Thoracic ultrasonography: A new method for the work-up of patients with dyspnea().

OBJECTIVE: Differential diagnosis of dyspnea is vital for the management of respiratory failure, where routine parameters can now be integrated with thoracic ultrasound data. The objective of this study was to evaluate the validity and accuracy of this approach in a department of internal medicine. MATERIALS AND METHODS: We enrolled 152 patients consecutively hospitalized with a diagnosis of dyspnea. After clinical evaluation, chest radiography, biochemical assays (NT-proBNP), and emergency treatment, patients underwent ultrasound examination of the lungs. Results were considered positive if the total number of lines B was higher than 8. The ultrasound examination and NT-proBNP assay were repeated after 48 h. The gold standard was the clinical diagnosis of heart failure made by medical experts in accordance with AHA guidelines. RESULTS: The group of patients with positive ultrasound findings had a higher frequency of heart failure diagnoses (X(2) 92.5, p < 0.005) and significantly higher values of NT-proBNP (10,384 ng/l vs 3889 ng/l, p < 0.05). Moreover, the decrease in the number of B lines at 48 h was significantly greater (p < 0.005) among patients treated for heart failure. There were no significant changes in the values of NT-proBNP (p = 0.37). DISCUSSION: In conclusion we have shown that even in a department of internal medicine, lung ultrasonography is a useful tool for diagnosing respiratory insufficiency and monitoring its response to therapy.

Thrombotic events in patients with congenital prekallikrein deficiency: a critical evaluation of all reported cases.

The occurrence of thrombotic events in patients with congenital bleeding conditions has received considerable attention in recent years. The same is true for asymptomatic defects of factors of the contact phase of blood coagulation, mainly FXII. Anecdotal reports on thrombosis in patients with prekallikrein deficiency have occasionally been reported. These involved both arterial and venous thrombosis. The purpose of the present article is to analyze the stories and the clinical pictures of all 75 cases of prekallikrein deficiency published so far. Among these patients were 9 with thrombosis, 6 arterial (myocardial infarction and ischemic stroke) and 3 venous (deep vein thrombosis with or without pulmonary embolism). In 6 cases acquired thrombosis risk factors were present; in 2 cases no associated risk factors were present and in 1 case no information was supplied in this regard. One patient who presented both a stroke and a pulmonary embolism had a fatal outcome. The article clearly indicates that prekallikrein deficiency does not protect from thrombosis in spite of the severe in vitro coagulation defect.

Congenital combined defects of factor VII: a critical review.

Factor VII deficiency is the least rare among uncommon congenital coagulation disorders. The majority of cases are isolated deficiencies. In some cases, FVII deficiency has been found to be associated with the deficiency in another coagulation factor or with non-coagulation-related abnormalities or defects. The evaluation of all published studies on the subject has shown that the FVII defect has been reported in association with FV, FVIII, FIX, FX, FXI and protein C defects. Furthermore, FVII deficiency has been described in association with bilirubin metabolism disorders, mental retardation, microcephaly, epicanthus, cleft palate and persistence of ductus arteriosus. The most interesting association appears to be that with FX. This has been shown to be due to a deletion in part of the long arm of chromosome 13. This arm contains genes coding for both FVII and FX. Interestingly, this combined coagulation defect has been found to be associated with carotid body tumors and several other malformations. Combined defects in blood coagulation often create diagnostic difficulties since results cannot be explained if a single factor deficiency is assumed. For example the combined FVII and FX defect yields a rather peculiar laboratory picture (prolonged prothrombin time and partial thromboplastin time, but normal thrombin time) that could suggest FII or FV or FX single deficiency and not FVII deficiency, indicating the need for specific factor assays whenever data are confusing. Finally, the elevated incidence of mental and skeletal malformations present in these combined defects indicates the need for a careful evaluation of all these patients lest some aspects of the defect are missed.

Specific inhibition of serine- and arginine-rich splicing factors phosphorylation, spliceosome assembly, and splicing by the antitumor drug NB-506.

Specific phosphorylation of serine- and arginine-rich pre-mRNA splicing factors (SR proteins) is one of the key determinants regulating splicing events. Several kinases involved in SR protein phosphorylation have been identified and characterized, among which human DNA topoisomerase I is known to have DNA-relaxing activity. In this study, we have investigated the mechanism of splicing inhibition by a glycosylated indolocarbazole derivative (NB-506), a potent inhibitor of both kinase and relaxing activities of topoisomerase I. NB-506 completely inhibits the capacity of topoisomerase I to phosphorylate, in vitro, the human splicing factor 2/alternative splicing factor (SF2/ASF). This inhibition is specific, because NB-506 does not demonstrate activity against other kinases known to phosphorylate SF2/ASF such as SR protein kinase 1 and cdc2 kinase. Importantly, HeLa nuclear extracts competent in splicing but not splicing-deficient cytoplasmic S100 extracts treated with the drug fail to phosphorylate SF2/ASF and to support splicing of pre-mRNA substrates containing SF2/ASF-target sequences. Native gel analysis of splicing complexes revealed that the drug affects the formation of the spliceosome, a dynamic ribonucleoprotein structure where splicing takes place. In the presence of the drug, neither pre-spliceosome nor spliceosome is formed, demonstrating that splicing inhibition occurs at early steps of spliceosome assembly. Splicing inhibition can be relieved by adding phosphorylated SF2/ASF, showing that extracts treated with NB-506 lack a phosphorylating activity required for splicing. Moreover, NB-506 has a cytotoxic effect on murine P388 leukemia cells but not on P388CPT5 camptothecin-resistant cells that carry two point mutations in conserved regions of topoisomerase I gene (Gly361Val and Asp709Tyr). After drug treatment, P388 cells accumulated hypophosphorylated forms of SR proteins and polyadenylated RNA in the nucleus. In contrast, neither SR protein phosphorylation nor polyadenylated mRNA distribution was affected in P388 CPT5-treated cells. Consistently, NB506 treatment altered the mRNA levels and/or splicing pattern of several tested genes (Bcl-X, CD 44, SC35, and Sty) in P388 cells but not in P388 CPT5 cells. The study shows for the first time that indolocarbazole drugs targeting topoisomerase I can affect gene expression by modulating pre-mRNA splicing through inhibition of SR proteins phosphorylation.

Distinctive features of Drosophila alternative splicing factor RS domain: implication for specific phosphorylation, shuttling, and splicing activation.

The human splicing factor 2, also called human alternative splicing factor (hASF), is the prototype of the highly conserved SR protein family involved in constitutive and regulated splicing of metazoan mRNA precursors. Here we report that the Drosophila homologue of hASF (dASF) lacks eight repeating arginine-serine dipeptides at its carboxyl-terminal region (RS domain), previously shown to be important for both localization and splicing activity of hASF. While this difference has no effect on dASF localization, it impedes its capacity to shuttle between the nucleus and cytoplasm and abolishes its phosphorylation by SR protein kinase 1 (SRPK1). dASF also has an altered splicing activity. While being competent for the regulation of 5' alternative splice site choice and activation of specific splicing enhancers, dASF fails to complement S100-cytoplasmic splicing-deficient extracts. Moreover, targeted overexpression of dASF in transgenic flies leads to higher deleterious developmental defects than hASF overexpression, supporting the notion that the distinctive structural features at the RS domain between the two proteins are likely to be functionally relevant in vivo.

Recognition of exonic splicing enhancer sequences by the Drosophila splicing repressor RSF1.

The Drosophila repressor splicing factor 1 (RSF1) comprises an N-terminal RNA-binding region and a C-terminal domain rich in glycine, arginine and serine residues, termed the GRS domain. Recently, RSF1 has been shown to antagonize splicing factors of the serine/arginine-rich (SR) family and it is, therefore, expected to play a role in processing of a subset of Drosophila pre-mRNAs through specific interactions with RNA. To investigate the RNA-binding specificity of RSF1, we isolated RSF1-binding RNAs using an in vitro selection approach. We have identified two RNA target motifs recognized by RSF1, designated A (CAACGACGA)- and B (AAACGCGCG)-type sequences. We show here that the A-type cognate sequence behaves as an SR protein-dependent exonic splicing enhancer. Namely, three copies of the A-type ligand bind SR proteins, stimulate the efficiency of splicing of reporter pre-mRNAs several fold and lead to inclusion of a short internal exon both in vitro and in vivo. However, three copies of a B-type ligand were much less active. The finding that RSF1 acts as a potent repressor of pre-mRNA splicing in vitro led us to propose that the equilibrium between a limited number of structurally-related general splicing activators or repressors, competing for common or promiscuous binding sites, may be a major determinant of the underlying mechanisms controlling many alternative pre-mRNA process-ing events.

Antagonism between RSF1 and SR proteins for both splice-site recognition in vitro and Drosophila development.

Specific recognition of splice sites within metazoan mRNA precursors (pre-mRNAs) is a potential stage for gene regulation by alternative splicing. Splicing factors of the SR protein family play a major role in this regulation, as they are required for early recognition of splice sites during spliceosome assembly. Here, we describe the characterization of RSF1, a splicing repressor isolated from Drosophila, that functionally antagonizes SR proteins. Like the latter, RSF1 comprises an amino-terminal RRM-type RNA-binding domain, whereas its carboxy-terminal part is enriched in glycine (G), arginine (R), and serine (S) residues (GRS domain). RSF1 induces a dose-sensitive inhibition of splicing for several reporter pre-mRNAs, an inhibition that occurs at the level of early splicing complexes formation. RSF1 interacts, through its GRS domain, with the RS domain of the SR protein SF2/ASF and prevents the latter from cooperating with the U1 small nuclear ribonucleoprotein particle (U1 snRNP) in binding pre-mRNA. Furthermore, overproduction of RSF 1 in the fly rescues several developmental defects caused by overexpression of the splicing activator SR protein B52/ SRp55. Therefore, RSF1 may correspond to the prototypical member of a novel family of general splicing repressors that selectively antagonize the effect of SR proteins on 5' splice-site recognition.

The C-terminal domain but not the tyrosine 723 of human DNA topoisomerase I active site contributes to kinase activity.

Human DNA topoisomerase I not only has DNA relaxing activity, but also splicing factors phosphorylating activity. Topo I shows strong preference for ATP as the phosphate donor. We used photoaffinity labeling with the ATP analogue [alpha-32P] 8-azidoadenosine-5'-triphosphate combined with limited proteolysis to characterize Topo I domains involved in ATP binding. The majority of incorporated analogue was associated with two fragments derived from N-terminal and C-terminal regions of Topo I, respectively. However, mutational analysis showed that deletion of the first 138 N-terminal residues, known to be dispensable for topoisomerase activity, did not change the binding of ATP or the kinase activity. In contrast, deletion of 162 residues from the C-terminal domain was deleterious for ATP binding, kinase and topoisomerase activities. Furthermore, a C-terminal tyrosine 723 mutant lacking topoisomerase activity is still able to bind ATP and to phosphorylate SF2/ASF, suggesting that the two functions of Topo I can be separated. These findings argue in favor of the fact that Topo I is a complex enzyme with a number of potential intra-cellular functions.

Interaction between the N-terminal domain of human DNA topoisomerase I and the arginine-serine domain of its substrate determines phosphorylation of SF2/ASF splicing factor.

Human DNA topoisomerase I, known for its DNA-relaxing activity, is possibly one of the kinases phosphorylating members of the SR protein family of splicing factors, in vivo. Little is known about the mechanism of action of this novel kinase. Using the prototypical SR protein SF2/ASF (SRp30a) as model substrate, we demonstrate that serine residues phosphorylated by topo I/kinase exclusively located within the most extended arginine-serine repeats of the SF2/ASF RS domain. Unlike other kinases such as cdc2 and SRPK1, which also phosphorylated serines at the RS domain, topo I/kinase required several SR dipeptide repeats. These repeats possibly contribute to a versatile structure in the RS domain thereby facilitating phosphorylation. Furthermore, far-western, fluorescence spectroscopy and kinase assays using the SF2/ASF mutants, demonstrated that kinase activity and binding were tightly coupled. Since the deletion of N-terminal 174 amino acids of Topo I destroys SF2/ASF binding and kinase activity but not ATP binding, we conclude that at least two distinct domains of Topo I are necessary for kinase activity: one in the C-terminal region contributing to the ATP binding site and the other one in the N-terminal region that allows binding of SF2/ASF.