MEKK-1, a component of the stress (stress-activated protein kinase/c-Jun N-terminal kinase) pathway, can selectively activate Smad2-mediated transcriptional activation in endothelial cells

Smad proteins are essential components of the intracellular signaling pathways utilized by members of the transforming growth factor-beta (TGF-beta) superfamily of growth factors. Certain Smad proteins (e.g. Smad1, -2, and -3) can act as regulated transcriptional activators, a process that involves phosphorylation of these proteins by activated TGF-beta superfamily receptors. We demonstrate that the intracellular kinase mitogen-activated protein kinase kinase kinase-1 (MEKK-1), an upstream activator of the stress-activated protein kinase/c-Jun N-terminal kinase pathway, can participate in Smad2-dependent transcriptional events in cultured endothelial cells. A constitutively active form of MEKK-1 but not mitogen-activated protein kinase kinase-1 (MEK-1) or TGF-beta-activated kinase-1, two distinct intracellular kinases, can specifically activate a Gal4-Smad2 fusion protein, and this effect correlates with an increase in the phosphorylation state of the Smad2 protein. These effects do not require the presence of the C-terminal SSXS motif of Smad2 that is the site of TGF-beta type 1 receptor-mediated phosphorylation. Activation of Smad2 by active MEKK-1 results in enhanced Smad2-Smad4 interactions, nuclear localization of Smad2 and Smad4, and the stimulation of Smad protein-transcriptional coactivator interactions in endothelial cells. Overexpression of Smad7 can inhibit the MEKK-1-mediated stimulation of Smad2 transcriptional activity. A physiological level of fluid shear stress, a known activator of endogenous MEKK-1 activity in endothelial cells, can stimulate Smad2-mediated transcriptional activity. These data demonstrate a novel mechanism for activation of Smad protein-mediated signaling in endothelial cells and suggest that Smad2 may act as an integrator of diverse stimuli in these cells.

Reliability of delta-crystallin as a marker for studies of chick lens induction

Induction of a lens by the optic vesicle of the brain was the first demonstration of how tissue interactions could influence cell fate during development. However, recent work with amphibians has shown that the optic vesicle is not the primary inducer of lens formation. Rather, an earlier interaction between anterior neural plate and presumptive lens ectoderm appears to direct lens formation. One problem with many early experiments was the absence of an unambiguous assay for lens formation. Before being able to test whether the revised model of lens induction applies to chicken embryos, we examined the suitability of using delta-crystallin as a marker of lens formation. Although delta-crystallin is the major protein synthesized in the chick lens, one or both of the two delta-crystallin genes found in chickens is transcribed in many non-lens tissues as well. In studies of lens formation where appearance of the delta-crystallin protein is used as a positive assay, synthesis of delta-crystallin outside of the lens could make experiments difficult to interpret. Therefore, polyacrylamide gel electrophoresis, immunoblotting, and immunofluorescence were used to determine whether the delta-crystallin messenger RNA detected in non-lens tissues is translated into protein, as it is in the lens. On Coomassie-blue-stained gels of several tissues from stage-22 embryos, a prominent protein was observed that co-migrated with delta-crystallin. However, on immunoblots, none of the nonlens tissues tested contained detectable levels of delta-crystallin at this stage. By imunofluorescence, delta-crystallin was observed in Rathke's pouch and in a large area of oral ectoderm near Rathke's pouch, yet none of the cells in these non-lens tissues showed the typical elongated morphology of lens fiber cells. When presumptive lens ectoderm or other regions of ectoderm from stage-10 embryos were cultured and tested for lens differentiation, both cell elongation and delta-crystallin synthesis were observed, or neither were observed. The results suggest that delta-crystallin synthesis and cell elongation together serve as useful criteria for assessing a positive lens response.

CREB binding protein is a required coactivator for Smad-dependent, transforming growth factor beta transcriptional responses in endothelial cells

The transforming growth factor-beta (TGF-beta) superfamily of growth factors and cytokines has been implicated in a variety of physiological and developmental processes within the cardiovascular system. Smad proteins are a recently described family of intracellular signaling proteins that transduce signals in response to TGF-beta superfamily ligands. We demonstrate by both a mammalian two-hybrid and a biochemical approach that human Smad2 and Smad4, two essential Smad proteins involved in mediating TGF-beta transcriptional responses in endothelial and other cell types, can functionally interact with the transcriptional coactivator CREB binding protein (CBP). This interaction is specific in that it requires ligand (TGF-beta) activation and is mediated by the transcriptional activation domains of the Smad proteins. A closely related, but distinct endothelial-expressed Smad protein, Smad7, which does not activate transcription in endothelial cells, does not interact with CBP. Furthermore, Smad2,4-CBP interactions involve the COOH terminus of CBP, a region that interacts with other regulated transcription factors such as certain signal transduction and transcription proteins and nuclear receptors. Smad-CBP interactions are required for Smad-dependent TGF-beta-induced transcriptional responses in endothelial cells, as evidenced by inhibition with overexpressed 12S E1A protein and reversal of this inhibition with exogenous CBP. This report demonstrates a functional interaction between Smad proteins and an essential component of the mammalian transcriptional apparatus (CBP) and extends our insight into how Smad proteins may regulate transcriptional responses in many cell types. Thus, functional Smad-coactivator interactions may be an important locus of signal integration in endothelial cells.

Wnt signaling: why is everything so negative?

The Wnt proteins constitute a family of secreted glycoproteins the members of which have essential signaling roles during embryogenesis. The recent identification of several new regulators of this signal transduction pathway have revealed unexpectedly intricate levels of constraint on Wnt-dependent gene activation, and studies in developing embryos and in cell culture systems have allowed a more complete understanding of the functional and biochemical interactions between components of this evolutionarily conserved pathway.

A review of 79 patients with malaria seen at a military hospital in Hawaii from 1979 to 1995

The goal of our study was to determine the epidemiological and clinical features of imported malaria seen at our military hospital in Hawaii. We reviewed the records of malaria cases seen from January 1, 1979, to December 31, 1995, and compared our results with published reviews from civilian hospitals in North America. Seventy-nine patients were diagnosed with malaria by blood smears. All acquired malaria abroad, mostly in southeast Asia. Sixty-seven percent of cases were vivax malaria, 22% were falciparum malaria, and 11% were caused by undetermined species. Common symptoms were fever (100%), alternate day fever (41%), rigors (91%), headache (59%), nausea (41%), fatigue (39%), dark urine (32%), and vomiting (31%). Ninety-one percent had fever during hospitalization, but 39% were afebrile on admission. Splenomegaly was detected in 49% of cases. The white blood cell count was normal in 65%, low in 31%, and elevated in 4% of cases. Other laboratory findings were anemia (58%), thrombocytopenia (74%), and mild hyperbilirubinemia (64%). Military physicians initially considered the diagnosis of malaria in only 54% of patients. The epidemiological features of our patients differ from those described in the civilian hospitals. Most of our patients were nonimmune, U.S.-born, military personnel infected in southeast Asia, whereas patients described in reviews from U.S. civilian hospitals were usually foreign-born civilians who were infected in Africa or India. The clinical features of malaria, and the problems of initial misdiagnosis in our patients, were similar to those reported from civilian hospitals. Military physicians, like their civilian colleagues, need more training and experience in malaria.

Venous thromboembolism associated with air travel: a report of 33 patients

BACKGROUND

The medical literature suggests long distance travel, particularly air travel, may be a risk factor for venous thromboembolism, but the risk is poorly quantified.

METHODS

We reviewed 134 records of patients hospitalized with venous thromboembolism for comments regarding recent travel. Patients who had traveled within 31 d prior to venous thromboembolism were defined as recent travelers.

RESULTS

Of 134 patients records, 66 (49%) had documented inquiries regarding travel and 33 (50%) were recent air travelers. Data regarding demographics, mode of travel, day of onset of symptoms in relation to travel, and other risk factors for venous thromboembolism were abstracted from the records of the recent travelers. There were 12 (36%) travelers who had no other predisposition for venous thromboembolism. All had traveled non-stop by aircraft for 4 or more hours; none was identified as a crew-member. The median day of onset of venous thromboembolism was on travel day 4 (range: day 1-31). There were 8 (24%) patients who had onset during air travel or on the day of arrival, and 27 (82%) had onset by travel day 15. Air travel for 4 or more hours within the preceding 31 d was the most common risk factor for venous thromboembolism in our study patients and was present in 50%. This incidence is much higher than previously described, perhaps due to limiting the study population to those in which the presence or absence of travel was documented.

CONCLUSION

Prospective studies are needed to better define the risk factors for venous thromboembolism among long distance air passengers and crew-members, and to determine effective preventive measures.

Outcome of subarachnoid haemorrhage. An analysis of surgical variables, cognitive and emotional sequelae related to SPECT scanning

A group of 48 patients, consecutive apart from exclusions, from a 1-year series of 60 cases of aneurysmal subarachnoid haemorrhage (SAH), was reviewed, in respect of clinical and radiological features, surgical management, clinical outcome, psychological distress and psychometric status, the neuropsychological assessment being compared with a closely-matched group of controls, the postoperative assessment being accompanied by a single positron emission computed tomogram (SPECT) scan. A review of those features which might have been expected to have a bearing on cognitive outcome (CT abnormalities at the outset, angiographic vasospasm, operative aneurysmal leakage, temporary vessel occlusion) failed to show a significant difference on cognitive tests. There was, however, a cognitive deficit shown by the patient group as a whole, when compared with the controls. Thus, SAH itself, the initial insult, would appear to be the essential factor in the production of persistent cognitive deficits.

The potential for catheter microbial contamination from a needleless connector

Needleless connectors have been widely introduced into clinical practice to allow the connection of syringes and luers to peripheral and central vascular catheters. The potential for microbial contamination of catheters via these devices is currently unclear. A recently introduced connector, the 'Connecta Clave', was assessed by various in-vitro methods. The 'Connecta Clave' is specifically devised to separate external components from the fluid pathway. The compression seals of 50 devices were contaminated with 1 x 10(4) cfu Staphylococcus epidermidis, disinfected with isopropanol, and fluid passed through. Only one device allowed organisms to pass through, despite this challenge, representing a contamination rate of 2%. In comparison, when 50 connectors were challenged with 20 cfu of S. epidermidis, no organisms passed through the device during use. In the clinical situation, after manipulation, < 16 cfu of skin organisms were found associated with the compression seal of the devices. It is, therefore, likely that the contamination rates in clinical practice will be extremely low. Three methods of disinfecting the compression seals and associated rims were also evaluated. A combination of alcohol chlorhexidine spray, followed by a 70% isopropanol swab, resulted in the most efficacious disinfection. The isopropanol swabs produced an adequate disinfection rate. The overall results suggest that by use of specially designed connectors, not only are needlestick injuries reduced, but the likelihood of microbial contamination of catheters via the internal route may also be diminished.

WNTs modulate cell fate and behavior during vertebrate development

Wnt genes encode a family of secreted glycoproteins that modulate cell fate and behavior in embryos through activation of receptor-mediated signaling pathways. Wnt sequences, patterns of expression and activities are highly conserved in evolution, so it has been possible to gain insights into the functions, and mechanisms of action, of the Wnt genes through a synthesis of genetic and cell biological approaches in different organisms. These studies suggest that there are functionally distinct WNT proteins as assayed by the ability to transform cells and by differences in embryonic responses to ectopic WNT signals. Moreover, gain-of-function and loss-of-function studies both support the involvement of Wnt proteins in modulating cell fate and cell behavior during vertebrate development, often through combinatorial interactions with other signaling pathways to regulate gene expression.

Using computer systems to enhance case management

This article describes how an on-line computer system can enhance case management by improving communication within internal departments and adding consistency and objectivity to the referral process. At PacifiCare, the computer system has supported case management's efforts to provide members with cost-effective medical care and has improved satisfaction with the health plan.

Use of prototype automated blood culture system and gas-liquid chromatography for the analysis of continuous ambulatory peritoneal dialysis associated infection

AIMS

(1) To compare the recovery of organisms from continuous ambulatory peritoneal dialysis (CAPD) effluent fluid obtained from patients with clinical evidence of peritonitis, with an automated system (AS) and the Septichek blood culture system; (2) to evaluate the times to detection of organisms with the two systems; (3) to identify anaerobes from CAPD samples by extended anaerobic culture and gas-liquid chromatography (GLC).

METHODS

168 CAPD effluent fluid samples were studied, representing 157 episodes of peritonitis in 97 patients. CAPD samples were inoculated into two AS bottles-one anaerobic, one aerobic-and a Septichek bottle; samples were also examined for cell count, Gram stain, and direct culture. Culture bottles were then subcultured onto various media, and any organisms isolated were identified. After routine culture, GLC was performed on culture fluid in the anaerobic AS and Septichek bottles. When volatile fatty acids were detected, the broths were cultured anaerobically on specialised medium for a further five days.

RESULTS

147 organisms were isolated from the 168 samples: 96 (57%) yielded growth of significant organisms by direct culture, as compared to 129 (76.8%) by both AS and Septichek. There was no significant difference in isolation rates between AS and Septichek, but time to detection was more rapid with the AS system (p < 0.002). GLC showed volatile fatty acid in 15 specimens; of these, 14 subsequently grew anaerobic organisms.

CONCLUSIONS

AS was comparable to Septichek for numbers of isolations. Speed to detection was faster with the AS, which may be an advantage in management of patients with CAPD peritonitis. GLC showed anaerobes in several cases which would not have been detected without prolonged anaerobic culture; thus anaerobic cultures are recommended for patients who are unresponsive to antimicrobials or who have evidence of bowel perforation.

Expression of a dominant-negative Wnt blocks induction of MyoD in Xenopus embryos

During gastrulation of Xenopus embryos the prospective mesoderm is induced initially with domains of dorsal and ventral fate, then further patterned to generate somitic mesoderm by signals from the gastrula organizer. Although Xwnt-8 is expressed in future ventrolateral mesoderm and induces prospective epidermis to differentiate in vitro as ventral mesoderm, no loss-of-function studies have demonstrated a requirement for Wnt signaling for the normal expression of mesodermal genes in the gastrula. We report development of a dominant-negative Wnt (dnXwnt-8) that inhibits embryonic responses to Wnt signaling in a cell-nonautonomous fashion. By expressing dnXwnt-8 in Xenopus embryos, we uncover a requirement of Wnt signaling for localized expression in prospective mesoderm of XMyoDa and Xenopus-posterior (Xpo). Because ectopic expression of functional Xwnt-8 in the dorsal marginal zone of the gastrula induces ectopic XMyoDa and Xpo, both gain-of-function and loss-of-function experiments support a model in which endogenous Xwnt-8 functions to induce expression of genes involved in specification of ventral and somitic mesoderm.

A frizzled homolog functions in a vertebrate Wnt signaling pathway

BACKGROUND

Wnts are secreted proteins implicated in cell-cell interactions during embryogenesis and tumorigenesis, but receptors involved in transducing Wnt signals have not yet been definitively identified. Members of a large family of putative transmembrane receptors homologous to the frizzled protein in Drosophila have been identified recently in both vertebrates and invertebrates, raising the question of whether they are involved in transducing signals for any known signaling factors.

RESULTS

To test the potential involvement of frizzled homologs in Wnt signaling, we examined the effects of overexpressing rat frizzled-1 (Rfz-1) on the subcellular distribution of Wnts and of dishevelled, a cytoplasmic component of the Wnt signalling pathway. We demonstrate that ectopic expression of Rfz-1 recruits the dishevelled proten-as well as Xenopus Wnt-8 (Xwnt-8), but not the functionally distinct Xwnt-5A-to the plasma membrane. Moreover, Rfz-1 is sufficient to induce the expression of two Xwnt-8-responsive genes, siamois and Xnr-3, in Xenopus explants in a manner which is antagonized by glycogen synthase kinase-3, which also antagonizes Wnt signaling. When Rfz-1 and Xwnt-8 are expressed together in this assay, we observe greater induction of these genes, indicating that Rfz-1 can synergize with a Wnt.

CONCLUSIONS

The results demonstrate that a vertebrate frizzled homolog is involved in Wnt signaling in a manner which discriminates between functionally distinct Wnts, which involves translocation of the dishevelled protein to the plasma membrane, and which works in a synergistic manner with Wnts to induce gene expression. These data support the likely function of frizzled homologs as Wnt receptors, or as components of a receptor complex.

Characterisation of the specific binding of the histamine H3 receptor antagonist radioligand [3H]GR168320

We have examined the specific binding of the tritiated derivative of the potent histamine H3 receptor antagonist, [3,4-3H2]-cyclohex-yl-¿[4-(3H-imidazol-4-yl)-piperidin-l-yl] iminomethyl¿- amine ([3H]GR168320), to homogenates of rat cerebral cortex. Specific binding of [3H]GR168320 at 37 degrees C associated and dissociated rapidly. Binding was saturable (Bmax 412 +/- 89 fmol/mg protein) and of high affinity (Kd 0.12 +/- 0.11 nM). Saturation studies suggested the involvement of a single site. Histamine H3 receptor agonists and antagonists inhibited [3H]GR168320 binding with high affinity. Agonist and antagonist affinities correlated when compared with affinities obtained using the tritiated histamine H3 agonist radioligand N alpha-methylhistamine.

Signal sequences specify the targeting route to the endoplasmic reticulum membrane

In the yeast Saccharomyces cerevisiae, only a subset of preproteins that are translocated across the ER membrane require the function of the signal recognition particle (SRP), suggesting that an alternative, SRP-independent pathway must exist (Hann, B.C., and P. Walter. 1991. Cell. 67:131-144). We have established that the two targeting pathways function in parallel. Mutant alleles of SEC62 and SEC63 were isolated that specifically impaired the translocation of SRP-independent preproteins in vivo and in vitro, whereas SRP-dependent preproteins were unaffected. Based on this analysis, preproteins fall into three distinct classes: SRP dependent, SRP independent, and those that can use both pathways. Pathway specificity is conferred by the hydrophobic core of signal sequences. Our studies show a previously unrecognized diversity in ER-directed signal sequences, that carry structural information that serves to identify the route taken.

The value of skeletal scintigraphy in predicting the need for revision surgery in total knee replacement

We have reviewed the results of 99mtech-netium-methylene diphosphonate (Tc-MDP) bone scintigrams performed on patients following total knee arthroplasty. In addition, 67gallium (Ga) citrate scintigrams were carried out sequentially on 29 patients. Three groups of patients were identified: those with asymptomatic knees (undergoing scans for other reasons); those with aseptic or septic loosening; and those with pain without radiologic evidence of loosening. There was good correlation between the results of the scans and the final outcome. We conclude that sequential 99mTc-MDP and 67Ga citrate scintigrams are useful for demonstrating the presence of aseptic and septic loosening in knee prostheses, and pain with a normal scan appearance is probably not due to loosening or infection.

Noninvasive ankle distraction: relationship between force, magnitude of distraction, and nerve conduction abnormalities

Seven healthy volunteers (14 ankles; four males, 3 females) with no history of ankle or foot pathology were placed in a modified beach chair position on an operating table for ankle distraction using a noninvasive ankle distractor. In-line traction of 0 to 225 N (50 lb) in 22.5-N (5-lb) increments was applied to the ankle. A direct lateral radiograph was obtained at each distraction force. The joint space was measured on the lateral radiographs using electronic microcalipers. Surface recordings of the superficial peroneal, deep peroneal dorsal digital cutaneous, and sural nerves were obtained. The ankle joint space increased progressively from an average 3.1 mm with no force applied to an average 4.2 mm with 225 N (50 lb) distraction force applied. The maximum joint distraction averaged 1.3 mm (range, 0.35 to 2.35 mm). The sensory amplitudes were diminished or absent with increasing time and force of distraction. The decreased amplitudes were most marked after 1 hour of distraction with 135 N (30 lb) or greater distraction force. This correlated with symptoms of paresthesias. The superficial and deep peroneal cutaneous nerves were affected to a much greater extent than the sural nerve. The amplitudes quickly returned to normal values with the weight being released from the ankle. The noninvasive ankle distractor safely increased ankle joint space by more than 1 mm. Distraction with 135 N (30 lb) or more for 1 hour is associated with reversible nerve conduction changes. Based on these findings, we recommend using the noninvasive ankle distraction apparatus for ankle arthroscopy, with up to 135 N (30 lb) of traction applied to the foot for up to 1 hour. Greater force, applied for longer periods, is associated with increasing nerve conduction abnormalities.