HOST CELL-SPECIFIC FOLDING OF THE NEURONAL NICOTINIC RECEPTOR ALPHA-8SUBUNIT

Heterologous expression of the neuronal nicotinic acetylcholine recept or alpha 8 subunit in cultured mammalian cell lines has revealed that the correct folding of this protein is dependent on the host cell type . The alpha 8 subunit, which is able to form homo-oligomeric ion chann els when expressed in Xenopus oocytes, could be detected in all transf ected cell lines by both immunoprecipitation and immunofluorescence mi croscopy with a monoclonal antibody that recognises a linear epitope. In contrast, the alpha 8 subunit could be detected in some but not in all transfected cell lines with a monoclonal antibody that recognises a conformation-sensitive epitope or by nicotinic radioligand binding. It is interesting that although correctly folded alpha 8 protein could be detected in transfected rat pituitary (GH(4)C(1)) cells, only misf olded alpha 8 protein could be detected in a large subpopulation of tr ansfectants (transient or clonal stable isolates). We have also found that the protein encoded by a chimaeric cDNA (constructed from the N-t erminal region of alpha 8 and the C-terminal domain of the serotonin 5 -HT3 receptor subunit) is expressed efficiently, and in a conformation that binds alpha-bungarotoxin, in all cell types examined. These resu lts, together with previous expression studies with the homo-oligomeri c alpha 7 subunit and hetero-oligomeric nicotinic receptor subunit com binations, suggest that the cell-specific folding described here is a phenomenon that may be characteristic of homo-oligomeric nicotinic rec eptors.