ABSTRACT
BACKGROUND: Data on infliximab efficacy in bio-exposed patients with ulcerative colitis (UC) are limited. AIMS: To evaluate infliximab effectiveness and its predictors in UC patients with prior exposure to subcutaneous (SC) anti-TNF agent. METHODS: In this multicenter retrospective study (8 centers), we included all consecutive UC patients with prior exposure to subcutaneous anti-TNF, starting infliximab for symptomatic UC, excluding acute severe colitis. Corticosteroid-free clinical remission (CFREM) was assessed at week 14 (W14) and W52 while endoscopic improvement (CFREM + endoscopic Mayo score≤1) was evaluated at W14. RESULTS: Overall, 104 patients were included (pancolitis=54.8%, primary failure to subcutaneous anti-TNF=57.4%, concomitant immunosuppressant=53.8%, median partial Mayo score at baseline=7[5-8]). The rate of CFREM was 33.6% (35/104) at W14 and 40.4% (42/104) at W52. At W14, endoscopic improvement was achieved in 29.8%(31/104). In multivariable analysis, concomitant immunosuppressant was associated with higher rate of CFREM at W14(OR=2.83[1.06-7.54], p = 0.037) and W52(OR=2.68[1.16-6.22];p = 0.021), while primary failure to a previous subcutaneous anti-TNF agent led to lower rate of CFREM at W14 (OR=0.37[0.14-0.98], p = 0.046). After a median follow-up of 20.9 months[11.7-33.7]), 50.0%(52/104) patients had discontinued infliximab. CONCLUSION: Infliximab is an effective option in UC patients previously exposed to prior subcutaneous anti-TNF agent and should be used with concomitant immunosuppressant.
Subject(s)
Colitis, Ulcerative , Gastrointestinal Agents , Infliximab , Humans , Colitis, Ulcerative/drug therapy , Infliximab/administration & dosage , Infliximab/therapeutic use , Male , Female , Retrospective Studies , Adult , Middle Aged , Injections, Subcutaneous , Gastrointestinal Agents/administration & dosage , Gastrointestinal Agents/therapeutic use , Treatment Outcome , Remission Induction , Tumor Necrosis Factor-alpha/antagonists & inhibitors , Multivariate Analysis , Immunosuppressive Agents/administration & dosage , Immunosuppressive Agents/therapeutic useABSTRACT
BACKGROUND: The long-term risk of relapse after switching from intravenous (IV) to subcutaneous (SC) infliximab remains unknown in inflammatory bowel disease (IBD). AIMS: To assess the long-term effectiveness and acceptability of switching from IV to SC infliximab in patients with IBD treated with or without an intensified IV regimen. METHODS: We extended the follow-up of the REMSWITCH study including patients with IBD in clinical remission who were switched from IV to SC infliximab (120 mg/2 weeks). Relapse was defined as clinical relapse or faecal calprotectin increase ≥150 µg/g compared to baseline. RESULTS: After median follow-up of 18 [15-20] months, among 128 patients, rates of relapse were 13.8% (8/58), 18.4% (7/38), 35.3% (6/17) and 86.7% (13/15) at last follow-up (p < 0.001), in those receiving 5 mg/kg/8 weeks, 10 mg/kg/8 weeks, 10 mg/kg/6 weeks and 10 mg/kg/4 weeks at baseline, respectively. Among relapsing patients, dose escalation led to clinical remission in 82.1% (23/28). In multivariable analyses, factors associated with higher risk of relapse were IV infliximab 10 mg/kg/4 weeks (OR = 61.0 [6.1-607.0], p < 0.001) or 10 mg/kg/6 weeks (OR = 4.7 [1.1-20.2], p = 0.017), and decreased (OR = 5.6 [1.5-20.3], p = 0.004) or stable (OR = 5.0 [1.6-15.0], p = 0.009) serum levels of infliximab between baseline and first post-switch visit. Acceptability was improved at 6 months and did not decrease over time (6.9 ± 1.6 before the switch vs. 8.8 ± 1.3 at 6 months and 8.8 ± 1.3 at last follow-up; p < 0.001). No severe adverse events were reported. CONCLUSIONS: Switching from IV to SC infliximab 120 mg every other week is safe and well accepted leading to low long-term risk of relapse. Tight monitoring and dose escalation should be recommended for patients receiving 10 mg/kg/6 weeks and 4 weeks, respectively.
Subject(s)
Biosimilar Pharmaceuticals , Inflammatory Bowel Diseases , Humans , Biosimilar Pharmaceuticals/therapeutic use , Gastrointestinal Agents , Inflammatory Bowel Diseases/drug therapy , Inflammatory Bowel Diseases/chemically induced , Infliximab/adverse effects , Recurrence , Time Factors , Treatment OutcomeABSTRACT
INTRODUCTION: Knowledge about the cancer risk when initiating a biologic in inflammatory bowel disease [IBD] patients with prior malignancy remains scarce, especially for vedolizumab. Our aim was to evaluate the rate of incident cancer in a cohort of IBD patients with prior non-digestive malignancy, according to the subsequent treatment given. METHODS: A multicentre retrospective study included consecutive IBD patients with prior non-digestive malignancy. Inclusion date corresponded to the diagnosis of index malignancy. Patients were categorized into different cohorts according to the first treatment [none, conventional immunosuppressant, anti-TNF, or vedolizumab] to which they were exposed after inclusion and before incident cancer [recurrent or new cancer]. RESULTS: Among the 538 patients {58% female; mean (standard deviation [SD]) age inclusion: 52 [15] years} analyzed, the most frequent malignancy was breast cancer [25%]. The first immunomodulator given after inclusion was a conventional immunosuppressant in 27% of patients, anti-TNF in 21%, or vedolizumab in 9%. With a median (interquartile range [IQR]) follow-up duration of 55 [23-100] months, 100 incident cancers were observed. Crude cancer incidence rates per 1000 person-years were 47.0 for patients receiving no immunomodulator, 36.6 in the anti-TNF cohort, and 33.6 in the vedolizumab cohort [p = 0.23]. Incident-cancer free survival rates were not different between patients receiving anti-TNF and those receiving vedolizumab [p = 0.56]. After adjustment, incidence rates were not different between patients receiving no immunomodulator, anti-TNF, or vedolizumab. CONCLUSIONS: In this large multicentre cohort study, there was no difference of cancer incidence in those IBD patients with prior non-digestive malignancy, treated with vedolizumab or anti-TNF.
Subject(s)
Inflammatory Bowel Diseases , Neoplasms , Humans , Female , Adolescent , Male , Cohort Studies , Retrospective Studies , Tumor Necrosis Factor Inhibitors , Inflammatory Bowel Diseases/drug therapy , Immunosuppressive Agents/therapeutic use , Neoplasms/chemically induced , Gastrointestinal Agents/therapeutic useABSTRACT
BACKGROUND: Better patient knowledge on inflammatory bowel disease [IBD] could improve outcome and quality of life. The aim of this study was to assess if an education programme improves IBD patients' skills as regards their disease. METHODS: The GETAID group conducted a prospective multicentre randomised controlled study. IBD patients were included at diagnosis, or after a significant event in the disease course. Patients were randomised between 'educated' or control groups for 6 months. Education was performed by trained health care professionals. A psycho-pedagogic score [ECIPE] was evaluated by a 'blinded' physician at baseline and after 6 and 12 months [M6 and M12]. The primary endpoint was the increase of ECIPE score at M6 of more than 20%. RESULTS: A total of 263 patients were included in 19 centres (male:40%; median age:30.8; Crohn's disease [CD]:73%). Of these, 133 patients were randomised into the educated group and 130 into the control group. The median relative increase in ECIPE score at M6 was higher in the educated group as compared with the control group (16.7% [0-42.1%] vs 7% [0-18.8%], respectively, p = 0.0008). The primary endpoint was met in 46% vs 24% of the patients in the educated and control groups, respectively [p = 0.0003]. A total of 92 patients met the primary endpoint. In multivariate analysis, predictors of an increase of at least 20% of the ECIPE score were randomisation in the educated group (odds ratio [OR] = 2.59) and no previous surgery [OR = 1.92]. CONCLUSIONS: These findings support the set-up of education programmes in centres involved in the management of IBD patients.
Subject(s)
Health Knowledge, Attitudes, Practice , Inflammatory Bowel Diseases/epidemiology , Patient Education as Topic , Self-Management , Adult , Educational Measurement , Female , France/epidemiology , Humans , Male , Prospective StudiesABSTRACT
BACKGROUND AND AIMS: Defining and assessing the reproducibility of Crohn's disease [CD] endoscopic lesions is essential in assessing endoscopic healing. METHODS: Twelve endoscopic CD experts from the GETAID defined aphthoid erosions [AE], superficial ulcerations [SU], deep ulcerations [DU], stenosis, and fistulas according to a Delphi-like method. Thirty different GETAID physicians declared if they found acceptable each definition. Intra- and inter-observer agreements were investigated using 100 videos with one tagged specific lesion [AE, SU, DU, or sham lesion] read by 15 independent endoscopists at baseline and 1 month later in a randomised order. Video quality was determined by an external reader. According to kappa estimate [κ ±standard error], intra or inter-observer agreement was qualified as 'moderate' [0.4-0.6], 'substantial' [0.6-0.8], or 'almost perfect' [0.8-1.0]. RESULTS: Among 30 different experts, 83% to 97% found acceptable the definitions retrieved from the Delphi-like method. Intra-observer κ was 0.717 [±0.019] for SU, 0.681 [±0.027] for AE, 0.856 [±0.014] for DU, showing 'substantial' agreement. It was 0.801 [±0.016] for any ulceration [DU or SU]. There was a high variability across readers from 'moderate' to 'almost perfect' agreement. Inter-observer κ was 0.548 [±0.042] for SU, 0.554 [±0.028] for AE 0.694 [±0.041] for DU, and 0.705 [±0.042] for any ulceration. Inter-observer agreement increased when reading the 53 high-quality videos: 0.787 [±0.064] [pâ =â 0.001], 0.607 [±0.043] [pâ =â 0.001], and 0.782 [±0.064][pâ =â 0.001] for DU, AE, and any ulceration, respectively. CONCLUSIONS: Despite variable intra-agreement level across readers, the GETAID definitions for CD endoscopic lesions provided 'substantial' inter-observer agreements, especially in case of high-quality videos.
Subject(s)
Crohn Disease/diagnosis , Endoscopy, Gastrointestinal , Intestines , Delphi Technique , Endoscopy, Gastrointestinal/methods , Endoscopy, Gastrointestinal/standards , Endoscopy, Gastrointestinal/statistics & numerical data , Humans , Intestines/diagnostic imaging , Intestines/pathology , Microscopy, Video/methods , Observer Variation , Quality Improvement , Reproducibility of Results , Severity of Illness Index , Terminology as TopicABSTRACT
BACKGROUND: Standard high-volume polyethylene glycol [PEG] bowel preparations [PEG-4L] are recommended for patients with inflammatory bowel disease [IBD] undergoing colonoscopy. However, low-volume preparations [≤2 L of active volume] are often used in clinical practice. The aim of this study was to evaluate the efficacy, tolerability, and safety of the various bowel preparations for patients with IBD, including low-volume preparations. METHODS: We conducted a French prospective multicentre observational study over a period of 1 month. Patients aged 18-75 years with IBD with an indication of colonoscopy independent of the study were enrolled. The choice of the preparation was left to the investigators, as per their usual protocol. The patients' characteristics, disease, and colonoscopy characteristics were recorded, and they were given self-reported questionnaires. RESULTS: Twenty-five public and private hospitals enrolled 278 patients. Among them, 46 had a disease flare and 41 had bowel stenoses. Bowel preparations for colonoscopy were as follows: 42% received PEG-2L, 29% received sodium picosulfate [Pico], 15% received PEG-4L, and 14% had other preparations. The preparation did not reach the Boston's score efficacy outcome in the PEG-4L group in 51.2% of the patients [p = 0.0011]. The preparation intake was complete for 59.5% in the PEG-4L group, compared with 82.9% in the PEG-2L group and 93.8% in the Pico group [p < 0.0001]. Tolerability, as assessed by the patients' VAS, was significantly better for both Pico and PEG-2L compared with PEG-4L, and better for Pico compared with PEG-2L [p = 0.008; p = 0.0003]. In multivariate analyses, low-volume preparations were independent factors of efficacy and tolerability. Adverse events occurred in 4.3% of the patients. CONCLUSIONS: Preparations with PEG-2L and Pico were equally safe, with better efficacy and tolerability outcomes compared with PEG-4L preparations. The best efficacy/tolerance/safety profile was achieved with the Pico preparation.
Subject(s)
Cathartics , Colonoscopy/methods , Inflammatory Bowel Diseases/diagnosis , Polyethylene Glycols , Adolescent , Adult , Aged , Aged, 80 and over , Cathartics/administration & dosage , Cathartics/adverse effects , Citrates/administration & dosage , Citrates/adverse effects , Colitis, Ulcerative/diagnosis , Colonoscopy/adverse effects , Crohn Disease/diagnosis , Female , Humans , Inflammatory Bowel Diseases/pathology , Male , Middle Aged , Organometallic Compounds/administration & dosage , Organometallic Compounds/adverse effects , Picolines/administration & dosage , Picolines/adverse effects , Polyethylene Glycols/administration & dosage , Polyethylene Glycols/adverse effects , Prospective Studies , Young AdultABSTRACT
doi:10.1093/ecco-jcc/jjy222 Abstract P528 from the 'Poster presentations' section of the main abstract book has been withdrawn and re-inserted as DOP63 in the 'Late-breaking abstracts' section.
ABSTRACT
BACKGROUND AND AIMS: Crohn's disease [CD] is associated with an increased risk of small bowel adenocarcinoma [SBA]. There are no recommendations on endoscopic screening of SBA in CD patients. The aim of this study was to evaluate the feasibility and value of endoscopic screening for SBA in CD patients at high-risk of SBA. METHODS: We performed an exploratory multi-centre study in a prospective cohort of CD patients at high-risk of SBA defined as long-term small bowel disease without bowel resection for the past 10 years. Depending on the location of the disease, baseline upper and/or lower enteroscopies were performed. Random and targeted biopsies using chromoendoscopy were taken. Patients were followed-up for at least 1 year after inclusion. RESULTS: In total, 101 patients [62 men; median age: 48 years; median duration of disease: 19 years] were recruited in ten centres. The endoscopic procedure was incomplete in 47 cases because of impassable strictures and dilation was performed in four patients. Indeterminate small bowel dysplasia was identified in two patients at endoscopic screening; SBA was confirmed in one after surgical resection. With an at least 1-year follow-up duration, two additional cases of SBA were identified in patients who underwent surgery for obstruction, resulting in a 33% sensitivity rate for SBA endoscopic screening. CONCLUSION: In a cohort of high-risk patients, the prevalence of dysplasia and SBA on CD was 4%. Because of its low sensitivity, endoscopic screening cannot be recommended for surveillance in CD patients at high-risk of SBA.
Subject(s)
Adenocarcinoma/diagnosis , Crohn Disease/complications , Endoscopy, Gastrointestinal , Intestinal Neoplasms/diagnosis , Adenocarcinoma/etiology , Adenocarcinoma/pathology , Adult , Crohn Disease/pathology , Female , Humans , Intestinal Neoplasms/etiology , Intestinal Neoplasms/pathology , Intestine, Small/pathology , Male , Middle Aged , Prospective Studies , Risk Factors , Sensitivity and SpecificityABSTRACT
BACKGROUND: The Rutgeerts score with 5 grades of severity (i0-i4) is a suitable endoscopic model to predict clinical recurrence following ileocolonic resection in Crohn's disease (CD). Definition of grade i2 includes lesions confined to the ileocolonic anastomosis (i2a) or moderate lesions on the neo-terminal ileum (i2b). The aim of the present study was to evaluate the probability of clinical recurrence in i2a and i2b patients. METHODS: This multicenter retrospective study included all CD patients classified i2 at the first postoperative ileocolonoscopy. The primary outcome was to evaluate the probability of clinical recurrence in patients classified i2a and i2b. The secondary outcome was to compare the rate of global recurrence of CD. RESULTS: Fifty patients were included: 23 were classified i2a and 27 were classified i2b. The median duration of follow-up was 40 (18.0-80.4) months in the i2a group and 53.5 (25.0-69.0) months in the i2b group (p = 0.9). The probability of clinical recurrence was not significantly different between patients classified i2a and i2b (p = 0.64). Median time to clinical recurrence after the first ileocolonoscopy and probability of global CD recurrence were not different between the two groups (p ≥ 0.19). CONCLUSIONS: The rate of clinical postoperative recurrence is not different in i2a and i2b patients. These results suggest that the same therapeutic strategy should be used in all patients classified i2 on the Rutgeerts score whatever the location of postoperative CD recurrence.
Subject(s)
Colon/surgery , Crohn Disease/surgery , Ileum/surgery , Intestinal Obstruction/surgery , Intestinal Perforation/surgery , Adult , Anastomosis, Surgical , Colon/pathology , Colonoscopy , Constriction, Pathologic/etiology , Constriction, Pathologic/surgery , Crohn Disease/complications , Crohn Disease/pathology , Female , Humans , Ileum/pathology , Intestinal Obstruction/etiology , Intestinal Perforation/etiology , Male , Postoperative Period , Prognosis , Recurrence , Retrospective StudiesABSTRACT
BACKGROUND: Therapeutic monoclonal anti-cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) antibodies are associated with immune-mediated enterocolitis. The aim of this study was to provide a detailed description of this entity. METHODS: We included patients with endoscopic signs of inflammation after anti-CTLA-4 infusions for cancer treatment. Other causes of enterocolitis were excluded. Clinical, biological and endoscopic data were recorded. A single pathologist reviewed endoscopic biopsies and colectomy specimens from 27 patients. Patients with and without enterocolitis after ipilimumab-treated melanoma were compared, to identify clinical factors associated with enterocolitis. RESULTS: Thirty-nine patients with anti-CTLA-4 enterocolitis were included (ipilimumab n = 37; tremelimumab n = 2). The most frequent symptom was diarrhoea. Ten patients had extra-intestinal manifestations. Most colonoscopies showed ulcerations involving the rectum and sigmoid, 66% of patients had extensive colitis, 55% had patchy distribution and 20% had ileal inflammation. Endoscopic colonic biopsies showed acute colitis in most patients, while half of the patients had chronic duodenitis. Thirty-five patients received steroids that led to complete clinical remission in 13 patients (37%). Twelve patients required infliximab, of whom 10 (83%) responded. Six patients underwent colectomy (perforation n = 5; toxic megacolon n = 1); one of them died postoperatively. Four patients had a persistent enterocolitis at follow-up colonoscopy. Patients with enterocolitis were more frequently prescribed NSAIDs compared with patients without enterocolitis (31 vs 5%, p = 0.003). CONCLUSIONS: Ipilimumab and tremelimumab may induce a severe and extensive form of inflammatory bowel disease. Rapid escalation to infliximab should be advocated in patients who do not respond to steroids. Patients treated with anti-CTLA-4 should be advised to avoid NSAIDs.
Subject(s)
Antibodies, Monoclonal/adverse effects , CTLA-4 Antigen/immunology , Immunotherapy/methods , Inflammatory Bowel Diseases/chemically induced , Melanoma/therapy , Adult , Aged , Aged, 80 and over , Antibodies, Monoclonal/immunology , Antibodies, Monoclonal/therapeutic use , Antibodies, Monoclonal, Humanized , Colectomy , Colon/pathology , Enterocolitis/chemically induced , Enterocolitis/immunology , Enterocolitis/pathology , Female , Humans , Immunotherapy/adverse effects , Inflammatory Bowel Diseases/immunology , Inflammatory Bowel Diseases/pathology , Ipilimumab , Male , Middle Aged , Young AdultABSTRACT
BACKGROUND AND AIMS: Anal fistula plug [AFP] is a bioabsorbable bioprosthesis used in ano-perineal fistula treatment. We aimed to assess efficacy and safety of AFP in fistulising ano-perineal Crohn's disease [FAP-CD]. METHODS: In a multicentre, open-label, randomised controlled trial we compared seton removal alone [control group] with AFP insertion [AFP group] in 106 Crohn's disease patients with non- or mildly active disease having at least one ano-perineal fistula tract drained for more than 1 month. Patients with abscess [collection ≥ 3mm on magnetic resonance imaging or recto-vaginal fistulas were excluded. Randomisation was stratified in simple or complex fistulas according to AGA classification. Primary end point was fistula closure at Week 12. RESULTS: In all, 54 patients were randomised to AFP group [control group 52]. Median fistula duration was 23 [10-53] months. Median Crohn's Disease Activity Index at baseline was 81 [45-135]. Fistula closure at Week 12 was achieved in 31.5% patients in the AFP group and in 23.1 % in the control group (relative risk [RR] stratified on AGA classification: 1.31; 95% confidence interval: 0.59-4.02; p = 0.19). No interaction in treatment effect with complexity stratum was found; 33.3% of patients with complex fistula and 30.8% of patients with simple fistula closed the tracts after AFP, as compared with 15.4% and 25.6% in controls, respectively [RR of success = 2.17 in complex fistula vs RR = 1.20 in simple fistula; p = 0.45]. Concerning safety, at Week 12, 17 patients developed at least one adverse event in the AFP group vs 8 in the controls [p = 0.07]. CONCLUSION: AFP is not more effective than seton removal alone to achieve FAP-CD closure.
Subject(s)
Absorbable Implants , Bioprosthesis , Crohn Disease/complications , Digestive System Surgical Procedures/methods , Perineum , Prosthesis Implantation/methods , Rectal Fistula/surgery , Adult , Female , Follow-Up Studies , Humans , Magnetic Resonance Imaging , Male , Rectal Fistula/diagnosis , Rectal Fistula/etiology , Retrospective Studies , Time Factors , Treatment OutcomeABSTRACT
PURPOSE: Ileoanal anastomoses (J-pouches) are an alternative to permanent ostomy. The functional outcomes associated with the use of J-pouches are usually good, but continence disorders persist in a significant number of cases and have a negative impact on quality of life. The aim of this study was to assess the efficacy of sacral nerve stimulation (SNS) for poor functional results after J-pouch ileoanal anastomosis. METHODS: Patients suffering from severe fecal incontinence (FI) following coloproctectomy underwent a staged implant SNS procedure. Demographic data and functional results for FI episodes, urgencies per week, frequency of stools, ability to defer defecation, and Wexner scores were obtained at specified intervals. Patients also completed quality-of-life assessments. RESULTS: Four female patients were included in this analysis. All 4 experienced active and passive FI at baseline and subsequently underwent test stimulation with a 75 % success rate. Three received definitive implants. These 3 patients experienced improvement in functional outcomes at 1, 3, and 6 month assessments. Improvements in quality of life were also noted. CONCLUSIONS: Our preliminary study suggests that SNS is effective for the treatment of poor functional results following J-pouch ileoanal anastomosis; however, larger studies with long-term follow-up are needed for confirmation of our findings.
Subject(s)
Anal Canal/innervation , Colonic Pouches , Electric Stimulation Therapy/methods , Fecal Incontinence/therapy , Lumbosacral Plexus/physiology , Proctocolectomy, Restorative/methods , Adult , Anastomosis, Surgical , Female , Follow-Up Studies , Humans , Middle Aged , Quality of Life , Treatment Outcome , Young AdultABSTRACT
The GTPase Ran has recently been shown to stimulate microtubule polymerization in mitotic extracts, but its mode of action is not understood. Here we show that the mitotic role of Ran is largely mediated by the nuclear transport factor importin beta. Importin beta inhibits spindle formation in vitro and in vivo and sequesters an aster promoting activity (APA) that consists of multiple, independent factors. One component of APA is the microtubule-associated protein NuMA. NuMA and other APA components are discharged from importin beta by RanGTP and induce spindle-like structures in the absence of centrosomes, chromatin, or Ran. We propose that RanGTP functions in mitosis as in interphase by locally releasing cargoes from transport factors. In mitosis, this promotes spindle assembly by organizing microtubules in the vicinity of chromosomes.
Subject(s)
Mitosis/physiology , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Spindle Apparatus/metabolism , Xenopus Proteins , ran GTP-Binding Protein/metabolism , Animals , Cell Line , Cloning, Molecular , Female , GTP Phosphohydrolases/genetics , GTP Phosphohydrolases/metabolism , Gene Expression/physiology , Karyopherins , Mammals , Microtubules/metabolism , Oocytes/cytology , Oocytes/metabolism , Xenopus , ran GTP-Binding Protein/geneticsABSTRACT
Transport of macromolecules across the nuclear envelope is an active process that depends on soluble factors including the GTPase Ran. Ran-GTP is predominantly located in the nucleus and has been shown to regulate cargo binding and release of import and export receptors in their respective target compartments. Recently, it was shown that transport of receptor-cargo complexes across the nuclear pore complex (NPC) does not depend on GTP-hydrolysis by Ran; however, the mechanism of translocation is still poorly understood. Here, we show that the direction of transport through the NPC can be inverted in the presence of high concentrations of cytoplasmic Ran-GTP. Under these conditions, two different classes of export cargoes are transported into the nucleus in the absence of GTP hydrolysis. The inverted transport is very rapid and can be blocked by known inhibitors of nuclear protein export. These results suggest that the NPC functions as a facilitated transport channel, allowing the selective translocation of receptor-cargo complexes. We conclude that the directionality of nucleocytoplasmic transport is determined mainly by the compartmentalized distribution of Ran-GTP.
Subject(s)
Karyopherins , Nuclear Envelope/ultrastructure , Nuclear Proteins/metabolism , Receptors, Cytoplasmic and Nuclear , Biological Transport , Carrier Proteins/metabolism , Cells, Cultured , GTP Phosphohydrolases/metabolism , GTP-Binding Proteins/metabolism , Guanosine Triphosphate/metabolism , Humans , Hydrolysis , Models, Biological , alpha Karyopherins , ran GTP-Binding Protein , Exportin 1 ProteinABSTRACT
Nuclear import of proteins containing a nuclear localization signal (NLS) is dependent on the presence of a cytoplasmic NLS receptor, the GTPase Ran, and p10/ NTF2. The NLS receptor is a heterodimeric proteins consisting of subunits of approximately 60 and 97 kDa, which have been termed importin alpha/beta, karyopherin alpha/beta, or PTAC 58/ 97. Members of the 60-kDa/importin alpha subunit family directly bind to the NLS motif and have been shown to function as adaptors that tether NLS-containing proteins to the p97/ importin beta subunit and to the downstream transport machinery. Herein we report the identification and characterization of hSRP1 gamma, a human importin alpha homologue. The hSRP1 gamma protein is around 45% identical to the previously identified human importin alpha homologues hSRP1 alpha/Rch1 and NPI/ hSRP1. hSRP1 gamma can form a complex with importin beta and is able to mediate import of a BSA-NLS substrate in an in vitro nuclear import system. Interestingly, hSRP1 gamma shows a very selective expression pattern and is most abundantly expressed in skeletal muscle, representing more than 1% of the total protein in this tissue. A potential role for hSRP1 gamma in tissue-specific transport events is discussed.