Phosphorylation of the Nicotinic Acetylcholine Receptor by Protein Tyrosine Kinases^a

Abstract

Most neurotransmitter receptors examined to date are either regulated by phosphorylation or contain consensus sequences for phosphorylation by protein kinases. The nicotinic acetylcholine receptor (AChR), which mediates depolarization at the neuromuscular junction, has served as a model for the study of the structure, function, and regulation of ligand-gated ion channels. The AChR is phosphorylated by protein kinase A, protein kinase C, and an unidentified protein tyrosine kinase. Tyrosine phosphorylation of the AChR is correlated with a modulation of the rate of receptor desensitization and is associated with AChR clustering. We showed that agrin, a neuronally derived extracellular matrix protein, induces AChR clustering and tyrosine phosphorylation. In addition, we identified two protein tyrosine kinases, Fyn and Fyk, that appear to be involved in the regulation of synaptic transmission at the neuromuscular junction by phosphorylating the AChR. The two kinases are highly expressed in Torpedo electric organ, a tissue enriched in synaptic components including the AChR. As demonstrated by coimmunoprecipitation, Fyn and Fyk associate with the AChR. Furthermore, the AChR is phosphorylated in Fyn and Fyk immunoprecipitates. We investigated the molecular basis for the association of the AChR with Fyn and Fyk using fusion proteins derived from the kinases. The AChR bound specifically to the SH2 domain fusion proteins of Fyn and Fyk. The association of the AChR with the SH2 domains is dependent on the state of AChR tyrosine phosphorylation and is mediated by the delta subunit of the receptor. These data provide evidence that the protein tyrosine kinases Fyn and Fyk may act to phosphorylate the AChR in vivo.

Rapsyn carboxyl terminal domains mediate muscle specific kinase–induced phosphorylation of the muscle acetylcholine receptor

“…This suggests that β subunit phosphorylation regulates protein interactions involved in receptor localization, whereas δ loop phosphorylation serves other functions. Indeed, tyrosine-phosphorylated δ subunit of Torpedo AChR binds the cytoplasmic tyrosine kinases fyn and fyk (Swope and Huganir, 1994), and the adaptor protein, Grb2, via their SH2 domains, consistent with a signaling role (Colledge and Froehner, 1997).…”

“…One candidate is src family kinases, which are associated with the AChR (Swope and Huganir, 1993, 1994, Fuhrer and Hall, 1996 and are specifically activated following agrin treatment of muscle cells . Src phosphorylates the β and δ subunits in heterologous cells and this is blocked, both by src dominant negative constructs and inhibitors (Mohamed and Swope, 1999).…”

ID1 Facilitates the Growth and Metastasis of Non-Small Cell Lung Cancer in Response to Nicotinic Acetylcholine Receptor and Epidermal Growth Factor Receptor Signaling

“…3D). Since it had been reported that Src family members like Fyn are induced by nicotine in certain cells (62,63), we examined whether Fyn contributes to the induction of ID1 by nicotine. Interestingly, while depletion of Src by siRNA prevented the induction of ID1 by nicotine as well as EGF, depletion of Fyn did not affect the induction of ID1 (Fig.…”

Tyrosine Phosphorylation of Nicotinic Acetylcholine Receptor Mediates Grb2 Binding

“…In electric organ, coimmunoprecipitation experiments demonstrated that tyrosine-phosphorylated AChRs are complexed with Fyn and a novel member of this family, Fyk (Swope and Huganir, 1993). The binding seems to be mediated by the SH2 domains of the kinases and the ␦ subunit of the AChR (Swope and Huganir, 1994). This raises the possibility that the SH2 domains of Fyn and Fyk may compete with Grb2 for binding to the ␦ subunit.…”