SV40-induced expression of calretinin protects mesothelial cells from asbestos cytotoxicity and may be a key factor contributing to mesothelioma pathogenesis.
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.
Unit of Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700 Fribourg, Switzerland.
Thomas
T
Henzi
Walter-Vincent
WV
Blum
Martine
M
Pfefferli
Tadeusz J
TJ
Kawecki
Valerie
V
Salicio
Beat
B
Schwaller
D000952:Antigens, Polyomavirus Transforming; D017638:Asbestos, Crocidolite / Q000009:adverse effects*; D015153:Blotting, Western; D064032:Calbindin 2; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D008654:Mesothelioma / Q000139:chemically induced* / Q000821:virology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D027601:Polyomavirus Infections / Q000150:complications / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013539:Simian virus 40; D014162:Transfection; D014412:Tumor Virus Infections / Q000150:complications / Q000378:metabolism; D015854:Up-Regulation
D000952:Antigens, Polyomavirus Transforming; C576764:CALB2 protein, human; D064032:Calbindin 2; D064030:S100 Calcium Binding Protein G; D017638:Asbestos, Crocidolite; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt