute exercise regulates the Na+-K+ pump of skeletal muscle.

Developmental toxicity of trichloroethylene, tetrachloroethylene and four of their metabolites in rat whole embryo culture

The embryotoxicity of trichloroethylene (TRI), tetrachloroethylene (PER), and of four of their oxidative metabolites i.e. trichloroacetic acid, dichloroacetic acid, chloral hydrate, and trichloroacetyl chloride, was studied in vitro, using the rat whole embryo culture system. Embryos from Sprague-Dawley rats were explanted on gestational day 10 (plug day = day 0) and cultured for 46 h in the presence of the test chemical. All of the tested chemicals produced concentration-dependent decreases in growth and differentiation and increases in the incidence of morphologically abnormal embryos. TRI and PER produced qualitatively similar patterns of abnormalities, while TRI and/or PER metabolites, each elicited clearly distinguishable dysmorphogenic profiles. The presence of hepatic microsomal fractions in the culture medium produced marked decreases in TRI- and PER-induced embryotoxic effects, including mortality, severity of malformations, and delayed growth and differentiation.

Immunoadsorption of hepatic vesicles carrying newly synthesized dipeptidyl peptidase IV and polymeric IgA receptor

Hepatocytes must transport newly synthesized apical membrane proteins from the basolateral to the apical plasma membrane. Our earlier morphological study showed that the apical proteins share a late (subapical) part of the transcytotic pathway with the well characterized polymeric immunoglobulin A receptor (Barr, V. A., and Hubbard, A. L. (1993) Gastroenterology 105, 554-571). Starting with crude microsomes from the livers of [35S]methionine-labeled rats, we sequentially immunoadsorbed first vesicles containing the endocytic asialoglycoprotein receptor and then (from the depleted supernatant) vesicles containing the polymeric IgA receptor. Biochemical characterization indicated that early basolateral and late endosomes were present in the first population but not in the second. Neither Golgi-, apical plasma membrane (PM)-, nor basolateral PM-derived vesicles were significant contaminants of either population. Both vesicle populations contained 35S-labeled receptor and 35S-labeled-dipeptidyl peptidase IV. Importantly, the elevated relative specific activity of the dipeptidyl peptidase (% of 35S-labeled/% immunoblotted) in the second population indicated that these vesicles must transport newly synthesized dipeptidyl peptidase IV. A distinct kind of vesicle was immunoadsorbed from a "carrier-vesicle fraction"; surprisingly, these vesicles contained little 35S-receptor and virtually no dipeptidyl peptidase IV. These results, together with previous kinetic data from in vivo experiments, are consistent with a computer-generated model predicting that newly synthesized dipeptidyl peptidase IV is delivered to basolateral endosomes, which also contain newly synthesized polymeric immunoglobulin A receptor. The two proteins are then transcytosed together to the subapical region.

Changes in physical properties of vacuolar membrane during transformation of protein bodies into vacuoles in germinating pumpkin seeds

Changes in membrane molecular dynamics associated with the transformation of protein body membranes into vacuolar membranes during pumpkin seed germination, were monitored by EPR-spin probe technique. Using highly purified membrane preparations as well as 5-SASL and 16-SASL spin labels, parameters like general membrane lipid fluidity, order parameter, semicone angle, rotational correlation times tau 2B and tau 2C, ratio of immobilized to mobile lipids were determined and the activation energy for rotational diffusion of 16-SASL was calculated. Analysis of these parameters at different temperatures indicated a more rigid nature of protein body membrane comparing to vacuolar membrane, as a result of a more restricted motional freedom of lipids. These differences are discussed in terms of protein composition and various functional specialization of both types of membranes.

Characterization of synaptic vesicles and related neuronal features in nerve growth factor and ras oncogene differentiated PC12 cells

PC12 cells can differentiate into neuron-like cells after treatment with either nerve growth factor (NGF) or transduction with a retrovirus which expresses the K-ras oncogene. The concomitant treatment of NGF plus ras differentiates PC12 cells further than either agent alone with respect to neurite outgrowth, acetylcholinesterase levels, and most strikingly, the number of synaptic vesicle (SV) clusters. These SV clusters in PC12 cell neurites closely resemble those in the presynaptic terminals of neurons. Such SV clusters have not been described in cell lines previously. The SV clusters from all three differentiated groups (NGF, ras, and NGF plus ras) were similar in size, shape, and configuration, except that the ones in the doubly treated group occur in higher frequency and have more vesicles. The synaptic nature of these vesicle clusters was demonstrated by their regulated depletion after potassium stimulation. Furthermore, these vesicle clusters stained positively for two SV-associated proteins, synapsin I and synaptophysin, by EM immunocytochemistry (ICC). Such SV clusters in a cell line are very useful for characterizing the regulated release of SVs and the distribution of SV-related antigens in intact cells. Analysis by SDS-gel electrophoresis and immunoblotting indicated that synapsin I levels are higher in all three differentiated groups compared to untreated cells; whereas synaptophysin levels are lower in cells exposed to NGF alone or with NGF and ras double treatment. Possible convergence and/or divergence on the mechanisms of NGF and ras differentiation in PC12 cells are discussed.

Generation and characterization of an antiserum reactive with a proteolytic processing site within rat procorticotrophin-releasing hormone

In this paper we report the generation of an antibody specific for the cleavage site within procorticotrophin-releasing hormone (proCRH) at the N-terminus proCRH/CRH (1-41) junction. Using radioimmunoassay techniques were show that the antibody generated (781) cross-reacts specifically with the proCRH (137-150) Tyr fragment, corresponding to the cleavage site within the full length precursor molecule. The anti-cleavage site antibody does not crossreact with the endoproteolytic products originated from the CRH precursor molecule, i.e. CRH (1-41) or proCRH (125-151) or with any of the CRH-immunoreactive fragments tested i.e. CRH (36-41), CRH (1-20) and CRH (30-41). It also shows no cross-reactivity with CRH-related substances from other species, i.e. urotensin I (fish) and sauvagine (frog). The cleavage site antibody (781), recognizes the full length proCRH molecule in Western blotting and in liquid phase radioimmunoassay from transfected CHO-K1 cells expressing the full length pre-proCRH cDNA. Using immunofluorescence and immunoprecipitation techniques followed by SDS-PAGE and autoradiography, we confirm the presence of the intact CRH precursor molecule within the nucleus and the cytoplasm of stably transfected CHO-K1 cells expressing immunoreactive proCRH. The immunofluorescence studies using primary cultures of hypothalamic neurons, show that immunoreactive (IR) proCRH is localized within the perinuclear region and was also seen along the neuronal processes where it accumulates at their tips. Our results, therefore, show that this antibody will be an invaluable tool in the study of intracellular trafficking in relation to the endoproteolytic processing of the CRH precursor molecule.

Local Ca2+ transients (Ca2+ sparks) originate at transverse tubules in rat heart cells

1. The origins of local [Ca2+]i transients (Ca2+ sparks) were studied using dual-channel confocal laser scanning microscopy. Line scan images showing [Ca2+]i (as fluo-3 fluorescence) and the transverse tubule membranes (as Di-8 fluorescence) were obtained simultaneously in single rat cardiac ventricular cells. 2. Line scan images of Di-8 fluorescence showed peaks regularly spaced at intervals of 1.83 +/- 0.30 microns (mean +/- S.D.). These peaks corresponded to the transverse tubules (T-tubules) in cross-section. 3. Line scan images of fluo-3 fluorescence showed local [Ca2+]i transients (LCTs or Ca2+ sparks) evoked by electrical stimulation. 4. Eighty-five per cent (85%) of all Ca2+ sparks evoked by electrical stimulation (n = 138, in 5 cells) occurred within 0.5 micron of a T-tubule. Thirty per cent (30%) occurred within 1 pixel (0.20 micron) of a T-tubule. 5. In some cells studied (3 out of 5), certain T-tubules had a higher probability of being sites of origin of Ca2+ sparks than others. 6. These results support local control theories of excitation-contraction coupling in which Ca2+ release from the sarcoplasmic reticulum (SR) is triggered by a high local [Ca2+]i established between the L-type Ca2+ channels in the T-tubules and associated ryanodine receptor(s) in the junctional SR.

Imaging of L-type Ca2+ channels in olfactory bulb neurones using fluorescent dihydropyridine and a styryl dye

We have imaged the fluorescence of dihydropyridine-Bodipy (fDHP) in cultured olfactory bulb neurones in order to investigate the subcellular distribution of L-type calcium channels in these neurones. The neurones were stained with both fDHP and the voltage-sensitive styryl dye RH414. The fluorescence emission maxima of these dyes were in the green and red ranges of the spectrum, respectively, and were recorded by the 2 photomultiplier channels of a laser scanning microscope. The fDHP images were ratioed with the RH414 images taken simultaneously. The resulting ratio images revealed the spatial distribution of the surface density of L-type calcium channels. This density was highest on somata, in particular at the base of dendrites, and decreased with the distance from this maximum. Two classes of dendritic L-type channel distributions were observed: one with a homogeneously low density and another one with a characteristic gradient of the L-type channel density along proximal dendrites. This subcellular localization of L-type calcium channels is discussed in the light of specific functional roles.

Cell cycle regulation of human WEE1

WEE1 kinase negatively regulates entry into mitosis by catalyzing the inhibitory tyrosine phosphorylation of CDC2/cyclin B kinase. We report here an investigation of human WEE1. Endogenous WEE1 migrates as an approximately 94 kDa protein in SDS-PAGE, substantially larger than the 49 kDa protein encoded by the original human WEE1 cDNA clone that was truncated at the 5'-end. Antibody depletion experiments demonstrate that WEE1 accounts for most of the activity that phosphorylates CDC2 on Tyr15 in an in vitro assay of HeLa cell lysates, hence it is likely to have an important role in the mitotic control of human cells. WEE1 activity was not found to be elevated in HeLa cells arrested in S phase, suggesting that unreplicated DNA does not delay M phase by hyperactivating WEE1. WEE1 activity is strongly suppressed during M phase, suggesting that negative regulation of WEE1 could be part of the mechanism by which activation of CDC2/cyclin B kinase is promoted during the G2/M transition. M phase WEE1 is re-activated in samples prepared in the absence of protein phosphatase inhibitors, demonstrating that WEE1 is inhibited by a mechanism that requires protein phosphorylation.

Reassembly of Golgi stacks from mitotic Golgi fragments in a cell-free system

Rat liver Golgi stacks were incubated with mitotic cytosol for 30 min at 37 degrees C to generate mitotic Golgi fragments comprising vesicles, tubules, and cisternal remnants. These were isolated and further incubated with rat liver cytosol for 60 min. The earliest intermediate observed by electron microscopy was a single, curved cisterna with tubular networks fused to the cisternal rims. Elongation of this cisterna was accompanied by stacking and further growth at the cisternal rims. Stacks also fused laterally so that the typical end product was a highly curved stack of 2-3 cisternae mostly enclosing an electron-lucent space. Reassembly occurred in the presence of nocodazole or cytochalasin B but not at 4 degrees C or in the absence of energy supplied in the form of ATP and GTP. Pretreatment of the mitotic fragments and cytosol with N-ethylmaleimide (NEM) also prevented reassembly. GTP gamma S and A1F prevented reassembly when added during fragmentation but not when added to the reassembly mixture. In fact, GTP gamma S stimulated reassembly such that all cisternae were stacked at the end of the incubation and comprised 40% of the total membrane. In contrast, microcystin inhibited stacking so that only single cisternae accumulated. Together these results provide a detailed picture of the reassembly process and open up the study of the architecture of the Golgi apparatus to a combined morphological and biochemical analysis.

Specific protein kinase C isozymes mediate the induction of keratinocyte differentiation markers by calcium

The maturation of epidermal keratinocytes is a tightly regulated, stepwise process which requires protein kinase C (PKC) activation. We investigated the effect of elevated extracellular Ca2+, a potent differentiation signal which increases cellular sn-1,2-diacylglycerol levels, on the PKC isozyme profile of cultured murine keratinocytes. Five PKC isozymes (alpha, delta, epsilon, zeta, and eta) were detected by immunoblotting. During Ca(2+)-induced differentiation, total cellular PKC alpha decreased, PKC epsilon and eta increased 3-5-fold, and the level of other PKC isozymes was relatively unchanged. PKC alpha underwent a progressive translocation from the soluble to the particulate fraction following elevation of extracellular Ca2+. The kinetics of PKC alpha translocation corresponded with the induction of keratinocyte differentiation markers. Both PKC delta and epsilon were selectively lost from the soluble fraction of keratinocytes exposed to elevated extracellular Ca2+, resulting in an increase in the proportion of these isoforms in the particulate fraction. PKC eta increased in both the soluble and particulate fractions, while PKC zeta did not change in amount or distribution during keratinocyte differentiation. Selective down-regulation of PKC isoforms by either 12-deoxyphorbol-13-phenylacetate or bryostatin 1 inhibited Ca(2+)-induced expression of differentiation markers at doses most specific for the down-regulation of PKC alpha. Taken together, these observations suggest that the induction of keratinocyte differentiation by Ca2+ results in the activation of specific PKC isozymes.

Cell-free apoptosis in Xenopus egg extracts: inhibition by Bcl-2 and requirement for an organelle fraction enriched in mitochondria

Apoptotic cell death involves a ritual series of morphological changes, presumably reflecting a conserved molecular pathway. We now report that the nuclear events typical of apoptosis can be reproduced in "apoptotic" Xenopus egg extracts. In this cell-free system, nuclear assembly and protein import are initially normal; after 2-4 hr, however, a process of nuclear destruction ensues involving chromatin condensation and the shrinkage and fragmentation of the nuclei. This apoptotic process, which also occurs in nuclei added exogenously, is blocked by the addition of baculovirus-expressed Bcl-2 protein. To block the disintegration of nuclei that are added later, Bcl-2 must be present during this latent period. "Apoptosis" in these extracts requires a dense organelle fraction enriched in mitochondria. The cell-free system described here provides a novel tool for understanding intracellular events in apoptosis and the inhibitory function of Bcl-2.

Selective changes in angiotensin II AT1 and AT2 receptor subtypes in the rat superior colliculus following eye enucleation

In the brain of young (two weeks old) rats, angiotensin II receptors (AT2 receptors) are found in brain nuclei which receive and integrate direct visual input from the retina, the suprachiasmatic nuclei (containing only AT1 receptors), the lateral geniculate nuclei (containing AT2 receptors) and the superior colliculus (which contains both receptor types with a majority of AT2). In adult rats, angiotensin II receptors are present in the suprachiasmatic nuclei and the superior colliculus but not in the lateral geniculate. Using quantitative autoradiography we found that, in adult rats, bilateral eye enucleation caused a significant decrease in AT2 receptor binding, but not in AT1 receptor binding, and only in the superior colliculus. Unilateral enucleation of 12-day-old pups led to a decrease in AT2 receptor binding from the contralateral superior colliculus, as early as day 2 post-enucleation. Conversely, there was a significant increase in binding to AT1 receptors in the ipsilateral superior colliculus after seven days. No changes were seen in the lateral geniculate or suprachiasmatic nuclei. Angiotensin II binding to subcellular fractions of tissue from the superior colliculus region of 19-day-old pups suggested that AT2 receptor sites were present on the plasma membrane of the postsynaptic cell body. Membrane binding studies also showed a significant decrease in AT2 receptor binding to the same subcellular fractions when 19-day-old pups, enucleated seven days earlier, were compared to sham-operated animals. Our results suggest that expression of AT1 and AT2 receptors in the superior colliculus may be regulated by retinal input.

Odor stimulation causes disappearance of R4B12 epitope on axonal surface molecule of olfactory sensory neurons

Monoclonal antibodies R4B12 and R1D1 label the same subsets of rabbit primary olfactory axons. In the present study, we characterized the R4B12 antigens using immunohistochemical, immunoelectron-microscopic, and biochemical techniques. The R4B12 antigens are expressed on the surface membrane of a subset of primary olfactory axons. Western blot analysis revealed the existence of two forms (115,000 and 90,000 mol.wt) of the R4B12 antigens with different membrane-anchoring structures. Of the two forms, the smaller antigen (90,000 mol. wt) is anchored to the plasma membrane via a phosphatidylinositol linkage and expressed exclusively by the olfactory system. When the rabbit olfactory epithelium was stimulated by odors for 2-8 h in situ, the R4B12 immunoreactivity disappeared from the primary olfactory axons in the glomeruli of the olfactory bulb. These results suggest that the cell surface antigens R4B12 expressed by subsets of primary olfactory axons undergo stimulus-dependent changes by odor stimulation and may be involved in plasticity of olfactory sensory neurons.

A third form of the G protein beta subunit. 1. Immunochemical identification and localization to cone photoreceptors

Vertebrate retinal cones play a major role in both photopic vision and color perception. Although the molecular mechanism of visual excitation in the cone is not as well understood as in the rod, it is generally thought to involve a cone-specific G protein (cone transducin) that couples the cone visual pigment to a cGMP phosphodiesterase. Like all other G proteins, cone transducin is most likely a heterotrimer consisting of G alpha, G beta, and G gamma subunits. A G alpha subunit of cone transducin has been localized to the outer segment of bovine cones, but its associated G beta and G gamma subunits are unknown. To identify the G beta subunit involved in the phototransduction process of cones, we have developed a panel of antipeptide antisera against the most diverse region of the amino acid sequences encoded by G beta 1, G beta 2, and G beta 3 cDNAs and used them to determine the distribution of the G beta isoforms in different retinal preparations. We found that the G beta 3 subunit is present in bovine retinal transducin and phosducin-T beta gamma complex preparations which were previously thought to contain only G beta 1. Analysis of its subcellular distribution indicated that G beta 3 is predominantly cytoplasmic. Immunocytochemical staining of bovine retinal sections with the anti-G beta 3 antiserum further revealed a specific localization of G beta 3 in cones but not in rods. In contrast, anti-G beta 1 antiserum stained only the rods. These results suggest that G beta 3 is the G beta subunit of cone transducin and confirms the proposition that rods and cones utilize distinct signaling proteins for phototransduction.

Physiological evidence for involvement of a kinesin-related protein during anaphase spindle elongation in diatom central spindles

We have developed a new model system for studying spindle elongation in vitro using the pennate, marine diatom Cylindrotheca fusiformis. C. fusiformis can be grown in bulk to high densities while in log phase growth and synchronized by a simple light/dark regime. Isolated spindles can be attained in quantities sufficient for biochemical analysis and spindle tubulin is approximately 5% of the total protein present. The spindle isolation procedure results in a 10-fold enrichment of diatom tubulin and a calculated 40-fold increase in spindle protein. Isolated spindles or spindles in permeabilized cells can elongate in vitro by the same mechanism and with the same pharmacological sensitivities as described for other anaphase B models (Cande and McDonald, 1986; Masuda et al., 1990). Using this model, in vitro spindle elongation rate profiles were developed for a battery of nucleotide triphosphates and ATP analogs. The relative rates of spindle elongation produced by various nucleotide triphosphates parallel relative rates seen for kinesin-based motility in microtubule gliding assays. Likewise ATP analogs that allow discrimination between myosin-, dynein-, and kinesin-mediated motility produce relative spindle elongation rates characteristic of kinesin motility. Also, isolated spindle fractions are enriched for a kinesin related protein as identified by a peptide antibody against a conserved region of the kinesin superfamily. These data suggest that kinesin-like motility contributes to spindle elongation during anaphase B of mitosis.