EFFECTS OF REVERSE-TRANSCRIPTASE INHIBITORS ON TELOMERE LENGTH AND TELOMERASE ACTIVITY IN 2 IMMORTALIZED HUMAN CELL-LINES

The ribonucleoprotein telomerase, a specialized cellular reverse trans criptase, synthesizes one strand of the telomeric DNA of eukaryotes. W e analyzed telomere maintenance in two immortalized human cell lines: the B-cell line JY616 and the T-cell line Jurkat E6-1, and determined whether known inhibitors of retroviral reverse transcriptases could pe rturb telomere lengths and growth rates of these cells in culture. Did eoxyguanosine (ddG) caused reproducible, progressive telomere shorteni ng over several weeks of passaging, after which the telomeres stabiliz ed and remained short. However, the prolonged passaging in ddG caused no observable effects on cell population doubling rates or morphology. Azidothymidine (AZT) caused progressive telomere shortening in some b ut not all T- and B-cell cultures. Telomerase activity was present in both cell lines and was inhibited in vitro by ddGTP and AZT triphospha te. Prolonged passaging in arabinofuranyl-guanosine, dideoxyinosine (d dI), dideoxyadenosine (ddA), didehydrothymidine (d4T), or phosphonofor mic acid (foscarnet) did not cause reproducible telomere shortening or decreased cell growth rates or viabilities. Combining AZT, foscarnet, and/or arabinofuranyl-guanosine with ddG did not significantly augmen t the effects of ddG alone. Strikingly, with or without inhibitors, te lomere lengths were often highly unstable in both cell lines and varie d between parallel cell cultures. We propose that telomere lengths in these T- and B-cell lines are determined by both telomerase and telome rase-independent mechanisms.