In Vitro Co-Effects of Chrysotile Fibres and Benzo(A)Pyrene on Morphological Transformation of Rat Pleural Mesothelial Cells Get access M.C. Jaurand, M.C. Jaurand *Inserm U 139 and UA 604 CHU Henri Mondor94010 Creteil Cedex, France Search for other works by this author on: Oxford Academic PubMed Google Scholar M.J. Paterour, M.J. Paterour *Inserm U 139 and UA 604 CHU Henri Mondor94010 Creteil Cedex, France Search for other works by this author on: Oxford Academic PubMed Google Scholar J. Tobaly, J. Tobaly †Inserm U 107 Hôpital Saint Louis75010 Paris, France Search for other works by this author on: Oxford Academic PubMed Google Scholar M. Salle, M. Salle †Inserm U 107 Hôpital Saint Louis75010 Paris, France Search for other works by this author on: Oxford Academic PubMed Google Scholar L. Medrano, L. Medrano *Inserm U 139 and UA 604 CHU Henri Mondor94010 Creteil Cedex, France Search for other works by this author on: Oxford Academic PubMed Google Scholar R. Ravier, R. Ravier †Inserm U 107 Hôpital Saint Louis75010 Paris, France Search for other works by this author on: Oxford Academic PubMed Google Scholar J. Bignon J. Bignon *Inserm U 139 and UA 604 CHU Henri Mondor94010 Creteil Cedex, France Search for other works by this author on: Oxford Academic PubMed Google Scholar The Annals of Occupational Hygiene, Volume 32, Issue inhaled_particles_VI, January 1988, Pages 1174–1176, https://doi.org/10.1093/annhyg/32.inhaled_particles_VI.1174 Published: 01 January 1988

Attempts to activate type C endogenous viruses in 129 mouse fibroblasts and in teratocarcinoma-derived cell lines have never been successful, although the genome of these cells contains xenotropic virus-related sequences. We have investigated the arrangement of these sequences and their methylation state by DNA restriction endonuclease digestion, electrophoresis of digests in agarose gels, Southern blotting and hybridization with specific probes. Our results show that the majority of the sequences are organized into two complete provirus families integrated at multiple sites in the cell genome and that they are hypermethylated in embryonal carcinoma cells as compared with differentiated cells. Having previously found a higher expression of viral RNA in 129 derived embryonal carcinoma cells, our data indicate an apparent direct correlation between methylation and type C virogenes expression.

We examined the expression of four cellular proto-oncogenes in two teratocarcinoma cell lines, one undifferentiated and malignant (PCC4), one differentiated and non malignant (PCD1). In this paper we report that transcript levels of c-Ki-ras, c-myc and c-fos are significantly higher in PCC4 cells whereas transcripts of c-Ha-ras are unchanged. Southern blot analysis does not reveal any structural alteration of c-myc and c-fos in PCC4 cells. On the contrary, the c-Ki-ras proto-oncogene is amplified 10 to 20 fold in PCC4 cells.

5-Azacytidine activates the production of intracisternal A particles (IAPs) in mouse Ki-BALB cell line as ascertained by electron microscopy scanning and numeration. Efficiency of the activation is higher than that obtained with iododeoxyuridine. The increase in particle production is concentration and time dependent. The results obtained in our system correlate the high IAP expression after drug treatment with a demethylation of IAP-related genes sequences.

Incoming type C retroviral genomic 35S RNA is present in polysomes of undifferentiated and differentiated murine teratocarcinoma cell lines at 4 hours after infection. At the same time a 65,000 daltons viral specific protein is produced by the infected cells. These data present evidence that incoming viral RNA serves as messenger for the synthesis of gag protein precursor Pr65 early in the infectious cycle of ecotropic murine retrovirus.

Murine type C retroviruses do not replicate in embryonal carcinoma cells (ECC), whilst they do normally in the differentiated derivatives of these cells. However, coculture in the presence of a fusing agent allows the recovery of the input virus up to 5 days after infection. Cytoplasmic and nuclear fractions were obtained at different times after infection by treatment of the infected ECC with cytochalasin B and differential centrifugation. Virus was recovered up to 24 h post-infection by fusion of the cytoplasmic fraction with a permissive cell, whereas beyond 24 h virus was only recovered from the nuclear fraction. These results indicate that the cytoplasmic events of viral replication in the restrictive ECC are seemingly normal and that the block is very probably localized in the nucleus.

Studies on the susceptibility of several human cell lines cultured in vitro, to infection by different type C xenotropic retroviruses, demonstrate the existence of a wide variation in the responses of the cells investigated. These results suggest a genetic control mechanism of the viral replication by human cells.

Retrovirus infection of cultured murine teratocarcinoma cells depends upon the state of differentiation. We have used two cell lines derived from a teratocarcinoma of mouse, strain 129. One, an undifferentiated pluripotential cell line (PCC4), is restrictive to viral infection, while the other, a differentiated myoblast-derived cell line (PCD1), is fully permissive to virus replication. We have shown that no virus RNA expression can be found in PCC4 cells 48 h post-infection and that no nucleic acid sequences can be found in an integrated form in PCC4 cells. However, the kinetics of formation of free proviral intermediates show that the three forms (I, II and III) of free virus DNA are synthesized in both PCC4 and PCD1. Free proviral DNA disappears gradually after 24 h in PCC4 cells while all forms increase in PCD1. These results suggest that the viral multiplication restriction occurs somewhere between the proviral DNA synthesis and integration of DNA in the cellular genome.

Production of Type C virus by Mouse cells generally activated by chemical agents does not occur in 129/J Mouse cells. No viral production, as tested by reverse transcriptase activity and electron microscopic methods can be detected in cells treated by chemical inducers. Immunofluorescence does not reveal the presence of viral specific proteins and viral RNA expression determined by molecular hybridization between cellular RNA and viral cDNA does not increase as it does in BALB/c cells under the action of the inducers studied.