Alterations in the p16 INK4a and p53 tumor suppressor genes ofhTERT-immortalized human fibroblasts

Exogenous expression ofthe catalytic subunit oftelome-rase, hTERT, in a normal human foreskin fibroblast cellstrain resulted in telomerase activity and an extendedproliferative lifespan prior to a period of crisis. Threeimmortalized cell lines with stably maintained telomerelengths were established from cells that escaped crisis.Each ofthese cultures underwent a significant down-regulation ofp16