tetracycline and Cell-Transformation--Viral

While Newcastle disease virus (NDV) causes serious infections in birds, it is apparently nonpathogenic in mammalian species, including humans. Previous observations and small-scale clinical trials indicated that NDV exerts oncolytic effects. Isolates of NDV were found to have selective affinity to transformed cells. We previously showed that the attenuated NDV strain MTH-68/H causes apoptotic cell death in cultures of PC12 rat pheochromocytoma cells. The aim of the present study was to extend MTH-68/H cytotoxicity testing with human tumor cell lines and to analyze certain biochemical aspects of its oncolytic effect. MTH-68/H was found to be able to kill a wide range of transformed cells by apoptosis. While caspase-8 and caspase-9 are not involved in MTH-68/H-induced apoptosis, activation of caspase-3 and caspase-12 was detected in virus-infected PC12 cells. A human glioblastoma cell line with repressible expression of the p53 protein did not show any difference in MTH-68/H sensitivity in its p53-expressing and p53-depleted states, indicating that the apoptotic process induced by MTH-68/H does not depend on p53. Apoptosis was accompanied by virus replication in two tumor cell lines tested (PC12 cells and HeLa human cervical cells), and signs of endoplasmic reticulum stress (phosphorylation of protein kinase R-like endoplasmic reticulum kinase and eIF2alpha) were also detected in transformed cells. In contrast, proliferation of nontransformed mouse and rat fibroblast cell lines and human primary fibroblasts was not affected by MTH-68/H treatment. MTH-68/H thus selectively kills tumor cell cultures by inducing endoplasmic reticulum stress leading to p53-independent apoptotic cell death.

Topics: Animals; Anti-Bacterial Agents; Apoptosis; Carcinoma; Caspase 12; Caspase 3; Cell Line, Transformed; Cell Line, Tumor; Cell Proliferation; Cell Transformation, Viral; Endoplasmic Reticulum; Enzyme Activation; Female; Glioblastoma; HCT116 Cells; HeLa Cells; HT29 Cells; Humans; Newcastle disease virus; Oxidative Stress; Pancreatic Neoplasms; PC12 Cells; Rats; Tetracycline; Tumor Suppressor Protein p53; Virus Replication

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is essential for the immortalization of human B cells and is linked etiologically to several human tumors. LMP1 is an integral membrane protein which acts like a constitutively active receptor. It binds tumor necrosis factor (TNF)-receptor-associated factors (TRAFs), activates NF-kappaB and triggers the transcription factor AP-1 via the c-Jun N-terminal kinase (JNK) cascade, but its specific contribution to B-cell immortalization has not been elucidated fully. To address the function of LMP1, we established B cell lines with a novel mini-EBV plasmid in which the LMP1 gene can be regulated at will without affecting the expression of other latent EBV genes. We demonstrate here that continuous expression of LMP1 is essential for the proliferation of EBV-immortalized B cells in vitro. Re-induction of LMP1 expression or activation of the cellular CD40 receptor both induce the JNK signaling cascade, activate the transcription factor NF-kappaB and stimulate proliferation of these B cells. Our findings strongly suggest that LMP1 mimics B-cell activation processes which are physiologically triggered by CD40-CD40 ligand signals. Since LMP1 acts in a ligand-independent manner, it replaces the T cell-derived activation signal to sustain indefinite B-cell proliferation.

Topics: B-Lymphocytes; Calcium-Calmodulin-Dependent Protein Kinases; CD40 Antigens; Cell Division; Cell Line, Transformed; Cell Transformation, Viral; Epstein-Barr Virus Nuclear Antigens; Gene Expression Regulation; Genetic Vectors; Herpesvirus 4, Human; Humans; JNK Mitogen-Activated Protein Kinases; Mitogen-Activated Protein Kinases; NF-kappa B; Repressor Proteins; Signal Transduction; Tetracycline; Viral Matrix Proteins

The role of viral oncoprotein expression in the maintenance of cellular transformation was examined as a function of time through controlled expression of simian virus 40 T antigen (TAg). Expression of TAg in the submandibular gland of transgenic mice from the time of birth induced cellular transformation and extensive ductal hyperplasia by 4 months of age. The hyperplasia was reversed when TAg expression was silenced for 3 weeks. When TAg expression was silenced after 7 months, however, the hyperplasia persisted even though TAg was absent. Although the polyploidy of ductal cells could be reversed at 4 months of age, cells at 7 months of age remained polyploid even in the absence of TAg. These results support a model of time-dependent multistep tumorigenesis, in which virally transformed cells eventually lose their dependence on the viral oncoprotein for maintenance of the transformed state.

Topics: Animals; Antigens, Polyomavirus Transforming; Cell Transformation, Neoplastic; Cell Transformation, Viral; Gene Expression; Hyperplasia; Mice; Mice, Transgenic; Polyploidy; Submandibular Gland; Tetracycline; Time Factors; Trans-Activators