The Neuropeptide Y Y1 Receptor: A Diagnostic Marker? Expression in MCF-7 Breast Cancer Cells Is Down- Regulated by Antiestrogens In Vitro and in Xenografts

The neuropeptide Y (NPY) Y1 receptor (Y1R) has been suggested as a tumor marker for in vivo imaging and as a therapeutic target. In view of the assumed link between estrogen receptor (ER) and Y1R in mammary carcinoma and with respect to the development of new diagnostic tools, we investigated the Y1R protein expression in human MCF-7 cell variants differing in ER content and sensitivity against antiestrogens. ER and Y1R expression were quantified by radioligand binding using [ 3H]-17b-estradiol and the Y1R selective antagonist [ 3H]-UR-MK114, respectively. The latter was used for cellular binding studies and for autoradiography of MCF-7 xenografts. The fluorescent ligands Cy5-pNPY (universal Y1R, Y2R and Y5R agonist) and UR-MK22 (selective Y1R antagonist), as well as the selective antagonists BIBP3226 (Y1R), BIIE0246 (Y2R) and CGP71683 (Y5R) were used to identify the NPY receptor subtype(s) by confocal microscopy. Y1R functionality was determined by mobilization of intracellular Ca2+. Sensitivity of MCF-7 cells against antiestrogen 4-hydroxytamoxifen correlated directly with the ER content. The exclusive expression of Y1Rs was confirmed by confocal microscopy. The Y1R protein was up-regulated (100%) by 17b-estradiol (EC50 20 pM) and the predominant role of ERa was demonstrated by using the ERa-selective agonist ‘‘propylpyrazole triol’’. 17b-Estradiol-induced over-expression of functional Y1R protein was reverted by th