Implantable loop recorders for assessment of syncope: increased diagnostic yield and less adverse outcomes with the latest generation devices.

AIM: Aim of the study was to compare the diagnostic yield of implantable loop recorders (ILR) of two successive generations for the assessment of syncope. METHODS: Data on patients who had undergone ILR implantation for unexplained syncope in four Italian public hospitals were retrospectively acquired from the Medtronic Clinical Service database. After implantation, routine follow-up examinations were performed every 90 days, while urgent examinations were carried out in the event of syncope recurrence. RESULTS: The following findings were regarded as diagnostic: ECG documentation of a syncope recurrence; documentation of any of the arrhythmias listed by the current guidelines as diagnostic findings even if asymptomatic. Between November 2002 and March 2010, 107 patients received an ILR (40 Medtronic Reveal® Plus; 67 Medtronic Reveal® DX/XT) and underwent at least one follow-up examination. Diagnoses were made in 7 (17.5%) and 24 (35.8%) (P=0.043) patients, with a median time of 228 and 65 days, respectively. Three (42.9%) and 21 (87.5%) (P=0.029) diagnoses were based on automatically detected events, while adverse outcomes occurred in 6 and in 1 (P=0.01) patients, respectively. CONCLUSION: Our results show that the new-generation device offer a higher diagnostic yield, mainly as a result of its improved automatic detection function, and is associated with fewer adverse outcomes.

A family of Shc related proteins with conserved PTB, CH1 and SH2 regions.

Shc proteins are targets of activated tyrosine kinases and have been implicated in the transmission of activation signals to Ras. Upon phosphorylation, Shc proteins form stable complexes with cellular tyrosine-phosphorylated proteins and with the Grb2 adaptor protein. Two Shc isoforms of 52 and 46 kDa have been characterized. They share a C-terminal SH2 domain, a proline- and glycine-rich region (collagen homologous region 1; CH1) and a N-terminal phospho-tyrosine binding domain (PTB). We report her ethe initial characterization of two Shc related human cDNAs: ShcB and ShcC. The ShcB and ShcC cDNAs code for proteins that are highly similar and share the same modular organization as Shc. PTB and SH2 domains of ShcB and ShcC have similar binding specificities in vitro and bind to activated EGFR in a phosphotyrosine-dependent manner. Based on these findings we propose to rename Shc as ShcA. Anti-ShcB and anti-ShcC antibodies recognize specific polypeptides of 52, 47 kDa (ShcB) and 54 kDa (ShcC) in mammalian cells. Since these two genes are predominantly expressed in specific brain tissues, these Shc family members may be involved in cell type-specific signaling, in the nervous system.

Inhibition of CD4/p56lck signaling by a dominant negative mutant of the Shc adaptor protein.

T-cell antigen receptor stimulation results in phosphorylation of the SH2 containing Shc proteins and recruitment of the Grb2/mSos complex suggesting that Shc proteins are involved in transducing T-cell activating signals to Ras. We have measured the effects of the isolated Shc-SH2 domain and the dominant negative RasN17 protein on activation of the T-cell specific transcription factor NF-AT. The isolated Shc-SH2 domain was designed to compete with endogenous Shc binding to upstream tyrosine phosphorylated proteins and to interfere with coupling to regulators of Ras activation. We have demonstrated that both the Shc-SH2 domain and the RasN17 protein significantly inhibited NF-AT activation by the CD4 coreceptor and the CD4 associated tyrosine kinase p56lck. In contrast, only the RasN17 protein reduced NF-AT activation by the TCR/CD3 complex. Furthermore, tyrosine kinase activity and p56lck protein were found in complexes immunoprecipitated with Shc specific antisera after CD4 triggering but not after CD3 triggering. These results indicate that both CD4 and CD3 signal to Ras and that this signaling is mediated by independent pathways of activation of the Shc adaptor protein.

Overexpression of Shc proteins potentiates the proliferative response to the granulocyte-macrophage colony-stimulating factor and recruitment of Grb2/SoS and Grb2/p140 complexes to the beta receptor subunit.

The high affinity receptor for GM-CSF consists of a unique alpha subunit and a beta subunit that is shared with receptors for IL-3 and IL-5. Activation of GM-CSF receptor (GMR) triggers two distinct cytoplasmic signalling pathways, JAK2 and Ras, and is sufficient to maintain proliferation of growth factor-dependent cell lines. Shc proteins are phosphorylated upon activation of GMR and may be involved in the transmission of GM-CSF signals to Ras. To define the role of Shc proteins in cells stimulated with GM-CSF, we investigated both the network of interactions that involve Shc after GM-CSF stimulation and the effects of overexpressing Shc proteins on the proliferative response to GM-CSF. Two cytoplasmic complexes, Grb2/Sos and Grb2/p140 bind through the Grb2 SH2 domain to phosphorylated Shc, and are thereby recruited to the beta subunit. Both complexes are stable, even in the absence of ligand, and depend on the direct association of p140 and Sos respectively with the SH3 domains of Grb2. p140 is an uncharacterized protein constitutively phosphorylated on tyrosine and, in its Grb2-bound form, expressed only in hematopoietic cells, the oligomeric complex formed by phosphorylated beta subunit-phosphorylated Shc-Grb2-SoS-p140 is also induced by IL-3 and L-5 stimulation of growth-factor dependent cell lines. Overexpression of wild-type Shc proteins in growth factor-dependent cells increases both MAP kinase activation and proliferation in response to GM-CSF. These effects require the association of Shc with Grb2. Taken together these results indicate that phosphorylation of Shc proteins is a crucial step in the transmission of GM-CSF proliferative stimuli, since it creates a high affinity binding site for the Grb2/SoS complex, whose function is to activate Ras and, for the Grb2/p140 complex, whose function remains unknown.

Shc products are substrates of erbB-2 kinase.

The shc genes encodes three widely expressed proteins of 46, 52 and 66 kDa. Overexpression of p46shc and p52shc in NIH3T3 fibroblasts induces a tumorigenic phenotype. Shc products are phosphorylated on tyrosine by the activated epidermal growth factor receptor (EGFR) and become physically associated with EGFR via their SH2 domain. Thus Shc oncoproteins may play a role in mitogenic signal transduction. Here we report that Shc products are substrates also of the erbB-2 kinase and form complexes with the erbB-2 product in intact cells. In vitro, the bacterially expressed Shc SH2 domain is sufficient to reconstitute the high affinity Shc/erbB-2 interaction. The erbB-2 region required for Shc binding was narrowed down to the most COOH-terminal 179 residues of gp185erbB-2; within this region, phosphorylation of one or more of the erbB-2 autophosphorylation sites is required for Shc/gp185erbB-2 complex formation as well as optimal phosphorylation of Shc products by the erbB-2 kinase. Thus, Shc proteins may play a role in signal transduction by gp185erbB-2.