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Functional studies and distribution define a family of transmembrane AMPA receptor regulatory proteins.

Tomita S, Chen L, Kawasaki Y, Petralia RS, Wenthold RJ, Nicoll RA, Bredt DS - J. Cell Biol. (2003)

Bottom Line: Functional expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in cerebellar granule cells requires stargazin, a member of a large family of four-pass transmembrane proteins.Here, we define a family of transmembrane AMPA receptor regulatory proteins (TARPs), which comprise stargazin, gamma-3, gamma-4, and gamma-8, but not related proteins, that mediate surface expression of AMPA receptors.These studies indicate a general role for TARPs in controlling synaptic AMPA receptors throughout the central nervous system.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, CA 94143, USA.

ABSTRACT
Functional expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in cerebellar granule cells requires stargazin, a member of a large family of four-pass transmembrane proteins. Here, we define a family of transmembrane AMPA receptor regulatory proteins (TARPs), which comprise stargazin, gamma-3, gamma-4, and gamma-8, but not related proteins, that mediate surface expression of AMPA receptors. TARPs exhibit discrete and complementary patterns of expression in both neurons and glia in the developing and mature central nervous system. In brain regions that express multiple isoforms, such as cerebral cortex, TARP-AMPA receptor complexes are strictly segregated, suggesting distinct roles for TARP isoforms. TARPs interact with AMPA receptors at the postsynaptic density, and surface expression of mature AMPA receptors requires a TARP. These studies indicate a general role for TARPs in controlling synaptic AMPA receptors throughout the central nervous system.

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Functional identification of a family of TRAPs. (A) Cerebellar granule cells from stargazer mutant mice were transfected with γ-1, stargazin (STG), γ-3, γ-4, γ-5, γ-8, or claudin-1, and whole cell responses to glutamate were recorded. The bar between traces represents 3-s applications of glutamate (100 μM) and cyclothiazide (100 μM). Calibration bars: 50 pA, and 1 s TARP family proteins. stargazin (STG), γ-3, γ-4, and γ-8 restore AMPA-type glutamate-evoked responses (recorded at –80 mV) in stg/stg cerebellar granule cells (n = 5, P < 0.01), but γ-1, γ-5, and claudin-1 do not. The NMDA-type glutamate-evoked responses (recorded at +60 mV) were not significantly altered by any of the transfections. Bottom bar graphs summarize data from these neuronal transfection experiments. (B) Phylogenetic tree shows relationship of TARPs to other related four pass transmembrane proteins.
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fig1: Functional identification of a family of TRAPs. (A) Cerebellar granule cells from stargazer mutant mice were transfected with γ-1, stargazin (STG), γ-3, γ-4, γ-5, γ-8, or claudin-1, and whole cell responses to glutamate were recorded. The bar between traces represents 3-s applications of glutamate (100 μM) and cyclothiazide (100 μM). Calibration bars: 50 pA, and 1 s TARP family proteins. stargazin (STG), γ-3, γ-4, and γ-8 restore AMPA-type glutamate-evoked responses (recorded at –80 mV) in stg/stg cerebellar granule cells (n = 5, P < 0.01), but γ-1, γ-5, and claudin-1 do not. The NMDA-type glutamate-evoked responses (recorded at +60 mV) were not significantly altered by any of the transfections. Bottom bar graphs summarize data from these neuronal transfection experiments. (B) Phylogenetic tree shows relationship of TARPs to other related four pass transmembrane proteins.

Mentions: Although stargazer mice lack functional AMPA receptors in cerebellar granule cells, AMPA receptors in forebrain neurons are intact (Chen et al., 1999; Hashimoto et al., 1999). This selective loss of AMPA receptor function in cerebellar granule cells might be explained by the expression of stargazin-related proteins in forebrain (Chen et al., 2000; Klugbauer et al., 2000; Sharp et al., 2001). Stargazin/γ-2 is related to a large family of transmembrane proteins (Tomita et al., 2001) including the following: γ-1, a stoichiometric component of skeletal muscle calcium channels (Jay et al., 1990; Hofmann et al., 1999); neuronal calcium channel γ-3, γ-4, γ-5, γ-6, γ-7, and γ-8 (Klugbauer et al., 2000; Burgess et al., 2001; Moss et al., 2002); claudin family proteins, cell adhesion molecules essential in forming epithelial tight junctions (Morita et al., 1999); and others. To determine whether these relatives share stargazin's AMPA receptor regulatory function, we cloned their cDNAs (Fig. S1, available at http://www.jcb.org/cgi/content/full/jcb.200212116/DC1) and assessed their capacity to rescue AMPA receptor–mediated responses in cerebellar granule cells from stargazer mutant mice. As reported previously (Chen et al., 2000), transfection of GFP-tagged stargazin into these neurons restored glutamate-evoked responses recorded at –80 mV, which are almost exclusively mediated by AMPA receptors (Fig. 1 A). Similarly, transfecting these neurons with GFP-tagged γ-3, γ-4, or γ-8 effectively rescued AMPA receptor currents (Fig. 1 A). On the other hand, transfecting GFP-tagged γ-1 calcium channel subunit, γ-5, or claudin-1 failed to rescue AMPA receptor currents (Fig. 1 A). None of the transfections altered NMDA receptor currents as indicated by similar currents recorded at +60 mV. Furthermore, all γ subunit isoforms and claudin-1 were expressed at similar levels as reflected by their GFP fluorescence (unpublished data).


Functional studies and distribution define a family of transmembrane AMPA receptor regulatory proteins.

Tomita S, Chen L, Kawasaki Y, Petralia RS, Wenthold RJ, Nicoll RA, Bredt DS - J. Cell Biol. (2003)

Functional identification of a family of TRAPs. (A) Cerebellar granule cells from stargazer mutant mice were transfected with γ-1, stargazin (STG), γ-3, γ-4, γ-5, γ-8, or claudin-1, and whole cell responses to glutamate were recorded. The bar between traces represents 3-s applications of glutamate (100 μM) and cyclothiazide (100 μM). Calibration bars: 50 pA, and 1 s TARP family proteins. stargazin (STG), γ-3, γ-4, and γ-8 restore AMPA-type glutamate-evoked responses (recorded at –80 mV) in stg/stg cerebellar granule cells (n = 5, P < 0.01), but γ-1, γ-5, and claudin-1 do not. The NMDA-type glutamate-evoked responses (recorded at +60 mV) were not significantly altered by any of the transfections. Bottom bar graphs summarize data from these neuronal transfection experiments. (B) Phylogenetic tree shows relationship of TARPs to other related four pass transmembrane proteins.
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Related In: Results  -  Collection

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fig1: Functional identification of a family of TRAPs. (A) Cerebellar granule cells from stargazer mutant mice were transfected with γ-1, stargazin (STG), γ-3, γ-4, γ-5, γ-8, or claudin-1, and whole cell responses to glutamate were recorded. The bar between traces represents 3-s applications of glutamate (100 μM) and cyclothiazide (100 μM). Calibration bars: 50 pA, and 1 s TARP family proteins. stargazin (STG), γ-3, γ-4, and γ-8 restore AMPA-type glutamate-evoked responses (recorded at –80 mV) in stg/stg cerebellar granule cells (n = 5, P < 0.01), but γ-1, γ-5, and claudin-1 do not. The NMDA-type glutamate-evoked responses (recorded at +60 mV) were not significantly altered by any of the transfections. Bottom bar graphs summarize data from these neuronal transfection experiments. (B) Phylogenetic tree shows relationship of TARPs to other related four pass transmembrane proteins.
Mentions: Although stargazer mice lack functional AMPA receptors in cerebellar granule cells, AMPA receptors in forebrain neurons are intact (Chen et al., 1999; Hashimoto et al., 1999). This selective loss of AMPA receptor function in cerebellar granule cells might be explained by the expression of stargazin-related proteins in forebrain (Chen et al., 2000; Klugbauer et al., 2000; Sharp et al., 2001). Stargazin/γ-2 is related to a large family of transmembrane proteins (Tomita et al., 2001) including the following: γ-1, a stoichiometric component of skeletal muscle calcium channels (Jay et al., 1990; Hofmann et al., 1999); neuronal calcium channel γ-3, γ-4, γ-5, γ-6, γ-7, and γ-8 (Klugbauer et al., 2000; Burgess et al., 2001; Moss et al., 2002); claudin family proteins, cell adhesion molecules essential in forming epithelial tight junctions (Morita et al., 1999); and others. To determine whether these relatives share stargazin's AMPA receptor regulatory function, we cloned their cDNAs (Fig. S1, available at http://www.jcb.org/cgi/content/full/jcb.200212116/DC1) and assessed their capacity to rescue AMPA receptor–mediated responses in cerebellar granule cells from stargazer mutant mice. As reported previously (Chen et al., 2000), transfection of GFP-tagged stargazin into these neurons restored glutamate-evoked responses recorded at –80 mV, which are almost exclusively mediated by AMPA receptors (Fig. 1 A). Similarly, transfecting these neurons with GFP-tagged γ-3, γ-4, or γ-8 effectively rescued AMPA receptor currents (Fig. 1 A). On the other hand, transfecting GFP-tagged γ-1 calcium channel subunit, γ-5, or claudin-1 failed to rescue AMPA receptor currents (Fig. 1 A). None of the transfections altered NMDA receptor currents as indicated by similar currents recorded at +60 mV. Furthermore, all γ subunit isoforms and claudin-1 were expressed at similar levels as reflected by their GFP fluorescence (unpublished data).

Bottom Line: Functional expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in cerebellar granule cells requires stargazin, a member of a large family of four-pass transmembrane proteins.Here, we define a family of transmembrane AMPA receptor regulatory proteins (TARPs), which comprise stargazin, gamma-3, gamma-4, and gamma-8, but not related proteins, that mediate surface expression of AMPA receptors.These studies indicate a general role for TARPs in controlling synaptic AMPA receptors throughout the central nervous system.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, CA 94143, USA.

ABSTRACT
Functional expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in cerebellar granule cells requires stargazin, a member of a large family of four-pass transmembrane proteins. Here, we define a family of transmembrane AMPA receptor regulatory proteins (TARPs), which comprise stargazin, gamma-3, gamma-4, and gamma-8, but not related proteins, that mediate surface expression of AMPA receptors. TARPs exhibit discrete and complementary patterns of expression in both neurons and glia in the developing and mature central nervous system. In brain regions that express multiple isoforms, such as cerebral cortex, TARP-AMPA receptor complexes are strictly segregated, suggesting distinct roles for TARP isoforms. TARPs interact with AMPA receptors at the postsynaptic density, and surface expression of mature AMPA receptors requires a TARP. These studies indicate a general role for TARPs in controlling synaptic AMPA receptors throughout the central nervous system.

Show MeSH
Related in: MedlinePlus