Epstein‐Barr virus‐encoded latent membrane protein 1 promotes stress‐induced apoptosis upstream of caspase‐2‐dependent mitochondrial perturbation

Abstract

Previous studies have shown that Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) enhances etoposideinduced apoptosis in epithelial cells. Our study was undertaken to further dissect the modulation of tumor cell apoptosis by this viral protein. Using an inducible system of LMP1 expression in HeLa cells, we show herein that etoposide-triggered apoptosis, as evidenced by nuclear condensation and caspase-3 activation, is enhanced by LMP1. LMP1 also potentiates etoposide-induced processing and activation of caspase-2 in this model and enhances the dissipation of mitochondrial transmembrane potential and the release of cytochrome c in response to etoposide. Moreover, cisplatin-triggered activation of caspases 2 and 3 is potentiated upon expression of LMP1. A similar LMP1-mediated enhancement of cisplatin-induced caspase activation was seen upon stable transfection of wild-type LMP1 into the nasopharyngeal carcinoma cell line, TW03. Finally, using deletion mutants of LMP1 to determine the region of LMP1 required for apoptosis potentiation, we found that amino acids 350 -386 (located within the CTAR2 domain) were responsible for sensitizing cells to cisplatin. We conclude that LMP1-dependent potentiation of stress-induced apoptosis occurs at an early step in the apoptosis cascade, upstream of the activation of caspase-2, and involves the C-terminal signaling domain of LMP1. These findings could have important ramifications for the treatment of EBV-associated malignancies of epithelial origin, including nasopharyngeal carcinoma.

Molecular Basis of Cytotoxicity of Epstein-Barr Virus (EBV) Latent Membrane Protein 1 (LMP1) in EBV Latency III B Cells: LMP1 Induces Type II Ligand-Independent Autoactivation of CD95/Fas with Caspase 8-Mediated Apoptosis

“…As already demonstrated by us and others, LMP1wt expression leads to Fas overexpression in LCLs (11,37,62). Here, we show that LMP1wt levels are very heterogeneous from cell to cell and that Fas expression parallels LMP1 expression (Fig.…”

“…LMP1 overexpression has been shown to sensitize cells to apoptosis induction in an NF-B-dependent manner (37,62). To study LMP1wt apoptotic features and to understand the underlying molecular process, the previously obtained LCL named PRI was stably transfected with the bidirectional Tet-on inducible vector pRT-1, which conditionally expresses both NGFRt and LMP1wt after doxycycline treatment (37).…”

“…LMP1 by itself can sensitize cells or promote apoptosis. It enhances HeLa cell apoptosis induced by Fas or by cytotoxic compounds, such as etoposide and cisplatin (61,62). In epithelial cell lines transfected with LMP1, apoptosis is also related to high expression levels of the protein (42).…”

Proinflammatory Caspase-2-Mediated Macrophage Cell Death Induced by a Rough Attenuated Brucella suis Strain

“…While this caspase-2-mediated pyroptosis is first found here in rough Brucella-infected macrophages, this type of cell death may also exist in many other systems. Caspase-2-mediated cell death exists in host cells infected with other pathogens, such as Salmonella (22) and Epstein-Barr virus (41), and also cancer (26). Some of the caspase-2-mediated cell death may also be proinflammatory, which deserves further analyses.…”

Betulinic acid, a natural cytotoxic agent, fails to trigger apoptosis in human Burkitt's lymphoma‐derived B‐cell lines

“…11 Cell lysates and substrate (50 lM) were thus combined in a standard reaction buffer and added to a 96-well plate. Enzyme-catalyzed release of AMC was measured every 70 sec during a 30-min period using a Fluoroscan II plate reader (Labsystems, Stockholm, Sweden) using 355 nm excitation and 460 nm emission wavelengths.…”