A novel telomere elongation in an adriamycin-resistant stomach cancer cell line with decreased telomerase activity.
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.
Kim
Jun Hyun
JH
Department of Biology and Protein Network Research Center, Yonsei University, Seoul, Korea.
Lee
Gun Eui
GE
Kim
Jin Cheon
JC
Lee
Jun Ho
JH
Chung
In Kwon
IK
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
D000970:Antineoplastic Agents; D021122:Protein Subunits; D004317:Doxorubicin; D019098:Telomerase