Regulation of the Functional Interaction between Cyclin D1 and the Estrogen Receptor

Abstract

We report that the functional interaction between cyclin D1 and the estrogen receptor (ER) is regulated by a signal transduction pathway involving the second messenger, cyclic AMP (cAMP). The cell-permeable cAMP analogue 8-bromo-cAMP caused a concentration-dependent enhancement of cyclin D1-ER complex formation, as judged both by coimmunoprecipitation and mammalian two-hybrid analysis. This effect was paralleled by increases in ligand-independent ER-mediated transcription from an estrogen response element containing reporter construct. These effects of 8-bromo-cAMP were antagonized by a specific protein kinase A (PKA) inhibitor, indicating that the signaling pathway involved was PKA dependent. Further, we show that culture of MCF-7 cells on a cellular substratum of murine preadipocytes also enhanced the functional interaction between cyclin D1 and ER in a PKA-dependent manner. These findings demonstrate a collaboration between cAMP signaling and cyclin D1 in the ligand-independent activation of ER-mediated transcription in mammary epithelial cells and show that the functional associations of cyclin D1 are regulated as a function of cellular context.

ACKNOWLEDGMENTS

We thank Joan Massague for the human p27 expression plasmid (pCMV5-p27), Bruce Spiegelman for 3T3-L1 cells, Ron Evans for pCMX-GAL4 and pCMX-VP16, and Donald McDonnell for pGAL4-TATA-luc.

This work was supported by grants from the Massachusetts Department of Public Health Breast Cancer Research Program (to J.L.), the National Health and Medical Research Council of Australia (to R.L.S.), the New South Wales Cancer Council (to R.L.S.), the National Institutes of Health (PO1 CA80111) (to M.E.E.), and Novartis Pharmaceutical Corp. (to M.E.E.). J.L. is a Suzanne Sheats Breast Cancer Research Fellow. M.E.E. is a Scholar for the Leukemia and Lymphoma Society of America.