Interaction between estrogen receptor and Pit-1 protein is influenced by estrogen in pituitary cells

The estrogen responsiveness of the rat prolactin gene expression requires t he presence of both the estrogen receptor (ER) and the tissue-specific tran scription factor, Pit-1 protein. We performed protein interaction assays us ing anti-rat Pit-1 antiserum (a-rPit-1) to investigate the physical interac tions which occur between ER and Pit-1 proteins following estrogen treatmen t. After fusing maltose binding protein (MBP) and Pit-1 protein, we used th e resulting MBP-Pit-l fusion protein to prepare a-rPit-1. Our results show that the estrogen receptor readily co-precipitated with the Pit-1 protein d rawn from the lysates of two prolactin-expressing pituitary cell lines GH(3 ) and PR1. The rate of precipitation appears to be both estrogen- and time- dependent. Cellular levels of estrogen receptors and Pit-1 proteins did not show significant changes during the time of estrogen treatment. We therefo re suggest that an estrogen-dependent physical interaction between ER and P it-1 protein exists in vivo, and that this interaction may play an importan t role in the regulation of prolactin gene expression. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.