AROMATASE GENE-EXPRESSION AND ITS EXON-I USAGE IN HUMAN BREAST-TUMORS- DETECTION OF AROMATASE MESSENGER-RNA BY REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION

The expression of aromatase in human breast tumors has been studied by the reverse-transcription polymerase chain reaction (RT-PCR) method o n 70 breast tissue specimens. An RT-PCR analysis using two oligonucleo tide primers derived from the exon II of the human aromatase gene reve aled that aromatase mRNA was detected in all but three tissue specimen s. Furthermore, primer-directed RT-PCR was performed to determine the exon I usage in aromatase mRNA in these breast tumor specimens. The an alysis has revealed that exons I.3 and PII are the two major exon Is p resent in aromatase mRNA isolated from breast tumors, suggesting that promoters I.3 and II are the major promoters driving aromatase express ion in breast cancer and surrounding adipose stromal cells. The RT-PCR analysis also detected two products, I.3A (334 bp in length) and I.3B (222 bp in length), when it was carried out using a primer derived fr om exon I.3 and a reverse primer derived from exon II. The nucleotide sequences of these products have been determined and indicate that I.3 A contains a region which was previously thought to be an intron. In a ddition, RT-PCR analyses of RNA isolated from eight pairs of breast tu mor and neighboring normal tissue specimens were performed to evaluate the exon I usage and the distribution of I.3A- and I.3B-containing ar omatase RNA messages in breast tumor and neighboring normal tissues. T he results suggest that I.3B- and I.3A-containing messages are mainly present in breast tumor and neighboring normal tissues, respectively. Finally, the exon I/promoter usage for aromatase expression in eight c ell lines (skin fibroblast, MCF-7, MDA-MB-231, T-47D, SK-BR-3, JAR, OV CAR-3, and human adipose stromal cells) was examined by primer-directe d RT-PCR analyses. These studies provide a basis for further evaluatio n of the control mechanism of aromatase expression and estrogen biosyn thesis in breast tumors. Copyright (C) 1996 Published by Elsevier Scie nce Ltd.