Incorporation of the β3 subunit has a dominant-negative effect on the function of recombinant central-type neuronal nicotinic receptors

The beta 3 neuronal nicotinic subunit is localized in dopaminergic areas of the central nervous system, in which many other neuronal nicotinic subunits are expressed. So far, beta 3 has only been shown to form functional receptors when expressed together with the alpha 3 and beta 4 subunits. We have systematically tested in Xenopus laevis oocytes the effects of coexpressing human beta 3 with every pairwise functional combination of neuronal nicotinic subunits likely to be relevant to the central nervous system. Expression of alpha 7 homomers or alpha/beta pairs (alpha 2, alpha 3, alpha 4, or alpha 6 together with beta 2 or beta 4) produced robust nicotinic currents for all combinations, save alpha 6 beta 2 and alpha 6 beta 4. Coexpression of wild-type beta 3 led to a nearly complete loss of function ( measured as maximum current response to acetylcholine) for alpha 7 and for all functional alpha/beta pairs except for alpha 3 beta 4. This effect was also seen in hippocampal neurons in culture, which lost their robust alpha 7-like responses when transfected with beta 3. The level of surface expression of nicotinic binding sites (alpha 3 beta 4, alpha 4 beta 2, and alpha 7) in tsA201 cells was only marginally affected by beta 3 expression. Furthermore, the dominant-negative effect of beta 3 was abolished by a valine-serine mutation in the 9' position of the second transmembrane domain of beta 3, a mutation believed to facilitate channel gating. Our results show that incorporation of beta 3 into neuronal nicotinic receptors other than alpha 3 beta 4 has a powerful dominant-negative effect, probably due to impairment in gating. This raises the possibility of a novel regulatory role for the beta 3 subunit on neuronal nicotinic signaling in the central nervous system.