The first parent-child diagnosis of a multifocal squamous odontogenic tumor: A case report.

Squamous odontogenic tumors (SOT) are rare, benign, odontogenic neoplasms of the jaws. The sporadically reported cases with multifocal SOTs seem to have a marked predilection for younger African American patients. In this case report a 14-year-old Caucasian male presented with swelling of the vestibular alveolar process, slight tooth divergence, and mobility. A multifocal squamous odontogenic tumor was diagnosed and subsequently treated twice with surgical enucleation. Two and a half years earlier his mother was diagnosed and treated for a similar multifocal SOT. Next-Generation-Sequencing targeted resequencing mutational analysis of the maternal surgical specimens was performed. No potential causal mutation could be identified. Postoperative follow-up of the patient showed no recurrence of the SOT after 2 years. This case report substantiates the possibility of a familial relationship in (multifocal) SOT, possibly changing current ideas concerning the etiology and treatment of these neoplasms.

Prediction of cardiovascular risk in rheumatoid arthritis: performance of original and adapted SCORE algorithms.

OBJECTIVES: Predictive performance of cardiovascular disease (CVD) risk calculators appears suboptimal in rheumatoid arthritis (RA). A disease-specific CVD risk algorithm may improve CVD risk prediction in RA. The objectives of this study are to adapt the Systematic COronary Risk Evaluation (SCORE) algorithm with determinants of CVD risk in RA and to assess the accuracy of CVD risk prediction calculated with the adapted SCORE algorithm. METHODS: Data from the Nijmegen early RA inception cohort were used. The primary outcome was first CVD events. The SCORE algorithm was recalibrated by reweighing included traditional CVD risk factors and adapted by adding other potential predictors of CVD. Predictive performance of the recalibrated and adapted SCORE algorithms was assessed and the adapted SCORE was externally validated. RESULTS: Of the 1016 included patients with RA, 103 patients experienced a CVD event. Discriminatory ability was comparable across the original, recalibrated and adapted SCORE algorithms. The Hosmer-Lemeshow test results indicated that all three algorithms provided poor model fit (p<0.05) for the Nijmegen and external validation cohort. The adapted SCORE algorithm mainly improves CVD risk estimation in non-event cases and does not show a clear advantage in reclassifying patients with RA who develop CVD (event cases) into more appropriate risk groups. CONCLUSIONS: This study demonstrates for the first time that adaptations of the SCORE algorithm do not provide sufficient improvement in risk prediction of future CVD in RA to serve as an appropriate alternative to the original SCORE. Risk assessment using the original SCORE algorithm may underestimate CVD risk in patients with RA.

An increased risk of non-melanoma skin cancer during TNF-inhibitor treatment in psoriasis patients compared to rheumatoid arthritis patients probably relates to disease-related factors.

BACKGROUND: Concerns exist about a risk of non-melanoma skin cancer (NMSC) in psoriasis patients and rheumatoid arthritis (RA) patients treated with TNF-inhibitors. However, current data also show that in some psoriasis patients, NMSC is diagnosed relatively short after the start of TNF-inhibitors, which suggests that these NMSC can be explained by previous therapies instead of by TNF-inhibitor therapy. OBJECTIVE: To investigate whether there was a difference in time until first NMSC and the rate of NMSC between psoriasis and RA patients on TNF-inhibitors. METHODS: Time until first NMSC and the rate of NMSC were compared between psoriasis and RA patients from the same region treated with TNF-inhibitors and followed up for at least one year in prospective cohort studies, by using Cox regression and Poisson regression. Both analyses were corrected for confounders (age, gender, disease duration, prior NMSC, duration of anti-TNF and other systemic therapies). RESULTS: The NMSC risk was significantly higher in the psoriasis group [fully adjusted HR 6.0 (1.6-22.4 95%CI)] with a shorter time until first NMSC in psoriasis compared to RA. By Poisson regression, psoriasis patients had a 5.5 (2.2-13.4 95%CI) higher rate of NMSC. CONCLUSION: The time until first NMSC was significantly shorter and the rate of NMSC was significantly higher in psoriasis compared with RA. This indicates that disease-related factors like phototherapy may be important contributing factors to NMSC diagnosed in psoriasis patients treated with TNF-inhibitors.

The effect of anti-TNF-α vs. DMARDs on fatigue in rheumatoid arthritis patients.

OBJECTIVES: Fatigue is experienced frequently by patients with rheumatoid arthritis (RA). Fatigue may be caused by high levels of pain and disease activity in RA but can remain present while disease activity is moderate to low. It is not clear whether RA patients receiving anti-tumour necrosis factor (TNF) treatment reach lower levels of acute fatigue than RA patients receiving disease-modifying anti-rheumatic drug (DMARD) treatment. The aim of our study was to analyse whether, in patients with RA, the effect of anti-TNF on fatigue is greater than the effect of DMARD treatment. METHOD: Sixty-seven RA patients receiving anti-TNF treatment and 104 RA patients receiving DMARDs were included. All patients were on stable treatment for at least 6 months prior to baseline measurement. Fatigue was measured monthly over 1 year with the fatigue severity subscale of the Checklist Individual Strength (CIS-fatigue). The association between persistent severe fatigue and medication group was analysed using multiple linear regression including confounders. RESULTS: In the anti-TNF group the mean (SD) level of persistent fatigue was significantly higher than in the DMARD group [32.2 (11.4) vs. 28.3 (10.9), p = 0.025] and more patients experienced persistent severe (CIS-fatigue score ≥ 35) fatigue (42% and 27% respectively, p = 0.043). However, when correcting for age, disease activity, haemoglobin, treatment duration, pain, physical disability, and clinical depression, medication type seemed to influence neither the mean level of persistent fatigue (p = 0.251) nor the percentage of patients with persistent severe fatigue (p = 0.745). CONCLUSIONS: When taking into account probable confounders including disease activity, medication type did not influence persistent fatigue in RA patients. It seems that, besides its anti-inflammatory effect, anti-TNF has no complementary effect on persistent fatigue.

Synchronized turbo apoptosis induced by cold-shock.

In our research on the role of apoptosis in the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE), we aim to evaluate the effects of early and late apoptotic cells and blebs on antigen presenting cells. This requires the in vitro generation of sufficiently large and homogeneous populations of early and late apoptotic cells. Here, we present a quick method encountered by serendipity that results in highly reproducible synchronized homogeneous apoptotic cell populations. In brief, granulocytic 32Dcl3 cells are incubated on ice for 2 h and subsequently rewarmed at 37°C. After 30-90 min at 37°C more than 80-90% of the cells become early apoptotic (Annexin V positive/propidium iodide negative). After 24 h of rewarming at 37°C 98% of the cells were late apoptotic (secondary necrotic; Annexin V positive/propidium iodide positive). Cells already formed apoptotic blebs at their cell surface after approximately 20 min at 37°C. Inter-nucleosomal chromatin cleavage and caspase activation were other characteristics of this cold-shock-induced process of apoptosis. Consequently, apoptosis could be inhibited by a caspase inhibitor. Finally, SLE-derived anti-chromatin autoantibodies showed a high affinity for apoptotic blebs generated by cold-shock. Overall, cold-shock induced apoptosis is achieved without the addition of toxic compounds or antibodies, and quickly leads to synchronized homogeneous apoptotic cell populations, which can be applied for various research questions addressing apoptosis.

Defining minimal disease activity in psoriatic arthritis: a proposed objective target for treatment.

OBJECTIVE: To create minimal disease activity (MDA) criteria for psoriatic arthritis (PsA). With recent therapeutic advances, this is now a goal for treatment and may represent a measure to compare therapies. It defines a satisfactory state of disease activity rather than a change, and encompasses all aspects of the disease. METHODS: 40 patient profiles were sampled from an observational PsA database. Sixty experts in PsA classified these as in MDA or not. A consensus of > or =70% was accepted, identifying 13 profiles in MDA. Summary statistics created possible cut-off points for the definition. Considering the number of measures that must be met, 35 candidate definitions were created and tested using receiver operating characteristic curves (ROC) for sensitivity and specificity. RESULTS: Four candidate definitions showed high area under the curve values on ROC testing. Definitions with high outlying values were excluded as they were not considered to represent MDA. Aiming for high specificity to reduce false positives resulted in a preference for the following definition: "A patient is classified as achieving MDA when meeting 5 of the 7 following criteria: tender joint count < or =1; swollen joint count < or =1; Psoriasis Activity and Severity Index < or =1 or body surface area < or =3; patient pain visual analogue score (VAS) < or =15; patient global disease activity VAS < or =20; health assessment questionnaire < or =0.5; tender entheseal points < or =1". CONCLUSION: This study provides the first definition of a "state" of MDA in PsA and defines a target for treatment. It must now be validated in other populations and tested in clinical trials.

Both early and late apoptotic blebs are taken up by DC and induce IL-6 production.

During apo blebs, containing nuclear components, are formed at the cells' surfaces. When these blebs separate from the dying cell an apo cell body remains. The contents of apo blebs are modified and can be released, especially in patients with systemic lupus erythematosus (SLE) since impaired clearance of apo material has been observed in this autoimmune condition. Accordingly, autoantibodies present in subjects with SLE bind to apo blebs. Based on AnxA5 binding, and permeability for PI, we show that apo blebs can be categorized as early (AnxA5(+)/PI(- )) or late (AnxA5(+)/PI(+)) apo ones. Both forms of blebs contain apo-induced chromatin modifications and are efficiently phagocytosed by dendritic cell (DC). Uptake by DC of late, but also early apo blebs, stimulate DC to produce IL-6. This bleb-induced effect on DC may be an important step in the initiation of the autoimmune responses in SLE.

Evaluating guidelines on continuation of anti-tumour necrosis factor treatment after 3 months: clinical effectiveness and costs of observed care and different alternative strategies.

OBJECTIVE: To study the adherence of rheumatologists to the Dutch guidelines for anti-tumour necrosis factor alpha (TNF-alpha) treatment. The secondary objective was to evaluate alternatives to the present guidelines with regard to the percentage of responders and costs. METHODS: The response (>1.2 DAS28 decrease) in patients who started on anti-TNF-alpha treatment for the first time was evaluated at 3 and 6 months after initiation. How many patients continued or discontinued their initial anti-TNF-alpha treatment was evaluated. Possible alternative guidelines were evaluated by means of a decision tree, with regard to the expected percentage of successfully (responders) and unsuccessfully treated patients and expected costs. RESULTS: At 3 months 56% (N = 306) and 44% (N = 233) of all 539 evaluable patients were classified as responders or non-responders, respectively. Despite the guidelines, most (81%) (N = 189) of the non-responders continued treatment. 37% of the non-responders who continued anti-TNF-alpha treatment were eventually classified as responders at 6 months. Decision analytical modelling showed that with equal expected costs all alternative strategies would result in more responders than according to theoretical full adherence with the guidelines. "Continuation in case of partial response" had the best trade-off between successfully treated patients (64%) and unsuccessfully treated patients (17%). CONCLUSION: There was suboptimal adherence to the Dutch guidelines for treatment with anti-TNF-alpha for rheumatoid arthritis patients. This seemed to be justified by the fact that a delayed response up to 6 months was shown. If treatment is continued despite a non-response at 3 months, this is only recommended in patients with at least a partial response (at least 0.6 DAS28 improvement).

Influence of age on the outcome of antitumour necrosis factor alpha therapy in rheumatoid arthritis.

OBJECTIVE: To investigate the influence of age on the effectiveness and tolerance of antitumour necrosis factor alpha (TNFalpha) therapy in rheumatoid arthritis (RA). METHODS: 730 patients of the Dutch Rheumatoid Arthritis Monitoring (DREAM) register were categorised into three groups according to their age at initiation of anti-TNFalpha therapy (<45, 45-65 and >65 years). Effectiveness of anti-TNFalpha therapy was primarily assessed by longitudinal analysis of the DAS28 during the first 12 months of treatment. RESULTS: Improvement in disease activity and physical functioning was significantly less in elderly patients, correcting for relevant confounders. Elderly patients reached the EULAR categories of good responders and remission less often than younger patients. Drug survival, co-medication use and tolerance were comparable between the three age groups. CONCLUSION: Anti-TNFalpha therapy significantly reduced disease activity in all age groups of patients; however, it appeared less effective in elderly compared with younger RA patients.

The tumour necrosis factor receptor superfamily member 1b 676T>G polymorphism in relation to response to infliximab and adalimumab treatment and disease severity in rheumatoid arthritis.

OBJECTIVE: To assess the effect of a functional polymorphism (676T>G, M196R) in the tumour necrosis factor receptor super family 1b (TNFSF1b) gene on disease activity, radiological joint damage and response to infliximab and adalimumab treatment in patients with rheumatoid arthritis (RA). METHODS: Two cohorts of patients with RA were genotyped for the 676T>G polymorphism (rs1061622) in exon 6 of the TNFSF1b gene by restriction fragment length polymorphism analysis. One cohort (n = 234) included patients from the Dutch Rheumatoid Arthritis Monitoring register with detailed information on their response to anti-TNF therapy (infliximab and adalimumab), the other cohort comprised patients from a long-term observational early inception cohort at our centre (n = 248). RESULTS: The 676T>G polymorphism was not associated with anti-TNF response after 3 or 6 months of treatment. Linear regression analysis showed no significant difference in the progression of radiological joint damage during the first 3 and 6 years of disease between the three genotype groups (TT, TG and GG). Additionally, no difference in mean disease activity between genotypes was seen after 3 and 6 years of disease. CONCLUSION: Despite its demonstrated functionality, the 676T>G polymorphism in the TNFSF1b gene does not have a major role in either the response to anti-TNF therapy or in the disease severity or radiological progression in RA.

The effectiveness and medication costs of three anti-tumour necrosis factor alpha agents in the treatment of rheumatoid arthritis from prospective clinical practice data.

AIM: to evaluate the effects of adalimumab, etanercept and infliximab on disease activity, functional ability and quality of life and the medication costs in a naturalistic design. METHODS: All patients from the Dutch Rheumatoid Arthritis Monitoring (DREAM) register starting on tumour necrosis factor (TNF)alpha-blocking agents for the first time were monitored and assessed by trained research nurses every 3 months. The primary outcome was the Disease Activity Score (DAS28) course over the 12 months follow-up, analysed by linear mixed models. Secondary outcomes were the Health Assessment Questionnaire (HAQ), EuroQol five dimensions (EQ-5D) and the Short-Form 36 items (SF36) scores, and medication-related total costs. RESULTS: The DAS28 and SF-36 physical component scale decreased in all three medication groups over 12 months, but the decrease was larger for adalimumab and etanercept in comparison to infliximab (p<0.001). The analyses of the HAQ and the EQ-5D scores showed the same (non-significant) trend, namely that at 12 months, the functionality and quality of life was better for adalimumab and etanercept patients. With regard to the medication costs, infliximab treatment resulted in significantly higher costs over the follow-up period than treatments with either adalimumab or etanercept. The comparison between adalimumab and etanercept showed a significant difference in the 12-month DAS28 course (p = 0.031). There were no additional indications for differences in effectiveness or costs between adalimumab and etanercept. CONCLUSION: The evaluation of the effectiveness and costs showed that adalimumab and etanercept are more or less equal and favourable compared to infliximab in the first year of treatment.

The efficacy of anti-TNF in rheumatoid arthritis, a comparison between randomised controlled trials and clinical practice.

BACKGROUND: Randomised controlled trials (RCTs) evaluating the efficacy of antagonists to tumour necrosis factor alpha (TNFalpha) showed high response percentages in the groups treated with active drugs. OBJECTIVE: To compare the efficacy of anti-TNF treatments for rheumatoid arthritis (RA) patients in RCTs and in daily clinical practice, with an emphasis on the efficacy for patients eligible and not eligible for RCTs of anti-TNF treatments. METHODS: First, randomised placebo-controlled trials written in English for etanercept, infliximab and adalimumab for patients with RA were selected by a systematic review. Second, the DREAM (Dutch Rheumatoid Arthritis Monitoring) register with patients starting for the first time on one of the TNF-blocking agents was used. Patient characteristics, doses of medication and co-medication as well as the ACR20 response percentages were compared between RCTs and DREAM data, stratified for trial eligibility. RESULTS: In 10 of 11 comparisons, the ACR20 response percentages were lower in daily clinical practice than in the RCT active drug group, which was significant in five of 11 comparisons. Only 34-79% of DREAM patients fulfilled the selection criteria for disease activity in the several RCTs examined. DREAM patients eligible for RCTs had higher response percentages than ineligible DREAM patients. ACR20 response percentages of eligible DREAM patients were comparable with the ACR20 response percentages of the RCT active drug group in 10 of 11 comparisons. CONCLUSION: The efficacy of TNF-blocking agents in RCTs exceeded the efficacy of these drugs in clinical practice. However, in clinical practice more patients with lower disease activity were treated with TNF-blocking agents compared with those treated in RCTs. For daily practice patients who were eligible for RCTs, responses were more similar to responses reached in RCTs.

Defining remission in psoriatic arthritis.

Driven in part by the introduction of highly effective agents, there has been growing interest in the overall therapeutic approach to patients with psoriatic arthritis (PsA). As with any form of arthritis, the goal of treatment for PsA would be to improve the outcome to the greatest extent possible. In other conditions, such as rheumatoid arthritis, recent discussions have centered on how best to define "remission." For patients with PsA, the heterogeneity among disease manifestations as well as the need to validate outcome measures make definition of remission challenging. In this paper we present a number of key principles and considerations critical to laying the groundwork for defining remission in PsA.

Performance of response criteria for assessing peripheral arthritis in patients with psoriatic arthritis: analysis of data from randomised controlled trials of two tumour necrosis factor inhibitors.

BACKGROUND: In recent clinical trials in patients with psoriatic arthritis (PsA), the response criteria and disease activity measures that have been used were those developed for rheumatoid arthritis. However, these have not yet been validated in PsA. OBJECTIVE: To compare the responsiveness and discriminative capacity of the psoriatic arthritis response criteria (PsARC), American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) response criteria and the Disease Activity Score (DAS) and core-set measures in patients with PsA and peripheral arthritis, using the data from two randomised placebo-controlled trials of tumour necrosis factor inhibitors. METHODS: In an infliximab trial, 104 patients with active PsA were randomised to receive placebo or infliximab for 16 weeks. In an etanercept trial, 60 patients with active PsA were randomised to receive placebo or etanercept for 12 weeks. Data from baseline and the end of the intervention phase were used from each study. Responsiveness was assessed using the standardised response mean and effect size. Capacity to discriminate between the active drug and placebo was assessed using t values or a chi2 test. Measures were ranked in order of their t value or chi2 value. RESULTS: The EULAR criteria performed better in discriminating the active drug from placebo than the ACR20 improvement criteria, which in turn performed better than the PsARC. It was also found that the pooled indices (DAS and DAS28) were generally more responsive, and performed better in discriminating active drug from placebo, than the single core-set measures. CONCLUSION: Response criteria and pooled indices developed for rheumatoid arthritis are useful for the assessment of arthritis in PsA clinical trials.

The cytoplasmic/transmembrane domain of dipeptidyl peptidase IV, a type II glycoprotein, contains an apical targeting signal that does not specifically interact with lipid rafts.

We investigated the signals involved in the apical targeting of dipeptidyl peptidase IV (DPP IV/CD26), an archetypal type II transmembrane glycoprotein. A secretory construct, corresponding to the DPP IV ectodomain, was first stably expressed in both the enterocytic-like cell line Caco-2 and the epithelial kidney MDCK cells. Most of the secretory form of the protein was delivered apically in MDCK cells, whereas secretion was 60% basolateral in Caco-2 cells, indicating that DPP IV ectodomain targeting is cell-type-dependent. A chimera (CTM-GFP) containing only the cytoplasmic and transmembrane domains of mouse DPP IV plus the green fluorescent protein was then studied. In both cell lines, this chimera was preferentially expressed at the apical membrane. By contrast, a secretory form of GFP was randomly secreted, indicating that GFP by itself does not contain cryptic targeting information. Comparison of the sequence of the transmembrane domain of DPP IV and several other apically targeted proteins does not show any consensus, suggesting that the apical targeting signal may be conformational. Neither the DPP IV nor the CTM-GFP chimera was enriched in lipid rafts. Together these results indicate that, besides the well-known raft-dependent apical targeting pathway, the fate of the CTM domain of DPP IV may reveal a new raft-independent apical pathway.

Transport and function of syntaxin 3 in human epithelial intestinal cells.

To follow the transport of human syntaxin (Syn) 3 to the apical surface of intestinal cells, we produced and expressed in Caco-2 cells a chimera made of the entire Syn3 coding sequence and the extracellular domain of the human transferrin receptor (TfR). This chimera (Syn3TfR) was localized to the apical membrane and was transported along the direct apical pathway, suggesting that this is also the case for endogenous Syn3. To test the potential role of Syn3 in apical transport, we overexpressed it in Caco-2 cells and measured the efficiency of apical and basolateral delivery of several endogenous markers. We observed a strong inhibition of apical delivery of sucrase-isomaltase (SI), an apical transmembrane protein, and of alpha-glucosidase, an apically secreted protein. No effect was observed on the basolateral delivery of Ag525, a basolateral antigen, strongly suggesting that Syn3 is necessary for efficient delivery of proteins to the apical surface of intestinal cells.

The small GTPase Rab6B, a novel Rab6 subfamily member, is cell-type specifically expressed and localised to the Golgi apparatus.

Members of the Rab subfamily of small GTPases play an important role in the regulation of intracellular transport routes. Rab6A has been shown to be a regulator of membrane traffic from the Golgi apparatus towards the endoplasmic reticulum (ER). Here, we report on the identification of a Rab6 isoform, termed Rab6B. The corresponding full-length cDNA was isolated from a Caco-2 cell library. The deduced amino acid sequence showed 91% identity with the Rab6A protein and revealed that sequence divergence is dispersed over a large region of the COOH-terminal domain. Rab6B is encoded by an independent gene which is located on chromosome 3 region q21-q23. In contrast to Rab6A whose expression is ubiquitous, northern blot analysis, immunohistochemistry, and immunofluorescence demonstrated that Rab6B is expressed in a tissue and cell-type specific manner. Rab6B is predominantly expressed in brain and the neuroblastoma cell line SK-N-SH. In brain, Rab6B was found to be specifically expressed in microglia, pericytes and Purkinje cells. Endogenous Rab6B localises to the Golgi apparatus and to ERGIC-53-positive vesicles. Comparable studies between Rab6A and Rab6B revealed distinct biochemical and cellular properties. Rab6B displayed lower GTP-binding activities and in overexpression studies, the protein is distributed over Golgi and ER membranes, whereas Rab6A is more restricted to the Golgi apparatus. Since the GTP-bound form of Rab6B (Rab6B Q72L) does interact with all known Rab6A effectors, including Rabkinesin-6, the results suggest a cell-type specific role for Rab6B in retrograde membrane traffic at the level of the Golgi complex.

Natural infection with schistosomes of the Schistosoma haematobium group in a dog in Zambia.

Post-mortem examination of an adult male Jack Russell dog from Zambia revealed that it was heavily infected with schistosomes. The dog had been admitted, with a history of retching, 4 days before its death. At necropsy, the liver was found to be enlarged, with multiple pin-point yellowish-white foci scattered diffusely throughout the organ. Multiple pin-point recent and old haemorrhages were seen on the mucosal surface of the gastrointestinal tract, particularly in the stomach and proximal duodenum. Large numbers of schistosome worm pairs and eggs were found in all mesenteric, gastric and hepatic veins. Histological examination of the intestines, mesenteric lymph nodes, liver, spleen, pancreas, stomach and lungs revealed numerous strongly fibrotic, encapsulated, epithelioid-giant cell granulomata containing dead, degenerating and viable eggs. A few examples of the Splendore-Hoeppli phenomenon were also detected. The eggs collected at necropsy had a terminal spine and an average length and breadth of 187.6+/-14.1 microm and 57. 3+/-4.1 microm, respectively. DNA analysis of female worms indicated that the schistosomes were either Schistosoma haematobium or a hybrid of Schistosoma mattheei and S. haematobium.

A FERM domain governs apical confinement of PTP-BL in epithelial cells.

PTP-BL is a cytosolic multidomain protein tyrosine phosphatase that shares homologies with several submembranous and tumor suppressor proteins. Here we show, by transient expression of modular protein domains of PTP-BL in epithelial MDCK cells, that the presence of a FERM domain in the protein is both necessary and sufficient for its targeting to the apical side of epithelial cells. Furthermore, immuno-electron microscopy on stable expressing MDCK pools, that were obtained using an EGFP-based cell sorting protocol, revealed that FERM domain containing fusion proteins are enriched in microvilli and have a typical submembranous location at about 10-15 nm from the plasma membrane. Immunofluorescence microscopy suggested colocalization of the FERM domain moiety with the membrane-cytoskeleton linker ezrin. However, at the electron microscopy level this colocalization cannot be confirmed nor can we detect a direct interaction by immunoprecipitation assays. Fluorescence recovery after photobleaching (FRAP) experiments show that PTP-BL confinement is based on a dynamic steady state and that complete redistribution of the protein may occur within 20 minutes. Our observations suggest that relocation is mediated via a cytosolic pool, rather than by lateral movement. Finally, we show that PTP-BL phosphatase domains are involved in homotypic interactions, as demonstrated by yeast two-hybrid assays. Both the highly restricted subcellular compartmentalization and its specific associative properties may provide the appropriate conditions for regulating substrate specificity and catalytic activity of this member of the PTP family.