Cell-type Specific Targeting of the α2c-Adrenoceptor: EVIDENCE FOR THE ORGANIZATION OF RECEPTOR MICRODOMAINS DURING NEURONAL DIFFERENTIATION OF PC12 CELLS

Abstract

We have previously shown differences in the intracellular targeting of alpha2a (alpha(2A))- and alpha2c (alpha(2C))-adrenoreceptors expressed in the same cell line (von Zastrow, M., Link, R., Daunt, D. , Barsh, G., and Kobilka, B. (1993) J. Biol. Chem. 268, 763-766; Daunt, D. A., Hurt, C., Hein, L., Kallio, J., Feng, F., and Kobilka, B. K. (1997) Mol. Pharmacol. 51, 711-720). alpha(2A)-Adrenoreceptors reside primarily in the plasma membrane in HEK 293 cells, while co-expressed alpha(2C)-adrenoreceptors are found mainly in an intracellular compartment. Since alpha(2c)-adrenoreceptors are expressed primarily in the brain, we compared the intracellular targeting of alpha(2C)-adrenoreceptors in two neuroendocrine cell lines with the targeting in three epithelial cell lines and one fibroblast cell line. In transiently transfected COS7 cells, and in stably transfected normal rat kidney cells, Madin-Darby canine kidney cells, and Rat1 fibroblasts, a significant proportion of alpha(2C)-adrenoreceptor detected by immunocytochemistry co-localized with markers for both the endoplasmic reticulum and the cis/medial Golgi compartments. In contrast, both PC12 cells and AtT20 cells efficiently targeted alpha(2C)-adrenoreceptors to the plasma membrane. Ligand binding and Western blot analyses indicate that intracellular receptor in normal rat kidney cells is functional and undergoes normal post-translational processing. In PC12 cells the expressed alpha(2C)-adrenoreceptors become concentrated in neurite outgrowths in discrete regions of the plasma membrane having a high density of F-actin following treatment with nerve growth factor. These findings provide evidence for cell-type specific factors that facilitate the targeting of the G protein-coupled receptors to the plasma membrane.