Two-dimensional electrophoretic analysis of down-regulated proteins in human fibroblasts immortalized by treatment with either 4-nitroquinoline 1-oxide or 60Co gamma rays.

Cellular proteins were examined by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) in order to determine the mechanisms of cellular aging and immortalization of human fibroblasts. A total of 10 cell lines were studied, four of which were immortalized. OUMS-24F and SUSM-1 cells were immortalized by repeated treatment with 4-nitroquinoline 1-oxide (4NQO), KMST-6 cells were immortalized by intermittent exposure to 60Co-gamma rays, and IMR-90/SV40 cells were immortalized with simian virus 40 (SV40). None of these immortalized cells were tumorigenic. Four normal human fibroblast cell lines, OUMS-24, AD 387, KMS-6 and IMR-90, and two human cervical cancer cell lines, HeLa and A-431, were also studied. Applying 2-D PAGE, the down-regulation of the identical proteins was observed in the four immortalized cell lines and in the two human cancer cell lines. Their molecular masses were about 80 kDa and the isoelectric points ranged between 5.5 and 6.3. We could not find any information on our proteins from the recent protein data bases. Further characterization of the proteins indicated that they might be phosphorylated cytoskeletal proteins.