The interaction of RGSZ1 with SCG10 attenuates the ability of SCG10 to promote microtubule disassembly

Palmitoylation of RGS20 affects Gαo-mediated signaling independent of its GAP activity

Regulator of protein signaling (RGS20) is a member of the RGS protein superfamily, which serve as key negative regulators of G protein-mediated signal transduction. Through their GTPase accelerating protein (GAP) activity, RGS proteins deactivate α-subunits of heterotrimeric G proteins. In addition, the majority of RGS proteins also have the ability to act through other, non-GAP related, functions. RGS20 is one of three members of the RZ subfamily, which all show selective GAP activity towards Gα_z, however emerging data suggest that RGS20 can also regulate Gi/o-mediated signaling. While increased RGS20 expression is associated with the progression of multiple cancers, a large gap still exists relating to the mechanisms of RGS20 regulation and function. RGS20 contains a poly-cysteine string motif and a conserved cysteine in RGS domain, which are assumed to be palmitoylated. Palmitoylation, an important post-translational modification, plays an important role in cells by changing cellular functions of proteins. Consequently, the aim of this study was to confirm that RGS20 is palmitoylated and determine how palmitoylation affects its inhibition of Gα_o-mediated signaling. We found a significant positive correlation between RGS20 palmitoylation and its association with active Gα_o. We also showed that a conserved cysteine residue in the RGS domain is a critical site for its palmitoylation, with large impact on its association with Gα_o. Palmitoylation on this site did not affect its GAP activity, however, it increased the inhibition of Gα_o-mediated cAMP signaling. Altogether these data suggest that palmitoylation is a regulatory mechanism controlling RGS20 function, and that RGS20 can inhibit Gα_o signaling through both GAP activity and non-GAP mechanisms.

Regulators of G Protein Signaling in Analgesia and Addiction

Regulator of G protein signaling (RGS) proteins are multifunctional proteins expressed in peripheral and neuronal cells, playing critical roles in development, physiologic processes, and pharmacological responses. RGS proteins primarily act as GTPase accelerators for activated Gα subunits of G-protein coupled receptors, but they may also modulate signal transduction by several other mechanisms. Over the last two decades, preclinical work identified members of the RGS family with unique and critical roles in intracellular responses to drugs of abuse. New information has emerged on the mechanisms by which RGS proteins modulate the efficacy of opioid analgesics in a brain region- and agonist-selective fashion. There has also been progress in the understanding of the protein complexes and signal transduction pathways regulated by RGS proteins in addiction and analgesia circuits. In this review, we summarize findings on the mechanisms by which RGS proteins modulate functional responses to opioids in models of analgesia and addiction. We also discuss reports on the regulation and function of RGS proteins in models of psychostimulant addiction. Using information from preclinical studies performed over the last 20 years, we highlight the diverse mechanisms by which RGS protein complexes control plasticity in response to opioid and psychostimulant drug exposure; we further discuss how the understanding of these pathways may lead to new opportunities for therapeutic interventions in G protein pathways. SIGNIFICANCE STATEMENT: Regulator of G protein signaling (RGS) proteins are signal transduction modulators, expressed widely in various tissues, including brain regions mediating addiction and analgesia. Evidence from preclinical work suggests that members of the RGS family act by unique mechanisms in specific brain regions to control drug-induced plasticity. This review highlights interesting findings on the regulation and function of RGS proteins in models of analgesia and addiction.

Regulator of G protein signaling 20 promotes proliferation and migration in bladder cancer via NF-κB signaling

BACKGROUND

Bladder cancer is a complicated disease with high rate of morbidity and mortality, in which proliferation and migration are both well acknowledged as aggressive phenotypes of bladder cancer cells. A better understanding of the mechanisms of tumor proliferation and migration would provide an insight into cancer progression and provide effective therapeutic strategies.

METHODS

The expression of RGS20 was detected using qRT-PCR,western blotting and immunohistochemistry. MTT, Colony formation, anchorage-independent growth assay, and transwell assay were used to evaluate the pro-proliferation and pro-migration potential of RGS20 in vitro. Tumor growth was monitored and analyzed in an animal model. Luciferase activity assay, nuclear extract analysis, and multiple blockade of NF-κB were used to evaluate NF-κB signaling activity.

RESULTS

It revealed that RGS20 was significantly upregulated in bladder cancer and increased RGS20 expression correlated significantly with worse 5-year overall survival. Ectopic overexpression of RGS20 accelerated the proliferation and migration of bladder cancer cells, whereas knockdown of RGS20 inhibited these effects. Mechanistically, RGS20 could activate NF-κB signaling, which played a crucial role in RGS20's effects on proliferation, migration, and tumorigenicity of bladder cancer cells.

CONCLUSION

Our study highlights that RGS20 acted as an oncogene in bladder cancer and a better understanding of RGS20's functions might provide the potential for clinical intervention in this disease.

Regulator of G protein signaling 20 enhances cancer cell aggregation, migration, invasion and adhesion

Several RGS (regulator of G protein signaling) proteins are known to be upregulated in a variety of tumors but their roles in modulating tumorigenesis remain undefined. Since the expression of RGS20 is elevated in metastatic melanoma and breast tumors, we examined the effects of RGS20 overexpression and knockdown on the cell mobility and adhesive properties of different human cancer cell lines, including cervical cancer HeLa, breast adenocarcinoma MDA-MB-231, and non-small cell lung carcinoma H1299 and A549 cells. Expression of RGS20 enhanced cell aggregation, migration, invasion and adhesion as determined by hanging drop aggregation, wound healing, transwell chamber migration and invasion assays. Conversely, shRNA-mediated knockdown of endogenous RGS20 impaired these responses. In addition, RGS20 elevated the expression of vimentin (a mesenchymal cell marker) but down-regulated the expression of E-cadherin, two indicators commonly associated with metastasis. These results suggest that the expression of RGS20 may promote metastasis of tumor cells.

Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling

Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.

Zebrafish rgs4 is essential for motility and axonogenesis mediated by Akt signaling

The schizophrenia susceptibility gene, Rgs4, is one of the most intensively studied regulators of G-protein signaling members, well known to be fundamental in regulating neurotransmission. However, little is known about its role in the developing nervous system. We have isolated zebrafish rgs4 and shown that it is transcribed in the developing nervous system. Rgs4 knockdown did not affect neuron number and patterning but resulted in locomotion defects and aberrant development of axons. This was confirmed using a selective Rgs4 inhibitor, CCG-4986. Rgs4 knockdown also attenuated the level of phosphorylated-Akt1, and injection of constitutively-activated AKT1 rescued the motility defects and axonal phenotypes in the spinal cord but not in the hindbrain and trigeminal neurons. Our in vivo analysis reveals a novel role for Rgs4 in regulating axonogenesis during embryogenesis, which is mediated by another schizophrenia-associated gene, Akt1, in a region-specific manner.

SUMO-SIM interactions regulate the activity of RGSZ2 proteins

The RGSZ2 gene, a regulator of G protein signaling, has been implicated in cognition, Alzheimer's disease, panic disorder, schizophrenia and several human cancers. This 210 amino acid protein is a GTPase accelerating protein (GAP) on Gαi/o/z subunits, binds to the N terminal of neural nitric oxide synthase (nNOS) negatively regulating the production of nitric oxide, and binds to the histidine triad nucleotide-binding protein 1 at the C terminus of different G protein-coupled receptors (GPCRs). We now describe a novel regulatory mechanism of RGS GAP function through the covalent incorporation of Small Ubiquitin-like MOdifiers (SUMO) into RGSZ2 RGS box (RH) and the SUMO non covalent binding with SUMO-interacting motifs (SIM): one upstream of the RH and a second within this region. The covalent attachment of SUMO does not affect RGSZ2 binding to GPCR-activated GαGTP subunits but abolishes its GAP activity. By contrast, non-covalent binding of SUMO with RH SIM impedes RGSZ2 from interacting with GαGTP subunits. Binding of SUMO to the RGSZ2 SIM that lies outside the RH does not affect GαGTP binding or GAP activity, but it could lead to regulatory interactions with sumoylated proteins. Thus, sumoylation and SUMO-SIM interactions constitute a new regulatory mechanism of RGS GAP function and therefore of GPCR cell signaling as well.

KBP interacts with SCG10, linking Goldberg-Shprintzen syndrome to microtubule dynamics and neuronal differentiation

Goldberg–Shprintzen syndrome (GOSHS) is a rare clinical disorder characterized by central and enteric nervous system defects. This syndrome is caused by inactivating mutations in the Kinesin Binding Protein (KBP) gene, which encodes a protein of which the precise function is largely unclear. We show that KBP expression is up-regulated during neuronal development in mouse cortical neurons. Moreover, KBP-depleted PC12 cells were defective in nerve growth factor-induced differentiation and neurite outgrowth, suggesting that KBP is required for cell differentiation and neurite development. To identify KBP interacting proteins, we performed a yeast two-hybrid screen and found that KBP binds almost exclusively to microtubule associated or related proteins, specifically SCG10 and several kinesins. We confirmed these results by validating KBP interaction with one of these proteins: SCG10, a microtubule destabilizing protein. Zebrafish studies further demonstrated an epistatic interaction between KBP and SCG10 in vivo . To investigate the possibility of direct interaction between KBP and microtubules, we undertook co-localization and in vitro binding assays, but found no evidence of direct binding. Thus, our data indicate that KBP is involved in neuronal differentiation and that the central and enteric nervous system defects seen in GOSHS are likely caused by microtubule-related defects.

RGS proteins: Swiss army knives in seven-transmembrane domain receptor signaling networks

Coordinated regulation of heterotrimeric guanine nucleotide-binding protein (G protein) activity is critical for the integration of information from multiple intracellular signaling networks. The human regulator of G protein signaling (RGS) protein family contains more than 35 members that are well suited for this purpose. Although all RGS proteins contain a core ~120-amino acid Galpha-interacting domain (called the RGS domain), they differ widely in size and organization of other functional domains. Architecturally complex RGS proteins contain multiple modular protein-protein interaction domains that mediate their interaction with diverse signaling effectors. Architecturally simple RGS proteins contain small amino-terminal domains; however, they show surprising versatility in the number of intracellular partners with which they interact. This Perspective focuses on RGS2, a simple RGS protein with the potential to integrate multiple signaling networks. In three recent studies, the amino-terminal domain of RGS2 was shown to interact with and regulate three different effector proteins: adenylyl cyclase, tubulin, and the cation channel TRPV6. To explain this growing list of RGS2-interacting partners, we propose two models: (i) The amino-terminal domain of RGS2 comprises several short effector protein interaction motifs; (ii) the amino-terminal domain of RGS2 adopts distinct structures to bind various targets. Whatever the precise mechanism controlling its target interactions, these studies suggest that RGS2 is a key point of integration for multiple intracellular signaling pathways, and they highlight the role of RGS proteins as dynamic, multifunctional signaling centers that coordinate a diverse range of cellular functions.

The "SCG10-LIke Protein" SCLIP is a novel regulator of axonal branching in hippocampal neurons, unlike SCG10

Stathmin family phosphoproteins participate in the control of microtubule dynamics and have been proposed to be involved in the control of neuronal differentiation. We examined the biological properties and functions of SCLIP, the stathmin family protein most similar to SCG10, a widely studied and recognized neuronal differentiation marker. SCLIP, like SCG10, is present from the earliest stages of hippocampal neuron differentiation in culture at vesicle-like structures following dynamic microtubules. Its inhibition by RNA interference resulted in increased axonal branching, revealing a novel biological role for SCLIP, distinct from SCG10 whose down-regulation in the same conditions promoted growth cone expansion. The enhanced axonal branching resulted from the formation of collateral lamellar protrusions, with cytoskeleton reorganization typical of normal branching. In addition to revealing a novel function for SCLIP in axonal morphogenesis, our results demonstrate for the first time that stathmin family proteins fulfill different and complementary roles during neuronal differentiation.

RGSZ1 interacts with protein kinase C interacting protein PKCI-1 and modulates mu opioid receptor signaling

Protein kinase C interacting protein (PKCI-1) was identified among the potential interactors from a yeast two hybrid screen of human brain library using N terminal of RGSZ1 as a bait. The cysteine string region, unique to the RZ subfamily, contributes to the observed interaction because PKCI-1 interacted with N-terminus of RGS17 and GAIP, but not with that of RGS2 or RGS7 where cysteine string motif is absent. The interaction between RGSZ1 and PKCI-1 was confirmed by coimmunoprecipitation and immunofluorescence. PKCI-1 and RGSZ1 could be detected by coimmunoprecipitation using 14-3-3 antibody in cells transfected with PKCI-1 or RGSZ1 respectively, but when transfected with PKCI-1 and RGSZ1 together, only RGSZ1 could be detected. Phosphorylation of Galphaz by protein kinase C (PKC) reduces the ability of the RGS to effectively function as GTPase accelerating protein for Galphaz, and interferes with ability of Galphaz to interact with betagamma complex. We investigated the roles of 14-3-3 and PKCI-1 in phosphorylation of Galphaz. Phosphorylation of Galphaz by PKC was inhibited by 14-3-3 and the presence of PKCI-1 did not provide any further inhibition. PKCI-1 interacts with mu opioid receptor and suppresses receptor desensitization and PKC related mu opioid receptor phosphorylation [W. Guang, H. Wang, T. Su, I.B. Weinstein, J.B. Wang, Mol. Pharmacol. 66 (2004) 1285.]. Previous studies have also shown that mu opioid receptor co-precipitates with RGSZ1 and influence mu receptor signaling by acting as effector antagonists [J. Garzon, M. Rodriguez-Munoz, P. Sanchez-Blazquez, Neuropharmacology 48 (2005) 853., J. Garzon, M. Rodriguez-Munoz, A. Lopez-Fando, P. Sanchez-Blazquez Neuropsychopharmacology 30 (2005) 1632.]. Inhibition of cAMP by mu opioid receptor was significantly reduced by RGSZ1 and this effect was enhanced in combination with PKCI-1. Our studies thus provide a link between the previous observations mentioned above and indicate that the major function of PKCI-1 is to modulate mu opioid receptor signaling pathway along with RGSZ1, rather than directly mediating the Galphaz RGSZ1 interaction.

Mammalian RGS proteins: Multifunctional regulators of cellular signalling

Regulators of G-protein signalling (RGS) proteins are a large and diverse family initially identified as GTPase activating proteins (GAPs) of heterotrimeric G-protein Galpha-subunits. At least some can also influence Galpha activity through either effector antagonism or by acting as guanine nucleotide dissociation inhibitors (GDIs). As our understanding of RGS protein structure and function has developed, so has the realisation that they play roles beyond G-protein regulation. Such diversity of function is enabled by the variety of RGS protein structure and their ability to interact with other cellular molecules including phospholipids, receptors, effectors and scaffolds. The activity, sub-cellular distribution and expression levels of RGS proteins are dynamically regulated, providing a layer of complexity that has yet to be fully elucidated.

RGS2 promotes formation of neurites by stimulating microtubule polymerization

Regulator of G-protein signaling (RGS) proteins interact with alpha subunits of heterotrimeric G-proteins via the RGS domain and attenuate their activity by accelerating GTPase activity. RGS2, a member of the RGS family, regulates synaptic development via hereto unknown mechanism. In this study, we found that RGS2 directly interacted with tubulin via a short region at the N-terminus: amino acids 41-60. RGS2 enhanced microtubule polymerization in vitro, and the tubulin binding region was necessary and sufficient for this activity. In Vero cells, polymerization of microtubule was stimulated when peptides containing the tubulin binding region were microinjected. Immunocytochemical analysis showed that endogenous RGS2 was localized at the termini of neurites in differentiated PC12 cells. Over-expression of RGS2 enhanced the nerve growth factor-induced neurite outgrowth in PC12 cells, while specific knock-down of endogenous RGS2 suppressed the neurite outgrowth. These findings demonstrate that RGS2 contributes to the neuronal cell differentiation via regulation of microtubule dynamics.

RGS17/RGSZ2 and the RZ/A family of regulators of G-protein signaling

Regulators of G-protein signaling (RGS proteins) comprise over 20 different proteins that have been classified into subfamilies on the basis of structural homology. The RZ/A family includes RGSZ2/RGS17 (the most recently discovered member of this family), GAIP/RGS19, RGSZ1/RGS20, and the RGSZ1 variant Ret-RGS. The RGS proteins are GTPase activating proteins (GAPs) that turn off G-proteins and thus negatively regulate the signaling of G-protein coupled receptors (GPCRs). In addition, some RZ/A family RGS proteins are able to modify signaling through interactions with adapter proteins (such as GIPC and GIPN). The RZ/A proteins have a simple structure that includes a conserved amino-terminal cysteine string motif, RGS box and short carboxyl-terminal, which confer GAP activity (RGS box) and the ability to undergo covalent modification and interact with other proteins (amino-terminal). This review focuses on RGS17 and its RZ/A sibling proteins and discusses the similarities and differences among these proteins in terms of their palmitoylation, phosphorylation, intracellular localization and interactions with GPCRs and adapter proteins. The specificity of these RGS protein for different Galpha proteins and receptors, and the consequences for signaling are discussed. The tissue and brain distribution, and the evolving understanding of the roles of this family of RGS proteins in receptor signaling and brain function are highlighted.

The control of microtubule stability in vitro and in transfected cells by MAP1B and SCG10

In neurons, the regulation of microtubules plays an important role for neurite outgrowth, axonal elongation, and growth cone steering. SCG10 family proteins are the only known neuronal proteins that have a strong destabilizing effect, are highly enriched in growth cones and are thought to play an important role during axonal elongation. MAP1B, a microtubule-stabilizing protein, is found in growth cones as well, therefore it was important to test their effect on microtubules in the presence of both proteins. We used recombinant proteins in microtubule assembly assays and in transfected COS-7 cells to analyze their combined effects in vitro and in living cells, respectively. Individually, both proteins showed their expected activities in microtubule stabilization and destruction respectively. In MAP1B/SCG10 double-transfected cells, MAP1B could not protect microtubules from SCG10-induced disassembly in most cells, in particular not in cells that contained high levels of SCG10. This suggests that SCG10 is more potent to destabilize microtubules than MAP1B to rescue them. In microtubule assembly assays, MAP1B promoted microtubule formation at a ratio of 1 MAP1B per 70 tubulin dimers while a ratio of 1 SCG10 per two tubulin dimers was needed to destroy microtubules. In addition to its known binding to tubulin dimers, SCG10 binds also to purified microtubules in growth cones of dorsal root ganglion neurons in culture. In conclusion, neuronal microtubules are regulated by antagonistic effects of MAP1B and SCG10 and a fine tuning of the balance of these proteins may be critical for the regulation of microtubule dynamics in growth cones.

Role of Ser50 phosphorylation in SCG10 regulation of microtubule depolymerization

Members of the stathmin-like protein family depolymerize microtubules (MTs), probably due to the ability of each stathmin monomer to bind two tubulin heterodimers in a complex (T(2)S complex). SCG10, a member of this family, is localized in the growth cone of neurons. It has four identified sites of serine phosphorylation (S50, S63, S73, and S97). Of these, S50 and S97 are phosphorylated by cAMP-dependent protein kinase, an enzyme involved in growth cone guidance. When the equivalent sites in stathmins are phosphorylated, they lose their ability to depolymerize MTs. We investigated the specific role of the two cAMP-dependent protein kinase (PKA) phosphorylation sites in SCG10. A mutant of SCG10 phosphorylated only on S50 retained the ability to depolymerize MTs, but SCG10 phosphorylated on S97 or on both S50 and S97 lost MT-depolymerizing activity. Surface plasmon resonance studies revealed that the phosphorylation of SCG10 at these sites reduced the tubulin heterodimer binding, mainly due to a reduced rate of association. In particular, compared to the two other phosphorylated forms, SCG10 phosphorylated at S50 had a significantly smaller dissociation constant for the binding of the first tubulin heterodimer and larger association and dissociation rate constants for the binding of the second heterodimer. This indicates that the phosphorylation of S50 compensates for the effect of phosphorylation at other sites by modulating T2S complex formation. Furthermore, these results suggest that S50-P maintains MT-depolymerizing activity, which indicates that the biological functions of phosphorylation at S50 and S97 are different.

Two separate motifs cooperate to target stathmin-related proteins to the Golgi complex

The appropriate targeting of membrane-associated proteins involves a diversity of motifs including post-translational modifications and specific protein sequences. Phosphoproteins of the stathmin family are important regulators of microtubule dynamics, in particular in the developing and mature nervous system. Whereas stathmin is cytosolic, SCG10, SCLIP and the splice variants RB3/RB3′/RB3″ are associated with Golgi and vesicular membranes, through their palmitoylated N-terminal A domains. In order to identify essential motifs involved in this specific targeting, we examined the subcellular distribution of various subdomains derived from domain A of SCG10 fused with GFP. We show that the Golgi localization of SCG10 results from the cooperation of two motifs: a membrane-anchoring palmitoylation motif and a newly identified Golgi-specifying sequence. The latter displayed no targeting activity by itself, but retained a Golgi-specifying activity when associated with another membrane-anchoring palmitoylation motif derived from the protein GAP-43. We further identified critical residues for the specific Golgi targeting of domain A. Altogether, our results give new insight into the regulation of the subcellular localization of stathmin family proteins, an important feature of their physiological functions in differentiating and mature neural cells. More generally we provide new information on essential mechanisms of functional protein subcellular targeting.

Analysis of interactions between regulator of G-protein signaling-14 and microtubules

Microtubules are dynamic polymers essential for mitosis and cell division, intracellular transport, and maintaining cell organization and structure. Microtubule dynamics are tightly controlled in a context-specific manner by a myriad of microtubule-associated proteins. We have identified regulator of G-protein signaling-14 (RGS14) as a microtubule-associated protein. RGS14 is a component of the mitotic apparatus that binds directly to and stabilizes microtubules in vitro and is essential for the first cell division in the mouse embryo. This article describes methods used for examining the impact of the RGS14/microtubule interaction in vivo and in vitro.

Reciprocal signaling between the transcriptional co-factor Eya2 and specific members of the Galphai family

As part of a program to elucidate signaling processes controlled by the heterotrimeric G protein Galphaz, a human fetal brain cDNA library was screened for proteins that specifically interact with the activated form of Galphaz. One of the most-encountered molecules in this screen was Eya2, a member of the Eyes absent family of proteins. Mammalian Eya proteins are predominantly cytosolic proteins that are known to interact with members of the Sine oculis (Six) family of homeodomain transcription factors. This interaction facilitates the translocation of Eya into the nucleus, where the Eya/Six complex regulates transcription during critical stages of embryonic development. In vitro binding studies confirmed that Galphaz interacts with Eya2 in an activation-dependent fashion; furthermore, most other members of the Galphai family including Galphai1, Galphai2, and Galphai3 were found to interact with Eya2. It is interesting that one of the most abundant Galphai proteins, Galphao, did not interact with Eya2. Coexpression of the activated forms of Galphai1, Galphai2, and Galphai3, but not Galphao, with Eya2 recruited Eya2 to the plasma membrane, prevented Eya2 translocation into the nucleus, and abrogated Eya2/Six4-mediated transcription. In addition, Eya2 impinged on G protein-mediated signaling, as evidenced by its ability to relieve Galphai2-mediated inhibition of adenylyl cyclase. These results demonstrate that the interaction between the Galphai proteins and Eya2 may impact on seemingly disparate regulatory events involving both classes of proteins.

RGS17/RGSZ2, a Novel Regulator of Gi/o, Gz, and Gq Signaling

To identify novel regulators of Galpha(o), the most abundant G-protein in brain, we used yeast two-hybrid screening with constitutively active Galpha(o) as bait and identified a new regulator of G-protein signaling (RGS) protein, RGS17 (RGSZ2), as a novel human member of the RZ (or A) subfamily of RGS proteins. RGS17 contains an amino-terminal cysteine-rich motif and a carboxyl-terminal RGS domain with highest homology to hRGSZ1- and hRGS-Galpha-interacting protein. RGS17 RNA was strongly expressed as multiple species in cerebellum and other brain regions. The interactions between hRGS17 and active forms of Galpha(i1-3), Galpha(o), Galpha(z), or Galpha(q) but not Galpha(s) were detected by yeast two-hybrid assay, in vitro pull-down assay, and co-immunoprecipitation studies. Recombinant RGS17 acted as a GTPase-activating protein (GAP) on free Galpha(i2) and Galpha(o) under pre-steady-state conditions, and on M2-muscarinic receptor-activated Galpha(i1), Galpha(i2), Galpha(i3), Galpha(z), and Galpha(o) in steady-state GTPase assays in vitro. Unlike RGSZ1, which is highly selective for G(z), RGS17 exhibited limited selectivity for G(o) among G(i)/G(o) proteins. All RZ family members reduced dopamine-D2/Galpha(i)-mediated inhibition of cAMP formation and abolished thyrotropin-releasing hormone receptor/Galpha(q)-mediated calcium mobilization. RGS17 is a new RZ member that preferentially inhibits receptor signaling via G(i/o), G(z), and G(q) over G(s) to enhance cAMP-dependent signaling and inhibit calcium signaling. Differences observed between in vitro GAP assays and whole-cell signaling suggest additional determinants of the G-protein specificity of RGS GAP effects that could include receptors and effectors.

Time-course study of SCG10 mRNA levels associated with LTP induction and maintenance in the rat Schaffer-CA1 pathway in vivo

The maintenance of long-term potentiation (LTP) depends on altered gene expression. Previously, we found the expression of neuronal growth associated protein SCG10, which is involved in neurite outgrowth and neural regeneration, was up-regulated by LTP induction in the rat hippocampal Schaffer-collateral CA1 pathway. Here we studied the temporal expression pattern of SCG10 mRNA after LTP induction using permanently implanted electrodes in the same CA1 pathway. The real-time RT-PCR showed that both SCG10 mRNA 1 and 2 kb forms were increased at the 3 h, but not at 1 or 24 h. In situ hybridization revealed an increase of SCG10 2 kb mRNA level in ipsilateral CA3 and CA1 areas, but not their contralateral counterparts or either side of dentate gyrus. These results suggest that SCG10 may play a role in the maintenance of synaptic plasticity through a transient regulation of microtubule dynamics, which facilitates the structural remodeling of the presynaptic element during the consolidation period.

Role of the microtubule destabilizing proteins SCG10 and stathmin in neuronal growth

The related proteins SCG10 and stathmin are highly expressed in the developing nervous system. Recently it was discovered that they are potent microtubule destabilizing factors. While stathmin is expressed in a variety of cell types and shows a cytosolic distribution, SCG10 is neuron-specific and membrane-associated. It contains an N-terminal targeting sequence that mediates its transport to the growing tips of axons and dendrites. SCG10 accumulates in the central domain of the growth cone, a region that also contains highly dynamic microtubules. These dynamic microtubules are known to be important for growth cone advance and responses to guidance cues. Because overexpression of SCG10 strongly enhances neurite outgrowth, SCG10 appears to be an important factor for the dynamic assembly and disassembly of growth cone microtubules during axonal elongation. Phosphorylation negatively regulates the microtubule destabilizing activity of SCG10 and stathmin, suggesting that these proteins may link extracellular signals to the rearrangement of the neuronal cytoskeleton. A role for these proteins in axonal elongation is also supported by their growth-associated expression pattern in nervous system development as well as during neuronal regeneration.

Analysis of the Regulation of Microtubule Dynamics by Interaction of RGSZ1 (RGS20) with the Neuronal Stathmin, SCG10

Regulators of G protein signaling (RGS proteins) are a diverse family of proteins that act to negatively regulate signaling by heterotrimeric G proteins; however, recent data have implied additional functions for RGS proteins. Previously, we employed the yeast two-hybrid system and identified the microtubule-destabilizing protein, superior cervical ganglia neural-specific 10 protein (SCG10), as a potential effector protein of RGSZ1. This article describes the expression and biochemical purification of both RGSZ1 and SCG10 and details the development of various in vitro assays to evaluate microtubule polymerization?depolymerization. Both turbidimetric and microscopy-based assays can be employed to study the impact that RGS proteins have on SCG10 function. The application of these in vitro assays may help identify a novel role for RGS proteins in regulating the cytoskeletal network.

Slow axonal transport and the genesis of neuronal morphology

The classic view of slow axonal transport maintains that microtubules, neurofilaments, and actin filaments move down the axon relatively coherently at rates significantly slower than those characteristic of known motor proteins. Recent studies indicate that the movement of these cytoskeletal polymers is actually rapid, asynchronous, intermittent, and most probably fueled by familiar motors such as kinesins, myosins, and cytoplasmic dynein. This new view, which is supported by both live-cell imaging and mechanistic analyses, suggests that slow axonal transport is both rapid and plastic, and hence could underlie transformations in neuronal morphology.

Regulator of G protein signaling Z1 (RGSZ1) interacts with Galpha i subunits and regulates Galpha i-mediated cell signaling

Regulator of G protein signaling (RGS) proteins constitute a family of over 20 proteins that negatively regulate heterotrimeric G protein-coupled receptor signaling pathways by enhancing endogenous GTPase activities of G protein alpha subunits. RGSZ1, one of the RGS proteins specifically localized to the brain, has been cloned previously and described as a selective GTPase accelerating protein for Galpha(z) subunit. Here, we employed several methods to provide new evidence that RGSZ1 interacts not only with Galpha(z,) but also with Galpha(i), as supported by in vitro binding assays and functional studies. Using glutathione S-transferase fusion protein pull-down assays, glutathione S-transferase-RGSZ1 protein was shown to bind (35)S-labeled Galpha(i1) protein in an AlF(4)(-)dependent manner. The interaction between RGSZ1 and Galpha(i) was confirmed further by co-immunoprecipitation studies and yeast two-hybrid experiments using a quantitative luciferase reporter gene. Extending these observations to functional studies, RGSZ1 accelerated endogenous GTPase activity of Galpha(i1) in single-turnover GTPase assays. Human RGSZ1 functionally regulated GPA1 (a yeast Galpha(i)-like protein)-mediated yeast pheromone response when expressed in a SST2 (yeast RGS protein) knockout strain. In PC12 cells, transfected RGSZ1 blocked mitogen-activated protein kinase activity induced by UK14304, an alpha(2)-adrenergic receptor agonist. Furthermore, RGSZ1 attenuated D2 dopamine receptor agonist-induced serum response element reporter gene activity in Chinese hamster ovary cells. In summary, these data suggest that RGSZ1 serves as a GTPase accelerating protein for Galpha(i) and regulates Galpha(i)-mediated signaling, thus expanding the potential role of RGSZ1 in G protein-mediated cellular activities.

RGS6 interacts with SCG10 and promotes neuronal differentiation. Role of the G gamma subunit-like (GGL) domain of RGS6

RGS proteins comprise a large family of proteins named for their ability to negatively regulate heterotrimeric G protein signaling. RGS6 is a member of the R7 RGS protein subfamily endowed with DEP (disheveled, Egl-10, pleckstrin) and GGL (G protein gamma subunit-like) domains in addition to the RGS domain present in all RGS proteins. RGS6 exists in multiple splice variant forms with identical RGS domains but possessing complete or incomplete GGL domains and distinct N- and C-terminal domains. Here we report that RGS6 interacts with SCG10, a neuronal growth-associated protein. Using yeast two-hybrid analysis to map protein interaction domains, we identified the GGL domain of RGS6 as the SCG10-interacting region and the stathmin domain of SCG10 as the RGS6-interacting region. Pull-down studies in COS-7 cells expressing SCG10 and RGS6 splice variants revealed that SCG10 co-precipitated RGS6 proteins with complete GGL domains but not those with incomplete GGL domains, and vice versa. Expression of SCG10-interacting forms of RGS6 with SCG10 in PC12 or COS-7 cells resulted in co-localization of both proteins. RGS6 potentiated the ability of SCG10 to disrupt microtubule organization in PC12 and COS-7 cells. Furthermore, expression of SCG10 and RGS6 each enhanced NGF-induced PC12 cell differentiation, and co-expression of SCG10 with RGS6 produced synergistic effects on NGF-induced PC12 differentiation. These effects of RGS6 on microtubules and neuronal differentiation were observed only with RGS6 proteins with complete GGL domains. Mutation of a critical residue required for interaction of RGS proteins with G proteins did not affect the ability of RGS6 to induce neuronal differentiation. These findings identify SCG10 as a binding partner for the GGL domain of RGS6 and provide the first evidence for regulatory effects of an RGS protein on neuronal differentiation. Our results suggest that RGS6 induces neuronal differentiation by a novel mechanism involving interaction of SCG10 with its GGL domain and independent of RGS6 interactions with heterotrimeric G proteins.