| Alpha-2 adrenergic receptors (alpha2-ARs) belong to the super family of seven transmembrane receptors. There are three alpha 2-ARs subtypes (alpha2a-, alpha2b- and alpha 2c-ARs) that are highly homologous and function similarly. However, they have distinct tissue expression distributions and subcellular localizations. The alpha2a- and alpha2c-ARs are highly expressed in neurons of peripheral nervous system (PNS). Little is known concerning the mechanisms that account for the differences in the cellular trafficking of the alpha2a and alpha2c-ARs. The work presented here examines the mechanisms of cellular processing and trafficking of alpha 2- and alpha2c-ARs expressed in multiple cell lines and cultured sympathetic ganglion neurons (SGNs) using indirect immunofluorescence, molecular biology and biochemical methods.; In non polarized cells such as, NRK cells, the heterologous expression of alpha2a and alpha2c-ARs resulted in distinctly different localization. The alpha2a-ARs were primarily localized to the plasma membrane, while the alpha2c-ARs were noted to have limited plasma membrane localization and extensive intracellular retention within the Golgi apparatus and endoplasmic reticulum. In contrast, alpha 2c-ARs expressed in neuroendocrine cell line, PC12 cells, were primarily localized to the plasma membrane. In mature SGNs, the alpha2-ARs were homogenously in the plasma membrane, while the alpha2c-ARs were focally restricted to presynaptic sites in the axon and homogenously present throughout the cell body and dendrite.; The structural determinates of alpha2c-AR that dictate intracellular retention in fibroblast and epithelial cell lines were identified using a chimeric alpha2a/alpha2c-AR strategy. A transplantable IC retention signal was localized to an evolutionary conserved hydrophobic sequence (ALAAALAAAAA) within the alpha2c-AR the amino terminus. The removal of the IC retention signal from alpha2c-AR resulted in both enhanced plasma membrane targeting of receptor and loss of IC retention. Transplanting the IC retention signal into the alpha2a-AR conferred IC retention similar to alpha2c-AR.; Our findings indicate that cells of neuronal origin express specialized trafficking and targeting proteins that assist in the appropriate trafficking of alpha2-AR to specific microdomains of neurons. The role of cellular context in the cellular processing, trafficking and signaling of alpha 2a- and alpha2c-ARs may provide new insight into the treatment of clinical diseases such as, heart failure, hypertension and acute/chronic pain. |
