Polymerase chain reaction amplification fails to detect aromatase cytochrome P450 transcripts in normal human endometrium or decidua

It has been proposed that the biosynthesis of estrogens by the human endometrium may be of physiological significance during the menstrual cycle. Local estrogen production was also suggested to be important in the development of endometrial cancer; however, the presence or absence of aromatase enzyme activity in normal human endometrium is controversial. To address this issue, we used a sensitive technique capable of detecting mRNA transcripts present in only very low copy number. The polymerase chain reaction linked to reverse transcription (RT-PCR) was used to evaluate the presence or absence of aromatase cytochrome P450 (P450arom) transcripts in endometrial tissues (n = 7) and endometrial stromal cells (n = 9) under various culture conditions. RNA was isolated from four proliferative and three secretory tissue samples and from cultured endometrial stromal cells isolated from seven proliferative and two secretory endometria. Five sets of cultures were treated with medroxyprogesterone acetate (MPA), estradiol (E₂), and forskolin. Additionally, RNA was isolated from decidualized endometrium obtained from a patient with tubal pregnancy. A single stranded cDNA was synthesized from total RNA using Moloney murine leukemia virus reverse transcriptase and a P450arom-specific oligonucleotide. The single stranded cDNA was used as a template for PCR and was amplified for 20-35 cycles using P450arom-specific primers. RNA from adipose tissue and placenta was amplified to provide positive controls, whereas myometrial RNA was used as a negative control. In two experiments involving two endometrial tissues and three sets of cells in culture, a rat P450arom cRNA was coamplified in each sample as an internal control to demonstrate that the remote possibility of RT-PCR failures in individual test samples cannot account for our negative results. By Southern or slot blot hybridization of the amplified fragments using human and rat P450arom-specific probes, we found no evidence for the presence of P450arom transcripts in normal endometrium, decidualized endometrium, or endometrial stromal cells in culture. In our hands, assay of aromatase activity using [3H]water release from [3H]androstenedione by endometrial stromal cells in culture treated with MPA and E₂, did not reveal any detectable aromatase activity. The same cells responded to MPA plus E₂ treatment by a significant increase in PRL secretion into the culture medium. Presently, RT-PCR is the most sensitive method available for the detection of specific mRNA species in low copy numbers. These findings are indicative of the absence of P450arom transcripts in normal human endometrium.