Asbestos induction of extended lifespan in normal human mesothelial cells:interindividual susceptibility and SV40 T antigen

Normal human mesothelial cells from individual donors were studied for susc eptibility to asbestos-induction of apoptosis and generation of an extended lifespan population. Such populations were generated after death of the ma jority of cells and arose from a subset of mesothelial cultures (4/16) wher eas fibroblastic cells (5/5) did not develop extended lifespan populations after asbestos exposure. All mesothelial cultures were examined for the pre sence of SV40 T antigen to obtain information on (i) the presence of SV40 T antigen expression in normal human mesothelial cells and (ii) the relation ship between generation of an extended lifespan population and expression o f SV40 T antigen. Immunostaining for SV40 T antigen was positive in 2/38 no rmal human mesothelial cultures. These cultures also had elevated p53 expre ssion, However, the two isolates expressing SV40 T antigen did not exhibit enhanced proliferative potential or develop an extended lifespan population . asbestos-generated extended lifespan populations were specifically resist ant to asbestos-mediated but not to a-Fas-induced apoptosis, Deletion of p1 6(Ink4a) was shown in 70% of tumor samples. All mesothelioma cell lines exa mined showed homozygous deletion of this locus which extended to exon 1 bet a, Extended lifespan cultures were examined for expression of p16(Ink4a) to establish whether deletion was an early response to asbestos exposure, Dur ing their rapid growth phase, extended lifespan cultures showed decreased e xpression of p16(Ink4a) relative to untreated cultures, but methylation was not observed, and p16(Ink4a) expression became elevated when cells entered culture crisis. These data extend the earlier observation that asbestos ca n generate extended lifespan populations, providing data on frequency and c ell type specificity. In addition, this report shows that generation of suc h populations does not require expression of SV40 T antigen. Extended lifes pan cells could represent a population expressing early changes critical fo r mesothelioma development. Further study of these populations could identi fy such changes.