Regulation of Fatty Acid Synthetase Ribonucleic Acid in the Human Endometrium during the Menstrual Cycle*

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Abstract
Fatty acid synthetase (FAS) is induced by progesterone in MCF7 and T47D breast cancer cell lines. We studied a possible in vivo regulation of expression of this gene by looking for FAS RNA in human endometrial biopsies at various periods of the menstrual cycle, using a cloned cDNA FAS probe. By Northern blot analysis, we detected the 8-kilobase FAS RNA throughout the cycle in 7 uterine samples. RNA in situ hybridization analysis of frozen sections from 22 endome-trial biopsies showed that FAS RNA was present during follicular and luteal phases of the menstrual cycle in stromal and epithelial cells. RNA levels were quantified by counting autora-diographic silver grains using a computer-aided image analyzer. FAS RNA levels were significantly higher in epithelial cells than in fibroblasts (P < 2 × 10−5). Furthermore, in both cell types, mean FAS RNA concentrations were higher in biopsies removed during the luteal phase than the follicular phase of the menstrual cycle (P = 2 × 10−3 and 9 × 10−5, respectively). A 2- to 3-fold increase in FAS RNA levels between days 8–14 and days 22–24 was detected in 2 normal patients who had previously undergone 2 successive biopsies. This increase was not observed in 2 patients with low plasma estradiol and progesterone concentrations, indicating a probable dysovulation. We conclude that FAS normally increases in both stromal and epithelial endometrial cells during the luteal phase. This increase is probably due to progesterone, which implies that FAS i s induced in normal endometrium, as demonstrated in breast cancer.