![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Vol. 16, Issue 12, 5572-5578, December 2005
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|| || || || ¶ ||
* CNRS UMR5203, Montpellier F-34094 France;
INSERM U661, Montpellier F-34094 France;
University of Montpellier I, Montpellier F-34094 France;
University of Montpellier II, Montpellier F-34094 France; and
|| Département de Pharmacologie Moléculaire, Institut de Génomique Fonctionnelle, Montpellier F-34094 Cedex 5, France
Submitted May 6, 2005;
Revised September 8, 2005;
Accepted September 12, 2005
Monitoring Editor: Akihiko Nakano
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
, Lee et al., 2004). More recently, the di-arginine RXR motif has been identified as an intracellular retention signal (Zerangue et al., 1999) also recognized by COPI (Yuan et al., 2003). Di-arginine retention signals are widely used, in particular in ion channels, including KATP and KCNK3 potassium channels (Zerangue et al., 1999; O'Kelly et al., 2002) or NMDA and kainate type glutamate receptors (Wenthold et al., 2003; Jaskolski et al., 2005).
Oligomeric assembly may overcome such intracellular retention through steric hindrance of the interaction with COPI (or possibly other proteins involved in the retention), as has been demonstrated, e.g., for the Fc
RI receptor (Letourneur et al., 1995). Alternatively, it has been proposed that 14-3-3 dimers may "sense" oligomeric protein assembly. Yuan et al. (2003) have demonstrated mutually exclusive binding of COPI and 14-3-3 proteins to the RKR retention signal of the Kir6.2 KATP channel subunit and proposed that oligomeric assembly may increase the affinity for 14-3-3 dimers. Thus, monomeric Kir6.2 subunits would be retained inside the cell because of their higher affinity for COPI, whereas assembled channels would be released from the retention because of their higher affinity for 14-3-3 dimers, competing COPI out. Mutually exclusive interaction with either COPI or 14-3-3 has also been proposed to play a role in the trafficking control of several other proteins (O'Kelly et al., 2002), but in these cases the 14-3-3 binding was regulated rather through serine phosphorylation, with no obvious link to oligomeric assembly. Competition between 14-3-3 and COPI was therefore proposed to be a general mechanism of cell surface expression control.
In the present study, we examined the molecular mechanisms involved in the quality control system of the 
-aminobutyric acid (GABA) type B receptor. This G proteincoupled receptor (GPCR) is an obligate heterodimer (Marshall et al., 1999). Its GB1 subunit carries the retention signal RSR in its cytosolic C-terminal tail and only reaches the cell surface when associated with the GB2 subunit (Margeta-Mitrovic et al., 2000; Calver et al., 2001; Pagano et al., 2001). However, the molecular mechanisms underlying the intracellular retention of GB1 and its assembly-dependent surface expression with GB2 were yet unknown. The similarity between the GB1 and the Kir6.2 RXR retention signals suggested that competition between COPI and 14-3-3 may also be involved here. In line with this, 14-3-3 proteins have previously been demonstrated to also interact with GB1, in a region encompassing its RSR retention signal (Couve et al., 2001).
|
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
) or site-directed mutagenesis by QuikChange (Stratagene, La Jolla, CA). Primers were synthesized by Eurogentec (Seraing, Belgium). Pfu Turbo Polymerase was from Stratagene, restriction enzymes from NEB (Beverly, MA), T4 DNA ligase from Fermentas (Hanover, MD), and DNA purification kits from Qiagen (Hilden, Germany). All PCR- or QuikChange-derived parts were verified by sequencing (Genome Express, Meylan, France). All constructs are in pRK, except for the 14-3-3
in pcDNA3. HA-GB1, HA-GB1ASA, HA-GB2, and cMyc-GB2 plasmids were described previously (Galvez et al., 2001). GFP was fused to the C-terminal ends of GB1 or GB2, respectively, via a linker reading AS, or introduced after residue 929 of GB1 via a linker reading LE (GB1
C-GFP). In GB1KKXX the KKTN was introduced after residue 921, in GB2KKXX after residue 820. To generate constructs with cleavable N-terminal HA and fluorescent tags, GFP and a thrombin cleavage site (taken from a plasmid generously provided by V. Homburger) were introduced via the MluI site between the HA tag and the receptors. A FLAG-14-3-3 plasmid was a generous gift from L. Limbird. An optimized ribosomal docking sequence (Kozak, 1987) was added in order to improve its expression.
Cell culture and transfection of HEK293 cells was performed as described (Galvez et al., 2001).
Immunofluorescence and Confocal Imaging
PFA-fixed and Triton-permeabilized cells were incubated overnight with anti-Calreticulin (1:100, Alexis Biochemicals, Lausen, Switzerland) or anti-GM130 (1:150, BD Biosciences, Palo Alto, CA), then 45 min with anti-rabbit-Cy3 (1:4000, Jackson ImmunoResearch, West Grove, PA) or anti-mouse-Alexa594 (1:2000, Molecular Probes, Eugene, OR), respectively. Coverslips were mounted with Gel/Mount (Biomeda, Foster City, CA).
Confocal imaging was performed on an LSM 510 Meta confocal microscope with a Plan-Apochromat 63x/1.4 oil objective and Immersol 518F (Carl Zeiss, Jena, Germany). Live cell imaging was performed at 37°C in 138 mM NaCl, 6 mM KCl, 1 mM MgCl2, 1 mM CaCl2, 5.5 mM glucose, 10 mM HEPES, pH 7.5, and 2 g/l bovine serum albumin (BSA). GFP was excited at 488 nm and detected through a 505-nm long pass or a 505–530-nm band pass filter in absence or presence of Cy3 or Alexa594, respectively, which were excited at 543 nm and detected through a 585–615-nm bandpass filter. Pinholes were adjusted to yield optical slices of <0.8 µm.
ELISA
PFA-fixed and Triton-permeabilized (or not) cells were blocked with phosphate-buffered saline + 1% fetal calf serum, incubated 30 min with 0.5 mg/l anti-HA (3F10; Roche, Penzberg, Germany), washed, incubated 30 min with 1 mg/l HRP-coupled anti-rat F(ab')2 (Jackson), and washed again. Bound antibody was detected using a SuperSignal substrate (Pierce, Rockford, IL) and a Wallac Victor2 counter (Molecular Devices, Sunnyvale, CA).
|
) in 50 mM Tris, pH 7.5, 1 mM EDTA, 10 mM CHAPS + protease inhibitors (Roche) and incubated with the extracts overnight. After washing, retained proteins were eluted with Laemmli buffer and analyzed by standard SDS-PAGE + immunoblotting (Sambrook et al., 1989) with antibodies against 
COP (Affinity BioReagents, Golden, CO), 
COP (clone maD, Sigma, St. Louis, MO), 14-3-3 (clone H-8; Santa Cruz Biotechnology, Santa Cruz, CA), or 14-3-3 (clone C-16; Santa Cruz), and peroxidasecoupled anti-mouse or -rabbit antibodies, respectively (Amersham).
Forward Transport Kinetics
Cells were incubated 2.5 h at 15°C, with 3 U/ml thrombin (Calbiochem, La Jolla, CA) during the last 1.5 h. After washing, cells were transferred to 37°C, fixed with PFA after different times, and analyzed by ELISA as described above.
Adenylate Cyclase Inhibition
Cells transfected with plasmids for both GABAB receptor subunits and Gi1 were stimulated 5 min with various concentrations of GABA (Sigma) and then 15 min with 10 µM forskolin (Sigma) in DMEM + 1% BSA and 0.1 mM of the phosphodiesterase inhibitor RO-20–1724 (Sigma). The reaction was stopped by addition of Triton X-100 to a final concentration of 0.5%. The amount of cAMP accumulated in the cells was quantified using the cAMP Dynamic kit (CIS Bio International, Bagnols sur Cèze, France) according to the manufacturer's instruction.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
; Calver et al., 2001; Pagano et al., 2001), GB2 alone was targeted to the plasma membrane, whereas GB1 was retained inside the cell, unless its RSR retention sequence was mutated to ASA or unless it was coexpressed with GB2 (Figure 1A). Similar results were obtained whether the GFP was fused to the N- or C-terminus of the subunits and are further confirmed by ELISA (Figure 1B). Interestingly, the retention of GB1 was abolished when GFP was fused in close proximity (7 instead of 38 amino acids distance) to the RSR (GB1C -GFP). This is in line with the hypothesis that the GB1 retention requires interaction of its RSR sequence with another, rather large protein or protein complex such as COPI, which can be sterically hindered by the bulky GFP close to the RSR.
|
), we used antibodies against COP and COP, i.e., one subunit of either subcomplex. Indeed, we found both - and COP immunoreactivity in the eluates of the KKXX and the RSR, but not the ASA peptide (Figure 2A), demonstrating that indeed the COPI complex specifically interacts with the GB1 RSR.
COPI is well known to retrieve proteins from the Golgi to the ER in COPI-coated vesicles. The interaction of the GB1 RSR with COPI therefore strongly suggests that the same mechanism is responsible for the GB1 intracellular retention. If this is true, then GB1 should not, as generally thought, be retained in the ER (Couve et al., 1998), but reach at least the cis-Golgi, where COPI-coated vesicles are formed. Indeed, immunofluorescence studies revealed that GB1 not only colocalized with the ER marker calreticulin, but also with the cis-Golgi marker GM130 (Figure 2B). Thus, GB1 can leave the ER and reach the cis-Golgi, in line with COPI mediating the GB1 intracellular retention by retrieving it from the cis-Golgi to the ER.
Interaction of the GB1 RSR with 14-3-3
The findings that not only COPI but also 14-3-3 and specifically bind to the Kir6.2 RKR sequence (Yuan et al., 2003), and that 14-3-3 and 
interact with GB1 through a region encompassing its RSR (Couve et al., 2001) suggested that the GB1 RSR may also interact with 14-3-3 and possibly other 14-3-3 isoforms. We therefore analyzed the eluates of our pulldown (see above) by immunoblot with antibodies recognizing 14-3-3 or all seven 14-3-3 isoforms. Both recognized a band in the eluates of the RSR, but not the ASA, nor the KKXX peptide (Figure 3A). Also when using extracts of cells expressing recombinant FLAG-tagged 14-3-3, the latter was specifically retained by the RSR, but not the ASA peptide (Figure 3B). Thus indeed 14-3-3 and possibly other 14-3-3 isoforms with similar electrophoretic mobility interact with the GB1 RSR.
|
). However, 14-3-3 binding was not enhanced, but rather abolished by phosphorylation of the RSR serine (RpSR; Figure 3B), even in presence of the phosphatase inhibitor NaVO3 (1 mM; unpublished data). In contrast, the COPI precipitation appeared slightly reduced, pointing to the possibility that the GB1 interaction with COPI might nevertheless be modulated by phosphorylation of the RSR serine, but not through competition with 14-3-3. Interestingly, the 14-3-3 binding was also markedly reduced by mutation of the RSR serine into alanine (RAR), whereas COPI binding was not or only marginally affected.
14-3-3 Binding Is Not Required for Surface Targeting of the GABAB Receptor
14-3-3 proteins have been proposed to release proteins from intracellular retention through competition with COPI binding (O'Kelly et al., 2002; Yuan et al., 2003). In particular, COPI and 14-3-3 have been demonstrated to both interact directly with the Kir6.2 RXR in a mutually exclusive way (Yuan et al., 2003), strongly suggesting the same for the GB1 RXR.
In contrast, 14-3-3 overexpression failed to increase surface expression of GB1 (unpublished data). Of note, also in the experiments of O'Kelly et al. (2002) 14-3-3 overexpression had no effect on KCNK3 trafficking. Both results might be explained by a relatively low overexpression with respect to the high level of endogenous 14-3-3 (about fourfold in our experiment).
Moreover, a GB1KKXX and a GB1RAR mutant were both not only retained inside the cell when expressed alone, but also surface-targeted when coexpressed with GB2, exactly like the wild-type GB1 (Figure 4), although these mutations abolished or markedly reduced 14-3-3 binding in our pulldown assays (see Figure 3). Thus, the GB1 interaction with 14-3-3 is not required for proper function of the GABAB receptor surface expression control system.
To test a possible role of the GB1 interaction with 14-3-3 in the kinetics of the GABAB receptor trafficking to the cell surface, we next used an assay combining selective enzymatic removal of HA tags from receptors at the cell surface with reversible temperature-induced block of forward transport from the ER/ERGIC to the plasma membrane (Rosenberg et al., 2001). Neither overexpression of 14-3-3, nor the RAR mutation affected the time course of the restoration of the cell surface expression of the HA-tagged receptor (Figure 5).
|
|
). We now tested whether the GB2 CC is also sufficient to bring GB1 to the cell surface and whether it requires to be attached to a transmembrane protein. As depicted in Figure 7, the GB1 retention was clearly overcome by coexpression of the GB2 CC domain as a soluble protein without any membrane attachment (only fused to GFP to verify its expression). Thus, no other parts of GB2 besides its CC domain are required to release GB1 from its intracellular retention.
|
GB2 Sterically Masks the GB1 Retention Signal
How does GB2 release GB1 from its COPI-mediated retention? The GB1 RSR being localized just adjacent to its CC domain, one may speculate that the interaction with the GB2 CC could sterically hinder the interaction of COPI with the RSR or the KKXX at the same position in our GB1KKXX. If this is true, then the masking should also work in the other way round, i.e., GB1 should be able to mask a retention signal introduced adjacent to the GB2 CC. Indeed, a GB2KKXX (with KKTN adjacent to its CC domain, equivalent to our GB1KKXX construct) was retained inside the cell and brought to the cell surface by GB1, as well as by GB1ASA or GB1KKXX, which do not bind 14-3-3 (Figure 8). Conversely, GB2KKXX was also capable of bringing GB1 to the surface, indicating that the two proteins mutually masked their retention signals.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
), in particular the assembly-dependent surface expression of oligomeric transmembrane proteins carrying RXR type retention signals (Yuan et al., 2003). The aim of our study was to further examine the role of COPI and 14-3-3 in assembly-dependent surface expression of oligomeric transmembrane proteins using the heterodimeric G protein-coupled GABAB receptor as a model system (Figure 1, A and B).
Intracellular Retention of GB1 by COPI
We demonstrate here that the RSR retention signal of the GABAB receptor's GB1 subunit specifically interacts with COPI (Figure 2A). This complex is well known to retrieve transmembrane proteins carrying KKXX type retention signals from the cis-Golgi to the ER in COPI-coated vesicles (Bonifacino and Lippincott-Schwartz, 2003; Lee et al., 2004), suggesting it may also mediate the intracellular retention of GB1 through the same mechanism. In agreement with this, the GB1 RSR can be replaced by KKXX without changing the trafficking properties of GB1 (Figure 4). Moreover, we show that GB1 is not, as previously thought, exclusively retained in the ER (Couve et al., 1998), but reaches the cis-Golgi, in line with COPI being responsible for its intracellular retention (Figure 2B).
RXR type intracellular retention signals, first described by Zerangue et al. in 1999, have meanwhile been identified in a large number of different transmembrane proteins. However, it has been demonstrated only recently and only for one example, the Kir6.2 RKR, that RXR retention signals may be recognized by COPI (Yuan et al., 2003). Our demonstration that the GB1 RSR also interacts with this complex now confirms that RXR type retention signals are generally recognized by COPI (Figure 2A). Interestingly, the COPI immunoreactive bands in our pulldown assays appeared stronger for the eluate of the RSR as compared with the KKXX peptide, suggesting that COPI may bind with higher affinity to RXR compared with KKXX retention signals. However, the interaction may be influenced by the local sequence context (Zerangue et al., 2001). Further, it remains to be elucidated whether RXR and KKXX motifs interact with the same or different sites of the COPI complex. Interestingly, the even more closely related KKXX and KXKXX retention signals have recently been shown to be recognized by different COPI subunits (Eugster et al., 2004).
The finding that GB1 needs to associate with GB2 to reach the cell surface had been striking evidence that GPCRs, traditionally believed to be monomers, can form dimers (Marshall et al., 1999). It has meanwhile become widely accepted that many (if not all) GPCRs can (if not must) exist and function as dimers, and it is emerging that dimerization may be a prerequisite for cell surface targeting also of other GPCRs (Bulenger et al., 2005). Intracellular retention of unassembled monomers by COPI may therefore apply to various GPCRs. In line with this, COPI has recently been demonstrated to also interact with the G protein-coupled V2 vasopressin receptor (Hermosilla et al., 2004). One may also speculate that COPI could recognize the arginine cluster in the C-terminal tail of the 1D -adrenergic receptor, which is retained inside the cell unless associated with the 1B -adrenergic receptor (Hague et al., 2004).
14-3-3 Is Not Involved in Surface Targeting of the GABAB Receptor
We demonstrate here that the GB1 RSR cannot only interact with COPI, but also with 14-3-3, and possibly other 14-3-3 isoforms (Figure 3), in line with the recently reported findings for the Kir6.2 RKR sequence (Yuan et al., 2003). That study nicely demonstrated direct and mutually exclusive interaction of either COPI or 14-3-3 with the Kir6.2 RKR in vitro, strongly suggesting the same is true for their interaction with the GB1 RSR. This pointed to the possibility that 14-3-3 proteins, through competition with COPI, might be involved in the trafficking control of proteins with RXR type retention signals such as Kir6.2 or GB1. Accordingly, Yuan et al. (2003) have proposed that oligomeric assembly of Kir6.2 subunits may increase the affinity for 14-3-3 dimers, competing COPI out and releasing the oligomer from the retention. Though this is an elegant model, it did not seem to apply to the assembly-dependent surface targeting of the GABAB receptor, because 14-3-3 has been reported to bind only to GB1, but not GB2 (Couve et al., 2001); hence the GB1/GB2 heterodimerization is not expected to increase the number of 14-3-3 binding sites and thus the affinity for 14-3-3 dimers. Further, GB1 also forms homodimers (Maurel et al., 2004), but these are still retained inside the cell (Villemure et al., 2005), albeit the dimeric presentation of the RXR.
Moreover, using GB1 mutants that do not bind 14-3-3, but still COPI (Figure 3), we now present unequivocal evidence that the GB1 interaction with 14-3-3 is not involved in the GABAB receptor trafficking control, because these mutants behave exactly like WT GB1 regarding their intracellular retention in absence and surface targeting in presence of GB2 (Figure 4). Of note, though both studies of O'Kelly et al. (2002) and Yuan et al. (2003) nicely demonstrate mutually exclusive binding of COPI and 14-3-3 to their proteins in vitro, neither study provides direct evidence that 14-3-3 proteins can indeed bring these proteins to the cell surface by preventing COPI binding in vivo.
We further demonstrate that the 14-3-3 interaction with the GABAB receptor does not affect its trafficking kinetics (Figure 5), nor its signaling function (Figure 6). The GB1 interaction with 14-3-3 may serve other functions yet to be elucidated.
CC Domain Interaction Prevents Recognition of Adjacent Retention Signals by COPI
But how is GB1 released from its intracellular retention? We demonstrate here that the GB2 CC domain is sufficient to bring GB1 to the cell surface (Figure 7). Moreover, a retention signal introduced adjacent to the CC domain in GB2 is also masked by GB1 (Figure 8). These data strongly suggest that the interaction of the two CC domains prevents the recognition of an adjacent retention signal by COPI, most likely by sterical hindrance. Alternatively, one might speculate that the CC domain interaction could induce a conformational change reducing the affinity of the adjacent retention signals for COPI. However, this appears unlikely to explain our results with the various combinations tested, i.e., with the RSR as well as the KKXX on GB1 (Figure 4) and even the KKXX on GB2 (Figure 8). Simple sterical hindrance appears more likely to explain the retention signal masking in all three combinations. Of note, the data presented by Yuan et al. (2003) do not rule out the possibility that the oligomeric assembly of Kir6.2 may also overcome the intracellular retention through simple sterical hindrance of COPI binding.
We have previously demonstrated that fusion with the GB1 and GB2 C-terminal tails can transfer the GABAB receptor quality control system to other GPCRs, permitting to partly control the subunit composition of surface-expressed receptor dimers (Kniazeff et al., 2004; Goudet et al., 2005; Hlavackova et al., 2005). However, although indeed the subunit carrying the GB1 C-terminal tail reached the cell surface only when associated with the subunit carrying the GB2 C-terminal tail, the latter could still also reach the cell surface as a monomer or homodimer, largely complicating the analysis. We now demonstrate that this system can be improved by introduction of an additional retention signal on the C-terminal tail of GB2. On coexpression of GB1 and GB2-KKXX, monomers or homodimers of either subunit are retained inside the cell, and only the heterodimers reach the cell surface, through mutual masking of their retention signals (Figure 8). This system may greatly facilitate the analysis of specific GPCR or other plasma membrane protein heterodimers.
Which Role for Competition between COPI and 14-3-3?
Taken together, our data demonstrate that although both COPI and 14-3-3 interact with the GABAB receptor's RXR retention motif, the interaction with 14-3-3 is not required to release the receptor from its COPI-mediated intracellular retention. Therefore, competition between COPI and 14-3-3 cannot, as previously proposed (O'Kelly et al., 2002; Yuan et al., 2003), be considered as a general mechanism in trafficking control.
Conversely, one may speculate that competition between COPI and 14-3-3 could rather occur in the other way round: 14-3-3 proteins could bind to GB1 already at the ER level, and, because of their dimeric nature, possibly link GB1 with other proteins. Because GB1 is not functional without GB2, such association would be useless and might even hinder correct assembly with GB2. At the Golgi level, COPI could then remove such undesired complexes from GB1 by competing 14-3-3 out. COPI-mediated retrieval of transmembrane proteins may thus also serve to dissociate prematurely associated protein complexes.
|
ACKNOWLEDGMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
|
Footnotes |
|---|
Abbreviations used: CC, coiled coil; COPI, coat protein I complex; GABA, -aminobutyric acid, GB1/2, GABA type B receptor 1/2; GPCR, G protein-coupled receptor; HEK, human embryonic kidney.
¶ Present address: Department of Molecular Pharmacology, Institute of Experimental Medicine, Academie of Science of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech Republic. 
Address correspondence to: J.-P. Pin (jppin{at}igf.cnrs.fr) or C. Brock (cbrock{at}igf.cnrs.fr).
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGMENTSREFERENCES |
|---|
Bulenger, S., Marullo, S., and Bouvier, M. ((2005). ). Emerging role of homo- and heterodimerization in G-protein-coupled receptor biosynthesis and maturation. Trends Pharmacol. Sci. 26, , 131–137.[CrossRef][Medline]
Bonifacino, J. S., and Lippincott-Schwartz, J. ((2003). ). Coat proteins: shaping membrane transport. Nat. Rev. Mol. Cell. Biol. 4, , 409–414.[CrossRef][Medline]
Calver, A. R. et al. ((2001). ). The C-terminal domains of the GABAB receptor subunits mediate intracellular trafficking but are not required for receptor signaling. J. Neurosci. 21, , 1203–1210.
Couve, A., Filippov, A. K., Connolly, C. N., Bettler, B., Brown, D. A., and Moss, S. J. ((1998). ). Intracellular retention of recombinant GABAB receptors. J. Biol. Chem. 273, , 26361–26367.
Couve, A., Kittler, J. T. Uren, J. M., Calver, A. R., Pangalos, M. N., Walsh, F. S., and Moss, S. J. ((2001). ). Association of GABAB receptors and members of the 14-3-3 family of signaling proteins. Mol. Cell. Neurosci. 17, , 317–328.[CrossRef][Medline]
Eugster, A., Frigerio, G., Dale, M., and Duden, R. ((2004). ). The - and '-COP WD40 domains mediate cargo-selective interactions with distinct di-lysine motifs. Mol. Biol. Cell 15, , 1011–1023.
Fiedler, K., Veit, M., Stamnes, M. A., and Rothman, J. E. ((1996). ). Bimodal interaction of coatamer with the p24 family of putative cargo receptors. Science 273, , 1396–1399.[Abstract]
Fu, H., Subramanian, R. R., and Masters, S. C. ((2000). ). 14-3-3 proteins: structure, function, and regulation. Annu. Rev. Pharmacol. Toxicol. 40, , 617–647.[CrossRef][Medline]
Galvez, T., Duthey, B., Kniazeff, J., Blahos, J., Rovelli, G., Bettler, B., Prezeau, L., and Pin, J.-P. ((2001). ). Allosteric interactions between GB1 and GB2 subunits are required for optimal GABAB receptor function. EMBO J. 20, , 2152–2159.[CrossRef][Medline]
Goudet, C., Kniazeff, J., Hlavackova, V., Malhaire, F., Maurel, D., Acher, F., Blahos, J., Prézeau, L., and Pin, J.-P. ((2005). ). Asymmetric functioning of dimeric metabotropic glutamate receptors disclosed by positive allosteric modulators. J. Biol. Chem. 280, , 24380–24385.
Hague, C., Uberti, M. A. Chen, Z. Hall, R. A., and Minneman, K. P. ((2004). ). Cell surface expression of 1D-adrenergic receptors is controlled by heterodimerization with 1B-adrenergic receptors. J. Biol. Chem. 279, , 15541–15549.
Hermosilla, R., Oueslati, M., Donalies, U., Schönenberger, E., Krause, E., Oksche, A., Rosenthal, W., and Schülein, R. ((2004). ). Disease-causing V2 vasopressin receptors are retained in different compartments of the early secretory pathway. Traffic 5, , 993–1005.[CrossRef][Medline]
Hlavackova, V., Goudet, C., Kniazeff, J., Zikova, A., Maurel, D., Vol, C., Trojanova, J., Prézeau, L., Pin, J.-P., and Blahos, J. ((2005). ). Evidence for a single heptahelical domain being turned on upon activation of a dimeric GPCR. EMBO J. 24, , 499–509.[CrossRef][Medline]
Jaskolski, F., Coussen, F., and Mulle, C. ((2005). ). Subcellular localization and trafficking of kainate receptors. Trends Pharmacol. Sci. 26, , 20–26.[CrossRef][Medline]
Kniazeff, J., Bessis, A.-S., Maurel, D., Ansanay, H., Prézeau, L., and Pin, J.-P. ((2004). ). Closed state of both binding domains of homodimeric mGlu receptors is required for full activity. Nat. Struct. Mol. Biol. 11, , 706–713.[CrossRef][Medline]
Kozak, M. ((1987). ). At least six nucleotides preceding the AUG initiator codon enhance translation in mammalian cells. J. Mol. Biol. 196, , 947–950.[CrossRef][Medline]
Lee, M.C.S., Miller, E. A., Goldberg, J., Orci, L., and Schekman, R. ((2004). ). Bi-directional protein transport between the ER and Golgi. Annu. Rev. Cell Dev. Biol. 20, , 87–123.[CrossRef][Medline]
Letourneur, F., Hennecke, S., Démollière, C., and Cosson, P. ((1995). ). Steric masking of a dilysine endoplasmic reticulum retention motif during assembly of the human high affinity receptor for immunoglobulin E. J. Cell Biol. 129, , 971–978.
Margeta-Mitrovic, M., Jan, Y. N., and Jan, L. Y. ((2000). ). A trafficking checkpoint controls GABAB receptor heterodimerization. Neuron 27, , 91–106.
Marshall, F. H., Jones, K. A., Kaupmann, K., and Bettler, B. ((1999). ). GABAB receptors—the first 7TM heterodimers. Trends Pharmacol. Sci. 20, , 396–399.[CrossRef][Medline]
Maurel, D., Kniazeff, J., Mathis, G., Trinquet, E., Pin, J.-P., and Ansanay, H. ((2004). ). Cell surface detection of membrane protein interaction with homogeneous time-resolved fluorescence resonance energy transfer technology. Anal. Biochem. 329, , 253–262.[CrossRef][Medline]
O'Kelly, I., Butler, M. H., Zilberberg, N., and Goldstein, S. A. ((2002). ). Forward transport: 14-3-3 binding overcomes retention in endoplasmic reticulum by dibasic signals. Cell 111, , 577–588.[CrossRef][Medline]
Pagano, A. et al. ((2001). ). C-terminal interaction is essential for surface trafficking but not for heteromeric assembly of GABAB receptors. J. Neurosci. 21, , 1189–1202.
Rosenberg, M., Meier, J., Triller, A., and Vannier, C. ((2001). ). Dynamics of glycine receptor insertion in the neuronal plasma membrane. J. Neurosci. 21, , 5036–5044.
Sambrook, J., Fritsch, E. F., and Maniatis, T. ((1989). ). Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.
Villemure, J.-F., Adam, L., Bevan, N. J., Gearing, K., Chénier, S., and Bouvier, M. ((2005). ). Sub-cellular distribution of GABAB receptor homo- and heterodimers. Biochem. J. 388, , 47–55.[CrossRef][Medline]
Wenthold, R. J., Prybylowski, K., Standley, S., Sans, N., and Petralia, R.-S. ((2003). ). Trafficking of NMDA receptors. Annu. Rev. Pharmacol. Toxicol. 43, , 335–358.[CrossRef][Medline]
Yuan, H., Michelsen, K., and Schwappach, B. ((2003). ). 14-3-3 dimers probe the assembly status of multimeric membrane proteins. Curr. Biol. 13, , 638–646.[CrossRef][Medline]
Zerangue, N., Schwappach, B., Jan, Y. N., and Jan, L. Y. ((1999). ). A new ER trafficking signal regulates the subunit stoichiometry of plasma membrane KATP channels. Neuron 22, , 537–548.[CrossRef][Medline]
Zerangue, N., Malan, M. J., Fried, S. R., Dazin, P. F., Jan, L. Y., and Schwappach, B. ((2001). ). Analysis of endoplasmatic reticulum trafficking signals by combinatorial screening in mammalian cells. Proc. Natl. Acad. Sci. USA 98, , 2431–2436.
This article has been cited by other articles:
|
|
 |
|
  M. Okamoto, T. Yoko-o, T. Miyakawa, and Y. Jigami The Cytoplasmic Region of {alpha}-1,6-Mannosyltransferase Mnn9p Is Crucial for Retrograde Transport from the Golgi Apparatus to the Endoplasmic Reticulum in Saccharomyces cerevisiae Eukaryot. Cell, February 1, 2008; 7(2): 310 - 318. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Brock, N. Oueslati, S. Soler, L. Boudier, P. Rondard, and J.-P. Pin Activation of a Dimeric Metabotropic Glutamate Receptor by Intersubunit Rearrangement J. Biol. Chem., November 9, 2007; 282(45): 33000 - 33008. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Michelsen, V. Schmid, J. Metz, K. Heusser, U. Liebel, T. Schwede, A. Spang, and B. Schwappach Novel cargo-binding site in the {beta} and {delta} subunits of coatomer J. Cell Biol., October 22, 2007; 179(2): 209 - 217. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Binet, B. Duthey, J. Lecaillon, C. Vol, J. Quoyer, G. Labesse, J.-P. Pin, and L. Prezeau Common Structural Requirements for Heptahelical Domain Function in Class A and Class C G Protein-coupled Receptors J. Biol. Chem., April 20, 2007; 282(16): 12154 - 12163. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Balasubramanian, S. R. Fam, and R. A. Hall GABAB Receptor Association with the PDZ Scaffold Mupp1 Alters Receptor Stability and Function J. Biol. Chem., February 9, 2007; 282(6): 4162 - 4171. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Vivithanaporn, S. Yan, and G. T. Swanson Intracellular Trafficking of KA2 Kainate Receptors Mediated by Interactions with Coatomer Protein Complex I (COPI) and 14-3-3 Chaperone Systems J. Biol. Chem., June 2, 2006; 281(22): 15475 - 15484. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
