SYSTEMATIC DETERMINATION OF TELOMERASE ACTIVITY AND TELOMERASE LENGTHDURING THE PROGRESSION OF HUMAN BREAST-CANCER IN CELL-CULTURE MODELS

The purpose of the study was to determine systematically the expressio n of telomerase activity and the length of telomere repeat arrays by u tilizing two different cell culture models that derive from normal ind ividual donors, and probably represent various stages of human breast oncogenesis in cell culture. The models consist of mortal, non-tumorig enic immortal and tumorigenic immortal human mammary epithelial cell ( MEC) lines. Using a recently developed polymerase chain reaction (PCR) -based telomeric repeat amplification protocol (TRAP) assay, telomeras e activity was undetectable in mortal MEC cells. In contrast, the immo rtal MEC that were nontumorigenic or tumorigenic in immunosuppressed a thymic mice, showed telomerase activity. The absence of telomerase act ivity in mortal and its presence in both non-tumorigenic and tumorigen ic immortal cell lines did not reflect their proliferative rate as dem onstrated by the similar pattern and intensity of reactivity of these cell lines with anti-Ki 67 antibody which recognizes a human nuclear c ell proliferation - associated antigen. Southern blot analyses of Hinf I-digested genomic DNA hybridized with a (TTAGGG)(4) probe revealed a rrays of telomeric repeat lengths ranging from 3 to 5, 3.5 to 9, 3.2 t o 9 or 3 to 15 kilobase pair (kbp) for mortal, nontumorigenic immortal , and tumorigenic immortal or established MEC lines respectively. Thes e results suggest that telomerase activity and stable telomeric repeat lengths may be a molecular phenotype of the early stages in the progr ession of breast cancer.