asbestos--crocidolite and Polyomavirus-Infections

The calcium-binding protein calretinin has emerged as a useful marker for the identification of mesotheliomas of the epithelioid and mixed types, but its putative role in tumor development has not been addressed previously. Although exposure to asbestos fibers is considered the main cause of mesothelioma, undoubtedly, not all mesothelioma patients have a history of asbestos exposure. The question as to whether the SV40 virus is involved as a possible co-factor is still highly debated. Here we show that increased expression of SV40 early gene products in the mesothelial cell line MeT-5A induces the expression of calretinin and that elevated calretinin levels strongly correlate with increased resistance to asbestos cytotoxicity. Calretinin alone mediates a significant part of this protective effect because cells stably transfected with calretinin cDNA were clearly more resistant to the toxic effects of crocidolite than mock-transfected control cells. Down-regulation of calretinin by antisense methods restored the sensitivity to asbestos toxicity to a large degree. The protective effect observed in clones with higher calretinin expression levels could be eliminated by phosphatidylinositol 3-kinase (PI3K) inhibitors, implying an important role for the PI3K/AKT signaling (survival) pathway in mediating the protective effect. Up-regulation of calretinin, resulting from either asbestos exposure or SV40 oncoproteins, may be a common denominator that leads to increased resistance to asbestos cytotoxicity and thereby contributes to mesothelioma carcinogenesis.

Topics: Antigens, Polyomavirus Transforming; Asbestos, Crocidolite; Blotting, Western; Calbindin 2; Cell Line, Tumor; Cell Transformation, Neoplastic; Gene Expression; Humans; Immunohistochemistry; Mesothelioma; Phosphatidylinositol 3-Kinases; Polyomavirus Infections; Proto-Oncogene Proteins c-akt; Reverse Transcriptase Polymerase Chain Reaction; S100 Calcium Binding Protein G; Signal Transduction; Simian virus 40; Transfection; Tumor Virus Infections; Up-Regulation

Malignant pleural mesothelioma (MPM) is a fatal neoplasm with no acceptable curative approaches. We used serial analysis of gene expression (SAGE) to compare the gene expression pattern of a surgically resected MPM to the autologous normal mesothelium. Intelectin gene overexpression (>139-fold) was found in the tumor. Online SAGE datasets revealed intelectin to be consistently present in mesothelioma(s), ovarian cancer, and colon cancer. Intelectin mRNA expression was found by RT-PCR in 4 of 5 resected MPM tumors, and Intelectin protein expression was confirmed by immunohistochemistry in 28 of 53 MPM tumors, and in 4 of 4 mesothelioma cell lines studied by Western blot. A marked induction in intelectin gene expression was observed among human primary mesothelial cells as a consequence of crocidolite asbestos exposure and simian virus 40 infection. Intelectin overexpression in mesothelioma could have potential screening, and therapeutic implications.

Topics: Asbestos, Crocidolite; Blotting, Western; Case-Control Studies; Colonic Neoplasms; Cytokines; Databases, Genetic; Female; Gene Expression Profiling; GPI-Linked Proteins; Humans; Immunohistochemistry; Lectins; Mesothelioma; Ovarian Neoplasms; Pleural Neoplasms; Polyomavirus Infections; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured; Tumor Virus Infections

The cytotoxic effects of asbestos are partly mediated by the production of free radicals, including nitric oxide (NO). SV40 has been suggested to synergize with asbestos in the pathogenesis of malignant mesothelioma. Crocidolite asbestos fibers induced in human mesothelial and malignant mesothelioma cells a significant increase of NO synthase activity and expression, which was absent in SV40-infected cells. Furthermore, SV40 infection prevented the NF kappa B activation elicited by crocidolite in both mesothelial and mesothelioma cells. These data suggest that SV40, by inhibiting the synthesis of NO, could favor the survival of transformed, potentially neoplastic cells.

Topics: Asbestos, Crocidolite; Cells, Cultured; Down-Regulation; Epithelial Cells; Humans; Mesothelioma; NF-kappa B; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Polyomavirus Infections; Simian virus 40; Tumor Virus Infections