5'-Nucleotidase levels in normal and virus-transformed cells: implications for cellular aging in vitro

5'-Nucleotidase activity in the postnuclear supernatant of normal and SV-40 virus-transformed human embryonic lung, chick embryo, and mouse embryo fibroblasts, WI-38, IMR-90, VA-13, CEF, 3T3, and SV3T3 cells was measured. In IMR-90 and CEF cells, both of which have a limited lifespan in vitro, 5'-nucleotidase activity increased 6- and 20-fold, respectively, with increasing population doublings. However, VA-13 cells, a permanent cell line, showed no increase in this enzyme activity with progressive population doublings. 5'-Nucleotidase activity was not detectable in two other permanent cell lines, 3T3 and SV3T3 cells. Of the six cell lines tested, the conspicuous enhancement in 5'-nucleotidase activity with increasing population doublings was observed only in normal cell lines and was absent in transformed cell lines. These observations suggest a molecular mechanism which may play a role in aging of normal cells in vitro and which may involve catabolism of nucleic acids.