The analysis confirmed the excess risk of death from lung cancer associated with low radon exposure. An excess risk of death from kidney cancer was also observed, apparently not associated with cumulative radon exposure.

Abstract. Postconfluent cultures of HT29 cells form a heterogeneous multilayer of which >95% of the cells are undifferentiated . In contrast, when stably adapted to normally lethal concentrations of methotrexate (10~-10-5 M), they form a monolayer of gobletlike cells (Lesuffieur et al ., 1990) which secrete large quantities of mucins and display a discrete brush border with the presence of villin, dipeptidylpeptidase-IV, and carcinoembryonic antigen . When adapted to even higher concentrations of methotrexate (10-4 and

The activity of superoxide dismutases (SOD) 1 and 2 was analysed in correlation with mRNA and chromosome content in 6 SV40-transformed (TF) and in non-transformed (NF) human fibroblast cell lines. Total SOD activity was fairly constant, whereas the ratio SOD2/SOD1 was much lower in TF than in NF. The decrease in SOD2 activity was correlated with a low mRNA content, and with the presence of various chromosomal rearrangements leading to deletions of the long arm of chromosome 6 where the gene is mapped. In contrast, chromosome 21, carrying the gene for SOD1, was not found to be deficient and the SOD1 activity was high. This shows that in TF, the activity of SOD2 is largely determined by gene dosage. It has been proposed that SOD activity could be inversely correlated with cell proliferation, and that SOD2 activity, in particular, was related to cell differentiation. Thus, there is a cascade of events occurring in cell transformation, involving gene deregulation, chromosome (gene) deletion, low mRNA and protein content, low enzyme activity, and acquisition of growth advantage which makes the SOD2 gene a possible new type of tumor-suppressor gene.