Structure of the human prolactin receptor gene. Novel truncated receptor species inhibit prolactin action.

ML Dufau, M.D., Ph.D, ZZ Hu, M.D., J Meng, M.D.

Endocrinology and Reproduction Research Branch, NICHD, National Institutes of Health, Bethesda, MD 20892

AIM: Prolactin receptors (PRLR) are expressed in normal and neoplastic human tissues, and prolactin exerts proliferative effects in human breast cancer cells. We sought insights into the control of prolactin actions by unraveling the complex genomic structure of the human PRLR receptor (hPRLR) gene, and by cloning two novel human forms of the hPRLR. METHODS: 5- and 3-prime RACE of RNAs of normal tissues and breast cancer cells (T-47D) and RT-PCR analysis. Co-transfection of hPRLR forms and β-casein reporter assay. RESULTS: We have resolved the complete genomic structure of the hPRLR gene. Transcription of the hPRLR is controlled by multiple promoters that utilize distinct mechanisms to regulate gene expression. In addition to its generic exon 1, the gene has five human- specific non-coding exons 1 that are alternatively spliced to a common non-coding exon 2. One of these exons is only expressed in cancer cells. In addition to coding exons 3-10, a novel exon-11 distinct from that of the rodent was found, and two novel short forms of the hPRLR with unique C-terminal domains, derived from alternative splicing of exons 10 and 11, were identified. These forms are present in several tissues and cancer cells and act as dominant negative repressors of the function of the long form of the receptor. CONCLUSIONS: This work provides novel information for the development of therapeutic strategies in breast cancer based on the genomic control of prolactin receptor expression, and dominant negative inhibition of prolactin's actions through the long form of the receptor.

KEY WORDS: Keywords transcriptional control, alternate non-coding exons/promoters, dominant negative function, breast cancer, T-47D cells.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Gene Expression, Part 2.