title: A novel telomere elongation in an adriamycin-resistant stomach cancer cell line with decreased telomerase activity.
abstract: Actively dividing cells show progressive loss of telomeric DNA during successive rounds of replication due to end-replication problem. Telomere shortening has been proposed as a regulatory mechanism that controls the replicative capacity of primary cells before undergoing cellular senescence. In immortal cells including cancer, cellular senescence can be overcome by reactivation of telomerase or by a telomerase-independent mechanism for lengthening telomeres. In this work, we present a novel example of telomere elongation mechanism in a human stomach adenocarcinoma cell line which was selected for resistance to adriamycin. The resistant cell line (MKN/ADR) had long terminal restriction fragments (TRFs) of up to approximately 50 kb, while its parent cell line (MKN-45) had the TRFs, consisting of a smear extending from approximately 4 to approximately 25 kb. The very large TRFs in MKN/ADR cell line were proven to be telomeric by digestion with the exonuclease Bal31. When telomerase activity was examined using the PCR-based telomeric repeat amplification protocol (TRAP) assay, MKN/ADR cell line showed reduced activity to about 10% of that in MKN-45 cell line. The correlation between reduced telomerase activity and mRNA expression of telomerase subunits in MKN/ADR cell line was assessed by the reverse transcriptase-PCR analysis. The level of human telomerase reverse transcriptase (hTERT) mRNA was lower in MKN/ADR cell line than in MKN-45 cell line. This observation correlates with the finding that telomerase activity is reduced about 10-fold in MKN/ADR cell line. Reverse transcriptase-PCR analysis also revealed a close correlation between telomerase-associated protein (TP1) mRNA expression and telomerase activity in MKN/ADR cell line. In contrast, expression levels of human telomerase RNA (hTR) were identical in both MKN/ADR and MKN-45 cell lines. Taken together, these data suggest that telomeres in MKN/ADR cell line may be regulated through a novel mechanism other than telomerase. Although the basis for telomere elongation mechanism in MKN/ADR cell line is not yet understood, the occurrence of alternative mechanism for telomere elongation in drug-resistant cancer cells may have an important implication for use of telomerase inhibitors in human cancer treatment.
authors.affiliation: Department of Biology and Protein Network Research Center, Yonsei University, Seoul, Korea.
authors.forename: Jun Hyun
authors.initials: JH
authors.lastname: Kim
authors.forename: Gun Eui
authors.initials: GE
authors.lastname: Lee
authors.forename: Jin Cheon
authors.initials: JC
authors.lastname: Kim
authors.forename: Jun Ho
authors.initials: JH
authors.lastname: Lee
authors.forename: In Kwon
authors.initials: IK
authors.lastname: Chung
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D002875:Chromosomes / Q000235:genetics / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007621:Karyotyping; D009693:Nucleic Acid Hybridization; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D013274:Stomach Neoplasms / Q000235:genetics / Q000378:metabolism*; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D021122:Protein Subunits; D004317:Doxorubicin; D019098:Telomerase