The peroxisomal membrane protein import receptor Pex3p is directly transported to peroxisomes by a novel Pex19p- and Pex16p-dependent pathway

Two distinct pathways have recently been proposed for the import of peroxisomal membrane proteins (PMPs): a Pex19p- and Pex3p-dependent class I pathway and a Pex19p- and Pex3p-independent class II pathway. We show here that Pex19p plays an essential role as the chaperone for full-length Pex3p in the cytosol. Pex19p forms a soluble complex with newly synthesized Pex3p in the cytosol and directly translocates it to peroxisomes. Knockdown of Pex19p inhibits peroxisomal targeting of newly synthesized full-length Pex3p and results in failure of the peroxisomal localization of Pex3p. Moreover, we demonstrate that Pex16p functions as the Pex3p-docking site and serves as the peroxisomal membrane receptor that is specific to the Pex3p–Pex19p complexes. Based on these novel findings, we suggest a model for the import of PMPs that provides new insights into the molecular mechanisms underlying the biogenesis of peroxisomes and its regulation involving Pex3p, Pex19p, and Pex16p

In vitro import of peroxisome-targeting signal type 2 (PTS2) receptor Pex7p into peroxisomes

AbstractPex7p, the peroxisome-targeting signal type 2 (PTS2) receptor, transports PTS2 proteins to peroxisomes from the cytosol. We here established a cell-free Pex7p translocation system. In assays using post-nuclear supernatant fractions each from wild-type CHO-K1 and pex7 ZPG207 cells, 35S-labeled Pex7p was imported into peroxisomes. 35S-Pex7p import was also evident using rat liver peroxisomes. 35S-Pex7p was not imported into peroxisomal remnants from a pex5 ZPG231 defective in PTS2 import and pex2 Z65. When the import of 35S-Pex5pL was inhibited with an excess amount of recombinant Pex5pS, 35S-Pex7p import was concomitantly abrogated, suggesting that Pex5pL was a transporter for Pex7p, unlike a yeast cochaperone, Pex18p. 35S-Pex7p as well as 35S-Pex5p was imported in an ATP-independent manner, whilst the import of PTS1 and PTS2 cargo-proteins was ATP-dependent. Thereby, ATP-independent import of Pex7p implicated that Pex5p export requiring ATP hydrolysis is not a limiting step for its cargo recruitment to peroxisomes. PTS1 protein import was indeed insensitive to N-ethylmaleimide, whereas Pex5p export was N-ethylmaleimide-sensitive. Taken together, the cargo-protein translocation through peroxisomal membrane more likely involves another ATP-requiring step in addition to the Pex5p export. Moreover, upon concurrent import into peroxisomes, 35S-Pex5pL and 35S-Pex7p were detected at mutually distinct ratios in the immunoprecipitates each of the import machinery peroxins including Pex14p, Pex13p, and Pex2p, hence suggesting that Pex7p as well as Pex5p translocated from the initial docking complex to RING complex on peroxisomes

Pex14p phosphorylation regulates peroxisome import

Peroxisomal matrix proteins are imported into peroxisomes via membrane-bound docking/translocation machinery. One central component of this machinery is Pex14p, a peroxisomal membrane protein involved in the docking of Pex5p, the receptor for peroxisome targeting signal type 1 (PTS1). Studies in several yeast species have shown that Pex14p is phosphorylated in vivo, whereas no function has been assigned to Pex14p phosphorylation in yeast and mammalian cells. Here, we investigated peroxisomal protein import and its dynamics in mitotic mammalian cells. In mitotically arrested cells, Pex14p is phosphorylated at Ser-232, resulting in a lower import efficiency of catalase, but not the majority of proteins including canonical PTS1 proteins. Conformational change induced by the mitotic phosphorylation of Pex14p more likely increases homomeric interacting affinity and suppresses topological change of its N-terminal part, thereby giving rise to the retardation of Pex5p export in mitotic cells. Taken together, these data show that mitotic phosphorylation of Pex14p and consequent suppression of catalase import are a mechanism of protecting DNA upon nuclear envelope breakdown at mitosis

The peroxisome counteracts oxidative stresses by suppressing catalase import via Pex14 phosphorylation

Most of peroxisomal matrix proteins including a hydrogen peroxide (H2O2)-decomposing enzyme, catalase, are imported in a peroxisome-targeting signal type-1 (PTS1)-dependent manner. However, little is known about regulation of the membrane-bound protein import machinery. Here, we report that Pex14, a central component of the protein translocation complex in peroxisomal membrane, is phosphorylated in response to oxidative stresses such as H2O2 in mammalian cells. The H2O2-induced phosphorylation of Pex14 at Ser232 suppresses peroxisomal import of catalase in vivo and selectively impairs in vitro the interaction of catalase with the Pex14-Pex5 complex. A phosphomimetic mutant Pex14-S232D elevates the level of cytosolic catalase, but not canonical PTS1-proteins, conferring higher cell resistance to H2O2. We thus suggest that the H2O2-induced phosphorylation of Pex14 spatiotemporally regulates peroxisomal import of catalase, functioning in counteracting action against oxidative stress by the increase of cytosolic catalase

Parkin‐mediated ubiquitylation redistributes MITOL/March5 from mitochondria to peroxisomes

Ubiquitylation of outer mitochondrial membrane (OMM) proteins is closely related to the onset of familial Parkinson's disease. Typically, a reduction in the mitochondrial membrane potential results in Parkin‐mediated ubiquitylation of OMM proteins, which are then targeted for proteasomal and mitophagic degradation. The role of ubiquitylation of OMM proteins with non‐degradative fates, however, remains poorly understood. In this study, we find that the mitochondrial E3 ubiquitin ligase MITOL/March5 translocates from depolarized mitochondria to peroxisomes following mitophagy stimulation. This unusual redistribution is mediated by peroxins (peroxisomal biogenesis factors) Pex3/16 and requires the E3 ligase activity of Parkin, which ubiquitylates K268 in the MITOL C‐terminus, essential for p97/VCP‐dependent mitochondrial extraction of MITOL. These findings imply that ubiquitylation directs peroxisomal translocation of MITOL upon mitophagy stimulation and reveal a novel role for ubiquitin as a sorting signal that allows certain specialized proteins to escape from damaged mitochondria

RETRACTED: The Chromatin-Remodeling Complex WINAC Targets a Nuclear Receptor to Promoters and Is Impaired in Williams Syndrome

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the Authors.Our paper reported that a chromatin-remodeling complex, WINAC, recruited the unliganded vitamin D receptor to promoters in cooperation with the transcription factor implicated in Williams syndrome, WSTF. The findings provided insights into the coordination between chromatin remodelers and sequence-specific transcription factors and pointed to a role of chromatin remodeling defects in Williams syndrome. We recently identified errors affecting several figure panels where original data were processed inappropriately such that the figure panels do not accurately report the original data. We believe that the most responsible course of action is to retract the paper. We sincerely apologize to the scientific community for any inconvenience that this might cause. The first author, H.K., declined to sign the retraction notice

Cut Out Complications and Anisomelia of the Lower Limbs In Surgery With Valgus Reduction for Intertrochanteric Fractures

Background: The proximal fractures of the femur are counted among the group of orthopedic and traumatic pathologies which consume most of the financial resources set aside for health worldwide. Surgical treatment continues to be the treatment of choice for intertrochanteric fractures of the femur. However, although the surgical treatment of the proximal fracture of the femur is widely known and accepted in the orthopedic field, it is not without risk with the cut out being the most feared complication. Objective: This paper describes the complications of cut out or the anisomelia of the lower limbs of patients with intertrochanteric fractures who underwent valgus reduction surgery. Method: Sixty-one patients with 3rd and 4th degree, according to Tronzo classification, intertrochanteric fractures underwent surgery with the use of Dynamic hip screw type sliding screw and valgus reduction. The data were analyzed one year after surgery, when a functional assessment was made by scanometry, Tip-Apex Distance index diaphyseal cervical angle and the modified Merle d'Aubigné & Postel questionnaire. Kruskal-Wallis and Mann-Whitney tests were used for the statistical analysis, Spearman’s correlation test for the quantitative variables and the chi-squared test for the qualitative variables. Results: The correlation between the Tip-Apex Distance index and the diaphyseal cervical angle was statistically significant (rho=0.391, p=0.002), while the correlations between the Tip-Apex Distance index and the scanometry and the diaphyseal cervical angle and the scanometry were not significantly correlated. In accordance with the modified Merle d’Aubigné & Postel questionnaire, 23 patients (37.7%) achieved a very good result, 29 patients (47.5%) had a good result, five patients (8.2%) obtained a moderately good result, one patient (1.6%) presented a reasonable result and three patients (4.9%) obtained a poor result. Conclusion: No cut out complications occurred in the 3rd and 4th degree intertrochanteric fractures with a Baumgaertner index ≥ 25 mm, when the reduction and valgus fixation of the intertrochanteric fracture was performed with the Dynamic hip screw type sliding pin, as there was also, in the majority of patients, no anisomelia of the lower limbs

A new method to evaluate glenoid erosion in instable shoulder

Background: We aimed to establish values and parameters using multislice reconstruction in axial computerized tomography (CT) in order to quantify the erosion of the glenoid cavity in cases of shoulder instability. Methods: We studied two groups using CT. Group I had normal subjects and Group II had patients with shoulder instability. We measured values of the vertical segment, the superior horizontal, medial and inferior segments, and also calculated the ratio of the horizontal superior and inferior segments of the glenoid cavity in both normal subjects and those with shoulder instability. These variables were recorded during arthroscopy for cases with shoulder instability.\ud \ud \ud \ud Results\ud The mean values were 40.87 mm, 17.86 mm, 26.50 mm, 22.86 mm and 0.79 for vertical segment, the superior horizontal, medial and inferior segments, and the ratio between horizontal superior and inferior segments of the glenoid cavity respectively, in normal subjects. For subjects with unstable shoulders the mean values were 37.33 mm, 20.83 mm, 23.07 mm and 0.91 respectively. Arthroscopic measurements yielded an inferior segment value of 24.48 mm with a loss of 2.39 mm (17.57%). The ratio between the superior and inferior segments of the glenoid cavity was 0.79. This value can be used as a normative value for evaluating degree of erosion of the anterior border of the glenoid cavity. However, values found using CT should not be used on a comparative basis with values found during arthroscopy. Conclusions: Computerized tomographic measurements of the glenoid cavity yielded reliable values consistent with those in the literature.The funding body provided financial support to make all procedures and in the decision to submit the manuscript for publication

Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).

Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)