PROLACTIN ACTS ON THE EXTREME 5' PORTION OF MMTV LTR INVOLVING A MAMMARY CELL-SPECIFIC ENHANCER

We have previously shown that a human mammotropic polypeptide hormone, prolactin (PRL) can act synergisticaIly with steroid hormones to regu late gene expression directed by the long terminal repeat of mouse mam mary tumor virus (MMTV LTR) in a human ductal carcinoma cell line T47D cells using a chloramphenicol acetyltransferase reporter gene system and gene transfection methods. In the present study, using various rec ombinant plasmids we analyzed functional elements in the MMTV LTR that is essential for the PRL responses. We show that the PRL-responsive e lements are located in the extreme 5' end of the MMTV LTR, a region pr eviously described by others to be a mammary cell-specific enhancer.