Novel targeting assay uncovers targeting information within peroxisomal ABC transporter Pxa1

The mechanism behind peroxisomal membrane protein targeting is still poorly understood, with only two yeast proteins believed to be involved and no consensus targeting sequence. Pex19 is thought to bind peroxisomal membrane proteins in the cytosol, and is subsequently recruited by Pex3 at the peroxisomal surface, followed by protein insertion via a mechanism that is as-yet-unknown. However, some peroxisomal membrane proteins still correctly sort in the absence of Pex3 or Pex19, suggesting that multiple sorting pathways exist. Here, we studied sorting of yeast peroxisomal ABC transporter Pxa1. Co-localization analysis of Pxa1-GFP in a collection of 86 peroxisome-related deletion strains revealed that Pxa1 sorting requires Pex3 and Pex19, while none of the other 84 proteins tested were essential. To identify regions with peroxisomal targeting information in Pxa1, we developed a novel in vivo re-targeting assay, using a reporter consisting of the mitochondrial ABC transporter Mdl1 lacking its N-terminal mitochondrial targeting signal. Using this assay, we showed that the N-terminal 95 residues of Pxa1 are sufficient for retargeting this reporter to peroxisomes. Interestingly, truncated Pxa1 lacking residues 1-95 still localized to peroxisomes. This was confirmed via localization of various Pxa1 truncation and deletion constructs. However, localisation of Pxa1 lacking residues 1-95 depended on the presence of its interaction partner Pxa2, indicating that this truncated protein does not contain a true targeting signal.

Systematic multi-level analysis of an organelle proteome reveals new peroxisomal functions

Seventy years following the discovery of peroxisomes, their complete proteome, the peroxi‐ome, remains undefined. Uncovering the peroxi‐ome is crucial for understanding peroxisomal activities and cellular metabolism. We used high‐content microscopy to uncover peroxisomal proteins in the model eukaryote – Saccharomyces cerevisiae. This strategy enabled us to expand the known peroxi‐ome by ~40% and paved the way for performing systematic, whole‐organellar proteome assays. By characterizing the sub‐organellar localization and protein targeting dependencies into the organelle, we unveiled non‐canonical targeting routes. Metabolomic analysis of the peroxi‐ome revealed the role of several newly identified resident enzymes. Importantly, we found a regulatory role of peroxisomes during gluconeogenesis, which is fundamental for understanding cellular metabolism. With the current recognition that peroxisomes play a crucial part in organismal physiology, our approach lays the foundation for deep characterization of peroxisome function in health and disease.

The chaperone-binding activity of the mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress

Most mitochondrial proteins are synthesized as precursors in the cytosol and post-translationally transported into mitochondria. The mitochondrial surface protein Tom70 acts at the interface of the cytosol and mitochondria. In vitro import experiments identified Tom70 as targeting receptor, particularly for hydrophobic carriers. Using in vivo methods and high-content screens, we revisit the question of Tom70 function and considerably expand the set of Tom70-dependent mitochondrial proteins. We demonstrate that the crucial activity of Tom70 is its ability to recruit cytosolic chaperones to the outer membrane. Indeed, tethering an unrelated chaperone-binding domain onto the mitochondrial surface complements most of the defects caused by Tom70 deletion. Tom70-mediated chaperone recruitment reduces the proteotoxicity of mitochondrial precursor proteins, particularly of hydrophobic inner membrane proteins. Thus, our work suggests that the predominant function of Tom70 is to tether cytosolic chaperones to the outer mitochondrial membrane, rather than to serve as a mitochondrion-specifying targeting receptor.

A piggybacking mechanism enables peroxisomal localization of the glyoxylate cycle enzyme Mdh2 in yeast

Eukaryotic cells have evolved organelles that allow the compartmentalization and regulation of metabolic processes. Knowledge of molecular mechanisms that allow temporal and spatial organization of enzymes within organelles is therefore crucial for understanding eukaryotic metabolism. Here, we show that the yeast malate dehydrogenase 2 (Mdh2) is dually localized to the cytosol and to peroxisomes and is targeted to peroxisomes via association with Mdh3 and a Pex5-dependent piggybacking mechanism. This dual localization of Mdh2 contributes to our understanding of the glyoxylate cycle and provides a new perspective on compartmentalization of cellular metabolism, which is critical for the perception of metabolic disorders and aging.

Unbiased yeast screens identify cellular pathways affected in Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is a rare lysosomal storage disease caused by mutations in either the NPC1 or NPC2 genes. Mutations in the NPC1 gene lead to the majority of clinical cases (95%); however, the function of NPC1 remains unknown. To gain further insights into the biology of NPC1, we took advantage of the homology between the human NPC1 protein and its yeast orthologue, Niemann-Pick C-related protein 1 (Ncr1). We recreated the NCR1 mutant in yeast and performed screens to identify compensatory or redundant pathways that may be involved in NPC pathology, as well as proteins that were mislocalized in NCR1-deficient yeast. We also identified binding partners of the yeast Ncr1 orthologue. These screens identified several processes and pathways that may contribute to NPC pathogenesis. These included alterations in mitochondrial function, cytoskeleton organization, metal ion homeostasis, lipid trafficking, calcium signalling, and nutrient sensing. The mitochondrial and cytoskeletal abnormalities were validated in patient cells carrying mutations in NPC1, confirming their dysfunction in NPC disease.

An ER surface retrieval pathway safeguards the import of mitochondrial membrane proteins in yeast

The majority of organellar proteins are translated on cytosolic ribosomes and must be sorted correctly to function. Targeting routes have been identified for organelles such as peroxisomes and the endoplasmic reticulum (ER). However, little is known about the initial steps of targeting of mitochondrial proteins. In this study, we used a genome-wide screen in yeast and identified factors critical for the intracellular sorting of the mitochondrial inner membrane protein Oxa1. The screen uncovered an unexpected path, termed ER-SURF, for targeting of mitochondrial membrane proteins. This pathway retrieves mitochondrial proteins from the ER surface and reroutes them to mitochondria with the aid of the ER-localized chaperone Djp1. Hence, cells use the expanse of the ER surfaces as a fail-safe to maximize productive mitochondrial protein targeting.

Phagocytic killing and antibody response during the first year after tetravalent meningococcal vaccine in complement-deficient and in normal individuals

Seven individuals with late complement component (LCC) deficiency and seven control subjects were vaccinated with tetravalent meningococcal vaccine. The response to vaccination was evaluated by measuring the antibody titer and the phagocyte killing of the bacteria, before, 5-7 weeks, and 12-14 months after vaccination. Prior to vaccination, no phagocytic killing and a low titer of antibody was found in the LCC-deficient group and a low killing (mean of 40-58%, according to the serogroup) in normal controls. The phagocytic killing increased significantly 5-7 weeks after vaccination. However, while in normal controls the phagocytic killing was close to 100% after 5-7 weeks and decreased only slightly during the first year, the mean killing of the various meningococcal subgroups in LCC-deficient individuals was 70-89% and dropped to only 53-71% one year after vaccination. Six weeks after vaccination the mean antimeningococcal antibody titer increased similarly in the sera of LCC-deficient patients and controls. One year after vaccination the controls maintained the high concentration, while the LCC-deficient patients had tendency toward a decrease. In addition, the interpersonal variability of the antibody concentration, both in LCC-deficient individuals and in normal controls, was much higher than the phagocytic killing, with only a very mild increase in some individuals. Thus, it is possible that in spite of adequate increase of antimeningococcal antibody titer after vaccination of LCC-deficient individuals their immunity against the bacteria may not be optimal. Our data show also that phagocytic killing of meningococci is probably a more consistent assay than antibody titer levels for antimeningococcal immunity, especially in LCC-deficient patients.

Hand metastasis from renal cell carcinoma with no bone involvement

Hand metastases account for 0.1% of all metastases and most of them involve primarily the bones. A case of a metastasis from renal cell carcinoma to the distal segment of the little finger with no bone involvement is described. In view of the fact that the kidneys are the origin of only 10% of hand metastases, such a case is extremely rare.

Compartmental syndrome due to high velocity missile injury of the calf: use of immediate mesh skin grafting

Two patients with high velocity missile injury to the soft tissues of the calf without major fractures are presented. Both of them developed compartmental syndrome and were treated by debridement, fasciotomy, and immediate mesh split thickness skin graft. The mechanisms of such injury and the advantage of immediate skin grafting are discussed.

Skin injury following contact with a complex amine

Eight patients with skin damage due to contact with an amine are described. The material is used in the potash industry under the commercial name of Armine to prevent bosselation. Although it is considered to be a strong base, no deep burns were encountered. The reaction to this material initially resembled a dermatitis; later the wound developed the typical appearance of a burn. In addition to the common conservative treatment, antihistamine drugs were used. When a true allergic reaction was suspected steroids were added to the regimen.

Burn hazard from cupping--an ancient universal medication still in practice

The ancient universal medication of cupping is still practised by devoted believers and people who, for various reasons, have lost faith in other more modern modalities of medical treatment. Faulty technique in producing the vacuum in the cups was the aetiology of the burns in several patients. The history, theories and indications for cupping are reviewed.

Burns during pregnancy: our experience

Although few women sustain thermal injuries during pregnancy, when pregnancy is complicated by thermal injury a clear management scheme plus a team approach is needed to provide optimal care both to the foetus and mother. The clinical course of eight pregnant women treated in our burn unit is presented. The relationship between the burn area, gestational age at treatment and prognosis is analysed. Active surgical treatment is advocated.

Cerebral arteriovenous malformation: papilledema as a presenting sign

Papilledema as a presenting sign of arteriovenous malformation without evidence of a space-occupying lesion or hydrocephalus is an unusual finding. The pathogenetic theory that seems to explain such cases is the increase of cerebral blood volume leading to intracranial hypertension, thus resulting in papilledema. We present the case of a 31-year-old woman complaining of headaches, with papilledema as the only objective finding. Computed tomography scan and right carotid angiography demonstrated a right mid rolandic arteriovenous malformation. The lesion was totally removed under intraoperative angiographic control.

Adjuvant therapy for Dukes C adenocarcinoma of colon

Forty-two patients with adenocarcinoma of the colon, who received surgery between 1975 and 1978 and were to found to have pericolonic fat infiltration and lymph node metastases, were analyzed for disease free period and overall survival. Twenty-one patients had received post-operative X ray therapy, and post-X ray therapy intravenous 5-Fluorouracil adjuvant therapy. Twenty-one patients, matched by age, sex, ethnic origin and site of disease were untreated. The 5 year survival rate for the treated group was 65% compared with 36% for the control group (P greater than 0.2). At 5 years 55% of the treated group were disease free but only 12% of the control group remained disease free (P = 0.04). The significance of this work needs to be established by a randomized and prospectively controlled clinical trial.

Effect of colchicine on immunoregulatory abnormalities in familial Mediterranean fever

The effect of colchicine on immunoregulatory T lymphocytes in children with familial Mediterranean fever (FMF) was studied. Concanavalin A (Con A)-induced suppressor cell function was significantly (P less than 0.0001) decreased in five untreated FMF patients (15 +/- 3%, mean +/- s.e.) as compared to six age matched paediatric controls (46 +/- 3%) and eight healthy adults (49 +/- 4%). When the five untreated FMF patients' mononuclear cells were pre-incubated in vitro with Con A plus 10(-5) M colchicine, their suppressor cell function was significantly increased (52 +/- 10%, P less than 0.01). Similarly, oral colchicine treatment (0.5 mg twice daily) significantly (P = 0.02) increased the five FMF patients' Con A-induced suppressor cell function to levels (34 +/- 6%) that were not significantly (P greater than 0.05) different than the paediatric controls or the healthy adults. The percentage of OKT8+ cells (but not OKT3+ or OKT4+ cells) was significantly (P less than 0.0001) decreased in 10 untreated FMF patients (16.0 +/- 0.9) as compared to 10 paediatric controls (27.6 +/- 2) or 10 healthy adults (25.7 +/- 0.6). The 10 untreated FMF patients had a significant (P less than 0.002) increase in the OKT4/OKT8 ratio (2.41 +/- 0.13) as compared to 10 FMF patients treated with 0.5 mg twice daily of colchicine (1.81 +/- 0.08), 10 pediatric controls (1.47 +/- 0.2), or 10 healthy adults (1.78 +/- 0.11). Colchicine appears to have corrected the FMF patients' elevated OKT4/OKT8 ratio by both decreasing the percentage of OKT4+ cells and increasing (but only partially correcting) the percentage of OKT8+ cells. Thus FMF patients have a suppressor cell deficiency in which colchicine treatment corrects their deficiency of Con A-induced suppressor cell function and their elevated OKT4/OKT8 ratio. This raises the possibility that colchicine might be potentially useful as an immunomodulating drug in treating patients with autoimmune or allergic diseases associated with a suppressor cell deficiency.