Proteasome is the main intracellular organelle involved in the proteolytic degradation of abnormal, misfolded, damaged or oxidized proteins (1, 2). Maintenance of proteasome activity was implicated... Show moreProteasome is the main intracellular organelle involved in the proteolytic degradation of abnormal, misfolded, damaged or oxidized proteins (1, 2). Maintenance of proteasome activity was implicated in many key cellular processes, like cell's stress response (3), cell cycle regulation and cellular differentiation (4) or in immune system response (5). The dysfunction of the ubiquitin-proteasome system has been related to the development of tumors and neurodegenerative diseases (4, 6). Additionally, a decrease in proteasome activity was found as a feature of cellular senescence and organismal aging (7, 8, 9, 10). Here, we present a method to measure ubiquitin-proteasome activity in living cells using a GFP-dgn fusion protein. To be able to monitor ubiquitin-proteasome activity in living primary cells, complementary DNA constructs coding for a green fluorescent protein (GFP)-dgn fusion protein (GFP-dgn, unstable) and a variant carrying a frameshift mutation (GFP-dgnFS, stable (11)) are inserted in lentiviral expression vectors. We prefer this technique over traditional transfection techniques because it guarantees a very high transfection efficiency independent of the cell type or the age of the donor. The difference between fluorescence displayed by the GFP-dgnFS (stable) protein and the destabilized protein (GFP-dgn) in the absence or presence of proteasome inhibitor can be used to estimate ubiquitin-proteasome activity in each particular cell strain. These differences can be monitored by epifluorescence microscopy or can be measured by flow cytometry. Show less
OBJECTIVE Prevalence of overweight in children is increasing, causing various health problems. This study aims to establish growth references for weight and to assess the prevalence rates of... Show moreOBJECTIVE Prevalence of overweight in children is increasing, causing various health problems. This study aims to establish growth references for weight and to assess the prevalence rates of overweight and obesity in a nationwide sample of Dutch children with Down syndrome (DS), taking into account the influence of comorbidity. METHODS In 2009, longitudinal growth data from Dutch children with trisomy 21 who were born after 1982 were retrospectively collected from medical records of 25 Dutch regional specialized DS centers. "Healthy" was defined as not having concomitant disorders or having only a mild congenital heart defect. Weight and BMI references were calculated by using the LMS method, and prevalence rates of overweight and obesity by using cutoff values for BMI as defined by the International Obesity Task Force. Differences in prevalence rates were tested by multilevel logistic regression analyses to adjust for gender and age. RESULTS Growth data of 1596 children with DS were analyzed. Compared with the general Dutch population, healthy children with DS were more often overweight (25.5% vs 13.3% in boys, and 32.0% vs 14.9% in girls) and obese (4.2% vs 1.8%, and 5.1% vs 2.2%, respectively). Prevalence rates of overweight between DS children with or without concomitant disorders did not vary significantly. CONCLUSIONS Dutch children with DS have alarmingly high prevalence rates of overweight and obesity during childhood and adolescence. Health care professionals should be aware of the risk of overweight and obesity in children with DS to prevent complications. Show less
In recent years a number of the genes that regulate muscle formation and maintenance in higher organisms have been identified. Studies employing invertebrate and vertebrate model organisms have... Show moreIn recent years a number of the genes that regulate muscle formation and maintenance in higher organisms have been identified. Studies employing invertebrate and vertebrate model organisms have revealed that many of the genes required for early mesoderm specification are highly conserved throughout evolution. Less is known about the molecules that mediate the steps subsequent to myogenesis, e. g. myotube guidance and attachment to tendon cells. We use the stereotypic pattern of the Drosophila embryonic body wall musculature in genetic approaches to identify novel factors required for muscle attachment site selection. Here, we show that Wnt5 is needed in this process. The lateral transverse muscles frequently overshoot their target attachment sites and stably attach at novel epidermal sites in Wnt5 mutant embryos. Restoration of WNT5 expression in either the muscle or the tendon cell rescues the mutant phenotype. Surprisingly, the novel attachment sites in Wnt5 mutants frequently do not express the Stripe (SR) protein which has been shown to be required for terminal tendon cell differentiation. A muscle bypass phenotype was previously reported for embryos lacking the WNT5 receptor Derailed (DRL). drl and Wnt5 mutant embryos also exhibit axon path finding errors. DRL belongs to the conserved Ryk receptor tyrosine kinase family which includes two other Drosophila orthologs, the Doughnut on 2 (DNT) and Derailed-2 (DRL-2) proteins. We generated a mutant allele of dnt and find that dnt, but not Drl-2, mutant embryos also show a muscle bypass phenotype. Genetic interaction experiments indicate that drl and dnt act together, likely as WNT5 receptors, to control muscle attachment site selection. These results extend previous findings that at least some of the molecular pathways that guide axons towards their targets are also employed for guidance of muscle fibers to their appropriate attachment sites. Show less
UNLABELLED BACKGROUND Chemokine receptor CXCR4, together with its ligand CXCL12, plays critical roles in cancer progression, including growth, metastasis and angiogenesis. Ewing sarcoma is a... Show moreUNLABELLED BACKGROUND Chemokine receptor CXCR4, together with its ligand CXCL12, plays critical roles in cancer progression, including growth, metastasis and angiogenesis. Ewing sarcoma is a sarcoma with poor prognosis despite current therapies, particularly for patients with advanced-stage disease. Lungs and bone (marrow), organs of predilection for (primary/metastatic) Ewing sarcoma, represent predominant CXCL12 sources. METHODS To gain insight into the role of the CXCR4-CXCL12 axis in Ewing sarcoma, CXCR4, CXCL12 and hypoxia-inducible factor-1α protein expression was studied in therapy-naïve and metastatic tumors by immunohistochemistry. CXCR4 function was assessed in vitro, by flow cytometry and proliferation/ cell viability assays, in the presence of recombinant CXCL12 and/or CXCR4-antagonist AMD3100 or under hypoxic conditions. RESULTS Whereas CXCR4 was predominantly expressed by tumor cells, CXCL12 was observed in both tumor and stromal areas. Survival analysis revealed an (expression level-dependent) negative impact of CXCR4 expression (p < 0.04). A role for the CXCR4-CXCL12 axis in Ewing sarcoma growth was suggested by our observations that i) CXCR4 expression correlated positively with tumor volume at diagnosis (p = 0.013), ii) CXCL12 was present within the microenvironment of virtually all cases, iii) CXCL12 induced proliferation of CXCR4-positive Ewing sarcoma cell lines, which could be abrogated by AMD3100. CXCR4 expression was not correlated with occurrence of metastatic disease. Also, therapy-naïve tumors demonstrated higher CXCR4 expression as compared to metastases (p = 0.027). Evaluation of in vivo hypoxia-inducible factor-1α expression and culture of cells under hypoxic conditions revealed no role for hypoxia in CXCR4 expression. CONCLUSIONS Together, our results imply a crucial role for the CXCR4-CXCL12 axis in auto- and/or paracrine growth stimulation. Integration of CXCR4-targeting strategies into first- and/or second-line treatment regimens may represent a promising treatment option for Ewing sarcoma. Show less
Autoantibodies against muscle-specific kinase (MuSK), a protein essential for clustering of acetylcholine receptors at the neuromuscular junction (NMJ), are detected in the serum of a proportion of... Show moreAutoantibodies against muscle-specific kinase (MuSK), a protein essential for clustering of acetylcholine receptors at the neuromuscular junction (NMJ), are detected in the serum of a proportion of myasthenia gravis (MG) patients. In most MuSK MG patients the anti-MuSK activity resides in the IgG4 subclass, a minor IgG component without very well-defined, but presumably anti-inflammatory, roles in immunity. In recent years, several animal model studies showed that anti-MuSK autoantibodies can cause muscle weakness by directly affecting NMJ function and, therefore, are likely not simply bystander disease markers in MuSK MG patients. In passive transfer mice, we recently provided proof that MuSK MG patient IgG4 is severely myasthenogenic, causing functional defects at NMJs. Against the clinical, serological, and pharmacological background of MuSK MG, here we discuss the MuSK MG animal models generated by our laboratory and others that have been instrumental in elucidating the etiological and pathophysiological roles of anti-MuSK antibodies. Show less
