RESUMO
Proteins of the membrane-associated guanylate kinase family play an important role in the anchoring and clustering of neurotransmitter receptors in the postsynaptic density (PSD) at many central synapses. However, relatively little is known about how these multifunctional scaffold proteins might provide a privileged site for activity- and cell type-dependent specification of the postsynaptic signaling machinery. Rho signaling pathway has classically been implicated in mechanisms of axonal outgrowth, dendrogenesis, and cell migration during neural development, but its contribution remains unclear at the synapses in the mature CNS. Here, we present evidence that Citron, a Rho-effector in the brain, is enriched in the PSD fraction and interacts with PSD-95/synapse-associated protein (SAP)-90 both in vivo and in vitro. Citron colocalization with PSD-95 occurred, not exclusively but certainly, at glutamatergic synapses in a limited set of neurons, such as the thalamic excitatory neurons; Citron expression, however, could not be detected in the principal neurons of the hippocampus and the cerebellum in the adult mouse brain. In a heterologous system, Citron was shown to form a heteromeric complex not only with PSD-95 but also with NMDA receptors. Thus, Citron-PSD-95/SAP-90 interaction may provide a region- and cell type-specific link between the Rho signaling cascade and the synaptic NMDA receptor complex.
Assuntos
Proteínas de Ciclo Celular , Proteínas do Tecido Nervoso/metabolismo , Proteínas Serina-Treonina Quinases , Proteínas/metabolismo , Fator Rho/metabolismo , Transdução de Sinais/fisiologia , Tálamo/fisiologia , Animais , Células Cultivadas , Cricetinae , Proteína 4 Homóloga a Disks-Large , Ácido Glutâmico/fisiologia , Guanilato Quinases , Peptídeos e Proteínas de Sinalização Intracelular , Proteínas de Membrana , Camundongos , Ligação Proteica , Receptores de N-Metil-D-Aspartato/metabolismo , Proteínas Associadas SAP90-PSD95 , Tálamo/metabolismoRESUMO
Using the yeast two hybrid system and overlay assays we identified a putative rholrac effector, citron, which interacts with the GTP-bound forms of rho and rac1, but not with cdc42. Extensive homologies to known proteins were not observed. This 183 kDa protein contains a C6H2 zinc finger, a PH domain, and a long coiled-coil forming region including 4 leucine zippers and the rholrac binding site. We recently identified three others putative rho effectors characterized by a common rho binding motif. Citron does not share this motif and displays a distinctive protein organization, thus defining a separate class of rho partners.