Limited lifespan in somatic cell hybrids and cybrids

Abstract

The transformed phenotype is believed to be dominant in fusions between limited lifespan cells and transformed cells, based on heterokaryon experiments and on the isolation of transformed hybrids from mass cultures of fused cells. A series of fusions has been performed between limited lifespan Lesch-Nyhan fibroblast cells and a permanent HeLa cell line with a complementary genetic marker. The growth of independently isolated hybrid clones was followed in parallel with Lesch-Nyhan cells. In fusions involving Lesch-Nyhan cells which had completed about 50% of their lifespan, all hybrids initially show fibroblastic properties. Thirty-five hybrids had a limited lifespan slightly longer than Lesch-Nyhan controls. Three other hybrid clones, and all mass cultures of hybrids, showed the appearance of transformed colonies at a rate of approx. one transformant in 2 × 10 5 hybrid cells. These transformed cells showed anchorage independence, low serum requirement, chromosome loss, and have been maintained in culture for 50–100 population doublings with no signs of senescence. Fusions involving enucleated HeLa cells did not show transformation. Fusions with senescent Lesch-Nyhan cells yielded hybrids which grew beyond the normal Lesch-Nyhan cell lifespan, but which again showed limited lifespan and low frequency transformation. It is concluded that limited lifespan is expressed in a dominant manner in these fusions, and that transformation or “escape from senescence” is a low frequency event requiring the presence of the HeLa nucleus.