Environmental Associations and Histopathologic Patterns of Carcinoma of the Lung: The Challenge and Dilemma in Epidemiologic Studies

Maeda

Murgia

et al. 2001

J Virol

108

163

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of a transmissible lung cancer of sheep known as ovine pulmonary carcinoma. Recently, we have found that the expression of the JSRV envelope (Env) is sufficient to transform mouse NIH 3T3 cells in classical transformation assays. To further investigate the mechanisms of JSRV oncogenesis, we generated a series of envelope chimeras between JSRV and the JSRVrelated endogenous retroviruses of sheep (enJSRVs) and assessed them in transformation assays. Chimeras containing the exogenous JSRV SU region and the enJSRV TM region were unable to transform NIH 3T3 cells. Additional chimeras containing only the carboxy-terminal portion of TM (a region that we previously identified as VR3) of the endogenous envelope with SU and the remaining portion of TM from the exogenous JSRV were also unable to transform NIH 3T3 cells. The VR3 region includes the putative membrane-spanning region and cytoplasmic tail of the JSRV TM glycoprotein; this suggested that the cytoplasmic tail of the JSRV Env mediates transformation, possibly via a cell signaling mechanism. Mutations Y590 and M593 in the cytoplasmic tail of the JSRV envelope were sufficient to inhibit the transforming abilities of these constructs. Y590 and Jaagsiekte sheep retrovirus (JSRV) is the etiological agent of a contagious lung cancer of sheep known as ovine pulmonary carcinoma (OPC) or sheep pulmonary adenomatosis (4,16,30,36). OPC is a naturally occurring disease in most countries of the world and is characterized by the transformation of the differentiated epithelial cells of the lungs, type II pneumocytes and Clara cells (17,33). OPC is being extensively studied for its similarities with a particular type of human lung cancer known as bronchioloalveolar carcinoma (BAC) (17,21,23,33). The causes of BAC are unknown. BAC is not strongly associated with cigarette smoking, and its incidence appears to be increasing in the United States (1,5,6,51). Thus, the JSRV/ OPC model can offer a foundation for understanding the molecular mechanisms of type II pneumocytes and Clara cell transformation, especially considering the role played by retroviruses in the discovery of cellular oncogenes (46). M593 are part of a Y-X-X-M motif that is recognized by the phosphatidylinositol 3-kinase (PI-3K). PI-3K initiates a cell signaling pathway that inhibits apoptosis and is required for a number of mitogens during the G 1 -to-S-phase transition of the cell cycle. PI-3K activatesCell transformation by JSRV is offering a new paradigm for retroviral oncogenesis (45). The JSRV genome does not contain a cell-derived oncogene, which would suggest that JSRV induces cell transformation by insertional activation of protooncogenes (46). However, the incubation period in experimentally inoculated lambs can be as short as 2 to 3 weeks (47, 52), which appears too short for insertional activation to occur. Our recent study showed that the expression of the envelope (Env) protein of JSRV is able to transform rodent fibroblasts in vitro (27). Thus, ...

mentioning

confidence: 99%

A Phosphatidylinositol 3-Kinase Docking Site in the Cytoplasmic Tail of the Jaagsiekte Sheep Retrovirus Transmembrane Protein Is Essential for Envelope-Induced Transformation of NIH 3T3 Cells

Maeda

Murgia

et al. 2001

J Virol

108

163

“…A characteristic feature of OPC tumors is the production of large amounts of fluid secreted from the tumor cells (containing infectious virus). OPC closely resembles human bronchiolo alveolar carcinoma (BAC), an adenocarcinoma not associated with cigarette smoking and whose etiology is currently unknown (6). Thus OPC is an important model for understanding human BAC pathogenesis.…”

mentioning

confidence: 99%

Direct transformation of rodent fibroblasts by jaagsiekte sheep retrovirus DNA

Maeda

Proc. Natl. Acad. Sci. U.S.A.

Murgia

et al. 2001

142

144

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary carcinoma, a unique animal model for human bronchioalveolar carcinoma. We previously isolated a JSRV proviral clone and showed that it was both infectious and oncogenic. Thus JSRV is necessary and sufficient for the development of ovine pulmonary carcinoma, but no data are available on the mechanisms of transformation. Inspection of the JSRV genome reveals standard retroviral genes, but no evidence for a viral oncogene. However, an alternate ORF in pol (orf-x) might be a candidate for a transforming gene. We tested whether the JSRV genome might encode a transforming gene by transfecting an expression plasmid for JSRV [pCMVJS21, driven by the cytomegalovirus (CMV) immediate early promoter] into mouse NIH 3T3 cells. Foci of transformed cells appeared in the transfected cultures 2-3 weeks posttransfection; cloned transformants showed anchorage independence for growth, and they expressed JSRV RNA. These results indicate that the JRSV genome contains information with direct transforming potential for NIH 3T3 cells. Transfection of a mutated version of pCMVJS21 in which the orf-x protein was terminated by two stop codons also gave transformed foci. Thus, orf-x was eliminated as the candidate transforming gene. In addition, another derivative of pCMVJS21 (pCMVJS21⌬GP) in which the gag, pol (and orf-x) coding sequences were deleted also gave transformed foci. These results indicate that the envelope gene carries the transforming potential. This is an unusual example of a native retroviral structural protein with transformation potential.

“…SPA is an animal model of human bronchioloalveolar carcinoma (BAC) (45), a human lung cancer that is not etiologically associated with smoking (29) and that is increasing in prevalence in the United States (6). Lung cancer is the main cause of mortality among cancer patients (32), and the characteristics BAC and SPA have in common suggest that the latter could offer novel insights into pulmonary carcinogenesis.…”

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confidence: 99%

The Long Terminal Repeat of Jaagsiekte Sheep Retrovirus Is Preferentially Active in Differentiated Epithelial Cells of the Lungs

Datta

Omid

et al. 2000

J Virol

101

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of a contagious lung cancer of sheep known as sheep pulmonary adenomatosis (SPA; also ovine pulmonary carcinoma) (5,17,39,41,43,60). SPA is an animal model of human bronchioloalveolar carcinoma (BAC) (45), a human lung cancer that is not etiologically associated with smoking (29) and that is increasing in prevalence in the United States (6). Lung cancer is the main cause of mortality among cancer patients (32), and the characteristics BAC and SPA have in common suggest that the latter could offer novel insights into pulmonary carcinogenesis. JSRV is the only retrovirus that transforms the differentiated epithelial cells of the lungs: type II pneumocytes (37, 56) and Clara cells (50). To fully understand the pathogenesis of SPA, it is necessary to investigate the nature of the association between JSRV and its target cells for transformation.In general, the envelope gene (env) and the long terminal repeat (LTR) are the major determinants of retroviral tropism. The env gene encodes the viral glycoprotein that specifically interacts with the cellular receptor(s) necessary for viral entry (57). Retroviruses are able to infect only cells expressing their specific receptor. On the other hand, the LTR contains the viral promoter and enhancer elements that specifically interact with the cellular transcription machinery. After viral entry and integration, the LTR drives viral expression more efficiently in those cells that express transcription factors that interact with the viral enhancer elements (1,20).A unique feature of JSRV is its extremely tight restriction of expression in vivo to the induced tumor cells. For most other retroviral systems, there is substantial infection in numerous cell types within the infected host in addition to the resulting tumor cells. However, in sheep with naturally or experimentally acquired SPA, JSRV is abundantly expressed only in tumor cells of the lungs (40), although it is also possible to detect JSRV DNA and RNA by sensitive PCR assays in a variety of lymphoid tissues of SPA-affected sheep (42). Proviral DNA has been found in adherent cells (macrophages), B lymphocytes, and CD4 ϩ and CD8 ϩ T lymphocytes of the mediastinal lymph nodes of SPA-affected animals (27). Therefore, although JSRV is highly expressed only in the epithelial tumor cells of the lungs, it infects many different cell types. In a recent study, we have shown that in vitro JSRV infects several different sheep cell lines of various tissue origins (44). Both of these in vivo and in vitro observations suggest that the cellular receptor for JSRV is common to a variety of cell types; thus, the restriction of viral expression to epithelial tumor cells in the lungs is likely not due to the presence of the JSRV receptor only on these cells. However, it is theoretically possible that there is higher expression of the JSRV receptor on lung epithelial cells. Nevertheless, it seemed possible that the JSRV