Mammaglobin 1: not only a breast-specific and tumour-specific marker, but also a hormone-responsive endometrial protein

Aims: The secretoglobin mammaglobin 1 (MGB1) is strongly expressed in breast tumours, and is therefore used to detect breast cancer metastases, although it has also been detected in other tissues. The aim of this study was to examine MGB1 expression and its hormonal regulation in human endometrium to further investigate the use of MGB1 as a marker molecule. Methods and results: Mammaglobin 1 expression was assessed immunohistochemically in endometrial samples from 60 normal fertile patients throughout the menstrual cycle, in 49 endometriotic tissue samples, in 15 endometrial adenocarcinomas, and in 36 breast carcinomas. In addition, 25 endometrial samples were analysed by western blot and quantitative real-time reverse transcription polymerase chain reaction. To prove hormonal regulation, primary endometrial epithelial cells were cultured with 17 beta-oestradiol and promegestone. MGB1 was detected in human endometrial tissue, with peak expression during the luteal phase, in 31% of endometriotic samples, in 53% of endometrial adenocarcinomas, and in 64% of breast carcinomas. MGB1 mRNA expression was increased in vitro by hormonal treatment. Conclusions: Our data show that MGB1 expression is not restricted to normal and malignant breast tissue. Besides its documented occurrence in endometriotic and malignant endometrial tissues, MGB1 is also expressed in normal human endometrium, and such expression is controlled by steroid hormones.