HUMAN TELOMERASE ACTIVITY IS MODULATED BY ESTROGENS IN EPITHELIAL CELLS WITH HIGHLY RENEWING POTENTIAL

Eukaryotic chromosomes terminate in specialized structures, telomeres, that are necessary for their stability and function. Telomere replication is catalyzed by telomerase, a ribonucleoprotein that utilizes its own RNA component as the template for de novo synthesis of telomeric DNA. Little is known about mechanisms underlying regulation of telomerase activity. We are currently investigating hormonal control of telomerase activity in human epithelial tissues or cell lines, known to be target of hormone action (ovary, endometrium, prostate, etc.). A highly sensitive PCR-based assay, the Telomeric Repeats Amplification Protocol (TRAP) was used to measure telomerase activity in extracts from human cells and tissues. Whole cell extracts obtained from primary cultures of ovary epithelial cells (GRO, LLO, LEA) were telomerase-negative. Addition of 17?-estradiol (10-7 M) to culture medium caused reactivation of telomerase, already after 6 hours upon hormone addition. This effect was paralleled by a similar induction of mRNA levels of hTERT, the protein catalytic component of telomerase, as measured by RT-PCR. The prompt estrogen induction of hTERT mRNA is in favour of a regulatory mechanism acting at the transcription level. An estrogen response element (ERE) was identified in the context of a 1.0 Kb genomic fragment of the recently cloned hTERT promoter and its sequence shown to bind baculovirus-expressed human estrogen receptor ? by electrophoretic mobility shift assays. This is the first demonstration of hormonal regulation of a non-traditional target, as that of the human telomerase gene, a suitable model for extending our knowledge on the juvenilizing effects of steroid hormones with interesting implications in the process of cell senescence.