Regulation of membrane targeting of the G protein-coupled receptor kinase 2 by protein kinase A and its anchoring protein AKAP79

The beta2 adrenergic receptor (beta2AR) undergoes desensitization by a process involving its phosphorylation by both protein kinase A (PKA) and G protein-coupled receptor kinases (GRKs). The protein kinase A-anchoring protein AKAP79 influences beta2AR phosphorylation by complexing PKA with the receptor at the membrane. Here we show that AKAP79 also regulates the ability of GRK2 to phosphorylate agonist-occupied receptors. In human embryonic kidney 293 cells, overexpression of AKAP79 enhances agonist-induced phosphorylation of both the beta2AR and a mutant of the receptor that cannot be phosphorylated by PKA (beta2AR/PKA-). Mutants of AKAP79 that do not bind PKA or target to the beta2AR markedly inhibit phosphorylation of beta2AR/PKA-. We show that PKA directly phosphorylates GRK2 on serine 685. This modification increases Gbetagamma subunit binding to GRK2 and thus enhances the ability of the kinase to translocate to the membrane and phosphorylate the receptor. Abrogation of the phosphorylation of serine 685 on GRK2 by mutagenesis (S685A) or by expression of a dominant negative AKAP79 mutant reduces GRK2-mediated translocation to beta2AR and phosphorylation of agonist-occupied beta2AR, thus reducing subsequent receptor internalization. Agonist-stimulated PKA-mediated phosphorylation of GRK2 may represent a mechanism for enhancing receptor phosphorylation and desensitization.

Circumcision using bipolar diathermy scissors: a simple, safe and acceptable new technique

BACKGROUND

Circumcision may be performed by a variety of techniques. Postoperative haemorrhage is a recognised complication of the procedure.

METHOD

A method of circumcision using bipolar diathermy scissors is described. Foreskin vessels are coagulated as the foreskin is cut away.

RESULTS

Thirty patients underwent this procedure without complication.

CONCLUSION

Circumcision using bipolar scissors can be a safe and simple operation.

Assembly of an A kinase-anchoring protein-beta(2)-adrenergic receptor complex facilitates receptor phosphorylation and signaling

Phosphorylation of G-protein-coupled receptors by second-messenger-stimulated kinases is central to the process of receptor desensitization [1-3]. Phosphorylation of the beta(2)-adrenergic receptor (beta(2)-AR) by protein kinase A (PKA), in addition to uncoupling adenylate cyclase activation, is obligatory for receptor-mediated activation of mitogen-activated protein kinase (MAP kinase) cascades [4] [5]. Although mechanisms for linking G-protein-coupled receptor kinases to the activated receptor are well established, analogous mechanisms for targeting second messenger kinases to the beta(2)-AR at the plasma membrane have not been elucidated. Here we show that the A-kinase-anchoring protein, AKAP79/150, co-precipitates with the beta(2)-AR in cell and tissue extracts, nucleating a signaling complex that includes PKA, protein kinase C (PKC) and protein phosphatase PP2B. The anchoring protein directly and constitutively interacts with the beta(2)-AR and promotes receptor phosphorylation following agonist stimulation. Functional studies show that PKA anchoring is required to enhance beta(2)-AR phosphorylation and to facilitate downstream activation of the MAP kinase pathway. This defines a role for AKAP79/150 in the recruitment of second-messenger-regulated signaling enzymes to a G-protein-coupled receptor.

Identification of cAMP-dependent protein kinase holoenzymes in preantral- and preovulatory-follicle-enriched ovaries, and their association with A-kinase-anchoring proteins

Undifferentiated cells from preantral (PA) follicles respond to high levels of cAMP in a different manner than do differentiated cells from preovulatory (PO) follicles. We hypothesized that this differential response of PA and PO cells to cAMP could be due, in part, to either a difference in the profile of isoforms that comprise the cAMP-dependent protein kinase (PKA) holoenzymes and/or a difference in the interaction of PKA with A-kinase-anchoring proteins (AKAPs). To test these hypotheses, PKA activity, PKA holoenzymes, PKA subunits and AKAPs from PA and PO ovaries were compared. Soluble PKA holoenzymes and regulatory (R) subunits were separated by DEAE-cellulose chromatography and sucrose-density-gradient centrifugation. PKA R subunits were distinguished by photoaffinity labelling, autophosphorylation, size, isoelectric point and immunoreactivity. AKAPs were identified by RII subunit overlay assays and immunoreactivity. The results showed that extracts from PA and PO ovaries exhibited equivalent PKA holoenzyme profiles and activities, characterized by low levels of PKA type I (PKAI) holoenzyme and two distinct PKAII holoenzyme peaks, one containing only RIIbeta subunits (PKAIIbeta) and one containing both PKAIIbeta and PKAIIalpha holoenzymes. Both PA and PO ovarian extracts also contained PKA catalytic (C)-subunit-free RIalpha, while only PO ovaries exhibited C-subunit-free RIIbeta. Consistent with the elevated levels of C-subunit-free RIIbeta in PO cells, PKA activation in PO cells required higher concentrations of forskolin than that in PA cells. While extracts of PA and PO ovaries exhibited a number of similar AKAPs, including four prominent ones reactive with anti-AKAP-KL antisera (where AKAP-KL is an AKAP especially abundant in kidney and liver), cAMP-agarose affinity chromatography revealed two major differences in AKAP binding to purified R subunits. PO ovaries contained increased levels of AKAP80 (AKAP of 80 kDa) bound selectively to R subunits in DEAE-cellulose peak 2 (comprising PKAIIbeta and RIalpha), but not to R subunits in DEAE-cellulose peak 3 (comprising PKAIIalpha, PKAIIbeta and RIIbeta). PO ovaries also showed increased binding of R subunits to AKAPs reactive with anti-AKAP-KL antisera at 210, 175, 150 and 115 kDa. Thus in PO ovaries, unlike in PA ovaries, the majority of AKAPs are bound to R subunits. These results suggest that altered PKA-AKAP interactions may contribute to the distinct responses of PA and PO follicles to high levels of cAMP, and that higher cAMP levels are required to activate PKA in PO ovaries.

Regulation of NMDA receptors by an associated phosphatase-kinase signaling complex

Regulation of N-methyl-D-aspartate (NMDA) receptor activity by kinases and phosphatases contributes to the modulation of synaptic transmission. Targeting of these enzymes near the substrate is proposed to enhance phosphorylation-dependent modulation. Yotiao, an NMDA receptor-associated protein, bound the type I protein phosphatase (PP1) and the adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase (PKA) holoenzyme. Anchored PP1 was active, limiting channel activity, whereas PKA activation overcame constitutive PP1 activity and conferred rapid enhancement of NMDA receptor currents. Hence, yotiao is a scaffold protein that physically attaches PP1 and PKA to NMDA receptors to regulate channel activity.

Osteomyelitis of the temporomandibular joint in patients with malignant otitis externa

Malignant (invasive) otitis externa is an infection involving the external ear canal, often in elderly diabetic patients, which carries a high morbidity and mortality. It may involve widespread areas of soft tissue around the skull base, and in more advanced cases, may give rise to osteomyelitis and cranial neuropathy. We describe two patients who were treated for malignant otitis externa complicated by destructive osteomyelitis of the temporomandibular joint (TMJ). For both patients, diagnosis was made using magnetic resonance imaging (MRI), and repeat scans were employed during follow-up. Improved scan appearances mirrored improvements in clinical condition in both cases.

Characterization of the functional properties of smooth muscle caldesmon domain 4a: evidence for an independent inhibitory actin-tropomyosin binding domain

Recent analysis has shown the presence of three sequences in the C-terminal 170 amino acids of human caldesmon (domain 4) which are involved in actin binding and tropomyosin-dependent inhibition of actomyosin ATPase. Two are in domain 4b (amino acids 715-793) and one is in domain 4a (amino acids 636-714). In the present work we have compared recombinant peptides containing either domain 4a or domain 4b to address the question as to whether domain 4a alone has any inhibitory activity. We have produced three new recombinant fragments containing domain 4a: H10 [622-708], H12 [506-708] and H13 [622-726] and we have characterized their functional properties. All three fragments bound to actin and tropomyosin. Caldesmon, but not domain 4b, was able to displace the fragments H10, H12 and H13 from actin. Thus the isolated caldesmon domain 4a peptides bind to the same region on actin as in the whole molecule while domains 4a and 4b occupy different sites on the actin molecule. Unlike domain 4b, none of the domain 4a fragments inhibited the actomyosin ATPase in the absence of tropomyosin. However both domain 4a and 4b fragments displayed an inhibitory activity in the presence of tropomyosin. H13 and H12 were more potent inhibitors than H10. Ca2+-calmodulin bound to H13 and reversed the inhibitory activity of this fragment but did not bind to H10 and H12. We conclude that domain 4a can act as an independent inhibitory actin-tropomyosin binding domain, but its properties are very different from the extreme C-terminal domain 4b.

A novel lipid-anchored A-kinase Anchoring Protein facilitates cAMP-responsive membrane events

Compartmentalization of protein kinases with substrates is a mechanism that may promote specificity of intracellular phosphorylation events. We have cloned a low-molecular weight A-kinase Anchoring Protein, called AKAP18, which targets the cAMP-dependent protein kinase (PKA) to the plasma membrane, and permits functional coupling to the L-type calcium channel. Membrane anchoring is mediated by the first 10 amino acids of AKAP18, and involves residues Gly1, Cys4 and Cys5 which are lipid-modified through myristoylation and dual palmitoylation, respectively. Transient transfection of AKAP18 into HEK-293 cells expressing the cardiac L-type Ca2+ channel promoted a 34 9% increase in cAMP-responsive Ca2+ currents. In contrast, a targeting-deficient mutant of AKAP18 had no effect on Ca2+ currents in response to the application of a cAMP analog. Further studies demonstrate that AKAP18 facilitates GLP-1-mediated insulin secretion in a pancreatic beta cell line (RINm5F), suggesting that membrane anchoring of the kinase participates in physiologically relevant cAMP-responsive events that may involve ion channel activation.

Structure-activity studies of the regulatory interaction of the 10 kilodalton C-terminal fragment of caldesmon with actin and the effect of mutation of caldesmon residues 691-696

We have used isotope-edited nuclear magnetic resonance spectroscopy, binding studies, and ATPase activity assays to investigate the interaction with F-actin of the 10 kDa C-terminal 658C fragment of chicken gizzard caldesmon and two site-directed mutants of this fragment. Simultaneous dual-sited contacts with F-actin are observed for the segments of the 658C sequence flanking tryptophan residues 692 and 722. Competition experiments showed that both 658C contacts with actin are displaced by substoichiometric concentrations of the short inhibitory region of troponin-I indicative of different binding sites on actin for these regions of troponin-I and caldesmon. Substitution of caldesmon serine-702 by aspartic acid within the spacer region linking the two actin contacts of 658C led to weaker binding but with retention of equivalent affinity for each interaction site. Differential binding affinity of the two sites was achieved by replacement of the sequence Glu691-Trp-Leu-Thr-Lys-Thr696 by Pro-Gly-His-Tyr-Asn-Asn. Consistent with these data, the concentration of this Cg1 mutant required to achieve 50% inhibition of actin-tropomyosin-activated myosin ATPase was 4-fold greater than found for the 658C fragment. Although calmodulin binding to Cg1 was observed, calmodulin proved ineffective in relieving the inhibition induced by the binding of this mutant to actin. These results are discussed in light of the actin contacts which are involved in the inhibitory activity possessed by different regions of the C-terminus of caldesmon.

Troponin I and troponin T interact with troponin C to produce different Ca2+-dependent effects on actin-tropomyosin filament motility

We have developed an in vitro motility assay to make a detailed quantitative analysis of Ca2+ control of skeletal-muscle troponin-tropomyosin control of actin-filament movement over immobilized myosin. Ca2+ regulates both filament velocity and the fraction of filaments that are motile. We have demonstrated that the two effects are due to separate interactions of troponin C with troponin I and troponin T. When 64nM of the complex actin-tropomyosin-troponin I-troponin C was added at pCa 5, more than 80% of filaments were moving and their velocity did not change. At pCa 9, more than 20% of the filaments were moving. When 20nM of the complex actin-tropomyosin-troponin T+troponin I+troponin C was added at pCa 5, filament motility remained high, whereas velocity increased. The 30% increase in velocity observed when troponin T was present was also observed when heavy meromyosin fragment 1 labelled with N-ethylmaleimide (NEM S-1) was added after actin-tropomyosin filaments. The NEM S-1 effect was not additive with the troponin T-dependent velocity increase. The pattern of motile behaviour is characteristic of myosin on silicone-treated glass and different from the behaviour on nitrocellulose-coated glass.

Mapping of contact sites in the caldesmon-calmodulin complex

The interaction of intact calmodulin and its four tryptic peptides with deletion mutants of caldesmon was analysed by native gel electrophoresis, fluorescence spectroscopy and zero-length cross-linking. Deletion mutants H2 (containing calmodulin-binding sites A and B) and H9 (containing sites B and B') interacted with intact calmodulin to form complexes whose stoichiometries varied from 2:1 to 1:1. The N-terminal peptides of calmodulin (TR1C, residues 1-77, and TR2E, residues 1-90) bound H2 with higher affinity than H9. At the same time H2 was less effective than H9 in binding to the C-terminal peptides of calmodulin TR2C (residues 78-148) and TR3E (residues 107-148). The N-terminal peptides of calmodulin (TR1C and TR2E) could be cross-linked to intact caldesmon and its deletion mutants H2 and H9. The similarity in the primary structures of sites A and B' of caldesmon and our measurements of the affinities of H2 and H9 to calmodulin and its peptides strongly indicate an orientation of the protein complex where sites A and B' interact with the N-terminal domain of calmodulin, whereas site B interacts with the C-terminal domain of calmodulin. The spatial organization of contact sites in the caldesmon-calmodulin complex agrees with the earlier proposed two-dimensional model of interaction of the two proteins [Huber, El-Mezgueldi, Grabarek, Slatter, Levine and Marston (1996) Biochem. J. 316, 413-420].

The inhibitory complex of smooth muscle caldesmon with actin and tropomyosin involves three interacting segments of the C-terminal domain 4

We have designed a series of recombinant peptides derived from the C-terminus of human caldesmon (amino acids 663-793, domain 4) to determine the structural basis of the multiple-sited caldesmon-actin-tropomyosin interaction. All the recombinant peptides are able to bind to actin and inhibit actin-activated myosin ATPase activity; 1 mol of peptide is bound per actin for >90% inhibition. However, equivalent inhibition of actin-tropomyosin activation of myosin ATPase requires less than one peptide per seven actin to be bound. We have found two sequences, H2 (amino acids 683-767) and H2+12 (amino acids 683-779), from the center of domain 4 which potentiate actin-tropomyosin filament activity; i.e., their effect is opposite to caldesmon. Maximum potentiation correlates with one H2 or H2+12 bound per four actin. This effect is completely dependent upon the presence of tropomyosin on the actin filament. H2 and H2+12 also increase actin-tropomyosin filament velocity in the in vitro motility assay. If the H2 sequence is extended by 20 amino acids at the N-terminal end to the N-terminus of domain 4, the peptide becomes an inhibitor. If H2 is extended by 19 amino acids at its C terminus, it becomes a tropomyosin-dependent inhibitor, and with a further extension of 7 amino acids to reach the C-terminus of human caldesmon (H2+26), inhibition is more potent. We conclude that three regions in domain 4 of caldesmon contribute to tropomyosin-dependent inhibition of actomyosin ATPase: a central segment [747-767 (690-710 in the chicken sequence)], which is essential but not sufficient for tropomyosin-dependent inhibition of actomyosin ATPase; and two actin binding segments N-terminal and C-terminal to this segment, 663-682 (606-625) and 770-793 (713-737). If only the central segment is present (H2, H2+12), the actin-tropomyosin-caldesmon peptide complex is not inhibitory, and its properties resemble actin-tropomyosin-caldesmon-Ca2+ x calmodulin.

A simple method for automatic tracking of actin filaments in the motility assay

A great deal of quantitative information about the actomyosin interaction can be obtained from the basic Kron and Spudich in vitro motility assay provided that care is taken to obtain consistency between experiments and that the data is examined comprehensively and not selectively. From observations of filament movement under a wide variety of conditions we have formulated the hypothesis that a large number of filaments moving over a short time period is indistinguishable from fewer filaments moving over a longer sequence of frames. This has been used to devise a simple automation of filament detection procedures. A sequence of images is digitized through a frame-grabber. If successive pairs of frames are compared the program will search for and detect the new position of every filament and show its vector on screen. Velocity is calculated and shown as a frequency histogram. The program regularly detects over 100 filaments moving in each pair of frames; usually a sequence of up to 15 pairs of frames are studied yielding 500-1000 vectors in total. The algorithm cannot deal with filaments that meet, cross or divide, however, when filaments are moving less than 2 microns between frames this is only a small proportion of the whole. The program outputs fraction of filaments motile, mean velocity with standard deviation and density of filaments (filaments microns-2). A cumulative frequency histogram gives an immediate visual indication of the performance of the population of filaments. Direct comparisons show that the data produced by automatic tracking is indistinguishable from manual tracking apart from the small apparent velocity of non-mobile filaments. The detection process takes about 5 min and requires little skill or judgement. This can lead to great increases in the rate of data analysis in motility work.

A comparative study of safety and efficacy of continuous low dose oestradiol released from a vaginal ring compared with conjugated equine oestrogen vaginal cream in the treatment of postmenopausal urogenital atrophy

OBJECTIVE

To compare the safety, efficacy and acceptability of a continuous low dose oestradiol releasing vaginal ring with conjugated equine oestrogen vaginal cream in the treatment of postmenopausal urogenital atrophy.

DESIGN

An open, parallel, comparative multicentre trial.

SETTING

Sydney and Melbourne, Australia.

PARTICIPANTS AND INTERVENTIONS

One hundred and ninety-four postmenopausal women with symptoms and signs of urogenital atrophy were randomised on a 2:1 basis to 12 weeks of treatment with an oestrogen vaginal ring versus an oestrogen cream.

MAIN OUTCOME MEASURES AND RESULTS

Equivalence (95% CI) was demonstrated between the two treatments for relief of vaginal dryness and dyspareunia, resolution of atrophic signs, improvement in vaginal mucosal maturation indices and reduction in vaginal pH. No significant difference was demonstrated in endometrial response to a progestogen challenge test and equivalence was demonstrated in the incidence of intercurrent bleeding episodes. The vaginal ring was significantly more acceptable than the cream P < 0.0001), and was preferred to the cream (P < 0.001).

CONCLUSION

With equivalent efficacy and safety and superior acceptability to vaginal cream, the low dose oestradiol vaginal ring is an advance in vaginal delivery systems for the treatment of urogenital atrophy.

A prospective, randomized study of the use of platelet concentrates irradiated with ultraviolet-B light in patients with hematologic malignancy

BACKGROUND

Irradiation of platelet concentrates (PCs) with ultraviolet-B (UVB) light inactivates the contaminating white cells and might be an alternative to filtration for the prevention of alloimmunization to HLA antigens and subsequent refractoriness to further platelet transfusions in multiply transfused patients with bone marrow failure.

STUDY DESIGN AND METHODS

Patients with hematologic malignancy, mainly acute myeloid leukemia, were prospectively assigned in a random manner to receive either UVB-irradiated or control, nonirradiated PCs. All patients were given red cells that were white cell reduced by filtration. Transfusion efficacy and alloimmunization were assessed by means of corrected count increments, requirement for red cells and PCs, and measurement of lymphocyte-reactive antibodies.

RESULTS

UVB-irradiated PCs had a clinical efficacy similar to controls as judged by corrected count increments at 1 to 6 and 12 to 24 hours and by the median requirement for red cell and platelet transfusions. Alloimmunization determined by measurements of lymphocyte-reactive antibodies using both conventional and antiglobulin-augmented lymphocytotoxicity techniques was not abolished in recipients of UVB-irradiated PCs (4/30, 13%) but was less than that in controls (5/20, 25%; p = NS). The mean number of platelet transfusion episodes prior to the occurrence of alloimmunization was greater in the control group (27 vs. 10; p = 0.017).

CONCLUSION

In this trial, UVB irradiation did not diminish the clinical efficacy of platelet transfusions. There was a small but nonsignificant reduction alloimmunization, but no difference in refractoriness of the two groups was observed. Larger prospective randomized studies are required to confirm these findings and to compare UVB irradiation with white cell reduction.

Location of smooth-muscle myosin and tropomyosin binding sites in the C-terminal 288 residues of human caldesmon

We have produced nine recombinant fragments, H1 to H9, from a human cDNA that codes for the C-terminal 288 residues of caldesmon. The fragment H1, encompassing the 288 residues, is equivalent to domains 3 and 4 of caldesmon (amino acids 506-793 in human, 476-737 in the chicken gizzard sequence). It has been shown [Huber, Redwood, Avent, Tanner and Marston (1993) J. Muscle Res. Cell Motil. 14, 385-391] to bind to actin, Ca(2+)-calmodulin, tropomyosin and myosin. The fragments, H2 to H9, differ in length between 60 and 176 residues and cover the whole of domains 3 and 4 with many of the fragments overlapping. We have characterized the myosin and tropomyosin binding of these fragments. The binding of both tropomyosin and myosin is highly dependent on salt concentration, indicating the ionic nature of these interactions. The location of the myosin binding is an extended region encompassing the junction of domains 3/4 and domain 4a (residues 622-714, human; 566-657, chicken gizzard). Tropomyosin binds in a smaller region within domain 4a of caldesmon (residues 663-714, human; 606-657 chicken gizzard). We confirmed predictions based on sequence similarities of a tropomyosin binding site in domain 3 of caldesmon; however, this site bound to skeletal-muscle tropomyosin and had little affinity for the smooth-muscle tropomyosin isoform. None of the protein fragments H2-H9 retained the affinity of the parent fragment H1 for either myosin or tropomyosin. This indicates the need for several interaction sites scattered over an extended region to attain higher affinity. The regions interacting with caldesmon in both tropomyosin and myosin are coiled-coil structures. This is probably the reason for their shared interaction sites on caldesmon and their similar natures of binding.

Human Rh D monoclonal antibodies (BRAD-3 and BRAD-5) cause accelerated clearance of Rh D+ red blood cells and suppression of Rh D immunization in Rh D- volunteers

The use of prophylactic anti-D to prevent Rh D immunization in Rh D- women and subsequent hemolytic disease in Rh D+ infants is widespread, but has led to shortages of the anti-D Ig. With the aim of substituting monoclonal anti-D for Rh D prophylaxis, we have compared the abilities of monoclonal and polyclonal anti-D to clear Rh D+ red blood cells (RBCs) infused into Rh D- male volunteers and to suppress Rh D immunization. Two human monoclonal antibodies (MoAbs), BRAD-3 (IgG3) and BRAD-5 (IgG1), produced from stable Epstein-Barr virus-transformed B-lymphoblastoid cell lines, were selected because of their proven in vitro activity in promoting RBC lysis in antibody-dependent cell-mediated cytotoxicity assays. RBC clearance was assessed by intravenous injection of 3 mL of 51chromium-labeled D+ RBCs into 27 volunteers 48 hours after intramuscular injection of monoclonal or polyclonal anti-D. Further 3-mL injections of unlabeled D+ cells were administered at 6 and 9 months to induce immunization. Blood samples were taken throughout the 12-month period of study for the serologic detection of anti-D. The mean half-life (t50%) of RBCs in 7 recipients of 300 micrograms BRAD-5 (5.9 hours) was similar to that in 8 recipients of 500 IU polyclonal anti-D (5.0 hours), whereas D+ cells were cleared more slowly in some of the 8 subjects injected with 300 micrograms BRAD-3 (mean t50% 12.7 hours) and in 1 individual administered 100 micrograms BRAD-3 (t50% 41.0 hours). The rate of RBC clearance in both groups administered 300 micrograms monoclonal anti-D correlated with the amount of antibody bound per cell, determined by flow cytometry. There was no evidence of primary immunization having occurred in any subject after 6 months of follow-up. Five of 24 subjects produced anti-D after one or two further injections of RBCs, confirming that they were responders who had been protected by the monoclonal or polyclonal anti-D administered initially. Four of these responders were recipients of monoclonal anti-D (3 BRAD-3, 1 BRAD-5). One individual who received BRAD-5 produced accelerated clearance of D+ RBCs at the third unprotected RBC challenge but did not seroconvert. This study shows that the human MoAbs BRAD-3 and BRAD-5 can prevent Rh D immunization, and indicates that they may be suitable replacements for the polyclonal anti-D presently used in prophylaxis of Rh D hemolytic disease of the newborn.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro motility analysis of smooth muscle caldesmon control of actin-tropomyosin filament movement

We have used the in vitro motility assay to investigate the effect of caldesmon on the movement of actin-tropomyosin filaments over thiophosphorylated smooth muscle myosin and skeletal muscle heavy meromyosin. Using either motor, incorporation of up to 8 nM caldesmon inhibited filament movement by decreasing the proportion of filaments motile from > 85% to < 30%. There was a minimal effect on filament attachment and a modest decrease in motile filament velocity in this concentration range. The reduction in the proportion of filaments motile could be completely reversed by incorporation of an excess of calmodulin at pCa 4.5. The expressed C-terminal fragment, 606C, which retains caldesmon's inhibitory capacity but does not bind to myosin, decreased the proportion of filaments motile but had no effect on velocity. We conclude that the velocity reduction by whole caldesmon is due to actin-myosin cross-linking. A significant decrease in filament attachment was observed when caldesmon was added to an excess over actin (> 10 nM). In the absence of tropomyosin, addition of an excess of caldesmon caused a similar decrease in the filament density, but there was no effect on the proportion of filaments that were motile. Our results demonstrate that caldesmon can switch actin-tropomyosin from motile to non-motile states without controlling velocity of movement or weak binding affinity and show the inhibitory action of caldesmon in the motility assay to be functionally indistinguishable from that reported for troponin.

In vitro motility analysis of actin-tropomyosin regulation by troponin and calcium. The thin filament is switched as a single cooperative unit

In striated muscles, contractility is controlled by Ca2+ binding to the regulatory protein complex troponin, which is a component of the thin filaments. Troponin is an allosteric inhibitor acting on tropomyosin to switch the thin filament between "on" and "off" states. We have used an in vitro motility assay to examine troponin regulation of individual actin-tropomyosin filaments moving over immobilized skeletal muscle heavy meromyosin. The most striking observation is that the actintropomyosin filament appears to be regulated as a single unit. At pCa 9.0, addition of up to 4 nM troponin causes the proportion of filaments motile to decrease from > 85% to 20% with no dissociation of the filaments from the heavy meromyosin surface or change in velocity. Increasing Ca2+ concentration causes the filaments to be switched back on with half-maximal increase in the proportion of filaments motile at pCa 5.8-6.0 and a modest increase in filament velocity. This is an "all or none" process in which an entire filament, up to 15 microns long, switches rapidly as a single cooperative unit. Thus, the effect of Ca2+ upon the thin filament is to recruit motile filaments.

Smooth muscle caldesmon controls the strong binding interaction between actin-tropomyosin and myosin

We have demonstrated that caldesmon does not alter the affinity of weak binding actomyosin complexes when it inhibits actin-tropomyosin activation at physiological ratios (1 per 14 actins), and we proposed that it acts upon the strong binding complexes in the same way that troponin-tropomyosin does. We therefore compared the effect of caldesmon, caldesmon fragments, and troponin upon the interaction of the strongly bound complexes S-1.ADP, S-1.adenylyl imidodiphosphate (AMP.PNP), and N-ethylmaleimide-treated myosin subfragment-1 (NEM-S-1) with actin-tropomyosin. In 0.17 M ionic strength buffer [14C]iodoacetamide-labeled S1.ADP bound to actin-smooth muscle tropomyosin with no evidence of cooperativity; Kd = 0.8 +/- 0.3 microM (n = 5). Inhibitory concentrations of sheep aorta caldesmon or rabbit skeletal muscle troponin made the binding highly cooperative. At low levels of saturation the apparent Kd was 10-40 microM with 10 microM caldesmon and 8-20 microM with 6 microM troponin; at > 50% saturation the binding was indistinguishable from actin-tropomyosin alone. A similar result was obtained for the binding of [14C]iodoacetamide-labeled S-1.AMP.PNP to actin-smooth muscle tropomyosin at 0.03 M ionic strength (Kd = 0.47 +/- 0.05 microM). Binding was slightly cooperative and became highly cooperative in the presence of inhibitory concentrations of troponin, caldesmon, and the human caldesmon fragments H7 (amino acids 622-767) and H9 (amino acids 726-793). We conclude that caldesmon and troponin both act as allosteric effectors of the "on"/"off" equilibrium of actin-tropomyosin. 0.1 NEM-S-1/actin potentiated actin-smooth muscle tropomyosin activation of myosin MgATPase 7-fold at 0.03 M ionic strength. Caldesmon inhibited the ATPase in the presence and absence of 0.5 microM NEM-S-1. NEM-S-1 reactivated actin-tropomyosin, which had been inhibited by troponin, caldesmon, H7, or H9. This is compatible with opposing effects of NEM-S-1 and caldesmon or troponin upon the actin-tropomyosin on/off equilibrium.

Localization of phospholipid-binding sites of caldesmon

The interaction of phosphatidylserine with intact smooth muscle caldesmon and caldesmon fragments obtained by bacterial expression was investigated by means of light scattering. Among these fragments only those derived from the C-terminal part of caldesmon (so-called domain 4) were able to interact with phospholipids. Fragments 606C (residues 606-756), H7 (566-710) and H2 (626-710) form tight complexes with phosphatidylserine, whereas fragments H8 (658-737), H9 (669-737) and fragment H4 (566-624) interact with phospholipids less effectively. It is concluded that the phospholipid-binding site is located in the sequence 626-710 of caldesmon. This sequence contains calmodulin-binding sites and serine residues phosphorylated by protein kinase C and pro-directed protein kinases. This could explain the effects of calmodulin and phosphorylation on the caldesmon-phospholipid interaction described earlier.

Location of two contact sites between human smooth muscle caldesmon and Ca(2+)-calmodulin

We measured Ca(2+)-calmodulin binding to expressed human caldesmon fragments by three techniques: tryptophan fluorescence enhancement, change in fluorescence of TA-calmodulin, and cosedimentation with calmodulin-Sepharose. Ca(2+)-calmodulin bound with similar affinity to peptide M73 (C714SMWEKGNVFSSPGF727, N terminus of domain 4b), to all the fragments of caldesmon containing this peptide, and also to H9 (Thr726-Val793), which did not contain this peptide (Kd = 0.2-0.8 microM). We conclude that Ca(2+)-calmodulin binds at two sites on caldesmon; site A is the sequence 715MWEKGNVFS723 previously identified by Zhan et al. (Zhan, Q., Wong, S. S., and Wang, C.-L.A. (1991) J. Biol. Chem. 266, 21810-21814), and site B is located nearer the C terminus of caldesmon. Ca(2+)-calmodulin binding at site B is coupled to reversal of caldesmon inhibition of actin-tropomyosin activated myosin MgATPase, while calmodulin binding at site A has no detectable function. H9 did not displace M73 from Ca(2+)-calmodulin, while the other fragments did. High concentrations of M73 (> 1000 x Kd) could not displace H9 bound to Ca(2+)-calmodulin-Sepharose. Thus sites A and B in calmodulin are functionally separate. Analysis of overlapping expressed fragments indicates that site B is located in the sequence Thr726-Leu767, which includes Trp749. The minimal Ca(2+)-calmodulin binding sequence could be 744SRINEWLTK752.

U.K. multicentre study on blood donors for surrogate markers of non-A non-B hepatitis. Part I: Alanine transferase and anti-HBc testing

Blood samples from 9,215 blood donors in three U.K. centres (North London, Bristol and Manchester) were tested for their alanine aminotransferase (ALT) level and the presence of anti-HBc and anti-HCV. This paper presents the results of the ALT and anti-HBc tests. The prevalence of ALT > 45 IU/l was 3.1% overall (North London 3.06%, Bristol 4.56% and Manchester 1.97%). Manchester results were skewed by the methodology used for ALT measurement, highlighting the need for standard test methods. Anti-HBc was detected using the Wellcome enzyme-immunosorbent assay (EIA) and confirmatory testing was performed using a radioimmunoassay (RIA) and the Corecell haemagglutination assay. Repeat reactive rates were 0.9, 0.79 and 0.94% for North London, Bristol and Manchester, respectively, with an overall rate of 0.9%. The confirmed positive rate was 0.73, 0.53 and 0.65% for the three centres with an overall rate of 0.63%. Donors with an ALT > 45 IU/l, or with confirmed anti-HBc, were interviewed with a medical questionnaire for risk factors. The major contributing factors in donors with a raised ALT were alcohol consumption and obesity.

Localization of the cAMP-dependent protein kinase to the postsynaptic densities by A-kinase anchoring proteins. Characterization of AKAP 79

Postsynaptic densities (PSD) are a network of proteins located on the internal surface of excitatory synapses just inside the postsynaptic membrane. Enzymes associated with the PSD are optimally positioned to respond to signals transduced across the postsynaptic membrane resulting from excitatory synaptic transmission or neurotransmitter release. We present evidence suggesting that type II cAMP-dependent protein kinase (PKA) is anchored to the PSD through interaction of its regulatory subunit (RII) with an A-Kinase Anchor Protein (AKAPs). A cDNA for the human RII-anchoring protein, AKAP 79, was isolated by screening an expression library with radiolabeled RII. This cDNA (2621 base pairs) encodes a protein of 427 amino acids with 76% identity to bovine brain AKAP 75 and 93% identity to a carboxyl-terminal RII-binding fragment of murine brain AKAP 150. A bacterially expressed 92-amino acid fragment, AKAP 79 (335-427) was able to bind RII alpha. Disruption of secondary structure by site-directed mutagenesis at selected residues within a putative acidic amphipathic helix located between residues 392 and 408 prevented RII binding. Immunological studies demonstrate that AKAP 79 is predominantly expressed in the cerebral cortex and is a component of fractions enriched for postsynaptic densities. AKAP antisera strongly cross-react with a 150-kDa protein in murine PSD believed to be AKAP 150. Co-localization of the type II PKA in purified PSD fractions was confirmed immunologically by detection of RII and enzymologically by measuring cAMP-stimulated phosphorylation of the heptapeptide substrate Kemptide. Approximately 30% of the PSD kinase activity was specifically inhibited by PKI 5-24 peptide, a highly specific inhibitor of PKA. We propose that AKAP 79 and AKAP 150 function to anchor the type II PKA to the PSD, presumably for a role in the regulation of postsynaptic events.

Association of the type II cAMP-dependent protein kinase with a human thyroid RII-anchoring protein. Cloning and characterization of the RII-binding domain

The type II cAMP-dependent protein kinase (PKA) is localized to specific subcellular environments through binding of the dimeric regulatory subunit (RII) to anchoring proteins. Subcellular localization is likely to influence which substrates are most accessible to the catalytic subunit upon activation. We have previously shown that the RII-binding domains of four anchoring proteins contain sequences which exhibit a high probability of amphipathic helix formation (Carr, D. W., Stofko-Hahn, R. E., Fraser, I. D. C., Bishop, S. M., Acott, T. E., Brennan, R. G., and Scott J. D. (1991) J. Biol. Chem. 266, 14188-14192). In the present study we describe the cloning of a cDNA which encodes a 1015-amino acid segment of Ht 31. A synthetic peptide (Asp-Leu-Ile-Glu-Glu-Ala-Ala-Ser-Arg-Ile-Val-Asp-Ala-Val-Ile-Glu-Gln-Val -Lys-Ala-Ala-Tyr) representing residues 493-515 encompasses the minimum region of Ht 31 required for RII binding and blocks anchoring protein interaction with RII as detected by band-shift analysis. Structural analysis by circular dichroism suggests that this peptide can adopt an alpha-helical conformation. Both Ht 31 (493-515) peptide and its parent protein bind RII alpha or the type II PKA holoenzyme with high affinity. Equilibrium dialysis was used to calculate dissociation constants of 4.0 and 3.8 nM for Ht 31 peptide interaction with RII alpha and the type II PKA, respectively. A survey of nine different bovine tissues was conducted to identify RII binding proteins. Several bands were detected in each tissues using a 32P-RII overlay method. Addition of 0.4 microM Ht 31 (493-515) peptide to the reaction mixture blocked all RII binding. These data suggest that all anchoring proteins bind RII alpha at the same site as the Ht 31 peptide. The nanomolar affinity constant and the different patterns of RII-anchoring proteins in each tissue suggest that the type II alpha PKA holoenzyme may be specifically targeted to different locations in each type of cell.

Interaction of the regulatory subunit (RII) of cAMP-dependent protein kinase with RII-anchoring proteins occurs through an amphipathic helix binding motif

The type II cAMP-dependent protein kinase is localized to specific subcellular environments through the binding of the regulatory subunit (RII) dimer to RII-anchoring proteins. Computer-aided analysis of secondary structure, performed on four RII-anchoring protein sequences (the microtubule-associated protein 2, P150, and two thyroid proteins Ht 21 and Ht 31), has identified common regions of approximately 14 residues which display high probabilities of forming amphipathic helices. The potential amphipathic helix region of Ht 31 (Leu-Ile-Glu-Glu-Ala-Ala-Ser-Arg-Ile-Val-Asp-Ala-Val-Ile) lies between residues 494 and 507. A bacterially expressed 318-amino acid fragment, Ht 31 (418-736), containing the amphipathic helix region, was able to bind RII alpha. Site-directed mutagenesis designed to disrupt the secondary structure in the putative binding helix reduced binding dramatically. Specifically, substitution of proline for Ala-498 significantly diminished RII alpha binding, and similar mutation of Ile-502 or Ile-507 abolished interaction. Mutation of Ala-522 to proline, which is located outside the predicted amphipathic helix region, had no effect on RII alpha binding. These data suggest that anchoring proteins interact with RII alpha via an amphipathic helix binding motif.

Comparison of platelet-rich plasma collection using the Haemonetics PCS and Baxter Autopheresis C

We have compared 118 platelet-rich plasma donations collected using the Autopheresis-C Platelet cell (Auto C) with 166 donations using the Haemonetics PCS. The median platelet yield from the Auto C was superior (2.51 vs. 1.54 x 10(11] although collection times differed (60 vs./40 min). There was greater variability in the platelet yield from the Auto C (0.45-5.6 vs./0.26-2.8 x 10(11], but leucocyte contamination was not significantly different. After secondary processing, there was significantly less residual platelet-poor plasma (272 vs. 369 ml). Platelet function assessed during 5 days of storage was satisfactory for both, although platelet aggregation responses to collagen and adenosine diphosphate were superior in the Auto C platelets.

Correlation of serological, quantitative and cell-mediated functional assays of maternal alloantibodies with the severity of haemolytic disease of the newborn

Serum samples containing IgG red blood cell (RBC) antibodies were collected without reference to clinical information from 131 pregnant alloimmunized women. Anti-D and anti-K were present in sera from 75 and 20 patients respectively. Antibody titres were determined by indirect antiglobulin test (IAGT), anti-D levels were measured by AutoAnalyzer, RBC-binding IgG was quantified using an enzyme-linked immunosorbent assay (SOL-ELISA), and functional activities were measured using the monocyte chemiluminescence (CL) test, antibody-dependent monocyte-mediated and K cell-mediated cytotoxicity (ADCC) assays, and rosette formation with U937 cells. Details of clinical outcomes were obtained retrospectively from 104 pregnancies. Forty-one babies were 'antigen-negative', and of the remainder, four required top-up transfusions, 12 required exchange transfusions, three received intrauterine transfusions, and two died in utero. A comparison of test results with severity of haemolytic disease of the newborn (HDN) showed that, provided sera tested were collected within 8 weeks of the expected delivery date, the CL test and the monocyte-mediated ADCC assay differentiated those D-positive babies which required exchange transfusions from those unaffected or only mildly affected. The usefulness of results from the AutoAnalyzer and IAGT in predicting disease severity was compromised by the wide range of results from mothers of unaffected babies. This variability was less apparent in the SOL-ELISA which predicted severe HDN with greater precision. Results from the U937 rosette assay and the K cell-mediated ADCC assay failed to correlate with disease severity.

Platelet concentrates irradiated with ultraviolet light retain satisfactory in vitro storage characteristics and in vivo survival

We have previously reported that platelet concentrates (PC) may be irradiated with ultraviolet light (UVL) in a cryostorage pack such that mixed lymphocyte reactions (MLR) are abolished whilst satisfactory platelet function is retained during subsequent storage using Fenwal PL-1240 containers. We have now studied both platelet structure and function after irradiation in DuPont Stericell bags which are both UV-permeable and biocompatible. The irradiation dosage was 3000 Joules/m2 of UVL at a mean wavelength of 310 nm; a dose previously shown to abolish MLR. No detriment to platelet function was observed when compared to control as measured by aggregation responses to adenosine diphosphate (ADP), collagen and ristocetin, hypotonic shock response and pH during 5 d of storage. Lactate levels were significantly higher (P less than 0.01) and glucose levels lower (P less than 0.01) in UV-treated PC, although in the majority the lactate level did not exceed 20 mmol/l. Betathromboglobulin and platelet factor 4 levels were higher during storage in the UV group, the latter reaching significance (P less than 0.05). When whole platelets and platelet membranes were stained with Coomassie blue or Periodic Acid-Schiff's reagent after electrophoresis in polyacrylamide gels no obvious alterations to major membrane constituents were observed on days 1 and 5 of storage. Paired in vivo autologous studies in healthy volunteers using 111Indium-labelling were performed at the end of 5 d of storage. The UV-treated platelets gave satisfactory and equivalent results for recovery, half life and survival when compared to controls. We conclude that PC irradiated with UVL and stored for 5 d in DuPont Stericell containers appear suitable for transfusion and may prove to be nonimmunogenic. Further in vivo studies of haemostatic efficacy and recipient alloimmunization are now warranted.

Two individuals with elliptocytic red cells apparently lack three minor erythrocyte membrane sialoglycoproteins

We have studied the erythrocytes of two individuals (P. L. and K. W.) who lack the Gerbich (Ge) blood-group antigen. The erythrocytes of P. L. and K. W. were not reactive with two monoclonal antibodies (NBTS/BRIC 4 and NBTS/BRIC 10) which reacted with normal erythrocytes. The membranes of P. L. and K. W. erythrocytes appeared to lack three minor sialoglycoproteins (beta, beta 1 and gamma). These three minor sialoglycoproteins were found to be associated with the cytoskeletons of normal erythrocytes. Approx. 10% of the erythrocytes of P. L. and K. W. were frankly elliptocytic. We suggest that one or more of the minor sialoglycoproteins may play a part in maintaining the discoid shape of the human erythrocyte.

Effect of new plastics and leucocyte contamination on in vitro storage of platelet concentrates

Platelet concentrates were prepared for in vitro storage in either Fenwal PL-732 or Cutter CLX platelet packs. The units were stored at 22 degrees C for seven days with either horizontal or tumbler agitation. Measurement of pH, hypotonic shock response and serotonin uptake indicated in vitro viability was well maintained during 5-7 days storage using either type of pack with either mode of agitation. The longer storage interval did not effect either plasma fibrinogen concentrations or binding of monoclonal antibody, AN51. However, gross contamination of the units with leucocytes caused increased glucose consumption, substantial fall in pH and loss of in vitro viability after five days storage. The work suggests the shelf-life of platelet concentrates can be extended to five days and that they are clinically effective providing the leucocyte contamination is minimised.

A device to stimulate the mechanical component of malignant bowel obstruction

A predictable and progressive experimental intestinal obstruction, simulating a malignancy but without neoplastic change has been produced by application of a silicone rubber ring around the bowel of 20 rats, seven dogs, and five monkeys. Serosal reaction produced fibrous tissue that resulted in an "apple core" obstruction. An easily assembled extraluminal balloon device of silicone rubber can be used to produce acute and progressive experimental obstruction, especially of the large bowel.

Longitudinal muscle of muscularis externa in human and nonhuman primate colon

The idea that the longitudinal muscle of the muscularis externa of the colon is confined to the colonic teniae in the monkey and human is a common conceptual error. Forty-six colon specimens taken from human and nonhuman primates were reviewed histologically and the distribution and structure of the longitudinal muscle were evaluated. We found that the longitudinal muscle forms a complete coat around the colon although it is considerably thicker in the region of the teniae coli. In addition to its anatomic importance, this observation has implications for the physiology of colon muscle and for certain current hypotheses concerning the etiology of diverticulitis.

Intestinal motility changes in experimental large bowel obstruction

Bipolar electrodes for recording electrical discharges of colon smooth muscle and strain gages for recording associated contractions of circular muscle were implanted in six rhesus monkeys. After recovery, baseline records were made. The animals then had an obstruction device implanted in sigmoid colon which resulted in progressive compromise of the lumen terminating in complete obstruction after 13 +/- 2 days. Recording were made daily during development of obstruction. As obstruction became more complete, contraction frequency decreased in right colon, increased in left colon proximal to the obstruction, and was unchanged in left colon distal to the obstruction. The frequency of distentions increased in colon proximal to the obstruction but was unchanged distally. Simultaneous mass actions, a complex of nonperistaltic high amplitude contractions and distentions occurring nearly simultaneously throughout the colon which is not seen in normal colon, appeared in colon both proximal and distal to the obstruction and became more frequent as the degree of obstruction progressed. Colon obstruction results in abnormal motility complexes, but not in hyperperistalsis. Mass actions probably are the basis for colic and rushing bowel sounds noted clinically in colon obstruction.

Evidence for a therapeutic effect of plasmapheresis in patients with systemic lupus erythematosus

Fourteen patients with active systemic lupus erythematosus (SLE) have been treated with plasmapheresis at a rate of two litres daily on three to four days per week, over a period of two to three weeks. Plasma was replaced isovolemically with either fresh frozen plasma or with human plasma protein fractions. Ten patients were receiving treatment with prednisone at the time of plasmapheresis, and four had received no prior treatment. Eight patients showed evidence of either clinical improvement or clinical and immunochemical improvement, at the time of plasmapheresis. In the three patients who showed high levels of circulating complexes before treatment, there was a sudden fall in the level of circulating immune complexes, which was quantitatively greater than could be explained by the amount removed. This suggests that in some patients with SLE, clearance of complexes by the mononuclear phagocytic system is initially blocked by high levels of circulating complexes and that one effect of plasmapheresis may be to relieve this blockade. Five patients showed a clinical response to plasmapheresis despite the fact that tests for immune complexes were negative. Three patients showed no response to plasmapheresis, and three were regarded as unevaluable. In a limited number of patients, who show a high level of circulating immune complexes, and whose condition is deteriorating despite treatment with corticosteroids, there may be an important therapeutic role for plasmapheresis.

Isochromosome 17q in two cases of acute blast transformation in myeloproliferative disorders

Two cases of acute blast cell transformation in myeloproliferative disorders associated with a dicentric 17q isochromosome are reported. In both cases, the karyotypes also included a Philadelphia 9q;22q translocation, and in one case, an additional chromosome 8 (trisomy 8).