Dominant negative mutations in yeast Hsp90 reveal triage decision mechanism targeting client proteins for degradation

Most of the fundamental processes of cells are mediated by proteins. However, the biologically-relevant mechanism of most proteins are poorly understood. Dominant negative mutations have provided a valuable tool for investigating protein mechanisms but can be difficult to isolate because of their toxic effects. We used a mutational scanning approach to identify dominant negative mutations in yeast Hsp90. Hsp90 is a chaperone that forms dynamic complexes with many co-chaperones and client proteins. In vitro analyses have elucidated some key biochemical states and structures of Hsp90, co-chaperones, and clients; however, the biological mechanism of Hsp90 remains unclear. For example, high throughput studies have found that many E3 ubiquitin ligases bind to Hsp90, but it is unclear if these are primarily clients or acting to tag other clients for degradation. We introduced a library of all point mutations in the ATPase domain of Hsp90 into yeast and noticed that 176 were more than 10-fold depleted at the earliest point that we could analyze. There were two hot spot regions of the depleted mutations that were located at the hinges of a loop that closes over ATP. We quantified the dominant negative growth effects of mutations in the hinge regions using a library of mutations driven by an inducible promoter. We analyzed individual dominant negative mutations in detail and found that addition of the E33A mutation that prevents ATP hydrolysis by Hsp90 abrogated the dominant negative phenotype. Pull-down experiments did not reveal any stable binding partners, indicating that the dominant effects were mediated by dynamic complexes. DN Hsp90 decreased the expression level of two model Hsp90 clients, glucocorticoid receptor (GR) and v-src kinase. Using MG132, we found that GR was rapidly destabilized in a proteasome-dependent fashion. These findings provide evidence that the binding of E3 ligases to Hsp90 may serve a quality control function fundamental to eukaryotes.

Contributions of Hyperactive Mutations in Mpro from SARS-CoV-2 to Drug Resistance

The appearance and spread of mutations that cause drug resistance in rapidly evolving diseases, including infections by the SARS-CoV-2 virus, are major concerns for human health. Many drugs target enzymes, and resistance-conferring mutations impact inhibitor binding or enzyme activity. Nirmatrelvir, the most widely used inhibitor currently used to treat SARS-CoV-2 infections, targets the main protease (Mpro) preventing it from processing the viral polyprotein into active subunits. Our previous work systematically analyzed resistance mutations in Mpro that reduce binding to inhibitors; here, we investigate mutations that affect enzyme function. Hyperactive mutations that increase Mpro activity can contribute to drug resistance but have not been thoroughly studied. To explore how hyperactive mutations contribute to resistance, we comprehensively assessed how all possible individual mutations in Mpro affect enzyme function using a mutational scanning approach with a fluorescence resonance energy transfer (FRET)-based yeast readout. We identified hundreds of mutations that significantly increased the Mpro activity. Hyperactive mutations occurred both proximal and distal to the active site, consistent with protein stability and/or dynamics impacting activity. Hyperactive mutations were observed 3 times more than mutations which reduced apparent binding to nirmatrelvir in recent studies of laboratory-grown viruses selected for drug resistance. Hyperactive mutations were also about three times more prevalent than nirmatrelvir binding mutations in sequenced isolates from circulating SARS-CoV-2. Our findings indicate that hyperactive mutations are likely to contribute to the natural evolution of drug resistance in Mpro and provide a comprehensive list for future surveillance efforts.

Systematic Analyses of the Resistance Potential of Drugs Targeting SARS-CoV-2 Main Protease

Drugs that target the main protease (Mpro) of SARS-CoV-2 are effective therapeutics that have entered clinical use. Wide-scale use of these drugs will apply selection pressure for the evolution of resistance mutations. To understand resistance potential in Mpro, we performed comprehensive surveys of amino acid changes that can cause resistance to nirmatrelvir (Pfizer), and ensitrelvir (Xocova) in a yeast screen. We identified 142 resistance mutations for nirmatrelvir and 177 for ensitrelvir, many of which have not been previously reported. Ninety-nine mutations caused apparent resistance to both inhibitors, suggesting likelihood for the evolution of cross-resistance. The mutation with the strongest drug resistance score against nirmatrelvir in our study (E166V) was the most impactful resistance mutation recently reported in multiple viral passaging studies. Many mutations that exhibited inhibitor-specific resistance were consistent with the distinct interactions of each inhibitor in the substrate binding site. In addition, mutants with strong drug resistance scores tended to have reduced function. Our results indicate that strong pressure from nirmatrelvir or ensitrelvir will select for multiple distinct-resistant lineages that will include both primary resistance mutations that weaken interactions with drug while decreasing enzyme function and compensatory mutations that increase enzyme activity. The comprehensive identification of resistance mutations enables the design of inhibitors with reduced potential of developing resistance and aids in the surveillance of drug resistance in circulating viral populations.

A complete allosteric map of a GTPase switch in its native cellular network

Allosteric regulation is central to protein function in cellular networks. A fundamental open question is whether cellular regulation of allosteric proteins occurs only at a few defined positions or at many sites distributed throughout the structure. Here, we probe the regulation of GTPases-protein switches that control signaling through regulated conformational cycling-at residue-level resolution by deep mutagenesis in the native biological network. For the GTPase Gsp1/Ran, we find that 28% of the 4,315 assayed mutations show pronounced gain-of-function responses. Twenty of the sixty positions enriched for gain-of-function mutations are outside the canonical GTPase active site switch regions. Kinetic analysis shows that these distal sites are allosterically coupled to the active site. We conclude that the GTPase switch mechanism is broadly sensitive to cellular allosteric regulation. Our systematic discovery of new regulatory sites provides a functional map to interrogate and target GTPases controlling many essential biological processes.

Comprehensive fitness landscape of SARS-CoV-2 Mpro reveals insights into viral resistance mechanisms

With the continual evolution of new strains of SARS-CoV-2 that are more virulent, transmissible, and able to evade current vaccines, there is an urgent need for effective anti-viral drugs SARS-CoV-2 main protease (M^pro) is a leading target for drug design due to its conserved and indispensable role in the viral life cycle. Drugs targeting M^pro appear promising but will elicit selection pressure for resistance. To understand resistance potential in M^pro, we performed a comprehensive mutational scan of the protease that analyzed the function of all possible single amino acid changes. We developed three separate high-throughput assays of M^pro function in yeast, based on either the ability of M^pro variants to cleave at a defined cut-site or on the toxicity of their expression to yeast. We used deep sequencing to quantify the functional effects of each variant in each screen. The protein fitness landscapes from all three screens were strongly correlated, indicating that they captured the biophysical properties critical to M^pro function. The fitness landscapes revealed a non-active site location on the surface that is extremely sensitive to mutation making it a favorable location to target with inhibitors. In addition, we found a network of critical amino acids that physically bridge the two active sites of the M^pro dimer. The clinical variants of M^pro were predominantly functional in our screens, indicating that M^pro is under strong selection pressure in the human population. Our results provide predictions of mutations that will be readily accessible to M^pro evolution and that are likely to contribute to drug resistance. This complete mutational guide of M^pro can be used in the design of inhibitors with reduced potential of evolving viral resistance.

Comprehensive fitness maps of Hsp90 show widespread environmental dependence

Gene-environment interactions have long been theorized to influence molecular evolution. However, the environmental dependence of most mutations remains unknown. Using deep mutational scanning, we engineered yeast with all 44,604 single codon changes encoding 14,160 amino acid variants in Hsp90 and quantified growth effects under standard conditions and under five stress conditions. To our knowledge, these are the largest determined comprehensive fitness maps of point mutants. The growth of many variants differed between conditions, indicating that environment can have a large impact on Hsp90 evolution. Multiple variants provided growth advantages under individual conditions; however, these variants tended to exhibit growth defects in other environments. The diversity of Hsp90 sequences observed in extant eukaryotes preferentially contains variants that supported robust growth under all tested conditions. Rather than favoring substitutions in individual conditions, the long-term selective pressure on Hsp90 may have been that of fluctuating environments, leading to robustness under a variety of conditions.

Skeletal muscle and plasma concentrations of cefazolin during complex paediatric spinal surgery

BACKGROUND

Surgical site infections (SSIs) can have devastating consequences for children who undergo spinal instrumentation. Prospective evaluations of prophylactic cefazolin in this population are limited. The purpose of this study was to describe the pharmacokinetics and skeletal muscle disposition of prophylactic cefazolin in a paediatric population undergoing complex spinal surgery.

METHODS

This prospective pharmacokinetic study included 17 children with adolescent idiopathic scoliosis undergoing posterior spinal fusion, with a median age of 13.8 [interquartile range (IQR) 13.4-15.4] yr and a median weight of 60.6 (IQR 50.8-66.0) kg. A dosing strategy consistent with published guidelines was used. Serial plasma and skeletal muscle microdialysis samples were obtained during the operative procedure and unbound cefazolin concentrations measured. Non-compartmental pharmacokinetic analyses were performed. The amount of time that the concentration of unbound cefazolin exceeded the minimal inhibitory concentration for bacterial growth for selected SSI pathogens was calculated.

RESULTS

Skeletal muscle concentrations peaked at a median of 37.6 (IQR 26.8-40.0) µg ml(-1) within 30-60 min after the first cefazolin 30 mg kg(-1) dose. For patients who received a second 30 mg kg(-1) dose, the peak concentrations reached a median of 40.5 (IQR 30.8-45.7) µg ml(-1) within 30-60 min. The target cefazolin concentrations for SSI prophylaxis for meticillin-sensitive Staphylococcus aureus (MSSA) and Gram-negative pathogens were exceeded in skeletal muscle 98.9 and 58.3% of the intraoperative time, respectively.

CONCLUSIONS

For children with adolescent idiopathic scoliosis undergoing posterior spinal fusion, the cefazolin dosing strategy used in this study resulted in skeletal muscle concentrations that were likely not to be effective for intraoperative SSI prophylaxis against Gram-negative pathogens.

Systematic Mutant Analyses Elucidate General and Client-Specific Aspects of Hsp90 Function

To probe the mechanism of the Hsp90 chaperone that is required for the maturation of many signaling proteins in eukaryotes, we analyzed the effects of all individual amino acid changes in the ATPase domain on yeast growth rate. The sensitivity of a position to mutation was strongly influenced by proximity to the phosphates of ATP, indicating that ATPase-driven conformational changes impose stringent physical constraints on Hsp90. To investigate how these constraints may vary for different clients, we performed biochemical analyses on a panel of Hsp90 mutants spanning the full range of observed fitness effects. We observed distinct effects of nine Hsp90 mutations on activation of v-src and glucocorticoid receptor (GR), indicating that different chaperone mechanisms can be utilized for these clients. These results provide a detailed guide for understanding Hsp90 mechanism and highlight the potential for inhibitors of Hsp90 that target a subset of clients.

Mechanistic Asymmetry in Hsp90 Dimers

Hsp90 is a molecular chaperone that facilitates the maturation of signaling proteins including many kinases and steroid hormone receptors. Through these client proteins, Hsp90 is a key mediator of many physiological processes and has emerged as a promising drug target in cancer. Additionally, Hsp90 can mask or potentiate the impact of mutations in clients with remarkable influence on evolutionary adaptations. The influential roles of Hsp90 in biology and disease have stimulated extensive research into the molecular mechanism of this chaperone. These studies have shown that Hsp90 is a homodimeric protein that requires ATP hydrolysis and a host of accessory proteins termed co-chaperones to facilitate the maturation of clients to their active states. Flexible hinge regions between its three structured domains enable Hsp90 to sample dramatically distinct conformations that are influenced by nucleotide, client, and co-chaperone binding. While it is clear that Hsp90 can exist in symmetrical conformations, recent studies have indicated that this homodimeric chaperone can also assume a variety of asymmetric conformations and complexes that are important for client maturation. The visualization of Hsp90-client complexes at high resolution together with tools to independently manipulate each subunit in the Hsp90 dimer are providing new insights into the asymmetric function of each subunit during client maturation.

Risk factors for tumor lysis syndrome in patients with chronic lymphocytic leukemia treated with the cyclin-dependent kinase inhibitor, flavopiridol

Tumor lysis syndrome (TLS) has been described in over 40% of patients with chronic lymphocytic leukemia treated with the cyclin-dependent kinase inhibitor, flavopiridol. We conducted a retrospective analysis to determine predictive factors for TLS. In 116 patients, the incidence of TLS was 46% (95% CI: 36-55%). In univariable analysis, female gender, greater number of prior therapies, Rai stages III-IV, adenopathy ≥ 10 cm, splenomegaly, del(11q), decreased albumin and increased absolute lymphocyte count, white blood cell count (WBC), β2-microglobulin, and lactate dehydrogenase were associated (P < 0.05) with TLS. In multivariable analysis, female gender, adenopathy ≥ 10 cm, elevated WBC, increased β2-microglobulin, and decreased albumin were associated with TLS (P < 0.05). With respect to patient outcomes, 49 and 44% of patients with and without TLS, respectively, responded to flavopiridol (P = 0.71). In a multivariable analysis, controlling for number of prior therapies, cytogenetics, Rai stage, age and gender, progression-free survival (PFS) was inferior in patients with TLS (P = 0.01). Female patients and patients with elevated β2-microglobulin, increased WBC, adenopathy ≥ 10 cm and decreased albumin were at highest risk and should be monitored for TLS with flavopiridol. TLS does not appear to be predictive of response or improved PFS in patients receiving flavopiridol.

Concomitant hypertension, bradycardia, and loss of transcranial electric motor evoked potentials during pedicle hook removal: report of a case

Neurophysiologic monitors in the form of transcranial electric motor evoked potentials (tceMEPs) and somatosensory evoked potentials (SSEPs) have become widely used modalities to monitor spinal cord function during major orthopedic spine procedures. In combination with invasive and non-invasive clinical monitoring and an anesthesia information management system (AIMS), we promptly recognized an acute change in hemodynamic and neurophysiologic parameters, managed intraoperative spinal cord contusion, and successfully minimized iatrogenic injury to the spinal cord during corrective spine surgery.

Role of wild-type estrogen receptor-beta in mitochondrial cytoprotection of cultured normal male and female human lens epithelial cells

The influence of sexual category as a modifier of cellular function is underinvestigated. Whether sex differences affect estrogen-mediated mitochondrial cytoprotection was determined using cell cultures of normal human lens epithelia (nHLE) from postmortem male and female donors. Experimental indicators assessed included differences in estrogen receptor-beta (ERbeta) isoform expression, receptor localization in mitochondria, and estrogen-mediated prevention of loss of mitochondrial membrane potential using the potentiometric fluorescent compound JC-1 after nHLE were exposed to peroxide. The impact of wild-type ERbeta (wtERbeta1) was also assessed using wtERbeta1 siRNA to suppress expression. A triple-primer PCR assay was employed to determine the proportional distribution of the receptor isoforms (wtERbeta1, -beta2, and -beta5) from the total ERbeta message pool in male and female cell cultures. Irrespective of sex, nHLE express wtERbeta1 and the ERbeta2 and ERbeta5 splice variants in similar ratios. Confocal microscopy and immunofluorescence revealed localization of the wild-type receptor in peripheral mitochondrial arrays and perinuclear mitochondria as well as nuclear staining in both cell populations. The ERbeta2 and ERbeta5 isoforms were distributed primarily in the nucleus and cytosol, respectively; no association with the mitochondria was detected. Both male and female nHLE treated with E(2) (1 muM) displayed similar levels of protection against peroxide-induced oxidative stress. In conjunction with acute oxidative insult, RNA suppression of wtERbeta1 elicited the collapse of mitochondrial membrane potential and markedly diminished the otherwise protective effects of E(2). Thus, whereas the estrogen-mediated prevention of mitochondrial membrane permeability transition is sex independent, the mechanism of estrogen-induced mitochondrial cytoprotection is wtERbeta1 dependent.

An international parentage and identification panel for the domestic cat (Felis catus)

Seventeen commercial and research laboratories participated in two comparison tests under the auspices of the International Society for Animal Genetics to develop an internationally tested, microsatellite-based parentage and identification panel for the domestic cat (Felis catus). Genetic marker selection was based on the polymorphism information content and allele ranges from seven random-bred populations (n = 261) from the USA, Europe and Brazil and eight breeds (n = 200) from the USA. Nineteen microsatellite markers were included in the comparison test and genotyped across the samples. Based on robustness and efficiency, nine autosomal microsatellite markers were ultimately selected as a single multiplex ‘core’ panel for cat identification and parentage testing. Most markers contained dinucleotide repeats. In addition to the autosomal markers, the panel included two gender-specific markers, amelogenin and zinc-finger XY, which produced genotypes for both the X and Y chromosomes. This international cat parentage and identification panel has a power of exclusion comparable to panels used in other species, ranging from 90.08% to 99.79% across breeds and 99.47% to 99.87% in random-bred cat populations.

Design principles of the proteolytic cascade governing the sigmaE-mediated envelope stress response in Escherichia coli: keys to graded, buffered, and rapid signal transduction

Proteolytic cascades often transduce signals between cellular compartments, but the features of these cascades that permit efficient conversion of a biological signal into a transcriptional output are not well elucidated. sigma(E) mediates an envelope stress response in Escherichia coli, and its activity is controlled by regulated degradation of RseA, a membrane-spanning anti-sigma factor. Examination of the individual steps in this protease cascade reveals that the initial, signal-sensing cleavage step is rate-limiting; that multiple ATP-dependent proteases degrade the cytoplasmic fragment of RseA and that dissociation of sigma(E) from RseA is so slow that most free sigma(E) must be generated by the active degradation of RseA. As a consequence, the degradation rate of RseA is set by the amount of inducing signal, and insulated from the "load" on and activity of the cytoplasmic proteases. Additionally, changes in RseA degradation rate are rapidly reflected in altered sigma(E) activity. These design features are attractive as general components of signal transduction pathways governed by unstable negative regulators.

Titanium elastic nailing of fractures of the femur in children

Between 1996 and 2003 six institutions in the United States and France contributed a consecutive series of 234 fractures of the femur in 229 children which were treated by titanium elastic nailing. Minor or major complications occurred in 80 fractures. Full information was available concerning 230 fractures, of which the outcome was excellent in 150 (65%), satisfactory in 57 (25%), and poor in 23 (10%). Poor outcomes were due to leg-length discrepancy in five fractures, unacceptable angulation in 17, and failure of fixation in one. There was a statistically significant relationship (p = 0.003) between age and outcome, and the odds ratio for poor outcome was 3.86 for children aged 11 years and older compared with those below this age. The difference between the weight of children with a poor outcome and those with an excellent or satisfactory outcome was statistically significant (54 kg vs 39 kg; p = 0.003). A poor outcome was five times more likely in children who weighed more than 49 kg.

Versatile modes of peptide recognition by the AAA+ adaptor protein SspB

Energy-dependent proteases often rely on adaptor proteins to modulate substrate recognition. The SspB adaptor binds peptide sequences in the stress-response regulator RseA and in ssrA-tagged proteins and delivers these molecules to the AAA+ ClpXP protease for degradation. The structure of SspB bound to an ssrA peptide is known. Here, we report the crystal structure of a complex between SspB and its recognition peptide in RseA. Notably, the RseA sequence is positioned in the peptide-binding groove of SspB in a direction opposite to the ssrA peptide, the two peptides share only one common interaction with the adaptor, and the RseA interaction site is substantially larger than the overlapping ssrA site. This marked diversity in SspB recognition of different target proteins indicates that it is capable of highly flexible and dynamic substrate delivery.

Sculpting the proteome with AAA(+) proteases and disassembly machines

Machines of protein destruction-including energy-dependent proteases and disassembly chaperones of the AAA(+) ATPase family-function in all kingdoms of life to sculpt the cellular proteome, ensuring that unnecessary and dangerous proteins are eliminated and biological responses to environmental change are rapidly and properly regulated. Exciting progress has been made in understanding how AAA(+) machines recognize specific proteins as targets and then carry out ATP-dependent dismantling of the tertiary and/or quaternary structure of these molecules during the processes of protein degradation and the disassembly of macromolecular complexes.

Modulating substrate choice: the SspB adaptor delivers a regulator of the extracytoplasmic-stress response to the AAA+ protease ClpXP for degradation

Adaptor proteins help proteases modulate substrate choice, ensuring that appropriate proteins are degraded at the proper time and place. SspB is an adaptor that delivers ssrA-tagged proteins to the AAA+ protease ClpXP for degradation. To identify new SspB-regulated substrates, we examined proteins captured by ClpXP(trap) in sspB(+) but not sspB(-) strains. RseA(1-108), a fragment of a transmembrane protein that regulates the extracytoplasmic-stress response, fits this criterion. In response to stress, RseA is cleaved on each side of the membrane and is released as a cytoplasmic fragment that remains bound in an inhibitory complex with the sigma(E) transcription factor. Trapping experiments together with biochemical studies show that ClpXP functions in concert with SspB to efficiently recognize and degrade RseA(1-108), and thereby releases sigma(E). Genetic studies confirm that ClpX and SspB participate in induction of the sigma(E) regulon in vivo, acting at the final step of an activating proteolytic cascade. Surprisingly, the SspB-recognition sequence in RseA(1-108) is unrelated to its binding sequence in the ssrA tag. Thus, these experiments elucidate the final steps in induction of the extracytoplasmic stress response and reveal that SspB delivers a broader spectrum of substrates to ClpXP than has been recognized.

Expression of N-formylated proteins in Escherichia coli

In bacteria, protein expression initiates with a formyl-methionine group. Addition of the antibiotic actinonin, a known peptide deformylase inhibitor, at the time of induction of protein expression results in the retention of the formyl group by the overexpressed protein. In addition, because deformylation is a prerequisite for removal of the initiating methionine, this post-translational processing step is also prevented by actinonin, and the N-formyl methionine residue is retained by proteins from which it is normally removed. We have demonstrated the applicability of this system for obtaining N-modified forms of several different proteins and use one of these modified molecules to show that the N-terminal amino group is not required for ClpXP degradation of proteins bearing an N-terminal recognition signal.

Latent ClpX-recognition signals ensure LexA destruction after DNA damage

The DNA-damage response genes in bacteria are up-regulated when LexA repressor undergoes autocatalytic cleavage stimulated by activated RecA protein. Intact LexA is stable to intracellular degradation but its auto-cleavage fragments are degraded rapidly. Here, both fragments of LexA are shown to be substrates for the ClpXP protease. ClpXP recognizes these fragments using sequence motifs that flank the auto-cleavage site but are dormant in intact LexA. Furthermore, ClpXP degradation of the LexA-DNA-binding fragment is important to cell survival after DNA damage. These results demonstrate how one protein-processing event can activate latent protease recognition signals, triggering a cascade of protein turnover in response to environmental stress.

Proteomic discovery of cellular substrates of the ClpXP protease reveals five classes of ClpX-recognition signals

ClpXP is a protease involved in DNA damage repair, stationary-phase gene expression, and ssrA-mediated protein quality control. To date, however, only a handful of ClpXP substrates have been identified. Using a tagged and inactive variant of ClpP, substrates of E. coli ClpXP were trapped in vivo, purified, and identified by mass spectrometry. The more than 50 trapped proteins include transcription factors, metabolic enzymes, and proteins involved in the starvation and oxidative stress responses. Analysis of the sequences of the trapped proteins revealed five recurring motifs: two located at the C terminus of proteins, and three N-terminal motifs. Deletion analysis, fusion proteins, and point mutations established that sequences from each motif class targeted proteins for degradation by ClpXP. These results represent a description of general rules governing substrate recognition by a AAA+ family ATPase and suggest strategies for regulation of protein degradation.

Displaced fractures of the hip in children. Management by early operation and immobilisation in a hip spica cast

Fractures of the hip in children have been associated with a very high rate of serious complications including avascular necrosis (up to 47%) and coxa vara (up to 32%). Over a period of 20 years, we have treated displaced fractures by early anatomical reduction, internal fixation and immobilisation in a spica cast to try to reduce these complications. We have reviewed 18 patients who had a displaced non-pathological fracture of the hip when under 16 years of age. Their mean age at the time of the injury was eight years (2 to 13). They returned for examination and radiography at a mean follow-up of eight years (2 to 17). Each patient had been treated by early (" 24 hours) closed or open reduction with internal fixation and 16 had immobilisation in a spica cast. By Delbet's classification, there was one type-I, eight type-II, eight type-III, and one type-IV fractures. There were no complications in 15 patients. Avascular necrosis occurred in one patient (type-III), nonunion in one (type-II, one of the two patients who did not have a cast) and premature physeal closure in one (type-I). There were no cases of infection or complications as a result of the cast. Our treatment of displaced hip fractures in children by early reduction, internal fixation, and immobilisation in a spica cast gave reduced rates of complications compared with that of large published series in the literature.

Investigation of primary cell-biomaterial interactions using silver nitrate staining of nucleolar organising regions

The quantification of silver nitrate staining of nucleolar organising regions (AgNORs) within the nucleus of the cell has been shown to give a relative measure of the metabolic activity of the cell. In the present study, silver nitrate staining was utilised to identify metabolic variations in cells cultured on different surfaces and compared with proliferative activity assessed using bromodeoxyuridine (BrdU) uptake. Primary osteoblast and periosteal cells, isolated from the calvaria of neonate rats, were cultured on tissue culture-grade (TCPS) and bacteriological-grade (BACPS) polystyrene petri dishes for 3, 5, 7 and 9 days (silver nitrate) or 14 days (BrdU). The phenotype of the cells was examined using RT-PCR of the mRNA for osteocalcin, collagen 1a, alkaline phosphatase and osteopontin. The number and area of AgNORs and the proportion of BrdU positive cells were statistically different in cells cultured on TCPS compared with BACPS at each culture period tested. The results suggest that the metabolic activity and proliferation of cells were affected by the substrate which they colonise.

Surgical treatment of congenital kyphosis

STUDY DESIGN

In this study, 26 cases of congenital kyphosis and kyphoscoliosis treated surgically were retrospectively reviewed.

OBJECTIVE

To assess the clinical outcomes and surgical indications for posterior only versus anteroposterior surgery in the child.

SUMMARY OF BACKGROUND DATA

Congenital kyphosis usually is progressive without surgical intervention. Current recommended treatment includes posterior arthrodesis for deformities of less than 50 degrees to 60 degrees, and anterior release or decompression, anterior fusion, and posterior instrumented arthrodesis for large deformities and cord compression.

METHODS

Cases involving myelodysplasia, spinal dysgenesis, and skeletal dysplasia were excluded from the study. Kyphoscoliosis was included if the kyphotic deformity was greater than the scoliotic deformity. Patients were grouped by age and surgical technique. The patients in group P1 underwent posterior arthrodesis at an age younger than 3 years, and those in group P2 underwent the procedure at an age older than 3 years. The patients in group AP1 underwent anterior and posterior procedures at an age younger than 3 years, and those in group AP2 underwent the procedures at an age older than 3 years. The preoperative deformity, complications, and postoperative deformity correction were analyzed. There were nine Type 1 (failure of formation), nine Type 2 (failure of segmentation), and eight Type 3 (mixed) deformities. Four patients had associated spinal dysraphism. Three patients with Type 1 deformities had clinical or radiographic evidence of cord compression.

RESULTS

In Group P1, five patients at an average age of 16 months underwent posterior arthrodesis alone for an average kyphotic deformity of 49 degrees. The immediate postoperative correction improved over a period of 6 years and 9 months by an additional 10 degrees, resulting in a final deformity of 26 degrees. Pseudarthrosis developed in two patients, requiring fusion mass augmentation or anterior arthrodesis. Neither patient was instrumented. In Group P2, five patients at an average age of 13 years and 7 months underwent posterior arthrodesis with instrumentation for kyphotic deformity of 59 degrees. Approximately 30 degrees of intraoperative correction was achieved safely using compression instrumentation and positioning. No further correction occurred with growth. The final residual kyphotic deformity was 29 degrees after a follow-up period of 4 years and 5 months. In Group AP1, seven patients underwent anterior release or vertebra resection for deformity correction and posterior arthrodesis for an average kyphotic deformity of 48 degrees at the age of 16 months. There were no iatrogenic neurologic injuries. The final residual kyphotic deformity was 22 degrees after a follow-up period of 6 years and 3 months. In Group AP2, nine patients underwent anterior release or decompression with posterior arthrodesis for kyphotic deformity of 77 degrees at the age of 11 years and 6 months. The deformity was corrected to 37 degrees, with no significant loss over a follow-up period of 5 years and 2 months. There were two postoperative neurologic complications.

CONCLUSIONS

After reviewing their experience, the authors made the following observations: 1) The pseudarthrosis rate was low even without routine augmentation of fusion mass if instrumentation was used; 2) gradual correction of kyphosis may occur with growth in patients younger than 3 years with Types 2 and 3 deformities after posterior fusion, but appears to be unpredictable; 3) the risk of neurologic injury with anterior and posterior fusion for kyphotic deformity was associated with greater age, more severe deformity, and preexisting spinal cord compromise.

Overlapping recognition determinants within the ssrA degradation tag allow modulation of proteolysis

The ssrA tag, an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP. Mutational analysis of the ssrA tag reveals independent, but overlapping determinants for its interactions with ClpX, ClpA, and SspB, a specificity-enhancing factor for ClpX. ClpX interacts with residues 9-11 at the C terminus of the tag, whereas ClpA recognizes positions 8-10 in addition to residues 1-2 at the N terminus. SspB interacts with residues 1-4 and 7, N-terminal to the ClpX-binding determinants, but overlapping the ClpA determinants. As a result, SspB and ClpX work together to recognize ssrA-tagged substrates efficiently, whereas SspB inhibits recognition of these substrates by ClpA. Thus, dissection of the recognition signals within the ssrA tag provides insight into how multiple proteins function in concert to modulate proteolysis.

Care for children with special health care needs in a managed care system: a patient satisfaction survey

In 1994 the government of Puerto Rico adopted a capitated managed health care system for the medically indigent. The new law has been implemented in most municipalities. A survey of children with special health care needs treated at a tertiary pediatric center under the capitated managed care system and the prior non-capitated system was analyzed using the Consumer Assessments of Health Plan Survey (CHAPS) instrument. One third of the patients who were under the new capitated managed care system were not satisfied with the medial care they were receiving. The parents of children with multidisciplinary conditions found it much more difficult to access care at the tertiary center. It took parents two years to learn to navigate within the capitated managed care system. Studies to measure outcome and health quality of children with special health care needs in capitated managed health care programs must be developed to learn how the potential benefits of managed care can be maximized and the potential harms minimized. The purpose of this study was to analyze the accessibility and satisfaction of caretakers of children with special health care needs under a capitated managed health care system.

Analysis of the cause, classification, and associated injuries of 166 consecutive pediatric pelvic fractures

SUMMARY

Pediatric pelvic fractures are serious injuries. Anatomical differences exist between pediatric and adult populations, leading to different causes and rates of death, fracture patterns, and associated injuries. This study is the largest consecutive series of pediatric pelvic fractures from one institution emphasizing the unique aspects seen in pediatrics. One hundred sixty-six children were included. Plain radiography and computed tomography scans were used to classify pelvic fractures. Multisystem injuries occurred in 60%, and 50% sustained additional skeletal injuries. The death rate was 3.6%. Head and/or visceral injuries were the causes of all deaths. Life-threatening hemorrhage did not occur. Urethral injury was not seen as often as in adults. Anterior ring fractures were the most common type, dominated by pedestrian versus motor vehicle trauma. Anatomical differences and mechanism of injury may play a role in these contrasting findings.

The orthopedists' perspective: bone tumors, scoliosis, and trauma

Although a detailed, comprehensive look at pediatric orthopedists' use of imaging is beyond the scope of this article, we offer an orthopedist's perspective of the role imaging plays in the care of children with tumors, scoliosis, and trauma. Given the growing, dynamic state of a child's skeleton, the long-term consequences of injury must always be considered.

Rethinking the role of phosducin: light-regulated binding of phosducin to 14-3-3 in rod inner segments

Phosducin (Pd), a small protein found abundantly in photoreceptors, is widely assumed to regulate light sensitivity in the rod outer segment through interaction with the heterotrimeric G protein transducin. But, based on histochemistry and Western blot analysis, Pd is found almost entirely in the inner segment in both light and dark, most abundantly near the rod synapse. We report a second small protein, 14-3-3, in the rod with a similar distribution. By immunoprecipitation, phospho-Pd is found to interact with 14-3-3 in material from dark-adapted retina, and this interaction is markedly diminished by light, which dephosphorylates Pd. Conversely, unphosphorylated Pd binds to inner segment G protein(s) in the light. From these results and reported functions of 14-3-3, we have constructed a hypothesis for the regulation of light sensitivity at the level of rod synapse. By dissociating the Pd/14-3-3 complex, light enables both proteins to function in this role.

A technique of occipitocervical arthrodesis in children using autologous rib grafts

STUDY DESIGN

Description of an operative technique with an illustrative case report.

OBJECTIVES

The technique is presented to provide an alternative to iliac crest graft procedures for achieving occipitocervical fusion in children. This technique is particularly useful in children with instability after extensive decompression or laminectomy and in children with a large protuberant occiput.

SUMMARY OF BACKGROUND DATA

The majority of techniques previously described for occipitocervical fusion in children rely on corticocancellous iliac crest autograft. Results generally have been promising; however, it can be difficult to harvest enough graft to span large defects after extensive decompression or to contour an iliac crest graft to a protuberant occiput. Structural rib autograft is superior in terms of availability and its unique and modifiable contour. Theoretical benefits of rib graft include superior strength and lower donor site morbidity.

METHODS

The surgical technique is described. A case of a 2-year-old boy with Down's syndrome and myelopathy secondary to cervical instability is reviewed.

RESULTS

The patient underwent occipitocervical arthrodesis using the technique described. The child made a full neurologic recovery, and at the 2-years follow-up evaluation, the graft had incorporated and the spine was stable.

CONCLUSION

A technique of occipitocervical arthrodesis in children is described using autologous rib graft. This procedure was designed to span large defects or to deal with a large protuberant occiput; however, it is also useful for less demanding cases and may offer several advantages compared with procedures relying on iliac crest graft.

The limping child: evaluation and diagnosis

A limp is a common reason for a child to present to the orthopaedist. Because of the long list of potential diagnoses, some of which demand urgent treatment, an organized approach to evaluation is required. With an understanding of normal and abnormal gait, a directed history and physical examination, and the development of a differential diagnosis based on the type of limp, the patient's age, and the anatomic site that is most likely affected, the orthopaedist can take a selective approach to diagnostic testing. Laboratory tests are indicated when infection, inflammatory arthritis, or a malignant condition is in the differential diagnosis. The C-reactive protein assay is the most sensitive early test for musculoskeletal infections; an abnormal value rapidly returns to normal with effective treatment. Imaging should begin with plain radiography. Ultrasonography is particularly valuable in assessing the irritable hip and guiding aspiration, if necessary.

Role of computed tomography in the classification and management of pediatric pelvic fractures

In adults, pelvic computed tomography (CT) scanning plays an important role in the treatment of pelvic fractures; however, the role of CT scanning in the management of pediatric pelvic fractures is unclear. The purpose of this study was to investigate the efficacy of CT scanning in the management of pelvic fractures in children. One hundred three consecutive patients were identified. All patients underwent anteroposterior plain radiographic evaluation; CT scans were performed in 62. Three orthopaedic surgeons independently reviewed the plain radiographs and determined fracture classification and management. Subsequently, each observer was shown corresponding CT scans and again determined classification and management. Interobserver agreement was calculated using Kappa statistics. After the addition of CT scans, the mean changes in classification were nine (15%) and in management two (3%). Plain radiographs alone reliably predicted the need and type of operative intervention. Kappa statistics demonstrated "excellent" agreement for classification and management without and with CT scans. We reliably determined fracture classification and management based on plain radiographs alone.

Titanium elastic nails for pediatric femur fractures: a multicenter study of early results with analysis of complications

Titanium elastic nailing is used instead of traction and casting in many European centers, but limited availability has prevented widespread use in North America. Before a planned general release in America, titanium elastic nails (TENs) were trialed at several major pediatric trauma centers. This multicenter study is a critical analysis of early results and complications of the initial experience. Overall, TENs allowed rapid mobilization with few complications. The results were excellent or satisfactory in 57 of the 58 cases. No child lost rotational alignment in the postoperative period. Irritation of the soft tissue near the knee by the nail tip occurred in four patients, leading to a deeper infection in two cases. As indications, implantation technique, and aftercare are refined, TENs may prove to be the ideal implant to stabilize many pediatric femur fractures, avoiding the prolonged immobilization and complications of traction and spica casting.

Campath-1H monoclonal antibody therapy

Monoclonal antibodies are receiving ever-increasing utilization in the treatment of hematologic malignancies. Campath-1 antibodies are directed against the surface antigen CD52 that is expressed on virtually all lymphocytes and monocytes. Murine forms, Campath-1G and Campath-1M, have been utilized extensively in allogeneic bone marrow transplants in order to purge the allograft of lymphocytes. The humanized form, Campath-1H, is currently the focus of many clinical trials in hematologic malignancies and autoimmune diseases. The genetically engineered Campath-1H has been utilized in the treatment of lymphomas and lymphoid leukemias with impressive results. T-cell prolymphocytic leukemia, chronic lymphocytic leukemia, and non-Hodgkin lymphomas appear to be particularly good targets for this agent. Campath-1H may be administered intravenously or subcutaneously. Infectious complications are the most significant side effect associated with its usage, with fevers, chills, nausea, and vomiting most common. Antibiotic prophylaxis has made the infectious morbidity associated with Campath-1H more manageable. The efficacy demonstrated in clinical trials and manageable toxicities make Campath-1H an appealing agent in the treatment of hematologic malignancies.

Closed ankle fractures in the diabetic patient

Systemic and local manifestations of diabetes mellitus may complicate the treatment of ankle fractures in the diabetic population. We studied 98 patients (73 non-diabetics and 25 diabetics) who were treated for closed ankle fractures by either surgical or non-surgical methods. We found that overall, the risk of infection in the diabetic population (32%) was 4 times higher than in the non-diabetic population (8%). The infection rate in the diabetic group treated surgically more than doubled that in the non-diabetic group. Four out of six diabetic patients treated with cast became infected compared to no infections in the five non-diabetics treated with a cast. Even though the diabetic foot and ankle are well studied, the medical literature is not conclusive regarding the management of ankle fractures in the diabetic patient. Diabetic patients treated conservatively had a tendency to become infected over those treated surgically. Peripherovascular disease, peripheral neuropathy and swelling and/or ecchymosis increased the risk of infection in the diabetic population. Diabetic patients with poor compliance had a tendency to become infected more than those who were compliant. We concluded that the diabetic patient who is poorly compliant with evidence of neuropathic disease, peripherovascular disease and severe swelling and ecchymosis presents the most difficult group to manage. Although these patients are poor surgical candidates, they are also the most difficult to manage and also most prone to infection and complications if treated conservatively. When faced with this difficult scenario a multidisciplinary team approach would probably yield the best possible results by early identification and intervention in these patients.

Fracture patterns in children and young adults who fall from significant heights

Trauma is a leading cause of morbidity and mortality for children and young adults. When all causes of trauma are considered, falls are the most common mechanism of injury. To address specifically age-related fracture patterns in children who fall, we identified 125 consecutive patients, 21 years old or younger, who fell from a height of 10 feet or greater. The medical records and radiographs for 110 of these patients were available for review. Patients were divided into three groups based on age: there were 25 infant/toddlers (0-2 years), 55 children (3-10 years), and 30 adolescent/young adults (11-21 years). We found statistically significant differences in fracture distribution between the groups. The adolescent/young adult group sustained a greater number of vertebral fractures (p<0.003) and total fractures per fall (p<0.015). The children, in contrast, had a greater number of long bone fractures (p<0.05). Knowledge of age-related fracture patterns could result in improved diagnosis and treatment of these injuries.

Objective evaluation of knee laxity in children

This study was designed to measure objectively knee laxity in children. Physical examination and the KT 1000 arthrometer were used to test the knee laxity of 150 healthy, uninjured children between 6 and 18 years of age. Data from the knee examinations and the KT 1000 measurements were compared and statistically analyzed to determine the change in knee laxity with age, laxity differences between boys and girls, and the correlation between the KT1000 measurements and subjective tests for laxity described by Carter and Wilkinson. There was no statistical difference in knee laxity between boys and girls of similar ages. We found that knee laxity, determined by measuring the millimeters of tibial translation using the KT 1000 arthrometer, was significantly greater in younger children.

Pyomyositis in children and adolescents: report of 12 cases and review of the literature

Pyomyositis initially was observed more commonly in the developing world but now is reported with increasing frequency in the United States. The presentation is nonspecific and the differential diagnoses are many. We found the clinical history, laboratory findings, and response to treatment similar to those observed in different areas of the world. Magnetic resonance imaging (MRI) with gadolinium injection, in addition to helping to make the diagnosis, may help differentiate between early and late stages that help guide treatment. Coexisting bone changes (58%) may represent either the sensitivity of MRI to reactive inflammatory changes or the presence of a coexisting osteomyelitis. All patients responded to antibiotics and drainage if abscesses were present. Although the optimal duration of antibiotic therapy remains unclear, a shorter course should be considered in patients with a good clinical response, even when MRI shows nonspecific bony abnormalities. Percutaneous drainage was successful in five cases and may represent an alternative to the traditional surgical approach.

Stem-cell transplantation in chronic lymphocytic leukemia: the time for designing randomized studies has arrived

Stem-cell transplantation in conjunction with myeloablative therapy has evolved as a standard treatment option for patients with several hematologic malignancies, including chemosensitive, relapsed non-Hodgkin's lymphoma and untreated multiple myeloma. The pharmacologic basis for this treatment includes a favorable tumor dose-response curve that abrogates intrinsic drug resistance associated with these diseases and facilitates cure or prolongation of survival even in the absence of a cure. The belief that chronic lymphocytic leukemia (CLL) is a palliative disease of the elderly has been perpetuated, limiting the application of more aggressive therapies. The introduction of fludarabine and its use in combination with other agents has increased the morphologic complete response rate observed in the initial treatment of CLL, providing the rationale to explore further disease-consolidative therapies. Concomitant with this, several phase II studies have demonstrated the feasibility of performing both allogeneic and autologous stem-cell transplantation in patients with CLL. In this regard, allogeneic transplantation has produced prolonged remissions in young patients with relapsed and refractory CLL, but at the cost of high treatment-related morbidity and mortality. Application of "minitransplantation" regimens may temper the frequency of these complications and warrants further study. Autologous stem-cell transplantation has also been explored with promising disease-free survival outcomes in less heavily pretreated patients. However, relapses continue to be the most frequent source of late mortality, as has been observed previously with multiple myeloma. With scientific justification established in similar diseases and demonstrated feasibility with low morbidity, we believe the time for a randomized comparison of standard chemotherapy versus autologous stem-cell transplantation in CLL has arrived. Despite promising results observed with allogeneic transplantation, further refinements that broaden the patient eligibility and lower treatment mortality will be required before similar investigations can occur with this modality.

Assessing, developing, and maintaining staff's competency in times of restructuring

Downsizing and reorganization in hospitals have resulted in nursing staff being realigned to different areas. During these times, nurse educators are continually challenged to provide effective educational programs to develop and upgrade staff competency. Nurse educators at a government health care facility in New York City experienced similar challenges as inpatient units were closed and staff had to develop or upgrade their skills. Two educational programs were designed to prepare staff to assume other duties, and competency assessments were developed and used to measure the effectiveness of the programs. Concepts relevant to competency assessment, development, and maintenance are discussed, and methods of assessments are described. Sample assessment tools and description of outcomes are included.

Seroprevalence of blood borne transmissible diseases in trauma orthopaedic surgical patients

OBJECTIVE

The purpose of this study is to determine the seroprevalence of blood borne transmissible diseases of the orthopaedic trauma surgical patients who deny or did not have knowledge of having disease or risk factors, but are positive for either human immunodeficiency virus, hepatitis B virus, and hepatitis C virus.

BACKGROUND

Orthopaedic surgeons practicing in areas with a high prevalence of HIV infection may expect that up to 7% of their patients who undergo emergency procedures and 1% to 3% of those who undergo elective surgery will be HIV-positive.

METHOD

All conscious adult patients consecutively admitted for surgical management by the orthopaedic service were evaluated. A detailed questionnaire was completed asking the patient of knowledge of having a transmissible disease and documenting certain risk factors. Blood samples were taken to test for HIV, HBV and HCV and all positive patients were sent to a follow up clinic.

RESULTS

Out of 100 patients the following results were found: 7% were positive for HIV, 12% positive for HBV, 12% positive for HCV, 19% were positive to at least one test, and 9% were positive in more than one test. Of the one hundred patients, 6% had a positive test in spite of denying having a disease or any risk factors. None of the patients with HBV and/or HCV knew they were positive and three (43%) of the seven with HIV were also unaware of their condition.

CONCLUSIONS

This study suggests that a worrisome number of patients are seropositive for a blood borne transmissible disease, even though they had no knowledge of such disease and claimed they had no risk factors. In order to protect orthopaedic surgeons from the unreliability of some patients' histories, all trauma orthopaedic surgical patients should be managed with universal precautions.

Segmental spinal dysgenesis: early neurologic deterioration and treatment

Segmental spinal dysgenesis is a rare congenital condition of the lumbar or thoracolumbar spine that can be associated with significant progressive or permanent neurologic defects, including paraplegia. In the past, both bracing and surgery have been recommended. Of the seven children we have seen with this problem, three have lost motor function between presentation and the time of surgery. Our experience suggests that to prevent catastrophic neurologic deterioration, surgery is indicated once the diagnosis is made.

Puerto Rico orthopaedic manpower study

Data regarding orthopaedic work-force is presented. Data is based on information obtained from the Puerto Rico Board of Medical Examiners, the Puerto Rico Department of Health and orthopaedic surgeon's practice. The purpose of this study is to compare the local orthopaedic manpower with the American Academy of Orthopaedic Surgeons most recent national manpower survey and to provide a database of the local orthopaedic work-force.

Single-bone fixation of both-bone forearm fractures

Seventeen children with diaphyseal both-bone forearm fractures, for which closed reduction had failed, were treated with fixation of either the radius or ulna. Sixteen were followed up to their clinical end point. Results in all children were excellent; all had a full return of motion except two who lacked 5 degrees of pronation. This retrospective series is the first reported to date looking exclusively at diaphyseal both-bone forearm fractures in children treated with fixation of a single bone. The rationale of treatment is to stabilize one bone while the other is rotated into reduction. Repeated anesthetics are avoided, and malreduction is prevented without adult-style both-bone plating. We prefer intramedullary fixation as hardware is easier and safer to place and remove.