Malignant perivascular epithelioid cell tumor of the esophagus.

Malignant perivascular epithelioid cell tumor (PEComa) is a rare tumor composed of hybrid tumor cells characterized by immunoreactivity for both melanocytic and smooth muscle markers. This paper describes the uncommon esophageal location of an 8 cm PEComa in a 75-year-old Caucasian man who was presented with ingravescent dysphagia. Although PEComas arising within the gastrointestinal tract are exceptional findings, clinicians should not exclude this class of tumors in the diagnostic investigation of a bulky lesion of the esophageal wall.

Identification of host factors involved in borna disease virus cell entry through a small interfering RNA functional genetic screen.

Borna disease virus (BDV), the prototypic member of the Bornaviridae family, within the order Mononegavirales, is highly neurotropic and constitutes an important model system for the study of viral persistence in the central nervous system (CNS) and associated disorders. The virus surface glycoprotein (G) has been shown to direct BDV cell entry via receptor-mediated endocytosis, but the mechanisms governing cell tropism and propagation of BDV within the CNS are unknown. We developed a small interfering RNA (siRNA)-based screening to identify cellular genes and pathways that specifically contribute to BDV G-mediated cell entry. Our screen relied on silencing-mediated increased survival of cells infected with rVSVDeltaG*/BDVG, a cytolytic recombinant vesicular stomatitis virus expressing BDV G that mimics the cell tropism and entry pathway of bona fide BDV. We identified 24 cellular genes involved in BDV G-mediated cell entry. Identified genes are known to participate in a broad range of distinct cellular functions, revealing a complex process associated with BDV cell entry. The siRNA-based screening strategy we have developed should be applicable to identify cellular genes contributing to cell entry mediated by surface G proteins of other viruses.

Cell entry of Borna disease virus follows a clathrin-mediated endocytosis pathway that requires Rab5 and microtubules.

Borna disease virus (BDV), the prototypic member of the Bornaviridae family within the order Mononegavirales, exhibits high neurotropism and provides an important and unique experimental model system for studying virus-cell interactions within the central nervous system. BDV surface glycoprotein (G) plays a critical role in virus cell entry via receptor-mediated endocytosis, and therefore, G is a critical determinant of virus tissue and cell tropism. However, the specific cell pathways involved in BDV cell entry have not been determined. Here, we provide evidence that BDV uses a clathrin-mediated, caveola-independent cell entry pathway. We also show that BDV G-mediated fusion takes place at an optimal pH of 6.0 to 6.2, corresponding to an early-endosome compartment. Consistent with this finding, BDV cell entry was Rab5 dependent but Rab7 independent and exhibited rapid fusion kinetics. Our results also uncovered a key role for microtubules in BDV cell entry, whereas the integrity and dynamics of actin cytoskeleton were not required for efficient cell entry of BDV.

Borna disease virus requires cholesterol in both cellular membrane and viral envelope for efficient cell entry.

Borna disease virus (BDV), the prototypic member of the family Bornaviridae within the order Mononegavirales, provides an important model for the investigation of viral persistence within the central nervous system (CNS) and of associated brain disorders. BDV is highly neurotropic and enters its target cell via receptor-mediated endocytosis, a process mediated by the virus surface glycoprotein (G), but the cellular factors and pathways determining BDV cell tropism within the CNS remain mostly unknown. Cholesterol has been shown to influence viral infections via its effects on different viral processes, including replication, budding, and cell entry. In this work, we show that cell entry, but not replication and gene expression, of BDV was drastically inhibited by depletion of cellular cholesterol levels. BDV G-mediated attachment to BDV-susceptible cells was cholesterol independent, but G localized to lipid rafts (LR) at the plasma membrane. LR structure and function critically depend on cholesterol, and hence, compromised structural integrity and function of LR caused by cholesterol depletion likely inhibited the initial stages of BDV cell internalization. Furthermore, we also show that viral-envelope cholesterol is required for BDV infectivity.

Bronchopulmonary carcinoid: phenotype and long-term outcome in a single-institution series of Italian patients.

PURPOSE: The histologic distinction between low-grade typical and intermediate-grade atypical bronchopulmonary carcinoids basically lies on cellular differentiation, mitotic activity, and presence of "neoplastic" necrosis; at single patient level, however, none of these features enables a reliable prediction of the clinicopathologic outcome. EXPERIMENTAL DESIGN: The long-term postsurgical outcome of a single-institution series of 67 radically treated bronchopulmonary carcinoids was correlated with the tumor phenotype assessed by combining conventional histology with a panel of immunohistochemical markers exploring cell differentiation (chromogranin, NSE, TTF1), cell turnover (Mib1), and apoptosis (Bcl2, Bax). RESULTS: Fifty-eight (86.6%) carcinoids were assessed as low-grade typical and nine (13.4%) were assessed as intermediate-grade atypical. The mean follow-up was of 85.13 months (range, 28-168; median, 82.0). All cases expressed neuroendocrine markers, whereas TTF1 was never expressed. At univariate analysis, tumor recurrence (n = 6) correlated significantly with the carcinoid histotype (P = 0.002) and with each of the following variables: tumor location (P = 0.01), mitotic index (P = 0.003), necrosis (P = 0.002), tumor vascular invasion (P = 0.0001), Mib1 expression (P = 0.005), Bcl2 expression (P = 0.024), and synchronous node metastasis (P = 0.028). The best cutoffs for Mib1 and Bcl2 expression (calculated by receiver operating characteristic curves) discriminating recurrent versus nonrecurrent tumors were 5.4% for Mib1 and 2.0% for Bcl2 (Mib1: sensitivity, 83%; specificity, 97%; area under curve, 0.844 +/- 0.14; Bcl2: sensitivity, 83%; specificity, 65%; area under curve, 0.769 +/- 0.12). By stratifying the patients according to the obtained cutoffs, significant differences emerged in the patients' disease-free survival (log-rank test: Mib1, P = 0.0001; Bcl2, P = 0.01). CONCLUSIONS: Mib1 and Bcl2 significantly discriminate between recurrent versus nonrecurrent tumors, producing a biologically plausible, diagnostically suitable immunohistochemical pattern.

Cell-to-cell spread of Borna disease virus proceeds in the absence of the virus primary receptor and furin-mediated processing of the virus surface glycoprotein.

Borna disease virus (BDV) is an enveloped virus with a nonsegmented negative-strand RNA genome whose organization is characteristic of Mononegavirales. BDV cell entry follows a receptor-mediated endocytosis pathway, which is initiated by the recognition of an as-yet-unidentified receptor at the cell surface by the virus glycoprotein G. BDV G is synthesized as a precursor (GPC) that is cleaved by the cellular protease furin to produce the mature glycoproteins GP1 and GP2, which have been implicated in receptor recognition and pH-dependent fusion events, respectively. BDV is highly neurotropic and its spread in cultured cells proceeds in the absence of detectable extracellular virus or syncytium formation. BDV spread has been proposed to be strictly dependent on the expression and correct processing of BDV G. Here we present evidence that cell-to-cell spread of BDV required neither the expression of cellular receptors involved in virus primary infection, nor the furin-mediated processing of BDV G. We also show that in furin-deficient cells, the release of BDV particles induced by the treatment of BDV-infected cells with hypertonic buffer was not significantly affected, while virion infectivity was dramatically impaired, correlating with the decreased incorporation of BDV G species into viral particles. These findings support the view that the propagation of BDV within the central nervous systems of infected hosts involves both a primary infection that follows a receptor-mediated endocytosis pathway and a subsequent cell-to-cell spread that is independent of the expression of the primary receptor and does not require the processing of BDV G into GP1 and GP2.

Generation and characterization of a recombinant vesicular stomatitis virus expressing the glycoprotein of Borna disease virus.

Borna disease virus (BDV) is an enveloped virus with a nonsegmented negative-strand RNA genome whose organization is characteristic of mononegavirales. However, based on its unique genetics and biological features, BDV is considered to be the prototypic member of a new virus family, Bornaviridae, within the order Mononegavirales. BDV cell entry occurs via receptor-mediated endocytosis, a process initiated by the recognition of an as yet unidentified receptor at the cell surface by the BDV surface glycoprotein (G). The paucity of cell-free virus associated with BDV infection has hindered studies aimed at the elucidation of cellular receptors and detailed mechanisms involved in BDV cell entry. To overcome this problem, we generated and characterized a replication-competent recombinant vesicular stomatitis virus expressing BDV G (rVSVDeltaG*/BDVG). Cells infected with rVSVDeltaG*/BDVG produced high titers (10(7) PFU/ml) of cell-free virus progeny, but this virus exhibited a highly attenuated phenotype both in cell culture and in vivo. Attenuation of rVSVDeltaG*/BDVG was associated with a delayed kinetics of viral RNA replication and altered genome/N mRNA ratios compared to results for rVSVDeltaG*/VSVG. Likewise, incorporation of BDV G into virions appeared to be restricted despite its high levels of expression and efficient processing in rVSVDeltaG*/BDVG-infected cells. Notably, rVSVDeltaG*/BDVG recreated the cell tropism and entry pathway of bona fide BDV. Our results indicate that rVSVDeltaG*/BDVG represents a unique tool for the investigation of BDV G-mediated cell entry, as well as the roles of BDV G in host immune responses and pathogenesis associated with BDV infection.

The oligomerization domain of VP3, the scaffolding protein of infectious bursal disease virus, plays a critical role in capsid assembly.

Infectious bursal disease virus (IBDV) capsids are formed by a single protein layer containing three polypeptides, pVP2, VP2, and VP3. Here, we show that the VP3 protein synthesized in insect cells, either after expression of the complete polyprotein or from a VP3 gene construct, is proteolytically degraded, leading to the accumulation of product lacking the 13 C-terminal residues. This finding led to identification of the VP3 oligomerization domain within a 24-amino-acid stretch near the C-terminal end of the polypeptide, partially overlapping the VP1 binding domain. Inactivation of the VP3 oligomerization domain, by either proteolysis or deletion of the polyprotein gene, abolishes viruslike particle formation. Formation of VP3-VP1 complexes in cells infected with a dual recombinant baculovirus simultaneously expressing the polyprotein and VP1 prevented VP3 proteolysis and led to efficient virus-like particle formation in insect cells.

Identification and molecular characterization of the RNA polymerase-binding motif of infectious bursal disease virus inner capsid protein VP3.

Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is the causative agent of one of the most important infectious poultry diseases. Major aspects of the molecular biology of IBDV, such as assembly and replication, are as yet poorly understood. We have previously shown that encapsidation of the putative virus-encoded RNA-dependent RNA polymerase VP1 is mediated by its interaction with the inner capsid protein VP3. Here, we report the characterization of the VP1-VP3 interaction. RNase A treatment of VP1- and VP3-containing extracts does not affect the formation of VP1-VP3 complexes, indicating that formation of the complex requires the establishment of protein-protein interactions. The use of a set of VP3 deletion mutants allowed the mapping of the VP1 binding motif of VP3 within a highly charged 16-amino-acid stretch on the C terminus of VP3. This region of VP3 is sufficient to confer VP1 binding activity when fused to an unrelated protein. Furthermore, a peptide corresponding to the VP1 binding region of VP3 specifically inhibits the formation of VP1-VP3 complexes. The presence of Trojan peptides containing the VP1 binding motif in IBDV-infected cells specifically reduces infective virus production, thus showing that formation of VP1-VP3 complexes plays a critical role in IBDV replication.