Synaptic localization of membrane-associated guanylate kinase-interacting protein mediated by the pleckstrin homology domain

Membrane-associated guanylate kinase-interacting protein (MAGUIN) has been identified as a protein binding postsynaptic density (PSD)-95 and synaptic scaffolding molecule (S-SCAM). MAGUIN has one sterile alpha motif, one conserved region in connector enhancer of ksr (Cnk) (CRIC), one PSD-95/Dlg-A/ZO-1 (PDZ) and one pleckstrin homology (PH) domain. There are two isoforms, MAGUIN-1 and -2. MAGUIN-1 binds the PDZ domains of PSD-95 and S-SCAM by the C-terminus, whereas MAGUIN-2 does not bind to PSD-95 or S-SCAM. Here, we have determined that MAGUIN-2 is also localized at synapses and that the synaptic localization of MAGUIN depends on the pleckstrin homology domain. The overexpressed C-terminal PDZ-binding region inhibits the synaptic targeting of PSD-95. Furthermore, the synaptic targeting of MAGUIN does not require N-methyl-d-aspartate (NMDA) receptor activity. These findings suggest that MAGUIN-1 and -2 are recruited to synapses by the PH domain and that MAGUIN-1 subsequently interacts with PSD-95 at synapses.     

NHERF and regulation of the renal sodium-hydrogen exchanger NHE3

The sodium-hydrogen exchanger 3 (NHE3) isoform is the major regulated sodium transporter in the proximal convoluted tubule of the kidney. Study of the regulation of NHE3 by hormonal stimuli has identified a number of PDZ adaptor proteins that form an apical/subapical membrane scaffold that binds NHE3 and facilitates down-regulation of its activity in response to cAMP and activation of protein kinase A. The precise relation of proximal tubule adaptor proteins such as sodium-hydrogen exchanger regulatory factor-1 (NHERF-1), NHERF-2, and PDZ domain-containing-protein-1 (PDZK1) with each other and with protein targets such as NHE3 has been evolving with the development of specific reagents and genetically altered animals. In this review, we trace the discovery of NHERF-1 and NHERF-2, and update our current understanding of the relation between these proteins and the regulation and trafficking of NHE3.     

Interactions between CAP70 and actinfilin are important for integrity of actin cytoskeleton structures in neurons

The integrity of dynamic actin structures is coupled to a variety of neurological processes. Actin-binding proteins play a critical role in regulating actin structure dynamics. A link between actin-binding proteins and receptor interacting scaffolding proteins may provide a conduit for transmitting signaling events to the cytoskeleton. Actinfilin is a brain-enriched actin-binding protein, though its functions are currently unknown. We report here that actinfilin interacts with the multi-PDZ domain protein CAP70. Recombinant expression of an actin-binding domain of actinfilin progressively causes marked changes of cellular morphology. The effect on cell morphology may be reduced by co-expression with CAP70. Mutation of actinfilin lacking the ability to interact with CAP70 abolished the effect by CAP70. The evidence suggests a role of actinfilin and possible regulation by scaffolding proteins.     

Characterization of the Enigma family in zebrafish.

The three Enigma subfamily proteins, Enigma, Enigma homologue, and Cypher/ZASP belong to the PDZ and LIM encoding protein family, which is characterized by the presence of a PDZ- and one or more LIM domains. PDZ/LIM proteins play important biological roles, and all members have been shown to associate with the actin cytoskeleton. We describe here the splice form specific expression patterns for the three Enigma subfamily members during zebrafish embryogenesis. Whole-mount in situ hybridization revealed common and distinct expression patterns for the different PDZ or LIM domain encoding splice variants. We further studied the role of enigma in zebrafish development. Enigma knockdown appeared to be embryonic lethal shortly after the end of gastrulation and in few surviving embryos led to elongation defects and disorganized somites. In summary, we show here the temporal and spatial expression patterns of the three Enigma family members and their PDZ and LIM domain encoding splice forms during zebrafish embryogenesis. Our results suggest that enigma is important for the formation and organization of somites and might play an important role for actin cytoskeleton organization during development.     

Human T-cell leukemia virus type 1 Tax induces an aberrant clustering of the tumor suppressor Scribble through the PDZ domain-binding motif dependent and independent interaction

Human T-cell leukemia virus type 1 (HTLV-1) is a causative agent of adult T-cell leukemia. HTLV-1 Tax1 transforming protein interacts with several PDZ domain-containing proteins, and the interaction is associated with the transforming activities of Tax1 as well as persistent HTLV-1 infection. In this study, we show that Tax1 interacts with the tumor suppressor Scribble containing PDZ domains. Unlike other Tax1-interacting PDZ domain proteins, the PDZ domain-binding motif (PBM) of Tax1 was not required for the interaction with transiently expressed Scribble in 293T cells, but it was essential for the interaction with endogenous Scribble. Endogenous Scribble in 293T cells was primarily localized at the plasma membrane and colocalized with Tax1 but not Tax1C lacking PBM, whereas transiently expressed Scribble was localized in the cytoplasm and colocalized with Tax1C as well as Tax1, thus suggesting that Tax1 is recruited to the site of endogenous Scribble, such as the plasma membrane, in a PBM-dependent manner, and thereafter it interacts with Scribble in a PBM-independent and PBM-dependent manner. Endogenous Scribble was diffusely localized at the plasma membrane of HTLV-1-uninfected T-cell lines, whereas it colocalized with Tax1 as small and large aggregate at the plasma membranes. These results suggest that Tax1 through two binding sites induce aberrant clustering of Scribble, thereby altering the functions in HTLV-1-infected cells, which may thus play a role in persistent HTLV-1 infection and the pathogenesis.     

PDZ interaction site in ephrinB2 is required for the remodeling of lymphatic vasculature

The transmembrane ligand ephrinB2 and its cognate Eph receptor tyrosine kinases are important regulators of embryonic blood vascular morphogenesis. However, the molecular mechanisms required for ephrinB2 transduced cellular signaling in vivo have not been characterized. To address this question, we generated two sets of knock-in mice: ephrinB2DeltaV mice expressed ephrinB2 lacking the C-terminal PDZ interaction site, and ephrinB2(5F) mice expressed ephrinB2 in which the five conserved tyrosine residues were replaced by phenylalanine to disrupt phosphotyrosine-dependent signaling events. Our analysis revealed that the homozygous mutant mice survived the requirement of ephrinB2 in embryonic blood vascular remodeling. However, ephrinB2DeltaV/DeltaV mice exhibited major lymphatic defects, including a failure to remodel their primary lymphatic capillary plexus into a hierarchical vessel network, hyperplasia, and lack of luminal valve formation. Unexpectedly, ephrinB2(5F/5F) mice displayed only a mild lymphatic phenotype. Our studies define ephrinB2 as an essential regulator of lymphatic development and indicate that interactions with PDZ domain effectors are required to mediate its functions.     

Control of synapse development and plasticity by Rho GTPase regulatory proteins

Synapses are specialized cell–cell contacts that mediate communication between neurons. Most excitatory synapses in the brain are housed on dendritic spines, small actin-rich protrusions extending from dendrites. During development and in response to environmental stimuli, spines undergo marked changes in shape and number thought to underlie processes like learning and memory. Improper spine development, in contrast, likely impedes information processing in the brain, since spine abnormalities are associated with numerous brain disorders. Elucidating the mechanisms that regulate the formation and plasticity of spines and their resident synapses is therefore crucial to our understanding of cognition and disease. Rho-family GTPases, key regulators of the actin cytoskeleton, play essential roles in orchestrating the development and remodeling of spines and synapses. Precise spatio-temporal regulation of Rho GTPase activity is critical for their function, since aberrant Rho GTPase signaling can cause spine and synapse defects as well as cognitive impairments. Rho GTPases are activated by guanine nucleotide exchange factors (GEFs) and inhibited by GTPase-activating proteins (GAPs). We propose that Rho-family GEFs and GAPs provide the spatiotemporal regulation and signaling specificity necessary for proper Rho GTPase function based on the following features they possess: (i) existence of multiple GEFs and GAPs per Rho GTPase, (ii) developmentally regulated expression, (iii) discrete localization, (iv) ability to bind to and organize specific signaling networks, and (v) tightly regulated activity, perhaps involving GEF/GAP interactions. Recent studies describe several Rho-family GEFs and GAPs that uniquely contribute to spinogenesis and synaptogenesis. Here, we highlight several of these proteins and discuss how they occupy distinct biochemical niches critical for synaptic development.     

Irving Page Lecture: 5-HT(2A) serotonin receptor biology: interacting proteins, kinases and paradoxical regulation

5-hydroxytryptamine_2A (5-HT_2A) serotonin receptors are important pharmacological targets for a large number of central nervous system and peripheral serotonergic medications. In this review article I summarize work mainly from my lab regarding serotonin receptor anatomy, pharmacology, signaling and regulation. I highlight the role of serotonin receptor interacting proteins and the emerging paradigm of G-protein coupled receptor functional selectivity.     

PICK1在中枢神经系统疾病中的作用

PICK1(protein interacting with C kinase 1)是一种含PDZ(PSD-95/Dlg/ZO1)结构域和BAR (Bin/amphiphysin/Rvs)结构域的蛋白,它可通过PDZ结构域与多种蛋白发生相互作用,其中一些蛋白与中枢神经系统(CNS)疾病密切相关.文中综述了近年来关于PICK1在几种中枢神经系统疾病中的作用研究,以期对疾病研究和临床治疗提供参考.