Abstract
The function and distribution of α1-adrenergic receptor (AR) subtypes in prostate cancer cells is well characterized. Previous studies have used RNA localization or low-avidity antibodies in tissue or cell lines to determine the α1-AR subtype and suggested that the α1 A-AR is dominant. Two androgen-insensitive, human metastatic cancer cell lines DU145 and PC3 were used as well as the mouse TRAMP C1-C3 primary and clonal cell lines. The density of α1-ARs was determined by saturation binding and the distribution of the different α1-AR subtypes was examined by competition-binding experiments. In contrast to previous studies, the major α1-AR subtype in DU145, PC3 and all of the TRAMP cell lines is the α1B-AR. DU145 cells contained 100% of the α1B-AR subtype, whereas PC3 cells were composed of 21% α1 A-AR and 79% α1B-AR. TRAMP cell lines contained between 66% and 79% of the α1B-AR with minor fractions of the other two subtypes. Faster doubling time in the TRAMP cell lines correlated with decreasing α 1B-AR and increasing α1 A- and α1D-AR densities. Transfection with EGFP-tagged α1B-ARs revealed that localization was mainly intracellular, but the majority of the receptors translocated to the cell surface after extended preincubation (18 hr) with either agonist or antagonist. Localization was confirmed by ligand-binding studies and inositol phosphate assays where prolonged preincubation with either agonist and/or antagonist increased the density and function of α 1-ARs, suggesting that the native receptors were mostly intracellular and nonfunctional. Our studies indicate that α1B-ARs are the major α1-AR subtype expressed in DU145, PC3, and all TRAMP cell lines, but most of the receptor is localized in intracellular compartments in a nonfunctional state, which can be rescued upon prolonged incubation with any ligand.