ALTERNATIVELY SPLICED TRANSCRIPTS OF THE AROMATASE CYTOCHROME-P450 (CYP19) GENE IN ADIPOSE-TISSUE OF WOMEN

Estrogen biosynthesis in adipose tissue has assumed great significance in terms of a number of estrogen-related diseases. The biosynthesis o f estrogens from C-19 steroids is catalyzed by a specific form of cyto chrome P450, namely aromatase cytochrome P450 (P450arom; the product o f the CYP19 gene). The human CYP19 gene comprises nine coding exons, I I-X, and its transcripts are expressed in the ovary, placenta, testes, adipose tissue, and brain. Tissue-specific expression of the CYP19 ge ne is determined at least in part by the use of tissue-specific promot ers, which give rise to transcripts with unique 5'-noncoding termini. Thus, the distal promoter I.1 is responsible for expression uniquely i n placenta. On the other hand, the proximal promoter II, which regulat es expression via a cAMP-dependent signaling pathway, is responsible f or expression in the gonads. Transcripts in breast adipose tissue cont ain 5'-termini corresponding to expression derived from promoters I.4, II, and I.3, with I.4-specific termini predominating. The latter are derived from promoter I.4, which contains a glucocorticoid response el ement and an interferon-gamma activation site element and is responsib le for expression in the presence of glucocorticoids and members of th e class I cytokine family. The object of the present study was to dete rmine the distribution of these various transcripts in adipose tissue from abdomen, buttocks, and thighs of women, as this would provide imp ortant clues ot the factors regulating aromatase expression in these s ites. To achieve this, we employed competitive reverse transcription-P CR to amplify unique 5'-ends of each of the transcripts of the CYP19 g ene that are expressed in adipose tissue as well as for the coding reg ion to evaluate total CYP19 gene (P450arom) transcript levels. We obse rved that exon I.4-specific transcripts were predominantly present in adipose tissue samples obtained from women regardless of the tissue si te or the age of the individual. In these tissues, promoter II- and ex on I.3-specific transcripts were present in lower copy numbers. We als o demonstrated that in these sites total or exon- specific P450arom tr anscripts levels increased in direct proportion to advancing age and t hat transcript levels were the highest in buttocks, followed by thighs , and lowest in the abdomen. These results suggest that in normal huma n adipose tissue, aromatase expression is mainly under local control b y a number of cytokines via paracrine adn autocrine mechanisms in the presence of systemic glucocorticoids.