Fascin-induced bundling protects actin filaments from disassembly by cofilin

Actin filament turnover plays a central role in shaping actin networks, yet the feedback mechanism between network architecture and filament assembly dynamics remains unclear. The activity of ADF/cofilin, the main protein family responsible for filament disassembly, has been mainly studied at the single filament level. This study unveils that fascin, by crosslinking filaments into bundles, strongly slows down filament disassembly by cofilin. We show that this is due to a markedly slower initiation of the first cofilin clusters, which occurs up to 100-fold slower on large bundles compared with single filaments. In contrast, severing at cofilin cluster boundaries is unaffected by fascin bundling. After the formation of an initial cofilin cluster on a filament within a bundle, we observed the local removal of fascin. Notably, the formation of cofilin clusters on adjacent filaments is highly enhanced, locally. We propose that this interfilament cooperativity arises from the local propagation of the cofilin-induced change in helicity from one filament to the other filaments of the bundle. Overall, taking into account all the above reactions, we reveal that fascin crosslinking slows down the disassembly of actin filaments by cofilin. These findings highlight the important role played by crosslinkers in tuning actin network turnover by modulating the activity of other regulatory proteins.

GFP-Tagged Protein Detection by Electron Microscopy Using a GBP-APEX Tool in Drosophila

In cell biology, detection of protein subcellular localizations is often achieved by optical microscopy techniques and more rarely by electron microscopy (EM) despite the greater resolution offered by EM. One of the possible reasons was that protein detection by EM required specific antibodies whereas this need could be circumvented by using fluorescently-tagged proteins in optical microscopy approaches. Recently, the description of a genetically encodable EM tag, the engineered ascorbate peroxidase (APEX), whose activity can be monitored by electron-dense DAB precipitates, has widened the possibilities of specific protein detection in EM. However, this technique still requires the generation of new molecular constructions. Thus, we decided to develop a versatile method that would take advantage of the numerous GFP-tagged proteins already existing and create a tool combining a nanobody anti-GFP (GBP) with APEX. This GBP-APEX tool allows a simple and efficient detection of any GFP fusion proteins without the needs of specific antibodies nor the generation of additional constructions. We have shown the feasibility and efficiency of this method to detect various proteins in Drosophila ovarian follicles such as nuclear proteins, proteins associated with endocytic vesicles, plasma membranes or nuclear envelopes. Lastly, we expressed this tool in Drosophila with the UAS/GAL4 system that enables spatiotemporal control of the protein detection.

Turning Squalene into Cationic Lipid Allows a Delivery of siRNA in Cultured Cells

Covalent binding of squalene to siRNA has already been shown to be an interesting way of delivering siRNA in vivo. Whether squalene derivatives could also be used to deliver siRNA in cells without covalent binding similar to usual transfection with cationic lipids is the question addressed in this article. Accordingly, we investigated the activity of two squalene derivatives bearing a quaternary ammonium head group and a guanidinium group, respectively. The second derivative displayed interesting properties for delivering siRNA into cells in vitro.

Influence of the internalization pathway on the efficacy of siRNA delivery by cationic fluorescent nanodiamonds in the Ewing sarcoma cell model

Small interfering RNAs (siRNAs) are powerful tools commonly used for the specific inhibition of gene expression. However, vectorization is required to facilitate cell penetration and to prevent siRNA degradation by nucleases. We have shown that diamond nanocrystals coated with cationic polymer can be used to carry siRNAs into Ewing sarcoma cells, in which they remain traceable over long periods, due to their intrinsic stable fluorescence. We tested two cationic polymers, polyallylamine and polyethylenimine. The release of siRNA, accompanied by Ewing sarcoma EWS-Fli1 oncogene silencing, was observed only with polyethylenimine. We investigated cell penetration and found that the underlying mechanisms accounted for these differences in behavior. Using drugs selectively inhibiting particular pathways and a combination of fluorescence and electronic microscopy, we showed that siRNA gene silencing occurred only if the siRNA:cationic nanodiamond complex followed the macropinocytosis route. These results have potential implications for the design of efficient drug-delivery vectors.

Abstract 1623: The spliceosome as a new therapeutic target for anticancer treatment

Background: Bioinformatics analyses of pathways that are differentially expressed between malignant and benign lesions could allow discovering new therapeutic targets. In the present study, we identified spliceosome assembly components as candidate target for cancer treatment. The spliceosome, an intracellular ribonucleoprotein complex, is involved in eukaryotic pre-mRNA processing by splicing out intronic nucleic acids.

Experimental procedures: Pathway analyses were done on exon and gene expression arrays datasets. Differential gene expression between malignant and benign lesions was applied to four public datasets. Small nuclear ribonucleoprotein E (SNRPE) downregulation was achieved by short interfering RNA technology in SKBr-3 and MDA-MB-231 human breast cancer cells. Functional effects of siRNA-induced knockdown of SNRPE expression on cell viability, cell cycle distribution and apoptosis were respectively determined using WST-1 assay, FACS analysis and annexin-V/7-AAD double-staining assay. Autophagy was investigated by electron microscopy (EM). We also evaluated alternative RNA splicing at the exon level using SpliceArray microarray.

Results: Pathway analyses with BioCarta database identified spliceosome assembly component (SAC) as the most differentially expressed pathway between breast malignant and benign lesions (permutation p=0.002). The differential expression of SAC was confirmed in four different public dataset on breast, ovarian, lung and skin cancers. Based on these data we investigated whether SNRPE, a component of spliceosome, could be a candidate target. Knockdown of SNRPE protein expression resulted in a high inhibition of SKBr-3 (70%) and MDA-MB-231 (48%) cell proliferation as compared to non-targeting siRNA-transfected cells. Splice array analyses suggested a deregulation of alternative splicing, together with a dramatic reduction of mTOR transcripts. mTOR downregulation, together with a decrease in phosphorylation of downstream protein in the mTOR pathway (i.e 4E-BP1) was confirmed by western blot analyses. We then investigated the mechanisms of cell death. siRNA-mediatd SNRPE knockdown was not found to induce typical apoptosis as annexin-V-positive cells were not detected. However, the presence of numerous vesicular organelle of autophagy revealed by EM is strongly amplified in SNRPE-transfected cells. This observed deregulation of the mTOR pathway in SNRPE-depleted cells might in part explain the induction of autophagy following SNRPE silencing.

Conclusion : Our data report that specific inactivation of SNRPE protein expression induces mTOR downregulation and autophagy in cancer cell lines, suggesting that the spliceosome could represent a new potential target that may open new perspectives in cancer therapy. Molecular mechanisms that lead to mTOR dowregulation by SNRPE extinction are being investigated.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1623. doi:10.1158/1538-7445.AM2011-1623

Multiple perforating and non perforating pilomatricomas in a patient with Churg-Strauss syndrome and Rubinstein-Taybi syndrome

We report an unusual association of multiple perforating and non-perforating pilomatricomas with Churg-Strauss syndrome, and a dysmorphic syndrome evocative of Rubinstein-Taybi syndrome. These syndromes may be independent, but these rare diseases and genetic abnormalities may be linked together.

[Intravascular papillary endothelial hyperplasia: multiple lesions appearing in the course of treatment with interferon beta]

INTRODUCTION

Intravascular papillary endothelial hyperplasia is a benign and rare vascular lesion. We report a case of multiple vascular lesions of the hand following 3 months treatment with beta-interferon injections for multiple sclerosis.

OBSERVATION

A 50 year-old man had multiple vascular nodules of the hands. He was treated with beta interferon injections for multiple sclerosis for 3 months. Histology showed typical changes of intravascular papillary endothelial hyperplasia: papillary endothelial proliferation in a dilated cavity associated with thrombosis.

DISCUSSION

Intravascular papillary endothelial hyperplasia is a benign and rare vascular lesion usually presenting as a simple nodule. It may be painful. Diagnosis is histologic, characterized by papillary endothelial proliferation associated with a thrombus within a vessel. It may be confused with hemangiosarcoma. Treatment is surgical and recurrence after treatment is rare. Intravascular papillary endothelial hyperplasia is generally considered as an unusual form of thrombus organization. Intravascular papillary endothelial hyperplasia is divided into two groups: a pure form occurring within a dilated vessel and a mixed form appearing in benign vascular lesions. The originality of this case is the rarity and the multiplicity of the lesions. The possible pathogenesis of interferon-induced cutaneous vascular lesions is discussed.

[Photoaggravated contact allergy and contact photoallergy caused by ketoprofen: 19 cases]

INTRODUCTION

Between September 1994 and September 1999, we observed 19 cases of photoaggraved contact allergy or contact photoallergy to ketoprofen (non steroidal anti-inflammatory derived from arylpropionic acid). We present a clinical and photobiological retrospective study of these 19 cases with investigation of cross-reactivity between benzophenone-containing molecules.

PATIENTS AND METHODS

On clinical level, we investigated the type of eruption, the delay of appearance, the initial area of eruption and areas of diffusion. Phototesting included patchtests and photopatchtests performed with the gel containing ketoprofen (17 patients), ketoprofen 2 p. 100 petrolatum (14 patients), fenofibrate 10 p. 100 petrolatum and 10 p. 100 water (15 patients), 3 benzophenones (19 patients): oxybenzone 10 p. 100 petrolatum, mexenone 2 p. 100 petrolatum, sulisobenzone 10 p. 100 petrolatum and the other arylpropionic derivatives (4 patients). Three identical series were applied: one was irradiated with 3/4 polychromatic minimal erythematosus dose, a second was irradiated with UVA 13 J/cm2 until January 1997, then 5 J/cm2, the third series was not irradiated (control series).

RESULTS

Patients were 9 men and 10 women with an average age of 41.2 years. The type of eruption was an eczema. The delay of appearance of the eruption was one day to 3 months. For 10 patients, the delay was between 4 and 18 days. The eruption was localized to the application area in 1 case, to the application area then to the same contralateral area in 3 cases, to the application area then to all photoexposed areas in 13 cases, to the application area then to the photoexposed areas and then to non-sun-exposed areas in 2 cases. Evolution showed prolonged photosensitivity in 3 cases after withdrawal of the contact and the contact photoallergy to ketoprofen was severe. Gel-containing ketoprofen photopatchtests showed 9 photoaggravated contact allergy, 6 contact photoallergy and 2 contact allergy. Ketoprofen photopatchtests showed 12 contact photoallergy and 2 photoaggraved contact allergy. Tiaprofenic acid photopatchtests were positive in all performed cases (4/4), but photopatchtests with the other arylpropionic derivatives, without benzophenone structure, were negative. Fenofibrate photopatchtests were always positive (15/15). Benzophenones photopatchtests only showed 4 cases of contact photoallergy to oxybenzone (4/19). In 68 p. 100 of cases, patients presented a contact allergy or photoallergy to fragrances.

CONCLUSIONS

This study shows the actual frequency of contact allergy and contact photoallergy to ketoprofen with a higher frequency of contact photoallergy. Thus, photopatchtesting is essential. In cases of contact photoallergy to ketoprofen, ketoprofen, tiaprofenic acid but not the other arylpropionic derivatives, fenofibrate and benzophenones have to be withdrawn.

Contribution of a pacemaker bradycardia detection algorithm in the study of patients with carotid sinus syndrome

While carotid sinus syndrome (CSS) is often suspected as a cause of syncope in the elderly, whether it represents an indication for cardiac pacing may remain uncertain. Bradycardia algorithms included in pacemakers are now able to establish a precise relationship between spontaneous asystole and occurrence of symptoms and strengthen the indication for permanent pacing. This study included seven men and three women (70.5 +/- 7.3 years of age) who, over an average period of 54.1 +/- 17 months, had suffered from syncope (12.6 episodes/patient) and presyncope (11.2 episodes/patient) attributed to pure cardioinhibition (2 patients) or mixed CSS (8 patients). Other sources of symptoms were excluded by thorough clinical evaluations, including Holter monitoring, echocardiography, and electrophysiological testing. All patients received a CHORUS 6234 pacemaker, the memory of which includes a dedicated bradycardia detection algorithm capable of storing atrial and ventricular chains, and date and time of the last ten pauses and/or bradycardic events. After a initial period of 14.7 +/- 8 months, during which symptoms were suppressed, the bradycardia algorithm was activated. From then on, a cumulative increase in the number of patients presenting with diurnal pauses was measured (1 month, n = 0; 3 months, n = 6; 9 months, n = 7; 2 years, n = 8). Fourteen episodes of diurnal asystole were recorded. The mean duration of the longest episodes of spontaneous ventricular standstill was 6,319 +/- 1,615 ms and was due to sinoatrial block (n = 7), atrioventricular block (n = 5), and a combination of both (n = 2). In conclusion, activation of the CHORUS bradycardia algorithm allowed confirmation of the appropriateness of permanent pacing in a majority of patients suffering from CSS.

[Short and medium-term outcome after radiofrequency ablation of the atrioventricular junction]

The aim of this retrospective study was to assess short and long-term mortality and morbidity after radiofrequency ablation of the atrioventricular junction in patients with supraventricular arrhythmias resistant to treatment. This cooperative series included 91 patients (47 men, mean age 68 +/- 9 years). The arrhythmia was paroxysmal in 56% of cases. The mean duration of symptoms was 67 +/- 61 months and 45 patients (49.4%) were in the NYHA Classes III and IV. An escape rhythm was present in 58 patients with a mean frequency of 39 +/- 9/min. Early complications were observed in 5 patients (venous thromboses, pulmonary embolism, mild pericardial effusion and haemothorax). The hospital mortality was 4 patients (4.4%). Death was of cardiac origin in 1 case (cardiac failure). The mean follow-up of patients was 14.5 +/- 8.6 months. Eleven patients died during this period, 8 of cardiac causes: cardiac failure (3 cases), sudden death (3 cases), thrombosis of a valve prosthesis (1 patient) and major electrolyte disturbances causing loss of stimulation in 1 case. Six patients had recurrences. Long-term morbidity was either related to cardiac pacing (3 cases) or cardiac failure (3 cases). Thirteen patients were in NYHA Classes III or IV at the end of follow-up. The authors conclude that radiofrequency ablation at the atrioventricular junction is an effective method of treating resistant supraventricular arrhythmias. Complications are not frequent but mortality appears to be high, probably due to the presence of advanced cardiac disease in the majority of cases. Sudden death seems to be rare and unrelated to pacing defects.