Telomere maintenance in telomerase‐positive human ovarian SKOV‐3 cells cannot be retarded by complete inhibition of telomerase

• Published in: FEBS letters 2002-09, Vol.527 (1-3), p.10-14
• Main Authors: Gan, Yuebo, Mo, Yiqun, Johnston, Jeffrey, Lu, Jie, Wientjes, M.Guillaume, Au, Jessie L.-S
• Format: Article
• Language: English
• Subjects: ALT, alternative lengthening of telomeres; Alternative lengthening of telomeres; AZT, 3′-azido-deoxythymidine; Cells, Cultured; Enzyme Inhibitors - pharmacology; Female; FISH, fluorescence in situ hybridization; hTR, human telomerase RNA component; Humans; IPTG, isopropyl-β-D-thiogalactopyranoside; NHEJ, non-homologous end joining; Oligonucleotides, Antisense - pharmacology; Osteosarcoma - metabolism; Osteosarcoma - pathology; Ovarian cancer; Ovary - cytology; Ovary - drug effects; Ovary - physiology; Pharynx - cytology; Pharynx - physiology; PML, promyelocytic leukemia; Telomerase; Telomerase - antagonists & inhibitors; Telomerase - genetics; Telomerase - metabolism; Telomere; Telomere - drug effects; Telomere - physiology; TERT, telomerase reverse transcriptase; TRAP, telomeric repeat amplification protocol; Zidovudine - pharmacology
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(02)03141-1

The two known mechanisms for telomere maintenance in eukaryocytes are telomerase in telomerase‐positive cells and alternative lengthening of telomeres (ALT) in telomerase‐negative cells. We report here that telomere maintenance in the telomerase‐positive human ovarian SKOV‐3 cells was not affected by inhibition of telomerase. For comparison, the effect of telomerase inhibitors on telomere maintenance in another telomerase‐positive cell line (i.e. human pharynx FaDu cells) and the telomerase‐negative human osteosarcoma Saos‐2 cells was examined. Telomerase activity was measured using a modified telomeric repeat amplification protocol and telomere length was measured using a solution hybridization‐based method and fluorescence in situ hybridization. A reverse transcriptase inhibitor (3′‐azido‐deoxythymidine or AZT) and an antisense against a component of human telomerase RNA (antisense hTR) were used to inhibit telomerase. FaDu and SKOV‐3 cells showed comparable baseline telomerase activity. Telomerase activity in both cells was inhibited about equally by AZT (maximal inhibition of ∼80%) and by expression of antisense hTR (complete inhibition in SKOV‐3 cells and maximal inhibition of ∼80% in FaDu cells). However, treatment with telomerase inhibitors resulted in ∼50% telomere shortening in FaDu cells but had no effect on SKOV‐3 nor Saos‐2 cells. SKOV‐3 cells did not show the characteristic features of ALT (i.e. heterogeneous telomere length and promyelocytic leukemia bodies), whereas these ALT features were observed in Saos‐2 cells. Collectively, these results suggest the existence of a telomerase‐independent mechanism of telomere maintenance in the telomerase‐positive SKOV‐3 cells.