Differential effects of adenosine on pulmonary vein ectopy after pulmonary vein isolation: implications for arrhythmogenesis.

BACKGROUND: The mechanism of pulmonary vein (PV) triggers of atrial fibrillation remains unclear. We performed adenosine (ADO) testing after PV isolation to characterize spontaneous dissociated PV rhythm and ADO-induced PV ectopy. METHODS AND RESULTS: Seventy-four patients (61 men; age, 61±10 years) undergoing PV isolation for atrial fibrillation were studied. For each isolated PV, dissociated ectopy was recorded and ADO was administered. After isolation of 270 PVs, 50 PVs with dissociated ectopy were identified. In 42 PVs exhibiting PV rhythm, ADO resulted in PV rhythm suppression in 35 (83%) PVs, with all occurring during ADO-induced bradycardia, and in PV rhythm acceleration in 13 (31%) PVs, with all occurring after resolution of ADO-induced bradycardia. In 11 PVs, both ADO-induced PV rhythm acceleration and suppression were seen. Among 220 electrically silent PVs, ADO induced PV ectopy in 28 (13%) veins. The timing of ADO-induced PV ectopy with respect to ADO effects on heart rate varied. ADO induced PV ectopy during the early phase of ADO effect only in 12 PVs, during the late phase of ADO effect only in 8 PVs, and during both early and late phases of ADO effect in 8 PVs. CONCLUSIONS: The mechanism of spontaneous PV rhythm after isolation is likely automaticity, given the close association of ADO effects on PV rhythm with its chronotropic and dromotropic effects. However, ADO can induce PV ectopy in electrically silent PVs in a manner not closely tied to its effects on heart rate and may be because of the activation of autonomic triggers.

Trp53 regulates Notch 4 signaling through Mdm2.

Notch receptors and their ligands have crucial roles in development and tumorigenesis. We present evidence demonstrating the existence of an antagonistic relationship between Notch 4 and Trp53, which is controlled by the Mdm2-dependent ubiquitylation and degradation of the Notch receptor. We show that this signal-controlling mechanism is mediated by physical interactions between Mdm2 and Notch 4 and suggest the existence of a trimeric complex between Trp53, Notch 4 and Mdm2, which ultimately regulates Notch activity. Functional studies indicate that Trp53 can suppress NICD4-induced anchorage-independent growth in mammary epithelial cells and present evidence showing that Trp53 has a pivotal role in the suppression of Notch-associated tumorigenesis in the mammary gland.

Cripto-1 is a cell surface marker for a tumorigenic, undifferentiated subpopulation in human embryonal carcinoma cells.

Deregulation of stem cells is associated with the generation and progression of malignant tumors. In addition, genes that are associated with early embryogenesis are frequently expressed in cancer. Cripto-1 (CR-1), a glycosylphosphatidylinositol-linked glycoprotein, is expressed during early embryogenesis and in various human carcinomas. We demonstrated that human embryonal carcinoma (EC) cells are heterogeneous for CR-1 expression and consist of two distinct subpopulations: a CR-1(High) and a CR-1(Low) population. By segregating CR-1(High) and CR-1(Low) populations of NTERA2/D1 EC cells by fluorescence-activated cell sorting, we demonstrated that CR-1(High) cells were more tumorigenic than CR-1(Low) cells by an in vitro tumor sphere assay and by in vivo xenograft formation. The CR-1(High) population was enriched in mRNA expression for the pluripotent embryonic stem (ES) cell genes Oct4, Sox2, and Nanog. CR-1 expression in NTERA2/D1 cells was regulated by a Smad2/3-dependent autocrine loop, by the ES cell-related transcription factors Oct4/Nanog, and partially by the DNA methylation status of the promoter region. These results demonstrate that CR-1 expression is enriched in an undifferentiated, tumorigenic subpopulation and is regulated by key regulators of pluripotent stem cells.

Enhancement of Notch receptor maturation and signaling sensitivity by Cripto-1.

Nodal and Notch signaling pathways play essential roles in vertebrate development. Through a yeast two-hybrid screening, we identified Notch3 as a candidate binding partner of the Nodal coreceptor Cripto-1. Coimmunoprecipitation analysis confirmed the binding of Cripto-1 with all four mammalian Notch receptors. Deletion analyses revealed that the binding of Cripto-1 and Notch1 is mediated by the Cripto-1/FRL-1/Cryptic domain of Cripto-1 and the C-terminal region of epidermal growth factor-like repeats of Notch1. Binding of Cripto-1 to Notch1 occurred mainly in the endoplasmic reticulum-Golgi network. Cripto-1 expression resulted in the recruitment of Notch1 protein into lipid raft microdomains and enhancement of the furin-like protein convertase-mediated proteolytic maturation of Notch1 (S1 cleavage). Enhanced S1 cleavage resulted in the sensitization to ligand-induced activation of Notch signaling. In addition, knockdown of Cripto-1 expression in human and mouse embryonal carcinoma cells desensitized the ligand-induced Notch signaling activation. These results suggest a novel role of Cripto-1 in facilitating the posttranslational maturation of Notch receptors.

Imaging case study of the month. Thyroglossal duct cyst with intralaryngeal extension.

OBJECTIVES: Thyroglossal duct cysts with intralaryngeal extension are rare. We present only the 10th reported case in the literature. METHODS: The clinical presentation, diagnosis, and treatment of the patient are reviewed and summarized. The uniqueness of the case, as well as the diagnostic and treatment pitfalls of this subgroup of patients, is presented. RESULTS: Our patient, at 76 years of age, is the only woman and the oldest person reported to have had a thyroglossal duct cyst with intralaryngeal extension. CONCLUSIONS: Intralaryngeal extension should be considered when there is hoarseness, dysphagia, or dyspnea associated with a thyroglossal duct cyst. Office laryngoscopy and computed tomography make the diagnosis. Care must be taken with airway management and intraoperative dissection for good outcomes.

The Tie2 5' untranslated region is inhibitory to 5' end-mediated translation initiation.

Tie2 is an endothelium-specific receptor tyrosine kinase required for normal blood vessel maturation, remodeling, and stability. Tie2 expression is also upregulated in various cancers implicating a role in tumor angiogenesis. Its mRNA transcript contains an unusually long (372 nucleotides) 5' untranslated region (UTR) with five upstream open reading frames (uORFs) and an internal ribosome entry site (IRES) that allows this mRNA to be translated under hypoxic conditions. This sets up an alternative initiation pathway with the potential to clash with 5' end-mediated initiation from the same template. Herein, we define experimental conditions under which the Tie2 IRES is not active, allowing us to assess the contribution of the 5' UTR to cap-dependent translation on the Tie2 transcript. We find that the Tie2 5' UTR is inhibitory to translation initiation with ribosome flow decreasing following encounters with each uORF. No single uORF was found to harbor significant cis-acting inhibitory activity. Our results suggest that the uORFs within the Tie2 5' UTR serve to decrease the percent of ribosomes competent for reinitiation as these traverse the mRNA 5' UTR, thus minimizing interference with the IRES.