Telomerase activity, estrogen receptors (α, β), Bcl-2 expression in human breast cancer and treatment response

BACKGROUND: The mechanism for maintaining telomere integrity is controlled by telomerase, a ribonucleoprotein enzyme that specifically restores telomere sequences, lost during replication by means of an intrinsic RNA component as a template for polymerization. Among the telomerase subunits, hTERT (human telomerase reverse transcriptase) is expressed concomitantly with the activation of telomerase. The role of estrogens and their receptors in the transcriptional regulation of hTERT has been demonstrated. The current study determines the possible association between telomerase activity, the expression of both molecular forms of estrogen receptor (ERα and ERβ) and the protein bcl-2, and their relative associations with clinical parameters. METHODS: Tissue samples from 44 patients with breast cancer were used to assess telomerase activity using the TRAP method and the expression of ERα, ERβ and bcl-2 by means of immunocytochemical techniques. RESULTS: Telomerase activity was detected in 59% of the 44 breast tumors examined. Telomerase activity ranged from 0 to 49.93 units of total product generated (TPG). A correlation was found between telomerase activity and differentiation grade (p = 0.03). The only significant independent marker of response to treatment was clinical stage. We found differences between the frequency of expression of ERα (88%) and ERβ (36%) (p = 0.007); bcl-2 was expressed in 79.5% of invasive breast carcinomas. We also found a significant correlation between low levels of telomerase activity and a lack of ERβ expression (p = 0.03). CONCLUSION: Lower telomerase activity was found among tumors that did not express estrogen receptor beta. This is the first published study demonstrating that the absence of expression of ERβ is associated with low levels of telomerase activity

cDNA microarray profiling of rat mammary gland carcinomas induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 7,12-dimethylbenz[a]anthracene

cDNA microarray analysis was used to examine gene expression profiles in normal female Sprague-Dawley rat mammary gland and in carcinomas induced by the cooked meat-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and the potent experimental carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). Nine tubulopapillary carcinomas (five from PhIP-treated rats and four from DMBA-treated rats) and normal mammary gland from virgin, pregnant and lactating rats were examined on a rat 6.9k cDNA microarray. Although histologically identical, PhIP- and DMBA-induced carcinomas could be distinguished by hierarchical clustering and multi-dimensional scaling analyses of cDNA expression. In addition, the expression of 21 clones was statistically different between PhIP- and DMBA-induced carcinomas (F-test, P \u3c 0.05). The data indicate that distinct chemical carcinogens induce unique gene expression patterns in mammary gland carcinomas. The specific chemical carcinogen-associated cDNA array profiles found in carcinomas may ultimately be applicable to better understanding cancer etiology. PhIP- and DMBA-induced carcinomas also shared similarities in cDNA expression profiles. By comparing the expression in carcinomas (PhIP plus DMBA induced) with normal rat mammary gland (at any stage of differentiation), 172 clones were found to be differentially expressed. Genes showing increased expression in carcinomas by cDNA microarray analysis (and further validated by immunohistochemistry and western blot analysis) include cyclin D1, PDGF-A chain, retinol binding protein 1, prohibitin and the transcription factor STAT5A. The similarities in gene expression between PhIP- and DMBA-induced carcinomas raise the possibility that several molecular pathways for rat mammary gland transformation are maintained irrespective of the carcinogenic initiating agent