In mammals, molecular mechanisms and factors involved in the tight regulation of telomerase expression and activity are still largely undefined. In this study, we provide evidence for a role of estrogens and their receptors in the transcriptional regulation of hTERT, the catalytic subunit of human telomerase and, consequently, in the activation of the enzyme. Through a computer analysis of the hTERT 5-flanking sequences, we identified a putative estrogen response element (ERE) which was capable of binding in vitro human estrogen receptor ␣ (ER␣). In vivo DNA footprinting revealed specific modifications of the ERE region in ER␣-positive but not ER␣-negative cells upon treatment with 17␤-estradiol (E2), indicative of estrogen-dependent chromatin remodelling. In the presence of E2, transient expression of ER␣ but not ER␤ remarkably increased hTERT promoter activity, and mutation of the ERE significantly reduced this effect. No telomerase activity was detected in human ovary epithelial cells grown in the absence of E2, but the addition of the hormone induced the enzyme within 3 h of treatment. The expression of hTERT mRNA and protein was induced in parallel with enzymatic activity. This prompt estrogen modulation of telomerase activity substantiates estrogen-dependent transcriptional regulation of the hTERT gene. The identification of hTERT as a target of estrogens represents a novel finding which advances the understanding of telomerase regulation in hormone-dependent cells and has implications for a potential role of hormones in their senescence and malignant conversion.Most human somatic cells do not express telomerase, the ribonucleoprotein that elongates telomeric DNA, or its catalytic protein, hTERT, which is limiting for enzyme activity (33). In humans, telomerase is regulated in a tissue-specific manner during development (42); the enzyme is present in early embryogenesis but is repressed upon cell differentiation in somatic tissues (27,42). Loss of enzymatic activity is accompanied by loss of the full-length transcript of hTERT and/or by the appearance of alternatively spliced transcripts that are unlikely to encode functional proteins (21, 42). In the adult, telomerase persists only in germ line cells and in progenitor cells of somatic tissues with self-renewing potential, in agreement with the requirement for the enzyme for sustained cell proliferation (16). How hTERT silencing is achieved and which factors contribute to this process are presently unknown, although the regulation of hTERT expression appears to be primarily at the transcriptional level (42). An understanding of the molecular mechanisms underlying the regulation of telomerase activity might allow the modulation of telomerase expression and, consequently, of cell life span (4, 43), with important potential therapeutic applications in aging and malignancy.Several lines of evidence suggest that sex steroid hormones may be good candidates as physiological regulators of hTERT expression. Recent findings are consistent with the hypothesis that te...

Steroid/thyroid/retinoid receptors are members of the nuclear receptor superfamily and ligand-inducible transcription factors. These receptors modulate transcription of various cellular genes, either positively or negatively, by interacting with specific hormone-response elements located in the target gene promoters. Recent data show that nuclear receptors enhance or inhibit transcription by recruiting an array of coactivator and corepressor proteins to the transcription complex. We examined and compared the expression of four coactivator (steroid receptor coactivator-1 and E1A-associated 300-kDa protein) and corepressor (SMRT and N-CoR) genes in a number of tissues including several endocrine glands and cell lines. We also addressed whether their messenger RNA levels are hormonally regulated by studying the effects of thyroid hormone (T3) and estrogen (E2) treatment in rat pituitary cells (GH3) in vitro and in anterior pituitary in vivo. Our studies show that there are distinct tissue-specific expression patterns of these genes. We show that T3 and E2 regulate the expression of steroid receptor coactivator-1 messenger RNA in the anterior pituitary in addition to a gender-related difference. These tissue variations may have physiological implications for heterogeneity of hormone responses that are observed in normal and malignant tissues.

3,5,3'-triiodothyronine (T3) is essential for the growth and the regulation of metabolic functions, moreover, the growth-stimulatory effect of T3 has largely been demonstrated and the pathways via which T3 promotes cell growth have been recently investigated. Type 1 diabetes (T1D) is due to the destruction of beta-cells, which occurs even through apoptosis. Aim of our study was to analyze whether T3 could have an antiapoptotic effect on cultured beta-cells undergoing apoptosis. We have demonstrated that T3 promotes cell proliferation in islet beta-cell lines (rRINm5F and hCM) provoking an increment in cell number (up to 55%: rRINm5F and 45%: hCM), cell viability, and BrdU incorporation, and regulating the cell cycle-related molecules (cyc A, D1, E, and p27(kip1)). T3 inhibited the apoptotic process induced by streptozocin, S-Nitroso-N-Acetylpenicylamine (SNAP), and H2O2 via regulation of the pro- and anti-apoptotic factors Bcl-2, Bcl-XL, Bad, Bax, and Caspase 3. The T3 protective effect was PI-3 K-, but not MAPK- or PKA-mediated, involving pAktThr308. Thus, T3 could be considered a survival factor protecting islet beta-cells from apoptosis.

Alterations of the tumor suppressor gene p53 are uncommon in dierentiated thyroid neoplasia but are detected at high frequency in anaplastic thyroid carcinoma suggesting that impaired p53 function may contribute to the undierentiated and highly aggressive phenotype of these tumors. Eects of wild type p53 (wtp53) re-expression were investigated in a human anaplastic thyroid carcinoma cell line (ARO) expressing a mutated p53. ARO cells were stably transfected with the temperature-sensitive p53 Val 135 gene (ts-p53) which exhibits wild type-like activity at 328C. Exogenous wtp53 function in ARO-tsp53 clones was assessed by evaluating its transcriptional activity on a CAT reporter vector containing p53 binding sites. At 328C, a signi®cant reduction in the proliferation rate (%50%) was observed, with accumulation of cells in the G 0 /G 1 phase of the cell cycle. This eect was accompanied by induction of the expression of the growth inhibitor p21/ Waf1 gene. At 328C, ARO-tsp53 clones also showed a marked impairment of their tumorigenic potential. Furthermore, transfected clones re-acquired the ability to respond to thyrotropin (TSH) stimulation showing an increased expression of thyroid-speci®c genes (thyroglobulin, thyroperoxidase and TSH receptor). In conclusion, re-expression of wt-p53 activity in ARO cells, inhibits cell proliferation and restores responsiveness to physiological stimuli.