Leucine Zipper-mediated Homodimerization of the Adaptor Protein c-Cbl

Bartkiewicz, Marcjanna; Houghton, Andrew R; Baron, Roland

doi:10.1074/jbc.274.43.30887

Cited by 69 publications

(36 citation statements)

References 59 publications

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“…cCbl contains a C-terminal ubiquitin-associated (UBA) domain whose function is unclear, although UBA domains in other proteins have been shown to bind ubiquitin. Further, the region containing the UBA domain may form a leucine zipper that mediates homodimerization (Bartkiewicz et al, 1999). In addition, c-Cbl undergoes tyrosine phosphorylation and subsequent SH2 domain-mediated binding to proteins such as Vav and the p85 subunit of the phosphatidylinositol 3 0 kinase (PI3K).…”

Section: Receptor Ubiquitylation By the Cbl Ubiquitin Ligasementioning

confidence: 99%

Role of protein ubiquitylation in regulating endocytosis of receptor tyrosine kinases

2004

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Section: Receptor Ubiquitylation By the Cbl Ubiquitin Ligasementioning

confidence: 99%

Role of protein ubiquitylation in regulating endocytosis of receptor tyrosine kinases

2004

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“…This leucine heptad repeat conforms to the arrangement found in canonical leucine zippers. Thus, by analogy with transcription factors (21), soluble proteins (22,23), and soluble domains of membrane proteins (24), TM2 in individual rGAT molecules may drive dimerization by adopting a leucine zipper-like conformation.…”

Section: Namentioning

confidence: 99%

Mutations within an Intramembrane Leucine Heptad Repeat Disrupt Oligomer Formation of the Rat GABA Transporter 1

Scholze

Freissmuth

Sitte

2002

Journal of Biological Chemistry

110

134

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Na؉ /Cl ؊ -dependent neurotransmitter transporters form constitutive oligomers, the significance of which is not known. In soluble proteins, leucine heptad repeats drive dimerization; the rat ␥-aminobutyric acid transporter GAT-1 (rGAT) contains a motif reminiscent of a leucine heptad repeat in the second transmembrane helix (TM2). We substituted leucine residues in TM2 of rGAT by alanine and tested the ability of the resulting mutants to form oligomers by three methods of Fö rster resonance energy transfer (FRET) microscopy. Replacement of one leucine (L97A) resulted in considerable loss of energy transfer, replacing two or more ablated it completely. Furthermore, intracellular trapping increased with the number of leucine substitutions. Only rGAT-L97A reached the cell surface to a sufficient amount such that, in intact cells, it was indistinguishable from wild type rGAT with respect to substrate transport, binding of inhibitors, and regulation by protein kinase C. However, in membrane vesicles prepared from transfected cells, all mutants were still functional. In addition, FRET was readily detected during maturation of wild type rGAT, when the bulk of the protein resided in the endoplasmic reticulum. Hence, our findings strongly argue for a role of oligomer formation during biosynthesis and subsequent delivery of the multimer from the endoplasmic reticulum to the plasma membrane. Naϩ /Cl Ϫ -dependent neurotransmitter transporters (e.g. the transporters for dopamine, serotonin, or GABA) 1 retrieve neurotransmitters from the synaptic cleft into the presynaptic specialization (1). The medical relevance of these proteins is obvious; for instance, it has long been known that antidepressant drugs block the transporter for norepinephrine and serotonin (2). Likewise, tiagabine, an inhibitor of GABA transport, is used as an anticonvulsant in the treatment of epileptic seizures (3). Transporters support bidirectional flux of substrate, i.e. not only do they mediate influx of substrate but they also allow for non-exocytotic release of substrate (4). Compounds that induce reverse transport enjoy widespread popularity among illicit drug users; this is particularly true for amphetamine and its congeners, including ecstasy.Increasing evidence suggests that neurotransmitter transporters are oligomers (5, 6). Constitutive oligomerization has been visualized in intact cells by FRET microscopy (7); the oligomeric nature of neurotransmitter transporters has also been demonstrated by other, more disruptive, approaches, e.g. co-immunoprecipitation from detergent extracts and crosslinking (8 -10) and by freeze-fracture electron microscopy (11). However, the functional role of oligomer formation remains enigmatic. The hypothesis has been formulated that neurotransmitter transporters function in a manner analogous to ligand-gated ion channels, as binding of substrate induces an ion current (12-14). There is still an ongoing debate whether the GAT operates in a channel-like mode (15, 16) or according to the conservative "alternating ac...

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“…This observation suggests that the interaction of the PLCg1 SH3 domain with Slp-76 is not crucial for TCRinduced PLCg1 phosphorylation and is consistent with the SH2N domain of PLCg1 as being the critical structure for TCR-induced recruitment of PLCg1 to the Lat scaffold. It has been suggested that cell activation by 70Z/3 Cbl can be explained by a direct blockade of endogenous cCbl through heterodimerization (Bartkiewicz et al, 1999;van Leeuwen et al, 1999a, b). Our data show that removal of the C-terminal leucine zipper did not eliminate the effect of 70Z/3 Cbl on PLCg1 phosphorylation, suggesting that the formation of 70Z/3 Cbl/cCbl heterodimers cannot be the sole basis for the activating potential of 70Z/3 Cbl.…”

Section: Discussionmentioning

confidence: 99%

“…70Z/3 Cbl and WT Cbl differ in a 17-amino acid deletion in 70Z/3 Cbl (aa 366-382) that abrogates E3 ubiquitin-ligase activity ( Figure 1) (Sawasdikosol et al, 2000), suggesting that the E3 function is required for c-Cbl to negatively regulate PLCg1. It is also possible that the signaling and oncogenic activity of 70Z/3 Cbl requires its ability to dimerize with endogenous c-Cbl via the C-terminal leucine zipper, resulting in blockade of the physiologic inhibitory function of c-Cbl (Bartkiewicz et al, 1999;van Leeuwen et al, 1999a, b).…”

Section: Introductionmentioning

confidence: 99%

70Z/3 Cbl induces PLCγ1 activation in T lymphocytes via an alternate Lat- and Slp-76-independent signaling mechanism

et al. 2003

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Leucine Zipper-mediated Homodimerization of the Adaptor Protein c-Cbl

Cited by 69 publications

References 59 publications

Role of protein ubiquitylation in regulating endocytosis of receptor tyrosine kinases

Role of protein ubiquitylation in regulating endocytosis of receptor tyrosine kinases

Mutations within an Intramembrane Leucine Heptad Repeat Disrupt Oligomer Formation of the Rat GABA Transporter 1

70Z/3 Cbl induces PLCγ1 activation in T lymphocytes via an alternate Lat- and Slp-76-independent signaling mechanism

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