Calcium-calmodulin dependent protein kinase II (CaMKII): a main signal responsible for early reperfusion arrhythmias

To explore whether CaMKII-dependent phosphorylation events mediate reperfusion arrhythmias, Langendorff perfused hearts were submitted to global ischemia/reperfusion. Epicardial monophasic or transmembrane action potentials and contractility were recorded. In rat hearts, reperfusion significantly increased the number of premature beats (PBs) relative to pre-ischemic values. This arrhythmic pattern was associated with a significant increase in CaMKII-dependent phosphorylation of Ser2814 on Ca(2+)-release channels (RyR2) and Thr17 on phospholamban (PLN) at the sarcoplasmic reticulum (SR). These phenomena could be prevented by the CaMKII-inhibitor KN-93. In transgenic mice with targeted inhibition of CaMKII at the SR membranes (SR-AIP), PBs were significantly decreased from 31±6 to 5±1 beats/3min with a virtually complete disappearance of early-afterdepolarizations (EADs). In mice with genetic mutation of the CaMKII phosphorylation site on RyR2 (RyR2-S2814A), PBs decreased by 51.0±14.7%. In contrast, the number of PBs upon reperfusion did not change in transgenic mice with ablation of both PLN phosphorylation sites (PLN-DM). The experiments in SR-AIP mice, in which the CaMKII inhibitor peptide is anchored in the SR membrane but also inhibits CaMKII regulation of L-type Ca(2+) channels, indicated a critical role of CaMKII-dependent phosphorylation of SR proteins and/or L-type Ca(2+) channels in reperfusion arrhythmias. The experiments in RyR2-S2814A further indicate that up to 60% of PBs related to CaMKII are dependent on the phosphorylation of RyR2-Ser2814 site and could be ascribed to delayed-afterdepolarizations (DADs). Moreover, phosphorylation of PLN-Thr17 and L-type Ca(2+) channels might contribute to reperfusion-induced PBs, by increasing SR Ca(2+) content and Ca(2+) influx.

Increased intracellular Ca2+ and SR Ca2+ load contribute to arrhythmias after acidosis in rat heart. Role of Ca2+/calmodulin-dependent protein kinase II

Returning to normal pH after acidosis, similar to reperfusion after ischemia, is prone to arrhythmias. The type and mechanisms of these arrhythmias have never been explored and were the aim of the present work. Langendorff-perfused rat/mice hearts and rat-isolated myocytes were subjected to respiratory acidosis and then returned to normal pH. Monophasic action potentials and left ventricular developed pressure were recorded. The removal of acidosis provoked ectopic beats that were blunted by 1 muM of the CaMKII inhibitor KN-93, 1 muM thapsigargin, to inhibit sarcoplasmic reticulum (SR) Ca(2+) uptake, and 30 nM ryanodine or 45 muM dantrolene, to inhibit SR Ca(2+) release and were not observed in a transgenic mouse model with inhibition of CaMKII targeted to the SR. Acidosis increased the phosphorylation of Thr(17) site of phospholamban (PT-PLN) and SR Ca(2+) load. Both effects were precluded by KN-93. The return to normal pH was associated with an increase in SR Ca(2+) leak, when compared with that of control or with acidosis at the same SR Ca(2+) content. Ca(2+) leak occurred without changes in the phosphorylation of ryanodine receptors type 2 (RyR2) and was blunted by KN-93. Experiments in planar lipid bilayers confirmed the reversible inhibitory effect of acidosis on RyR2. Ectopic activity was triggered by membrane depolarizations (delayed afterdepolarizations), primarily occurring in epicardium and were prevented by KN-93. The results reveal that arrhythmias after acidosis are dependent on CaMKII activation and are associated with an increase in SR Ca(2+) load, which appears to be mainly due to the increase in PT-PLN.

Secretion of annexin V from cultured cells requires a signal peptide

Annexin V is an intracellular protein that lacks a hydrophobic signal peptide. However, there are several studies reporting the extracellular presence of annexin V. In this study, we designed transgenes of annexin V with or without an attached secretory signal peptide and investigated the secretion of the transgene products in COS-7 cells. The signal peptide, targeted annexin V to the endoplasmic reticulum (ER), the Golgi and culture media of transfected cells. In contrast, without the signal peptide, annexin V was present only in the cytoplasm and was not detected in the medium. To confirm our results we also evaluated the presence of extracellular annexin V in two cultured cell lines: BeWo, a choriocarcinoma cell model of placental trophoblasts, and human umbilical vein endothelial cells (HUVEC). Our results showed that annexin V was immunolocalized on the surfaces of both cells but could not be detected in the culture medium of either cell type. Our results suggest that the secretion of annexin V required the recombinant addition of a hydrophobic signal peptide and that the limited quantities of endogenous cell surface annexin V on BeWo and HUVEC cells is most likely derived from adjacent damaged cells.

Phosphorylation mutants elucidate the mechanism of annexin IV-mediated membrane aggregation

Site-directed mutagenesis, electron microscopy, and X-ray crystallography were used to probe the structural basis of annexin IV-induced membrane aggregation and the inhibition of this property by protein kinase C phosphorylation. Site-directed mutants that either mimic (Thr6Asp, T6D) or prevent (Thr6Ala, T6A) phosphorylation of threonine 6 were produced for these studies and compared with wild-type annexin IV. In vitro assays showed that unmodified wild-type annexin IV and the T6A mutant, but not PKC-phosphorylated wild-type or the T6D mutant, promote vesicle aggregation. Electron crystallographic data of wild-type and T6D annexin IV revealed that, similar to annexin V, the annexin IV proteins form 2D trimer-based ordered arrays on phospholipid monolayers. Cryo-electron microscopic images of junctions formed between lipid vesicles in the presence of wild-type annexin IV indicated a separation distance corresponding to the thickness of two layers of membrane-bound annexin IV. In this orientation, a single layer of WT annexin IV, attached to the outer leaflet of one vesicle, would undergo face-to-face self-association with the annexin layer of a second vesicle. The 2.0-A resolution crystal structure of the T6D mutant showed that the mutation causes release of the N-terminal tail from the protein core. This change would preclude the face-to-face annexin self-association required to aggregate vesicles. The data suggest that reversible complex formation through phosphorylation and dephosphorylation could occur in vivo and play a role in the regulation of vesicle trafficking following changes in physiological states.

Annexin V--heparin oligosaccharide complex suggests heparan sulfate--mediated assembly on cell surfaces

BACKGROUND

Annexin V, an abundant anticoagulant protein, has been proposed to exert its effects by self-assembling into highly ordered arrays on phospholipid membranes to form a protective anti-thrombotic shield at the cell surface. The protein exhibits very high-affinity calcium-dependent interactions with acidic phospholipid membranes, as well as specific binding to glycosaminoglycans (GAGs) such as heparin and heparan sulfate, a major component of cell surface proteoglycans. At present, there is no structural information to elucidate this interaction or the role it may play in annexin V function at the cell surface.

RESULTS

We report the 1.9 A crystal structure of annexin V in complex with heparin-derived tetrasaccharides. This structure represents the first of a heparin oligosaccharide binding to a protein where calcium ions are essential for the interaction. Two distinct GAG binding sites are situated on opposite protein surfaces. Basic residues at each site were identified from the structure and site-directed mutants were prepared. The heparin binding properties of these mutants were measured by surface plasmon resonance. The results confirm the roles of these mutated residues in heparin binding, and the kinetic and thermodynamic data define the functionally distinct character of each distal binding surface.

CONCLUSION

The annexin V molecule, as it self-assembles into an organized array on the membrane surface, can bind the heparan sulfate components of cell surface proteoglycans. A novel model is presented in which proteoglycan heparan sulfate could assist in the localization of annexin V to the cell surface membrane and/or stabilization of the entire molecular assembly to promote anticoagulation.

Targeted neutralization of calcineurin, by expression of an inhibitor peptide under the control of a cholinergic specific promoter in PC12 cells, promotes neurite outgrowth in the presence of NGF

We have characterized a region of the mouse vesicular acetylcholine transporter(VAChT)/choline acetyltransferase (ChAT) gene locus that serves as a cholinergic-specific promoter for the expression of both VAChT and ChAT genes, as well as a reporter gene (LacZ) in vivo. We have used this promoter to direct the expression of an inhibitor peptide, derived from the calcineurin (CalN) autoregulatory domain, to directly neutralize the function of CalN to define the role of this Ca2+/Calmodulin regulated phosphatase in neurite outgrowth. Targeted inhibition of CalN promotes neurite outgrowth in PC12 cells in the presence of NGF, as early as 24 h after transfection. Inhibition of CalN-mediated enhancement of neurite outgrowth in PC12 cells reaches a maximum effect within the first 4 to 6 days after transfection, and does not cause adverse effects when highly expressed for up to 12 days. Cyclosporin A, a nontargeted CalN inhibitor, increases the number of neurites in mock transfected cells by 1.5 fold, while in transfected PC12 cells, the expression of the CalN inhibitor peptide increases the neurite number by 1.8 fold. These data demonstrate that CalN is an important regulator of the neurotrophic response in cholinergic cells and may prove valuable in developing treatment strategies to promote recovery from neurological injury.

Phospholipid membranes form specific nonbilayer molecular arrangements that are antigenic

Hexagonal phase (H(II))-preferring lipids such as phosphatidate, cardiolipin, and phosphatidylserine form nonbilayer molecular arrangements in lipid bilayers. While their presence in biological membranes has not been established, in vitro studies suggest that alterations in membrane properties modify their function. In this study, antiphospholipid monoclonal antibodies were developed against nonbilayer structures. One of the monoclonal antibodies identifies nonplanar surfaces in liposomes and in membranes of cultured cells. These results are the first evidence that natural membranes maintain a fragile balance between bilayer and nonbilayer lipid arrangements. Therefore, these antibodies can be used to evaluate the role of H(II)-preferring lipids in the modulation of membrane activities. Our studies demonstrated that nonplanar surfaces are highly immunogenic. Although these structures are normally transient, their formation can be stabilized by temperature variations, drugs, antibiotics, apolar peptides, and divalent cations. Our studies demonstrated that abnormal exposure of nonbilayer arrangements may induce autoimmune responses as found in the antiphospholipid syndrome.

Mutation of highly conserved arginine residues disrupts the structure and function of annexin V

BACKGROUND

Annexins are a family of structurally related proteins that bind to phospholipid membranes in a Ca(2+)-dependent manner. Annexins are characterized by highly conserved canonical domains of approximately 70 amino acids. Annexin V contains four such domains. Each of these domains has a highly conserved arginine (R).

METHODS

To evaluate the role of the conserved arginines in the molecular structure of annexin V, negatively charged amino acids were substituted for arginines at positions R43, R115, R199, and R274 using site-directed mutagenesis.

RESULTS

Mutants R199D and R274E were rapidly degraded when expressed in bacteria, and were not further characterized. R43E exhibited an electrophoretic mobility similar to the wild-type protein, while R115E migrated significantly in a slower fashion, suggesting a less compact conformation. R43E and R115E exhibited much greater susceptibility to proteolytic digestion than the wild type. While Ca(2+)-dependence for phospholipid binding was similar in both mutants (half-maximal 50-80 microM Ca2+), R43E and R115E exhibited a 6- and 2-fold decrease in phospholipid affinity, respectively. Consistent with the different phospholipid affinities of the annexins, a phospholipid-dependent clotting reaction, the activated partial thromboplastin time (aPTT), was significantly prolonged by the wild-type protein and mutants R115E and R115A. The aPTT was unaffected by R43E.

CONCLUSIONS

Our data suggest that mutation of these highly conserved arginine residues in each of the four canonical domains of annexin have differential effects on the phospholipid binding, tertiary structure, and proteolytic susceptibility of annexin V. The site I mutation, R43E, produced a large decrease in phospholipid affinity associated with an increase in proteolytic susceptibility. The site II mutation, R115E, produced a small change in phospholipid binding but a significant modification of electrophoretic mobility. Our data suggest that highly conserved arginine residues are required to stabilize the tertiary structure of annexin V by establishing hydrogen bonds and ionic bridges.

Annexin V is critical in the maintenance of murine placental integrity

OBJECTIVES

Recurrent fetal loss can be a consequence of placental thrombosis, frequently occurring in autoimmune disorders such as antiphospholipid syndrome. A potent anticoagulant, annexin V, is abundant in placental tissues. We investigated the role of annexin V in maintaining fetal viability.

STUDY DESIGN

Sites of annexin V activity in placenta were found and neutralized, and the physiologic consequences on fetal development were evaluated. To find extracellular binding sites for annexin V on placental membrane, 2 approaches were taken. An epitope-tagged recombinant annexin V was infused into pregnant BALB/c mice. Endogenous annexin V was evaluated by immunohistochemical techniques. To define a role for annexin V during pregnancy, annexin V was neutralized by tail-vein infusion of affinity-purified anti-annexin V antibodies immediately before mating, 16 hours before the vaginal plugs were observed. Fetal viability, number, and size were evaluated at days 11 or 15 after conception.

RESULTS

Endogenous annexin V is enriched along the apical surfaces of trophoblasts. Animals infused with epitope-tagged annexin V had confirmed presence of extracellular binding sites for annexin V exclusively along these surfaces. In mice infused with anti-annexin V antibodies, various degrees of fetal absorption were observed. Thrombosis and necrosis were present in the fetal component of placentas from partially absorbed embryos. Focal necrosis and fibrosis were present in the decidua of placentas from embryos that were significantly smaller than the normal embryos in the same uterus.

CONCLUSIONS

Apical surfaces of syncytiotrophoblasts in the placenta possess annexin V binding sites. The binding of annexin V to these coagulation-promoting surfaces is crucial for the maintenance of blood flow through the placenta and consequently for fetal viability. Infusion of anti-annexin V antibodies decreased the availability of annexin V to bind to the trophoblast surfaces and caused placental thrombosis, necrosis, and fetal loss. Our study suggests that anti-annexin V autoantibodies may contribute to recurrent pregnancy failure resulting from placental thrombosis, as found in patients with certain autoimmune diseases.

Identification and transgenic analysis of a murine promoter that targets cholinergic neuron expression

Choline acetyltransferase (ChAT) is a specific phenotypic marker of cholinergic neurons. Previous reports showed that different upstream regions of the ChAT gene are necessary for cell type-specific expression of reporter genes in cholinergic cell lines. The identity of the mouse ChAT promoter region controlling the establishment, maintenance, and plasticity of the cholinergic phenotype in vivo is not known. We characterized a promoter region of the mouse ChAT gene in transgenic mice, using beta-galactosidase (LacZ) as a reporter gene. A 3,402-bp segment from the 5'-untranslated region of the mouse ChAT gene (from -3,356 to +46, +1 being the translation initiation site) was sufficient to direct the expression of LacZ to selected neurons of the nervous system; however, it did not provide complete cholinergic specificity. A larger fragment (6,417 bp, from -6,371 to +46) of this region contains the requisite regulatory elements that restrict expression of the LacZ reporter gene only in cholinergic neurons of transgenic mice. This 6.4-kb DNA fragment encompasses 633 bp of the 5'-flanking region of the mouse vesicular acetylcholine transporter (VAChT), the entire open reading frame of the VAChT gene, contained within the first intron of the ChAT gene, and sequences upstream of the start coding sequences of the ChAT gene. This promoter will allow targeting of specific gene products to cholinergic neurons to evaluate the mechanisms of diseases characterized by dysfunction of cholinergic neurons and will be valuable in design strategies to correct those disorders.

Temporal inhibition of calmodulin in the nucleus

Calmodulin (CaM) acts as a primary mediator of calcium signaling by interacting with target proteins. We have previously shown that nuclear CaM is critical for cell cycle progression using a transgene containing four repeats of a CaM inhibitor peptide and nuclear targeting signals (J. Wang et al., J. Biol. Chem. 270 (1995) 30245 30248; Biochim. Biophys. Acta 1313 (1996) 223-228). To evaluate the role of CaM in the nucleus specifically during S phase of the cell cycle, a motif which stabilizes the mRNA only during S phase was included in the transgene. The CaM inhibitor mRNA transcript contains a self-annealing stem-loop derived from histone H2B at the 3' end. This structure provides stability of the mRNA only during S phase, thereby restricting CaM inhibitor expression to S phase. The inhibitor accumulates in the nucleus, particularly in the nucleoli. Flow cytometric analysis demonstrated that the CaM inhibitor is expressed in S and G2. Transfected cells show growth inhibition and a reduction in DNA synthesis. The CaM inhibitor peptide is a versatile reagent that allows spatial as well as temporal dissection of calmodulin function.

Annexins

The annexins are a family of proteins that bind anionic phospholipid surfaces in a Ca(2+)-dependent manner (general reviews include Raynal & Pollard 1994, Swairjo & Seaton 1994, Seaton 1996, Mollenhauer, 1997). Due to this functional property, individual annexins have been discovered independently by numerous laboratories with diverse experimental goals. Ca2+ characteristically causes the annexins to shift from a soluble to membrane associated state. This shift is believed to be the mechanism that underlies annexin cellular function.

Mutational and crystallographic analyses of interfacial residues in annexin V suggest direct interactions with phospholipid membrane components

Annexin V belongs to a family of eukaryotic calcium-dependent membrane-binding proteins. The calcium-binding sites at the annexin-membrane interface have been investigated in some detail; however, little is known about the functional roles of highly conserved interfacial residues that do not coordinate calcium themselves. In the present study, the importance of tryptophan 185, and threonine or serine at positions 72, 144, 228, and 303, in rat annexin V is investigated by site-directed mutagenesis, X-ray crystallography, and functional assays. The high-resolution crystal structures of the mutants show that the mutations do not cause structural perturbations of the annexin molecule itself or disappearance of bound calcium ions from calcium-binding sites. The assays indicate that relative to wild-type annexin V, loss of the methyl substituent at position 72 (Thr72-->Ser) has no effect while loss of the hydroxyl group (Thr72-->Ala or Thr72-->Lys) causes reduction of membrane binding. Multiple lysine substitutions (e.g., Thr72,Ser144,Ser228,Ser303-->Lys) have a greater adverse effect than the single lysine mutation, suggesting that in annexin V the introduction of potentially favorable electrostatic interactions between the lysine side chains and the net negatively charged membrane surface is not sufficient to overcome the loss of the hydroxyl side chains. Replacement of the unique tryptophan, Trp185, by alanine similarly decreases membrane binding affinity. Taken together, the data suggest that the side chains mutated in this study contribute to phospholipid binding and participate directly in intermolecular contacts with phospholipid membrane components.

Altered cardiac annexin mRNA and protein levels in the left ventricle of patients with end-stage heart failure

Annexins are a unique family of membrane-associated, Ca2+ and phospholipid-binding proteins found in various tissues. Among the 12 isoforms, Annexin II, V and VI exist in heart tissue in the highest amounts. Annexin VI has been shown to affect intracellular Ca2+ cycling and contractility in isolated cardiomyocytes. Annexin V is present in both cardiomyocytes and non-myocyte cell types in the heart and may play a role in the regulation of cellular ion fluxes, organization and secretion, while the cardiac effects of annexin II are unclear. To identify changes in annexin II, V and VI isoforms that might occur in human heart failure, we measured mRNA and protein levels of these three annexins in transplanted left ventricular tissue of 12 patients with end-stage congestive heart failure due to coronary artery disease (CAD, n=6) or idiopathic dilated cardiomyopathy (DCM, n=6) who underwent cardiac transplantation. Normal heart tissue (C, n=6) was used as a control. Northern blot analyses showed a significant decrease (61%) in annexin VI mRNA levels in heart failure patients compared with controls (1.08+/-0.16 v 2.79+/-0.20 A.U.C. unit, determined by laser densitometry, mean+/-s.e.). In contrast, we found a 67% increase (2. 32+/-0.27 v 3.88+/-0.29) in annexin II mRNA levels and a two-fold increase (1.00+/-0.24 v 2.21+/-0.29) in annexin V mRNA levels in cardiomyopathic hearts as compared to normal hearts. Western blot analyses demonstrated a corresponding decrease (46.1%) in annexin VI protein levels in the heart failure group as compared to controls (2. 63+/-0.22 v 4.88+/-0.52), while annexin II protein levels showed a significant 40.7% increase in patients with heart failure compared to those in normal hearts (5.08+/-0.67 v 3.61+/-0.32). Annexin V protein levels were also significantly increased (45%) in heart failure patients compared with normal (2.14+/-0.19 v 1.48+/-0.11). No difference in either annexins II, V or VI mRNA and protein levels were found between CAD and DCM patients. We conclude that human end-stage heart failure is associated with a down regulation of annexin VI and up regulation of annexin II and V proteins. Coordinate changes were observed in steady-state mRNA levels. These results suggest that these annexin isoforms may contribute to the regulation of intracellular Ca2+ homeostasis in the cardiomyopathic heart.

Electrophorus electricus as a model system for the study of membrane excitability

The stunning sensations produced by electric fish, particularly the electric eel, Electrophorus electricus, have fascinated scientists for centuries. Within the last 50 years, however, electric cells of Electrophorus have provided a unique model system that is both specialized and appropriate for the study of excitable cell membrane electrophysiology and biochemistry. Electric tissue generates whole animal electrical discharges by means of membrane potentials that are remarkably similar to those of mammalian neurons, myocytes and secretory cells. Electrocytes express ion channels, ATPases and signal transduction proteins common to these other excitable cells. Action potentials of electrocytes represent the specialized end function of electric tissue whereas other excitable cells use membrane potential changes to trigger sophisticated cellular processes, such as myofilament cross-bridging for contraction, or exocytosis for secretion. Because electric tissue lacks these functions and the proteins associated with them, it provides a highly specialized membrane model system. This review examines the basic mechanisms involved in the generation of the electrical discharge of the electric eel and the membrane proteins involved. The valuable contributions that electric tissue continues to make toward the understanding of excitable cell physiology and biochemistry are summarized, particularly those studies using electrocytes as a model system for the study of the regulation of membrane excitability by second messengers and signal transduction pathways.

Annexins II and V inhibit cell migration

Cell motility is a crucial component involved in wound healing, development, and tumor metastasis. This study investigated whether extracellular annexins, members of a calcium- and phospholipid-binding family of proteins, play a role in the migration of Lewis lung carcinoma cells. Using assays for wound closure and migration through 8-micron pores, it was found that annexins II and V significantly (> 40%) inhibited migration of these highly metastatic cells. Additionally, anti-annexin II antibodies enhanced migration of these same cells in the wound closure assay, while an irrelevant antibody (anti-calmodulin) showed no effect. These effects may be due to annexin-membrane binding and inhibition of phospholipid movement that is necessary for the formation of membrane protrusions.

Molecular characterization of the mouse vesicular acetylcholine transporter gene

The organization of the mouse choline acetyltransferase (ChAT) gene has been previously analyzed. Here we show that the first intron of the mouse ChAT gene contains an uninterrupted open reading frame. It is in the same transcriptional orientation as ChAT and encodes the vesicular acetylcholine (ACh) transporter (VAChT), the protein responsible for the translocation of cytoplasmic ACh into synaptic vesicles. The sequence of this transporter is very similar to the VAChT from rat and human (99% and 95% identity, respectively). Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed expression of mouse VAChT mRNA in spinal cord, brain (excluding the cerebellum) and brain stem, but not in peripheral tissues such as liver and kidney. Transgenic mouse analysis revealed that the 5'-flanking region of the mouse ChAT gene encompasses regulatory elements that allowed elevated expression of VAChT in the cholinergic system of transgenic mice.

Regulation of gene expression by hypoxia: a molecular approach

Oxygen is a strict requirement for cell function. The cellular mechanisms by which organisms detect and respond to changes in oxygen tension remain a major unanswered question in pulmonary physiology. Part of the difficulty in addressing this question is due to the limited scope of experiments that can be performed in vivo. In the past few years, several laboratories have begun to make progress in this area, using a variety of cell culture model systems and sophisticated genetic manipulations. Here, we review the current state of knowledge of regulation of gene expression by hypoxia, and describe novel experimental approaches that promise to broaden our understanding of how cells and whole organisms respond to alterations in O2 tension.

A major second messenger mediator of Electrophorus electricus electric tissue is CaM kinase II

Electric tissue of the electric eel, Electrophorus electricus, has been used extensively as a model system for the study of excitable membrane biochemistry and electrophysiology. Membrane receptors, ion channels, and ATPases utilized by electrocytes are conserved in mammalian neurons and myocytes. In this study, we show that Ca2+ predominates as the major mediator of electric tissue phosphorylation relative to cyclic AMP and cyclic GMP-induced phosphorylation. Mastoparan, a calmodulin inhibitor peptide, and a peptide corresponding to the pseudosubstrate region of mammalian calmodulin-dependent protein kinase II (CaMKII (281-302)) attenuated Ca(2+)-dependent phosphorylation in a dose-dependent manner. These experiments demonstrated that calmodulin-dependent protein kinase II activity predominates in electric tissue. The Electrophorus kinase was purified by a novel affinity chromatography procedure utilizing Ca2+/calmodulin-dependent binding to the CaMKII (281-302) peptide coupled to Sepharose. The purified 51 kDa calmodulin-dependent protein kinase II demonstrated extensive autophosphorylation and exhibited a 3- to 4-fold increase in Ca(2+)-independent activity following autophosphorylation. Immunofluorescent localization experiments demonstrated calmodulin to be abundant in electrocytes, particularly subjacent to the plasma membrane. Calmodulin-dependent protein kinase II had a punctate distribution indicating that it may be compartmentalized by association with vesicles or the cytoskeleton. As the primary mediator of phosphorylation within electric tissue, CaM kinase II may be critical for the regulation of the specialized electrophysiological function of electrocytes.

Annexin VI modulates Ca2+ and K+ conductances of spinal cord and dorsal root ganglion neurons

Annexin VI is a member of a Ca(2+)-dependent phospholipid-binding protein family that participates in the transduction of the intracellular Ca2+ signal. We have identified annexin VI as one of the major annexins expressed differentially by sensory neurons of dorsal root ganglia (DRG) and by neurons of spinal cord (SC) of the rat and the mouse. This annexin shows a preferential localization at the plasma membrane of the soma and cellular processes, particularly in motoneurons of the SC. This finding suggests an active role of annexin VI in the Ca(2+)-dependent regulation of plasma membrane functions. To test this possibility, the neuronal function of annexin VI was evaluated by whole cell electrophysiology of mouse embryo SC and DRG neurons. An antibody was developed that has the property of neutralizing annexin VI-phospholipid interactions. The intracellular perfusion of individual neurons in culture, either from SC or DRG, with monospecific affinity-purified anti-annexin VI antibodies resulted in an increase in the magnitude of the K+ current and in an increase in the Ca2+ current in sensory neurons. Our results suggest that the endogenous annexin VI regulates the Ca2+ conductance, which indirectly modifies Ca(2+)-dependent ionic conductances in SC and DRG neurons.

Targeted neutralization of calmodulin in the nucleus blocks DNA synthesis and cell cycle progression

Calmodulin (CaM) is a major intracellular calcium binding protein which has been implicated in the regulation of cell proliferation. Previous studies using chemically synthesized CaM antagonists and anti-sense RNA indicated that CaM is important for initiation of DNA synthesis and cell cycle progression. However, these methods reduce total intracellular CaM and globally interfering with all the CaM-dependent processes. In order to explore the function of nuclear CaM during the cell cycle, a CaM inhibitor peptide was targeted to the nucleus of intact mammalian cells. Cell progression through S-phase was assessed by incorporation of the thymidine analogue, BrdU. Cells were transfected for 48 h with either the CaM inhibitor peptide gene or the control plasmid prior to analysis. Approx. 70% of the control cells incorporated BrdU. In striking contrast, double immunofluorescent labeling demonstrated that none of the cells expressing the CaM inhibitor peptide entered S-phase. This result indicates that neutralization of nuclear CaM by targeted expression of a CaM inhibitor peptide blocks DNA synthesis and cell cycle progression.

Expression of a calmodulin inhibitor peptide in progenitor alveolar type II cells disrupts lung development

Calmodulin (CaM) is a major intracellular Ca2+ mediator protein involved in cell growth and differentiation. To evaluate calmodulin function in lung, it was necessary to construct a gene that encodes a high-affinity calmodulin binding peptide, since chemically synthesized calmodulin inhibitors lack binding and targeting specificity. This calmodulin inhibitor peptide gene was targeted to type II epithelial cells in transgenic mice using the human surfactant protein C promoter. Neutralization of calmodulin function in progenitor type II epithelial pneumocytes alters epithelial cell growth and differentiation, which prevents branching morphogenesis of the bronchial tree. Newborn transgenic animals have undeveloped lungs. This study indicates that type II lung epithelial cells require functional CaM for proliferation and development. The targeting of specific inhibitor peptides to a single lung cell type is an approach to evaluate the role of calmodulin, the ubiquitous calcium-dependent regulator protein, in lung development and disease.

Inositol 3,4,5,6-tetrakisphosphate inhibits the calmodulin-dependent protein kinase II-activated chloride conductance in T84 colonic epithelial cells

The mechanism by which inositol 3,4,5,6-tetrakisphosphate (Ins(3,4,5, 6)P4) regulates chloride (Cl-) secretion was evaluated in the colonic epithelial cell line T84 using whole cell voltage clamp techniques. Our studies focused on the calcium-dependent chloride conductance (gClCa) that was activated either by mobilizing intracellular calcium (Cai) stores with thapsigargin or by introduction of the autonomous, autophosphorylated calmodulin-dependent protein kinase II (CaMKII) into the cell via the patch pipette. Basal concentrations of Ins(3,4,5,6)P4 (1 microM) present in the pipette solution had no significant effect on Cl- current; however, as the concentration of the polyphosphate was increased there was a corresponding reduction in anion current, with near complete inhibition at 8-10 microM Ins(3,4,5,6)P4. Corresponding levels are found in cells after sustained receptor-dependent activation of phospholipase C. The Ins(3,4,5, 6)P4-induced inhibition of gClCa was isomer specific; neither Ins(1, 3,4,5)P4, Ins(1,3,4,6)P4, Ins(1,4,5,6)P4, nor Ins(1,3,4,5,6)P5 induced current inhibition at concentrations of up to 100 microM. Annexin IV also plays an inhibitory role in modulating gClCa in T84 cells. When 2 microM annexin IV was present in the pipette solution, a concentration that by itself has no effect on gClCa, the potency of Ins(3,4,5,6)P4 was approximately doubled. The combination of Ins(3,4,5,6)P4 and annexin IV did not alter the in vitro activity of CaMKII. These data demonstrate that Ins(3,4,5,6)P4 is an additional cellular signal that participates in the control of salt and fluid secretion, pH balance, osmoregulation, and other physiological activities that depend upon gClCa activation. Ins(3,4,5,6)P4 metabolism and action should also be taken into account when designing treatment strategies for cystic fibrosis.

Differential expression of annexins I-VI in the rat dorsal root ganglia and spinal cord

The annexins are a family of Ca(2+)-dependent phospholipid-binding proteins. In the present study, the spatial expression patterns of annexins I-VI were evaluated in the rat dorsal root ganglia (DRG) and spinal cord (SC) by using indirect immunofluorescence. Annexin I is expressed in small sensory neurons of the DRG, by most neurons of the SC, and by ependymal cells lining the central canal. Annexin II is expressed by most sensory neurons of the DRG but is primarily expressed in the SC by glial cells. Annexin III is expressed by most sensory neurons, regardless of size, by endothelial cells lining the blood vessels, and by the perineurium. In the SC, annexin III is primarily expressed by astrocytes. In the DRG and the SC, annexin IV is primarily expressed by glial cells and at lower levels by neurons. In the DRG, annexin V is expressed in relatively high concentrations in small sensory neurons in contrast to the SC, where it is expressed mainly by ependymal cells and by small-diameter axons located in the superficial laminae of the dorsal horn areas. Annexin VI is differentially expressed by sensory neurons of the DRG, being more concentrated in small neurons. In the SC, annexin VI has the most striking distribution. It is concentrated subjacent to the plasma membrane of motor neurons and their processes. The differential localization pattern of annexins in cells of the SC and DRG could reflect their individual biological roles in Ca(2+)-signal transduction within the central nervous system.

Regulation of epithelial sodium channels by the cystic fibrosis transmembrane conductance regulator

Cystic fibrosis airway epithelia exhibit enhanced Na+ reabsorption in parallel with diminished Cl- secretion. We tested the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) directly affects epithelial Na+ channel activity by co-incorporating into planar lipid bilayers immunopurified bovine tracheal CFTR and either heterologously expressed rat epithelial Na+ channel ( alpha,b eta,gamma-rENaC) or an immunopurified bovine renal Na+ channel protein complex. The single channel open probability (Po) of rENaC was decreased by 24% in the presence of CFTR. Protein kinase A (PKA) plus ATP activated CFTR, but did not have any effect on rENaC. CFTR also decreased the extent of elevation of the renal Na+ channel Po following PKA-mediated phosphorylation. Moreover, the presence of CFTR prohibited the inward rectification of the gating of this renal Na+ channel normally induced by PKA-mediated phosphorylation, thus down-regulating inward Na+ current. This interaction between CFTR and Na+ channels occurs independently of whether or not wild-type CFTR is conducting anions. However, the nonconductive CFTR mutant, G551D CFTR, cannot substitute for the wild-type molecule. Our results indicate that CFTR can directly down-regulate single Na+ channel activity, thus accounting, at least in part, for the observed differences in Na+ transport between normal and cystic fibrosis-affected airway epithelia.

Annexin VI overexpression targeted to heart alters cardiomyocyte function in transgenic mice

Annexin VI is a member of a family of Ca(2+)-dependent phospholipid-binding proteins that is expressed in many tissues, including the heart. It is a regulator of membrane-associated events, including the skeletal muscle ryanodine-sensitive Ca2+ release channel and the cardiac Na+/Ca2+ exchanger. The potential roles of annexin VI in Ca2+ signaling in cardiac myocytes were evaluated by targeting its overexpression to the hearts of transgenic mice. Expression of full-length human annexin VI cDNA was targeted to the heart using the alpha-myosin heavy chain gene promoter (Subramaniam, A., W. K. Jones, J. Gulick, S. Wert, J. Neumann, and J. Robbins. J. Biol. Chem. 266: 24613-24620, 1991). Five transgenic lines exhibited at least 10-fold overexpression of annexin VI protein in both atria and ventricles. Pathological evaluation indicated mice overexpressing annexin VI had enlarged dilated hearts, acute diffuse myocarditis, lymphocytic infiltration, moderate to severe fibrosis throughout the heart, and mild fibrosis around the pulmonary veins of the lungs. Contractile mechanics of cardiomyocytes isolated from hearts of transgenic animals showed frequency-dependent reduced percent shortening and decreased rates of contraction and relaxation compared with control animals. Cardiomyocytes isolated from transgenic animals had lower basal levels of intracellular free Ca2+ and a reduced rise in free Ca2+ following depolarization. After stimulation, intracellular free Ca2+ returned to basal levels faster in transgenic cells than in cells from control animals. These data demonstrate that the overexpression of annexin VI in the heart disrupts normal Ca2+ homeostasis and suggests that this dysfunction may be due to annexin VI regulation of pumps and/or exchangers in the membranes of cardiomyocytes.

Shrinkage activates a nonselective conductance: involvement of a Walker-motif protein and PKC

The ability of all cells to maintain their volume during an osmotic challenge is dependent on the regulated movement of salt and water across the plasma membrane. We demonstrate the phosphorylation-dependent gating of a nonselective conductance in Caco-2 cells during cellular shrinkage. Intracellular application of exogenous purified rat brain protein kinase C (PKC) resulted in the activation of a current similar to that activated during shrinkage with a Na(+)-to-Cl- permeability ratio of approximately 1.7:1. To prevent possible PKC- and/or shrinkage-dependent activation of cystic fibrosis transmembrane regulator (CFTR), which is expressed at high levels in Caco-2 cells, a functional anti-peptide antibody, anti-CFTR505-511, was introduced into the cells via the patch pipette. Anti-CFTR505-511, which is directed against the Walker motif in the first nucleotide binding fold of CFTR, prevented the PKC/shrink-age current activation. The peptide CFTR505-511 also induced current inhibition, suggesting the possible involvement of a regulatory element in close proximity to the channel that shares sequence homology with the first nucleotide binding fold of CFTR and whose binding to the channel is required for channel gating.

Functional elimination of calmodulin within the nucleus by targeted expression of an inhibitor peptide

Genetic manipulation has proven valuable in identifying the role of specific genes in cellular function. Genomic disruption of genes that are expressed during embryonic development or in multiple tissue types, however, complicates phenotypic analysis. We demonstrate that targeted expression of an inhibitor peptide derived from myosin light chain kinase can neutralize the function of calmodulin. We have shown that elimination of the nuclear function of Ca(2+)-calmodulin causes disruption of the nuclear structure. Targeted expression of this calmodulin inhibitor gene in the lung epithelium of transgenic mice leads to cellular death and dysfunctional lung development. This approach is a strategy to modify the activity of a targeted protein within a specific organelle in order to evaluate its role in cellular and tissue function.

Interaction between cystic fibrosis transmembrane conductance regulator and outwardly rectified chloride channels

We have previously described a protocol for the simultaneous isolation and reconstitution of a protein kinase A (PKA)-sensitive outwardly rectified chloride channel (ORCC) and the cystic fibrosis transmembrane conductance regulator (CFTR) from bovine tracheal epithelium. Immunoprecipitation of CFTR from this preparation prevented PKA activation of the ORCC, suggesting that CFTR regulated the ORCC and that this regulatory relationship was preserved throughout the purification procedure. We now report the purification of CFTR from bovine tracheal epithelia and the purification of a CFTR conduction mutant (G551D CFTR) from retrovirally transduced mouse L cells using a combination of alkali stripping, Triton-X extraction, and immunoaffinity chromatography. Immunopurified CFTR proteins were reconstituted in the absence and presence of ORCC. To test the hypothesis that only functional CFTR can support activation of ORCC by PKA and ATP, we used an inhibitory anti-CFTR505-511 peptide antibody or G551D CFTR. When anti-CFTR505-511 peptide antibodies were present prior to the addition of PKA and ATP, activation of both the ORCC and CFTR was prevented. If the antibody was added after activation of the ORCC and CFTR Cl- channels by PKA and ATP, only the CFTR Cl- channel was inhibited. When ORCC and G551D CFTR were co-incorporated into planar bilayers, only the ORCC was recorded and this channel could not be further activated by the addition of PKA and ATP. Thus, functional CFTR is required for activation of the ORCC by PKA and ATP. We also tested the hypothesis that PKA activation of ORCC was dependent on the extracellular presence of ATP. We added ATP on the presumed extracellular side of the lipid bilayer under conditions where it was not possible to activate the ORCC, i.e. in the presence of inhibitory anti-CFTR505-511 antibody or G551D CFTR. In both cases the ORCC regained PKA sensitivity. Moreover, the addition of hexokinase + glucose to the extracellular side prevented activation of the ORCCs by PKA and ATP in the presence of CFTR. These experiments confirm that both the presence of CFTR as well as the presence of ATP on the extracellular side is required for activation of the ORCC by PKA and ATP.

Ca(2+)-bridging mechanism and phospholipid head group recognition in the membrane-binding protein annexin V

Structural evidence is presented for a 'Ca(2+)-bridging' mechanism, proposed for Ca(2+)-binding interfacial membrane proteins such as annexins, protein kinase C, and certain coagulation proteins. Crystal structures of Ca(2+)-annexin V complexes with phospholipid polar heads provide molecular details of 'Ca(2+)-bridges' as key features in the membrane attachment exhibited by these proteins. Distinct binding sites for phospholipid head groups are observed, including a novel, double-Ca2+ recognition site for phosphoserine that may serve as a phosphatidylserine receptor site in vivo.

Annexins: Novel Ca2+-Dependent Regulators of Membrane Function

The annexins are a family of Ca2+-dependent membrane binding proteins that have been shown to regulate ion conductances, aggregate vesicles and the cytoskeleton, inhibit phospholipase A2, and inhibit blood coagulation. The annexins represent a unique mechanism of cellular regulation by modifying membrane functions in a Ca2+-dependent manner.

Annexin IV inhibits calmodulin-dependent protein kinase II-activated chloride conductance. A novel mechanism for ion channel regulation

Ca(2+)-activated Cl- current (ICl,Ca) in colonic T84 cells is inhibited by the specific peptide inhibitor of Ca2+/calmodulin-dependent kinase II (CaM KII). Annexin IV, a Ca(2+)-dependent phospholipid binding protein also inhibits Ca(2+)-dependent anion current activation (Kaetzel, M.A., Chan, H.-C., Dubinsky, W.P., Dedman, J.R., and Nelson, D.J. (1994) J. Biol. Chem. 269, 5297-5302). Intracellular injection of antibodies against annexin IV enhances current activation; this activation is inhibited by the peptide inhibitor of CaM KII. Intracellular application of autonomously active CaM KII in the presence of ATP induced a Cl- current similar to that activated by the Ca2+ ionophore A23187. Current activation by the exogenous kinase was completely inhibited in the presence of purified annexin IV. In vitro, annexin IV does not inhibit CaM KII activity nor does it act as a substrate for CaM KII. Thus, it appears that annexin IV inhibits phosphorylation-dependent anion conductance activation by preventing CaM KII-ion channel interaction rather than by direct interaction with the enzyme itself. These findings suggest a novel mechanism by which Ca(2+)-dependent membrane binding proteins, cytoplasmic kinases, and ion channels interact to regulate membrane conductance. The characterization of unique channel regulatory pathways in Cl- transporting epithelia may identify potential avenues of alternate therapy to compensate for the loss of functional Cl- channels in the disease of cystic fibrosis.

Annexin VI isoforms are differentially expressed in mammalian tissues

Purified annexin VI migrates as a closely spaced doublet when separated by SDS-PAGE. Immunolocalization of annexin VI in heart demonstrates staining at different defined subcellular compartments. Moss et al. identified two cDNAs, one having an insert of 18 bases encoding VAAEIL at the beginning of repeat domain seven. We have identified the splicing site of the murine annexin VI gene. It contains a single small exon of 18 bases. PCR amplification of reverse transcribed (RT) mRNA demonstrates that, in all tissues tested, the mRNA isoform containing the insert is predominant. Site-directed antibody was produced and affinity purified against peptides reflecting the insert and deletion sequences. The steady-state isoform ratio of the annexin VI protein is consistent with the RT-PCR data. Chromatographic experiments demonstrate that the annexin VI protein isoforms have biochemical differences. These differences may target the individual isoforms to unique cellular compartments or alter functional properties.

Annexin V binding to the outer leaflet of small unilamellar vesicles leads to altered inner-leaflet properties: 31P- and 1H-NMR studies

Calcium-dependent binding to phospholipid membranes is closely associated with annexin functional properties. In these studies, 31P- and 1H-nuclear magnetic resonance (NMR) experiments have been performed to study the effects of binding of recombinant rat annexin V to sonicated small unilamellar vesicles (SUVs). High-resolution 31P-NMR spectra of SUVs containing mixtures of synthetic phosphatidic acid (PA) and phosphatidylcholine (PC) show resolvable resonances corresponding to the inner-leaflet PA, outer-leaflet PA, and PC phosphoryl groups. When annexin binding occurs, the outer-leaflet PA 31P resonance shifts while that of PC is unaffected, consistent with selective binding of the protein to the phosphoryl moiety of the PA component. Further, annexin V binding to membrane outer-leaflet phospholipids has a measurable effect on inner-leaflet phospholipids of intact vesicles. 1H-NMR T1 relaxation measurements of SUVs containing acyl-chain-perdeuterated PC show no effects on the PA hydrocarbon-chain segmental motions upon annexin binding. Circular dichroism measurements indicate that the protein does not undergo a significant conformational change upon binding to the vesicles. The observed NMR changes do not correspond to proton or calcium gradients, nor to lateral segregation of extended patches of homogeneous phospholipids. The combined evidence suggests that selective, peripheral annexin-membrane interactions influence the environment of the inner vesicular surface. The mechanism proposed is a protein-induced change in vesicle morphology that corresponds to reduced curvature.

A role for annexin IV in epithelial cell function. Inhibition of calcium-activated chloride conductance

The cellular function of annexin IV was evaluated by correlating tissue expression, cellular localization, and whole-cell electrophysiology. Immunolocalization and biochemical data demonstrate that annexin IV is concentrated along the apical membranes of many epithelia. Introduction of purified exogenous annexin IV into colonic T84 cells through a patch pipette specifically prevented Ca(2+)-dependent Cl- current activation. Affinity-purified antibody against annexin IV applied in the same manner enhanced the activation. Reduction of the endogenous level of annexin IV with a derivatized oligodeoxynucleotide antisense to annexin IV mRNA lowered the threshold for the Ca(2+)-induced current response, mimicking the enhancement of current activation exerted by anti-annexin IV antibody. The inhibitory effect of annexin IV on Ca(2+)-dependent Cl- conductance represents a novel mechanism by which Ca(2+)-binding proteins modulate membrane channel activity.

Activation of the cystic fibrosis transmembrane conductance regulator by cGMP in the human colonic cancer cell line, Caco-2

Intestinal chloride (Cl-) secretion can be induced by the heat-stable enterotoxin (STa) from Escherichia coli via generation of cGMP. We investigated the regulatory pathway responsible for cGMP-mediated Cl- secretion in the human colonic carcinoma cell line Caco-2 using whole-cell voltage clamp techniques. Cyclic GMP or cAMP induced a 5-fold increase in Cl- conductance (gCl) in the presence of intracellular ATP and 3-isobutyl-1-methylxanthine. Current activation by cGMP persisted in the presence of the type I cGMP-dependent protein kinase (PKG) inhibitor, KT5823, but was inhibited by the specific peptide inhibitor of the cAMP-dependent protein kinase A (PKA), PKI5-24. The stimulatory effects of cGMP and cAMP on gCl were not additive. The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl- channel that is regulated by intracellular ATP and by cAMP-dependent phosphorylation. In order to determine whether CFTR was involved in the cGMP-dependent increase in gCl, we tested the effect of intracellularly injected anti-CFTR505-511 antibodies previously shown to inhibit CFTR function. Antibodies introduced into individual cells via the patch pipette completely inhibited cGMP-dependent current activation. Cyclic GMP also failed to activate gCl in cystic fibrosis cells. Taken together, these studies demonstrate that activation of the CFTR via PKA-dependent phosphorylation accounts for the cGMP-mediated increase in Cl- secretion in Caco-2 cells.

Selection of targeted biological modifiers from a bacteriophage library of random peptides. The identification of novel calmodulin regulatory peptides

The interaction of short amino acid sequences is the basis of molecular recognition and biological regulation in many cellular systems. Libraries of random peptides provide an approach to identify peptides that can be used to modulate, in a targeted fashion, the function of specific gene products. We have used a library of random peptides designed and constructed in the M13 bacteriophage to select calcium-dependent calmodulin binding-peptides. Twenty-eight independent sequences were obtained; all contained a tryptophan within the fifteen-amino acid insert. In 11 sequences, the tryptophan was located in the first possible variable position of the inserted sequence and was followed by a proline. The tryptophan-proline combination was also present in six additional isolates but at various other positions within the peptide insert. Synthetic peptides, representative of the calmodulin binding sequences, bound to calmodulin in a calcium-dependent fashion, competed with known calmodulin inhibitors and, when introduced via a patch pipette, inhibited calcium-activated chloride conductance of the colonic epithelial cell line, T84. This report demonstrates the utility of identifying modifiers of biological function and should prove to be a valuable approach in understanding the cellular role of proteins of unknown function.

Rat annexin V crystal structure: Ca(2+)-induced conformational changes

Annexins are a family of calcium- and phospholipid-binding proteins implicated in mediating membrane-related processes such as secretion, signal transduction, and ion channel activity. The crystal structure of rat annexin V was solved to 1.9 angstrom resolution by multiple isomorphous replacement. Unlike previously solved annexin V structures, all four domains bound calcium in this structure. Calcium binding in the third domain induced a large relocation of the calcium-binding loop regions, exposing the single tryptophan residue to the solvent. These alterations in annexin V suggest a role for domain 3 in calcium-triggered interaction with phospholipid membranes.

Expression of annexins on the surfaces of non-metastatic and metastatic human and rodent tumor cells

Annexins are a large group of calcium-dependent cytoskeletal- and membrane-associated proteins whose properties include cytoskeleton and phospholipid binding and mitotic signal transduction. Although annexin-like molecules have been reported on the external plasma membranes of certain cells, in general they are considered to be cytoplasmic proteins. We report here the heterogenous expression of certain annexins (I-VI) on the external cell surfaces of non-metastatic and metastatic murine (RAW117 large-cell lymphoma), rat (13762NF mammary adenocarcinoma) and some human (KM12 and HT29 colorectal carcinoma) cell lines but not on some other cell lines such as human (A375 and MeWo) and mouse (B16) melanoma. The implication of annexin cell surface expression in the metastatic process is discussed with respect to tumor cell adhesion.

Annexin V forms calcium-dependent trimeric units on phospholipid vesicles

The quaternary structure of annexin V, a calcium-dependent phospholipid binding protein, was investigated by chemical cross-linking. Calcium was found to induce the formation of trimers, hexamers, and higher aggregates only when anionic phospholipids were present. Oligomerization occurred under the same conditions annexin-vesicle binding. A model is proposed in which cell stimulation leads to calcium-induced organization of arrays of annexin V lining the inner membrane surface, thus altering properties such as permeability and fluidity.

Antibody against a cystic fibrosis transmembrane conductance regulator-derived synthetic peptide inhibits anion currents in human colonic cell line T84

The cystic fibrosis (CF) phenotype is characterized by a regulatory defect in Cl- permeability in epithelia. A gene (250,000 base pairs) that is associated with this autosomal genetic disorder has been identified. To determine the cellular function of the recently cloned gene product, the cystic fibrosis transmembrane conductance regulator (CFTR), we have produced antibody against a synthetic peptide deduced from the CFTR cDNA sequence corresponding to positions 505-511. This site includes phenylalanine 508, the deletion of which is the most commonly expressed mutation in CF. We sought to determine whether the anti-CFTR505-511 peptide antibody could modulate the activation of the volume-sensitive, Ca(2+)-dependent, as well as the cAMP-dependent Cl- conductances present in the Cl(-)-secreting human colonic T84 cell line. Affinity-purified anti-CFTR505-511 antibody was introduced into the cytoplasm of individual T84 cells and its function studied using the whole-cell patch-clamp technique. Although cAMP-dependent Cl- current activation was inhibited in cells perfused with the anti-CFTR505-511 peptide antibody, Ca(2+)-dependent anion current activation remained unaffected. Chloride current activation, which accompanies cellular swelling, was partially attenuated in anti-CFTR505-511 antibody-loaded cells as compared with control cells perfused with either saline or irrelevant antibody. These results further support a role for CFTR in anion transport in epithelial cells and suggest its possible involvement in a number of anion transport pathways in chloride secretory epithelia.

Glucocorticoid regulation of rat liver urate oxidase

Urate oxidase, an enzyme involved in purine catabolism, comprises the crystalline core of rat liver peroxisomes. An affinity-purified monospecific antibody was developed to study the expression of urate oxidase protein levels. Immunoreactive urate oxidase was not detectable in prenatal liver; however, it is present at low levels after birth until approximately day 15 (postnatal age); expression sharply increases just prior to day 20, after which the enzyme is maintained at adult levels. This pattern of expression was similar to that of another peroxisomal enzyme, catalase; these developmental increases reflect the increase in peroxisomal number. Administration of exogenous glucocorticoid hormone to 10-day-old rats resulted in a precocious rise (2.5-fold) in urate oxidase levels. Adrenalectomy at 10 days of age did not cause decreased levels in the fourth week of life. In adult animals, while exogenous glucocorticoid administration did not influence urate oxidase levels, adrenalectomy at 60 days of age decreased urate oxidase levels to 40 percent of control levels. Subsequent administration of exogenous glucocorticoid hormone restored urate oxidase to normal levels. Parallel studies of catalase levels indicate that this glucocorticoid-sensitive response is not generalized for all peroxisomal proteins. Our results suggest that peroxisomes proliferate during early postnatal development, but after this process is complete, the biogenesis of individual peroxisomal proteins may be independently regulated.

Differential localization of annexins in ram germ cells: a biochemical and immunocytochemical study

We used antibodies that specifically bind annexins on Western blots to determine the distribution and abundance of these proteins in ram spermatids and sperm by immunogold electron microscopy. Annexins I and II were found essentially within the entire acrosome of spermatids. During epididymal maturation, they concentrated in the postacrosomal region or the acrosomal equatorial segment, respectively. They were also present in sperm flagellum, on the surface of the coarse fibers and fibrous sheath. These findings show that during ram germ cell maturation, annexins I and II are exported from the spermatid acrosome towards structurally and functionally defined parts of the sperm. Annexins III, IV, and V were not found in ram germ cells. Annexin VI was isolated from testis and sperm. In spermatids, it was found to be associated with endoplasmic reticulum and the mitochondria but was absent from the acrosome. In sperm, it was confined to the flagellum, the mitochondria, and on the coarse fibers and fibrous sheath. The presence of three annexins, in addition to calmodulin, in functional areas may indicate differential ways for sperm to control and regulate events that are known to be calcium dependent, such as flagellar motility, acrosome reaction, and fertilization.

Regulation of the sarcoplasmic reticulum Ca(2+)-release channel requires intact annexin VI

Annexin VI has eight highly conserved repeated domains; all other annexins have four. Díaz-Muñoz et al. (J Biol Chem 265:15894, 1990) reported that annexin VI alters the gating properties of the ryanodine-sensitive Ca(2+)-release channel isolated from sarcoplasmic reticulum. The investigate the domain structure of rat annexin VI (67 kDa calcimedin) required for this channel regulation, various proteolytic digestions were performed. In each case, protease-resistant core polypeptides were produced. Annexin VI was digested with V8 protease and two core polypeptides were purified by Ca(2+)-dependent phospholipid binding followed by HPLC. The purified fragments were shown to be derived from the N- and C-terminal halves of annexin VI, and demonstrated differential immunoreactivity with monoclonal antibodies to rat annexin VI. While both core polypeptides retained their ability to bind phospholipids in a Ca(2+)-dependent manner, they did not regulate the sarcoplasmic reticulum Ca(2+)-dependent manner, they did not regulate the sarcoplasmic reticulum Ca(2+)-release channel as did intact annexin VI.

Annexin VI is associated with calcium-sequestering organelles

Annexin VI is a member of a Ca(2+)-dependent, phospholipid-binding protein family. Although functions for this annexin have been proposed from in vitro studies, most remain controversial. Díaz-Muñoz et al. (J Biol Chem 265:15894, 1990) demonstrated that annexin VI modified, in a Ca(2+)-dependent manner, the gating behavior of the sarcoplasmic reticulum Ca(2+)-release channel, reconstituted into artificial bilayers, by increasing both the open probability and the mean open time. This effect was specific to the trans chamber, which represents the luminal side of the sarcoplasmic reticulum. In agreement with those findings, we show herein that annexin VI produced no effect on Ca(2+)-uptake or -release by intact heavy sarcoplasmic reticulum vesicles (analogous to the cis chamber). We also used monospecific antibodies to evaluate the subcellular localization of annexin VI by immunofluorescent microscopy. Studies in rat skeletal muscle suggest that annexin VI is present surrounding individual myofibrils. Double immunolocalization studies with cultured muscle cells (chick myotubes) using anti-annexin VI and anti-SR Ca(2+)-ATPase antibodies demonstrated superimposable staining patterns. In non-muscle tissue (normal rat kidney (NRK) cells), a punctate, perinuclear anti-annexin VI staining pattern was observed. Collectively, these data suggest that annexin VI may play a regulatory role in the Ca(2+)-release/uptake cycle in the sarcoplasmic reticulum as well as in non-muscle organelles, a key process in stimulus-response systems.

Co-distribution of annexin VI and actin in secretory ameloblasts and odontoblasts of rat incisor

Annexin VI and actin were detected by immunoblot analysis in the enamel- and dentin-related portions of dental tissues. Annexin VI was found mainly in the particulate fraction whereas actin was detected in both the soluble and particulate fractions. By immunoelectron microscopy, annexin VI antibodies conjugated with colloidal gold were seen to label the mitochondria, the cytosol and the nucleus of secretory ameloblasts and odontoblasts of rat incisor. In the processes of these cells, the plasmalemmal undercoat was labeled. Anti-actin antibodies labeled the desmosome-like junctions, the cytosol, and the mitochondria of the cell bodies. Extensive labeling was seen at the periphery of the Tomes' processes and odontoblast processes. These results suggest that annexin VI may play a role in Ca2(+)-regulation in the cell bodies, especially as a calcium receptor protein in the mitochondria. Moreover, annexin VI and actin seem to be co-distributed in secretory processes. Thus, these proteins might be both involved in exocytotic and endocytotic events.

Annexins I-VI in secretory ameloblasts and odontoblasts of rat incisor

Immunoblot analyses and ultrastructural immunogold studies have been conducted on annexins in the secretory ameloblasts and odontoblasts of the rat incisor. Annexins I and II were seen in the soluble and particulate fractions of the enamel-related portion but not in the dentin-related portion. These proteins were visualized in the cytosol, near to the plasma membrane of Tomes' processes and in secretory vesicles in the ameloblasts. The forming enamel was also labeled. Annexins III, VI an V were detected in both the soluble and particulate fractions of the enamel-and dentin-related portions. Annexin IV was mainly localized in the proximal and distal areas of the secretory ameloblasts and virtually absent from in the supranuclear area. Annexin V was mainly detected in the cytosol of the cells and to a lesser extent near the plasma membrane. Annexin VI was mainly detected in the particulate fraction of enamel- and dentin-related portions. It was seen in the mitochondria and in the subplasmalemmal undercoat. All these proteins may play a role in exocytosis and endocytosis. They are implied in the regulation of cell calcium, but not in the transfer of calcium through the cells in the direction of the forming enamel and dentin, except annexins I and II since they are both present in the secretory vesicles and in the forming enamel.

Neuronal protection correlates with prevention of calcium-calmodulin binding in rats

We correlated the efficacy of several clinically relevant pharmacotherapies with their ability to prevent calcium influx into neurons and subsequent binding to calmodulin. We studied the administration of CGS 19755, nimodipine, nicardipine, and combinations of these drugs before or immediately after ischemia in globally ischemic rats. Calcium-calmodulin binding was graded by an immunohistochemical assay after 2 and 24 hours of reperfusion (n = 5-6 at each time period), and histologic damage was graded by light microscopy after 72 hours of reperfusion (n = 6). Calcium-calmodulin binding correlated with the severity of delayed histologic damage in various brain regions. In untreated ischemic control rats, marked calcium-calmodulin binding was seen in CA1 and CA3 after 24 hours of reperfusion (p less than or equal to 0.01). Administered before ischemia, CGS 19755 prevented calcium-calmodulin binding across all brain regions after 2 and 24 hours of reperfusion compared with controls (p less than or equal to 0.05). This effect was most prominent in CA3 and CA1, where the drug also reduced delayed neuronal damage (p less than or equal to 0.05). Lower doses or postischemic administration of CGS 19755, nimodipine, nicardipine, and a combination of postischemic CGS 19755 and nicardipine had a more limited effect on calcium-calmodulin binding and did not protect against delayed neuronal damage.(ABSTRACT TRUNCATED AT 250 WORDS)