Irreversible telomere shortening by 3'-azido-2',3'-dideoxythymidine (AZT) treatment

Telomeres shorten by 30 to 50 bp with each cell division. Germ line, tumor and stem cells overcome progressive shortening by elongating their telomeres with telomerase. Previously we demonstrated that 3'-azido-2',3'-dideoxythymidine (AZT), incorporates into telomeric DNA. To determine if telomeric AZT incorporation was a telomerase mediated phenomenon, we subjected tumor cells to long-term AZT exposure. Here we report the shortening of the telomeric sequences of HeLa cells cultured with 800 microM AZT for 15 passages. Southern blots of HeLa DNA cultured with AZT and digested with SAU 3AI, Alu I, and Rsa I revealed a progressive shortening of the telomeric repeats when probed with a human biotinylated telomeric probe. The shortened telomeric repeats did not elongate after culturing without AZT for an additional 25 passages. No evidence of senescence could be detected.