Oncogenic transformation of 3T3 cells is associated with conversion from an ‘adult’ to an ‘embryonic’ esterase isoenzyme pattern

Soluble esterases from virus-transformed sublines of 3T3 Swiss mouse fibroblasts exhibit an isoenzyme pattern in polyacrylamide gel electrophoresis similar to the pattern exhibited by primary mouse embryo cells but distinct from that exhibited by 3T3 cells. The soluble esterase isoenzyme pattern exhibited by 3T3 cells is similar to that exhibited by primary and secondary fibroblastoid cells derived from adult Swiss mouse kidney, suggesting that, despite its embryonic origin, 3T3 is an ‘adult’ cell line selected and maintained in that state by the requirement that it exhibits a low saturation density and a characteristic morphology in culture. The pattern of soluble esterase isoenzymes is similar in growing and non-growing 3T3 cells, although the specific activity is higher in preparations from non-growing cells. Sparse 3T3 cells contain at least three detergent-soluble esterase isoenzymes present at much lower levels in denser cultures.The esterase and amidase enzyme activities measured in solution with the fluorogenic substrates fluorescein diacetate and rhodamine diacetate, respectively, are substantially higher in three subcellular fractions from virus-transformed 3T3 mouse fibroblasts than in the corresponding fractions from 3T3 mouse fibroblasts or from primary mouse embryo cells. The largest increases in activity associated with viral transformation were observed in membrane-associated esterases.