Wernicke Encephalopathy: Typical and Atypical Findings in Alcoholics and Non-Alcoholics and Correlation with Clinical Symptoms.

PURPOSE: Clinical diagnosis of Wernicke encephalopathy (WE) can be challenging due to incomplete presentation of the classical triad. The aim was to provide an update on the relevance of standard MRI and to put typical and atypical imaging findings into context with clinical features. METHODS: In this two-center retrospective observational study, the local radiology information system was searched for consecutive patients with clinical or imaging suspicion of WE. Two independent raters evaluated T2-weighted imaging (WI), fluid-attenuation inversion recovery (FLAIR), diffusion WI (DWI), T2*WI and/or susceptibility WI (SWI), and contrast-enhanced (CE)-T1WI, and noted the involvement of typical (i.e., mammillary bodies (MB), periaqueductal grey (PAG), thalamus, hypothalamus, tectal plate) and atypical (all others) lesion sites. Unusual signal patterns like hemorrhages were also documented. Reported clinical features together with the diagnostic criteria of the latest guidelines of the European Federation of Neurological Societies (EFNS) were used to test for relationships with MRI biomarkers. RESULTS: 47 patients with clinically confirmed WE were included (Jan '99-Apr '23; mean age, 53 yrs; 70% males). Interrater reliability for imaging findings was substantial (κ = 0.71), with lowest agreements for T2WI (κ = 0.85) compared to all other sequences and for PAG (κ = 0.65) compared to all other typical regions. In consensus, 77% (n = 36/47) of WE cases were rated MRI positive, with FLAIR (n = 36/47, 77%) showing the strongest relation (χ2 = 47.0; P < 0.001) compared to all other sequences. Microbleeds in the MB were detected in four out of ten patients who received SWI, not visible on corresponding T2*WI. Atypical findings were observed in 23% (n = 11/47) of cases, always alongside typical findings, in both alcoholics (n = 9/44, 21%) and non-alcoholics (n = 2/3, 67%). Isolated involvement of structures, explicitly PAG (n = 4/36; 11%) or MB (n = 1/36; 3%), was present but observed less frequently than combined lesions (n = 31/36; 86%). A cut-off width of 2.5 mm for the PAG on 2D axial FLAIR was established between cases and age- and sex-matched controls. An independent association was demonstrated only between short-term memory loss and changes in the MB (OR = 2.2 [95% CI: 1.1-4.5]; P = 0.024). In retrospect, EFNS criteria were positive (≥ 2 out of 4) in every case, but its count (range, 2-4) showed no significant (P = 0.427) relationship with signal changes on standard MRI. CONCLUSION: The proposed sequence protocol (FLAIR, DWI, SWI and T1WI + CE) yielded good detection rates for neuroradiological findings in WE, with SWI showing microbleeds in the MB with superior detectability. However, false negative results in about a quarter of cases underline the importance of neurological alertness for the diagnosis. Awareness of atypical MRI findings should be raised, not only in non-alcoholics. There is limited correlation between clinical signs and standard MRI biomarkers.

Long-term safety of certolizumab pegol in plaque psoriasis: pooled analysis over 3 years from three phase III, randomized, placebo-controlled studies.

BACKGROUND: Certolizumab pegol (CZP) is an Fc-free, PEGylated anti-tumour necrosis factor biologic. OBJECTIVES: To report 3-year safety data from three phase III trials of CZP in adults with plaque psoriasis. METHODS: Data were pooled from CIMPASI-1 (NCT02326298), CIMPASI-2 (NCT02326272) and CIMPACT (NCT02346240). Included patients had moderate-to-severe plaque psoriasis of ≥ 6 months' duration; had been randomized to CZP 200 mg every 2 weeks (Q2W) (400 mg at weeks 0, 2 and 4) or CZP 400 mg Q2W; and had received at least one dose of CZP with up to 144 weeks of exposure. Treatment-emergent adverse events (TEAEs) were classified using MedDRA v18·1. Reported incidence rates (IRs) are incidence of new cases per 100 patient-years (PY). RESULTS: Over 144 weeks, 995 patients received at least one dose of CZP (exposure: 2231·3 PY); 731 and 728 received at least one dose of CZP 200 mg Q2W (1211·4 PY) and/or 400 mg Q2W (1019·9 PY), respectively. The IR [95% confidence interval (CI)] of TEAEs was 144·9 (135·3-155·0) for all patients, 134·1 (123·2-145·7) for CZP 200 mg Q2W and 158·3 (145·5-171·9) for CZP 400 mg Q2W. The IR (95% CI) of serious TEAEs for all patients was 7·5 (6·4-8·8); the IRs were 6·7 (5·2-8·3) and 8·7 (6·9-10·8) for CZP 200 mg and 400 mg Q2W, respectively. Overall, 3·2% of patients reported serious infections (2·2% within each of the CZP 200 and 400 mg Q2W groups). Overall, there was one case of active tuberculosis, 16 malignancies in 14 patients and seven deaths (two considered treatment-related). The cumulative IR of TEAEs did not increase over time. CONCLUSIONS: No new safety signals were identified compared with previously reported data. Risk did not increase with longer or higher CZP exposure.

Comparison of contrast-enhanced videofluoroscopy to unenhanced dynamic MRI in minor patients following surgical correction of velopharyngeal dysfunction.

OBJECTIVES: To compare dynamic magnetic resonance imaging (MRI) with videofluoroscopy (VFS) regarding image quality and assessment of gap size between soft palate (SP) and posterior pharyngeal wall (PPW) in children and adolescents following surgical correction of velopharyngeal dysfunction (VPD). METHODS: Twenty-one patients undergoing unenhanced 3-T MRI and contrast-enhanced VFS were included in this IRB-approved prospective study. The MRI scan protocol comprised refocused gradient-echo sequences in transverse and sagittal planes during speech, with TE 1.97 ms, TR 3.95 ms, flip angle 8°, matrix size 128 × 128, and 5-mm slice thickness. Radial k-space sampling and sliding window reconstruction were used to achieve an image acquisition rate of 28 frames per second (fps). VFS with 30 fps was similarly performed in both planes. Closure of the velopharyngeal port during phonation was evaluated by two experienced radiologists. RESULTS: Eleven (52.4%) patients displayed a complete closure, whereas ten (47.6%) patients showed a post-operative gap during speech. VFS and MRI equally identified the cases with persistent or recurrent VPD. Differences in SP-PPW distance between VFS (3.9 ± 1.6 mm) and MRI (4.1 ± 1.5 mm) were not statistically significant (p = 0.5). The subjective overall image quality of MRI was rated inferior (p < 0.001) compared with VFS, with almost perfect inter-rater agreement (κ = 0.90). The presence of susceptibility artifacts did not limit anatomical measurements. CONCLUSION: Dynamic MRI is equally reliable as VFS to assess persistent or recurrent inadequate velum closure in patients following surgical treatment of VPD. KEY POINTS: • Unenhanced 3-T dynamic MRI and contrast-enhanced videofluoroscopy are equally useful for the identification of patients with incomplete velopharyngeal closure during speech. • MRI using refocused gradient-echo acquisition with radial k-space sampling and sliding window reconstruction generates diagnostic images with 28 frames per second. • MRI can offer a radiation-free alternative to currently established videofluoroscopy for young patients.

Erratum to: After ISCHEMIA: Is cardiac MRI a reliable gatekeeper for invasive angiography and myocardial revascularization?

In the above mentioned article, the family name of the second author was not given correctly: it is Carerj instead of Careri.The authors apologize for this mistake.The original article has been ….

After ISCHEMIA: Is cardiac MRI a reliable gatekeeper for invasive angiography and myocardial revascularization?

This review surveys the findings of the International Study of Comparative Health Effectiveness with Medical and Invasive Approaches (ISCHEMIA) trial and puts them into a clinical perspective regarding its effect of the role of cardiac magnetic resonance imaging (CMR) as a well-validated gatekeeper for invasive angiography and myocardial revascularization. Noninvasive stress testing of patients with intermediate-to-high pretest likelihood for obstructive coronary artery disease (CAD) using perfusion CMR provides excellent diagnostic accuracy in detecting ischemic myocardium, and additional information from tissue characterization can guide the management of patients with stable angina toward a more individualized therapy as other non-coronary underlying causes of chest pain can be detected. Since ISCHEMIA failed to show that an invasive strategy using percutaneous coronary intervention or coronary artery bypass grafting was associated with an improved prognosis compared with initial conservative medical therapy among stable patients with moderate-to-severe ischemia, CMR as a multifaceted diagnostic imaging approach to explain patients' symptoms should be preferred over anatomical and stress testing alone. Nevertheless, the exclusion of left main coronary artery stenosis either by coronary CT or MR angiography may be required. In conclusion, the results of the ISCHEMIA trial are in good accordance with those of the MR-INFORM trial recently published in the New England Journal of Medicine, as the noninvasive management of a large proportion of patients with CAD was shown to be noninferior to current invasive strategies. Recent outcome data from trials may therefore have an impact on future guidelines to further reduce the execution of unnecessary left heart catheterizations.

Certolizumab pegol for the treatment of patients with moderate-to-severe chronic plaque psoriasis: pooled analysis of week 16 data from three randomized controlled trials.

BACKGROUND: Certolizumab pegol, an Fc-free, PEGylated, anti-tumour necrosis factor (TNF) biologic, has demonstrated favourable results in three ongoing, phase 3, randomized, double-blinded, placebo-controlled trials in adults with psoriasis. OBJECTIVE: Data were pooled from the ongoing trials to investigate efficacy in selected subgroups and add precision to estimates of treatment effects during the initial 16 weeks of treatment. METHODS: In each trial, patients ≥18 years with moderate-to-severe chronic plaque psoriasis for ≥6 months were randomized to receive certolizumab 400 mg, certolizumab 200 mg or placebo every 2 weeks for 16 weeks. Coprimary endpoints for the pooled analysis were responder rates at Week 16, defined as ≥75% reduction in psoriasis area and severity index (PASI 75) and physician global assessment (PGA) of 0/1 ('clear'/'almost clear' with ≥2-category improvement). Safety was assessed by treatment-emergent adverse events. RESULTS: A total of 850 patients treated with certolizumab 400 mg (N = 342), certolizumab 200 mg (N = 351) or placebo (N = 157) were included in the pooled analysis. At Week 16, PASI 75 and PGA 0/1 responder rates were 80.1% and 63.7% in the certolizumab 400 mg group, 74.5% and 54.6% in the certolizumab 200 mg group, and 7.5% and 2.8% in the placebo group (P < 0.0001 for each dose versus placebo). In patients with and without prior biologic therapy, both doses of certolizumab resulted in substantially higher responder rates versus placebo. The incidence of adverse events was generally similar between the 400 mg and placebo groups, and somewhat lower in the 200 mg group versus placebo. No new safety signals were identified. CONCLUSION: Certolizumab pegol 400 mg or 200 mg every 2 weeks for 16 weeks was associated with statistically significant and clinically meaningful improvements in signs and symptoms of psoriasis in patients with and without prior biologic therapy, and a safety profile consistent with the anti-TNF class in psoriasis.

Dual-energy CT in patients with abdominal malignant lymphoma: impact of noise-optimised virtual monoenergetic imaging on objective and subjective image quality.

AIM: To investigate the impact of noise-optimised virtual monoenergetic imaging (VMI+) reconstructions on quantitative and qualitative image parameters in patients with malignant lymphoma at dual-energy computed tomography (DECT) examinations of the abdomen. MATERIALS AND METHODS: Thirty-five consecutive patients (mean age, 53.8±18.6 years; range, 21-82 years) with histologically proven malignant lymphoma of the abdomen were included retrospectively. Images were post-processed with standard linear blending (M_0.6), traditional VMI, and VMI+ technique at energy levels ranging from 40 to 100 keV in 10 keV increments. Signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were objectively measured in lymphoma lesions. Image quality, lesion delineation, and image noise were rated subjectively by three blinded observers using five-point Likert scales. RESULTS: Quantitative image quality parameters peaked at 40-keV VMI+ (SNR, 15.77±7.74; CNR, 18.27±8.04) with significant differences compared to standard linearly blended M_0.6 (SNR, 7.96±3.26; CNR, 13.55±3.47) and all traditional VMI series (p<0.001). Qualitative image quality assessment revealed significantly superior ratings for image quality at 60-keV VMI+ (median, 5) in comparison with all other image series (p<0.001). Assessment of lesion delineation showed the highest rating scores for 40-keV VMI+ series (median, 5), while lowest subjective image noise was found for 100-keV VMI+ reconstructions (median, 5). CONCLUSION: Low-keV VMI+ reconstructions led to improved image quality and lesion delineation of malignant lymphoma lesions compared to standard image reconstruction and traditional VMI at abdominal DECT examinations.

Certolizumab pegol in combination with dose-optimised methotrexate in DMARD-naïve patients with early, active rheumatoid arthritis with poor prognostic factors: 1-year results from C-EARLY, a randomised, double-blind, placebo-controlled phase III study.

OBJECTIVES: To assess the efficacy and safety of certolizumab pegol (CZP)+dose-optimised methotrexate (MTX) versus placebo (PBO)+dose-optimised MTX in inducing and sustaining clinical remission in DMARD-naïve patients with moderate-to-severe, active, progressive rheumatoid arthritis (RA), with poor prognostic factors over 52 weeks. METHODS: DMARD-naïve patients with ≤1 year of active RA were randomised (3:1) in a double-blind manner to CZP (400 mg Weeks 0, 2, 4, then 200 mg Q2W to Week 52)+MTX or PBO+MTX (the mean optimised-MTX dose=21 and 22 mg/week, respectively). Sustained remission (sREM) and sustained low disease activity (sLDA; DAS28(ESR)<2.6 and DAS28(ESR)≤3.2, respectively, at both Weeks 40 and 52) were the primary and secondary endpoints. RESULTS: Patients were randomised to CZP+MTX (n=660) and PBO+MTX (n=219). At Week 52, significantly more patients assigned to CZP+MTX compared with PBO+MTX achieved sREM (28.9% vs 15.0%, p<0.001) and sLDA (43.8% vs 28.6%, p<0.001). Inhibition of radiographic progression and improvements in physical functioning were significantly greater for CZP+MTX versus PBO+MTX (van der Heijde modified total Sharp score (mTSS) mean absolute change from baseline (CFB): 0.2 vs 1.8, p<0.001, rate of mTSS non-progressors: 70.3% vs 49.7%, p<0.001; least squares (LS) mean CFB in Health Assessment Questionnaire-Disability Index (HAQ-DI): -1.00 vs -0.82, p<0.001). Incidence of adverse events (AEs) and serious AEs was similar between treatment groups. Infection was the most frequent AE, with higher incidence for CZP+MTX (71.8/100 patient-years (PY)) versus PBO+MTX (52.7/100 PY); the rate of serious infection was similar between CZP+MTX (3.3/100 PY) and PBO+MTX (3.7/100 PY). CONCLUSIONS: CZP+dose-optimised MTX treatment of DMARD-naïve early RA resulted in significantly more patients achieving sREM and sLDA, improved physical function and inhibited structural damage compared with PBO+dose-optimised MTX. TRIAL REGISTRATION NUMBER: NCT01519791.

Taste preference and psychopathology.

OBJECTIVE: Excessive food intake has been linked to many factors including taste preference and the presence of psychopathology. The purpose of this study was to investigate the association between sweet and salty taste preference and psychopathology in patients with severe obesity. METHODS: A consecutive series of patients applying for bariatric surgery was recruited for the study. Taste preference was self-reported. Psychopathology was assessed using the revised version of the Minnesota Multiphasic Personality Inventory-2 (MMPI-2). 190 patients were included in the study. RESULTS: In comparison with patients who had salty taste preference, patients with sweet taste preference had significantly higher elevations on the depression (OD: 4.090, p = 0.010) and the hysteria (OD: 2.951, p = 0.026) clinical scales of the MMPI-2. CONCLUSION: The results suggest the presence of an association between taste preference and psychopathology. The findings may be of interest for clinicians who are involved in the treatment of obesity. In particular, they may wish to pay increased attention to patients with sweet taste preference or who have a strong attraction for both sweet and salty foods, in order to detect psychopathology and to adapt the treatment.

[Life-threatening macroglossia following cleft palate palatoplasty]. / Lebensbedrohliche Makroglossie nach Gaumenspaltenverschluss.

The case of a 13-month-old child who developed a life-threatening macroglossia with airway obstruction following palatoplasty for a cleft palate is reported. As direct laryngoscopy was not feasible a laryngeal mask (LM) was inserted to secure the airway. Under fiber optic guidance an endotracheal tube was then introduced via the LM. In this article the incidence, pathophysiology, clinical dynamics, options for emergency anesthesia management and organizational implications of this rare but typical complication in the field of oral and craniomaxillofacial surgery are reported.

HIV: master of the host cell.

The human immunodeficiency virus has evolved various mechanisms to exploit its host cells, including the interruption and augmentation of signal transduction pathways. Recently, two DNA microarray studies have illustrated a remarkably broad-based perturbation in host transcriptional responses, which is in part mediated by the HIV-encoded Nef protein. HIV therefore seems to function as a 'master regulator' of cellular gene expression.

Absorption, distribution, metabolism and excretion of [14C]levocetirizine, the R enantiomer of cetirizine, in healthy volunteers.

The main goal of the present study was to investigate the absorption and disposition of levocetirizine dihydrochloride, the R enantiomer of cetirizine dihydrochloride, following a single oral administration (5 mg) of the 14C-labelled compound in healthy volunteers. Configurational stability was also investigated. Levocetirizine was rapidly and extensively absorbed: 85.4% and 12.9% of the radioactive dose were recovered 168 h post-dose in urine and faeces, respectively. Levocetirizine and/or its metabolites were not, or only very poorly, associated with blood cells, as the blood-to-plasma ratio was 0.51 to 0.68. The mean apparent volume of distribution (Vz/F) was 26.9 1 (0.3 l/kg) indicating that the distribution of levocetirizine is restrictive. The protein binding of radiolabelled levocetirizine was 96.1% l h after administration. In vitro, at concentrations ranging from 0.2 microg/ml to 1 microg/ml, the protein binding was 94.8% to 95.0%. Levocetirizine is very poorly metabolised. The cumulative 48-h excretion as parent compound accounted for 85.8% of the oral dose, equivalent to 95% of the total radioactivity excreted at this time. At least 13 minor metabolites were detected in urine and represented 2.4% of the dose at 48 h. The metabolic pathways involved in levocetirizine metabolism are oxidation (hydroxylation, O-dealkylation, N-oxidation and N-dealkylation), glucuroconjugation, taurine conjugation and glutathione conjugation with formation of the mercapturic acids. There was no evidence of chiral inversion of levocetirizine in humans. This result is consistent with that obtained in preclinical studies.

Efficacy and safety of levocetirizine in seasonal allergic rhinitis.

OBJECTIVE: Pharmacodynamic studies have demonstrated that levocetirizine is the active enantiomer of cetirizine. This first therapeutic trial of levocetirizine aimed at determining the dosage with the best benefit/risk ratio in patients with seasonal allergic rhinitis (SAR). METHODS: Patients with seasonal allergic rhinitis were randomised in a placebo-controlled, double-blind, parallel-group multicentre study 2.5, 5, 10 mg levocetirizine or placebo once daily during 2 weeks. Patients filled in a diary evaluation card every evening before taking study medication using the classical (0-3) scale for assessment of severity of sneezing, rhinorrhea, nasal congestion, nasal pruritus and ocular pruritus over the preceding 24 hours. The Total Four-Symptom Score (T4SS) was calculated by adding the individual symptom scores, excluding nasal congestion. RESULTS: 470 patients were included and constituted the intent-to-treat population. All 3 doses of levocetirizine were significantly superior to placebo in reducing the mean T4SS over the 2 weeks (all P (0.001). Additionally, individual symptom severity scores for sneezing, rhinorrhea, itchy nose, and itchy eyes were also significantly decreased for all doses of levocetirizine. Levocetirizine was significantly superior to placebo in reducing symptom severity with an important global treatment effect (P = 0.0001), except for nasal congestion. Furthermore, there was simple linear relationship between levocetirizine dosages and reduction of T4SS (P = 0.001). All doses were well tolerated, somnolence was higher with 10 mg (10.2%) than 5 mg (1.7%) and other adverse events were more frequent with the highest dose. CONCLUSION: Levocetirizine 5 mg once daily has an optimal benefit/risk ratio in the treatment of SAR.

Two distinct domains of the beta-subunit of glucosidase II interact with the catalytic alpha-subunit.

Recent purification and cDNA cloning of the endoplasmic reticulum processing enzyme glucosidase II have revealed that it is composed of two soluble proteins: a catalytic alpha-subunit and a beta-subunit of unknown function, both of which are highly conserved in mammals. Since the beta-subunit, which contains a C-terminal His-Asp-Glu-Leu (HDEL) motif, may function to link the catalytic subunit to the KDEL receptor as a retrieval mechanism, we sought to map the regions of the mouse beta-subunit protein responsible for mediating the association with the alpha-subunit. By screening a panel of recombinant beta-subunit glutathione S-transferase fusion proteins for the ability to precipitate glucosidase II activity, we have identified two non-overlapping interaction domains (ID1 and ID2) within the beta-subunit. ID1 encompasses 118 amino acids at the N-terminus of the mature polypeptide, spanning the cysteine-rich element in this region. ID2, located near the C-terminus, is contained within amino acids 273-400, a region occupied in part by a stretch of acidic residues. Variable usage of 7 alternatively spliced amino acids within ID2 was found not to influence the association of the two sub-units. We theorize that the catalytic subunit of glucosidase II binds synergistically to ID1 and ID2, explaining the high associative stability of the enzyme complex.

PKC-theta is required for TCR-induced NF-kappaB activation in mature but not immature T lymphocytes.

Productive interaction of a T lymphocyte with an antigen-presenting cell results in the clustering of the T-cell antigen receptor (TCR) and the recruitment of a large signalling complex to the site of cell-cell contact. Subsequent signal transduction resulting in cytokine gene expression requires the activation of one or more of the multiple isoenzymes of serine/threonine-specific protein kinase C (PKC). Among the several PKC isoenzymes expressed in T cells, PKC-theta is unique in being rapidly recruited to the site of TCR clustering. Here we show that PKC-theta is essential for TCR-mediated T-cell activation, but is dispensable during TCR-dependent thymocyte development. TCR-initiated NF-kappaB activation was absent from PKC-theta(-/-) mature T lymphocytes, but was intact in thymocytes. Activation of NF-kappaB by tumour-necrosis factor alpha and interleukin-1 was unaffected in the mutant mice. Although studies in T-cell lines had suggested that PKC-theta regulates activation of the JNK signalling pathway, induction of JNK was normal in T cells from mutant mice. These results indicate that PKC-theta functions in a unique pathway that links the TCR signalling complex to the activation of NF-kappaB in mature T lymphocytes.

The Saccharomyces cerevisiae ubiquitin-proteasome system.

Our studies of the yeast ubiquitin-proteasome pathway have uncovered a number of general principles that govern substrate selectivity and proteolysis in this complex system. Much of the work has focused on the destruction of a yeast transcription factor, MAT alpha 2. The alpha 2 protein is polyubiquitinated and rapidly degraded in alpha-haploid cells. One pathway of proteolytic targeting, which depends on two distinct endoplasmic reticulum-localized ubiquitin-conjugating enzymes, recognizes the hydrophobic face of an amphipathic helix in alpha 2. Interestingly, degradation of alpha 2 is blocked in a/alpha-diploid cells by heterodimer formation between the alpha 2 and a1 homeodomain proteins. The data suggest that degradation signals may overlap protein-protein interaction surfaces, allowing a straightforward steric mechanism for regulated degradation. Analysis of alpha 2 degradation led to the identification of both 20S and 26S proteasome subunits, and several key features of proteasome assembly and active-site formation were subsequently uncovered. Finally, it has become clear that protein (poly) ubiquitination is highly dynamic in vivo, and our studies of yeast de-ubiquitinating enzymes illustrate how such enzymes can facilitate the proteolysis of diverse substrates.

Use of chemokine receptors by poxviruses.

Chemokine receptors serve as portals of entry for certain intracellular pathogens, most notably human immunodeficiency virus (HIV). Myxoma virus is a member of the poxvirus family that induces a lethal systemic disease in rabbits, but no poxvirus receptor has ever been defined. Rodent fibroblasts (3T3) that cannot be infected with myxoma virus could be made fully permissive for myxoma virus infection by expression of any one of several human chemokine receptors, including CCR1, CCR5, and CXCR4. Conversely, infection of 3T3-CCR5 cells can be inhibited by RANTES, anti-CCR5 polyclonal antibody, or herbimycin A but not by monoclonal antibodies that block HIV-1 infection or by pertussis toxin. These findings suggest that poxviruses, like HIV, are able to use chemokine receptors to infect specific cell subtypes, notably migratory leukocytes, but that their mechanisms of receptor interactions are distinct.

Eukaryotic 20S proteasome catalytic subunit propeptides prevent active site inactivation by N-terminal acetylation and promote particle assembly.

Proteins targeted for degradation by the ubiquitin-proteasome system are degraded by the 26S proteasome. The core of this large protease is the 20S proteasome, a barrel-shaped structure made of a stack of four heptameric rings. Of the 14 different subunits that make up the yeast 20S proteasome, three have proteolytic active sites: Doa3/beta5, Pup1/beta2 and Pre3/beta1. Each of these subunits is synthesized with an N-terminal propeptide that is autocatalytically cleaved during particle assembly. We show here that the propeptides have both common and distinct functions in proteasome biogenesis. Unlike the Doa3 propeptide, which is crucial for proteasome assembly, the Pre3 and Pup1 propeptides are dispensable for cell viability and proteasome formation. However, mutants lacking these propeptide-encoding elements are defective for specific peptidase activities, are more sensitive to environmental stresses and have subtle defects in proteasome assembly. Unexpectedly, a critical function of the propeptide is the protection of the N-terminal catalytic threonine residue against Nalpha-acetylation. For all three propeptide-deleted subunits, activity of the affected catalytic center is fully restored when the Nat1-Ard1 Nalpha-acetyltransferase is mutated. In addition to delineating a novel function for proteasome propeptides, these data provide the first biochemical evidence for the postulated participation of the alpha-amino group in the proteasome catalytic mechanism.

Alternative splicing of transcripts encoding the alpha- and beta-subunits of mouse glucosidase II in T lymphocytes.

Glucosidase II is a processing enzyme of the endoplasmic reticulum that functions to hydrolyze two glucose residues in immature N -linked oligosaccharides attached to newly synthesized polypeptides. We previously reported the cDNA cloning of the alpha- and beta-subunits of mouse glucosidase II from T cells following copurification of these proteins with the highly glycosylated transmembrane protein-tyrosine phosphatase CD45. Subsequent examination of additional cDNA clones, coupled with partial genomic DNA sequencing, has revealed that both subunits are encoded by gene products that undergo alternative splicing in T lymphocytes. The catalytic alpha-subunit possesses two variably expressed segments, box Alpha1, consisting of 22 amino acids located proximal to the amino-terminus, and box Alpha2, composed of 9 amino acids situated between the amino-terminus and the putative catalytic site in the central region of the molecule. Box Beta1, a variably expressed 7 amino acid segment in the beta-subunit of glucosidase II, is located immediately downstream of an acidic stretch near the carboxyl-terminus. Screening of reverse transcribed RNA by polymerase chain reaction confirms the variable inclusion of each of these segments in transcripts obtained from a panel of T-lymphocyte cell lines. Thus, distinct isoforms of glucosidase II exist that may perform specialized functions.