Cbl-b regulates the CD28 dependence of T-cell activation

Chiang, Y. Jeffrey; Kole, Hemanta K.; Brown, Karen E.; Naramura, Mayumi; Fukuhara, Shigetomo; Hu, Ren Ju; Jang, Ihn Kyung; Gutkind, J. Silvio; Shevach, Ethan M.; Gu, Hua

doi:10.1038/35003235

Cited by 562 publications

(688 citation statements)

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“…Consistent with the negative regulation assigned to the Cbl family of proteins, T cells from c-Cbl À/À and Cbl-b À/À mice were hyperactive upon TCR engagement, although some biochemical distinctions between the phenotypes exist [21][22][23][24][25]. T cells from double-knockout mice lacking both c-Cbl and Cbl-b failed to modulate surface TCR after ligand engagement, resulting in sustained TCR signaling and ERK1/2 phosphorylation.…”

Section: Introductionmentioning

confidence: 82%

Reduced Cbl phosphorylation and degradation of the ζ‐chain of the T‐cell receptor/CD3 complex in T cells with low Lck levels

et al. 2008

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T cells with short interfering RNA-mediated Lck-knockdown (kd) display paradoxical hyper-responsiveness upon TCR ligation. We have previously reported a possible mechanism for T-cell activation in cells with low levels of Lck depending on Grb2-SOS1 recruitment to the zeta-chain of TCR/CD3 (Methi et al., Eur. J. Immunol. 2007, 37: 2539-2548. Here, we show that short interfering RNA-mediated targeting of Lck caused a dramatic reduction in c-Cbl phosphorylation and a general reduction in protein ubiquitination after TCR stimulation. Specifically, this resulted in reduced ubiquitination of the zeta-chain, yet internalization of TCR/CD3 appeared to be normal after receptor engagement. However, zeta-chain levels were elevated in Lck-kd cells, and confocal microscopy revealed reduced colocalization of CD3-containing vesicles with endosomal and lysosomal compartments.We hypothesize that prolonged stability of internalized T-cell receptor complex may result in extended signaling in T cells with low Lck levels. Key words: Cbl Á CD3 Á Lck Á T cells Á T-cell receptors IntroductionEngagement of the TCR leads not only to activation of T cells, but also to internalization and lysosomal degradation of the receptor complex [1]. The latter process serves to terminate signaling, and has been shown to be dependent on the tyrosine kinase activity of Lck [2,3] and ubiquitination by c-Cbl [4][5][6]. The E3 ubiquitin ligase c-Cbl functions as a negative regulator of many signaling pathways and ubiquitination marks active enzymes and receptors for degradation [reviewed in 7 and 8]. Notable targets for c-Cbl-mediated ubiquitination are Lck [9], Vav [10], Fyn [11][12][13], , as well as the already mentioned TCR/ CD3-complex. c-Cbl itself is activated by tyrosine phosphorylation on several residues, most importantly Y700, Y731 and Y774 [13,[15][16][17]. These residues are not, however, substrates of Lck or but of Fyn and Syk [13,16,18,19], which are activated directly or indirectly by Lck [20].Cbl exists in two main isoforms, c-Cbl and Cbl-b, with a high level of sequence conservation. Consistent with the negative regulation assigned to the Cbl family of proteins, T cells from c-Cbl À/À and Cbl-b À/À mice were hyperactive upon TCR engagement, although some biochemical distinctions between the phenotypes exist [21][22][23][24][25]. T cells from double-knockout mice lacking both c-Cbl and Cbl-b failed to modulate surface TCR after ligand engagement, resulting in sustained TCR signaling and ERK1/2 phosphorylation. However, signaling through the major TCR pathways were not increased [26]. These observations are comparable to what we found in T cells with low levels of Lck, which also display prolonged ERK1/2 activation while expression levels of other proteins (Fyn, Csk, PKCa, PLCg1, LAT, FAK, and Pyk2) remained unaffected [27,28]. We therefore investigated the impact of short interfering RNA (siRNA)-mediated Lck-knockdown (kd) on c-Cbl activity and TCR/CD3 turnover in T cells. As expected, c-Cbl phosphorylation and ubiquitination of the z-c...

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Section: Introductionmentioning

confidence: 82%

Reduced Cbl phosphorylation and degradation of the ζ‐chain of the T‐cell receptor/CD3 complex in T cells with low Lck levels

et al. 2008

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“…Nevertheless, the finding of Rac-1 regu- lates fibronectin-mediated binding of T cells from MS patients may help to bring together several previous findings. Specifically, Vav, a guanine exchange factor that negatively regulates the active (GTP-bound) state of Rac-1 [35], and Cbl-b, which negatively regulates Vav in the development of autoimmunity [36], have been associated with MS. Although our efforts here focused on downstream functional implications of Rac-1/CYFIP2 activation (cell adhesion), studies have indicated that activation of any of several signaling events involved in the T cell receptor or CD28-mediated activation (and thus, Rac-1 activation) plays a prominent role in driving the T cell activation associated with MS.…”

Section: Discussionmentioning

confidence: 99%

CYFIP2 is highly abundant in CD4⁺ cells from multiple sclerosis patients and is involved in T cell adhesion

et al. 2004

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DNA microarray profiling of CD4 + and CD8 + cells from non-treated relapsing and remitting multiple sclerosis (MS) patients determined that the cytoplasmic binding partner of fragile X protein (CYFIP2, also called PIR121) was increased significantly compared to healthy controls. Western analysis confirmed that CYFIP2 protein was increased approximately fourfold in CD4 + cells from MS compared to inflammatory bowel disorder (IBD) patients or healthy controls. Because CYFIP2 acts as part of a tetrameric complex that regulates WAVE1 activation we hypothesized that high levels of CYFIP2 facilitate T cell adhesion, which is elevated in MS patients. Several findings indicated that increased levels of CYFIP2 facilitated adhesion. First, adenoviral-mediated overexpression of CYFIP2 in Jurkat cells increased fibronectin-mediated adhesion. Secondly, CYFIP2 knock-down experiments using antisense oligodeoxynucleotides reduced fibronectin-mediated binding in Jurkat and CD4 + cells. Thirdly, inhibition of Rac-1, a physical partner with CYFIP2 and regulator of WAVE1 activity, reduced fibronectin-mediated adhesion in Jurkat and CD4 + cells. Finally, inhibition of Rac-1 or reduction of CYFIP2 protein decreased fibronectin-mediated adhesion in CD4 + cells from MS patients to levels similar to controls. These studies suggest that overabundance of CYFIP2 protein facilitates increased adhesion properties of T cells from MS patients.

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“…The RING-type E3 ligase Cbl-b (Casitas B-cell lymphoma-b) was the first identified E3 ligase involved in T-cell activation and tolerance in vivo [32][33][34]. Ablation of Cbl-b renders peripheral T cells hyperproliferative and able to be fully activated in the absence of CD28 co-stimulation, suggesting that Cbl-b is a critical modulator of T cells, uncoupling T-cell activation from the requirement of costimulation [32,33,35].…”

Section: Physiological and Molecular Roles Of E3 Ligases In T-cell Tomentioning

confidence: 99%

“…Ablation of Cbl-b renders peripheral T cells hyperproliferative and able to be fully activated in the absence of CD28 co-stimulation, suggesting that Cbl-b is a critical modulator of T cells, uncoupling T-cell activation from the requirement of costimulation [32,33,35]. At the molecular level, Cbl-b-mediated ubiquitylation of p85, the catalytic subunit of PI3K, alters its intracellular localization, thereby preventing its interaction with CD28 and TCRz at the plasma membrane.…”

Section: Physiological and Molecular Roles Of E3 Ligases In T-cell Tomentioning

confidence: 99%

E3 ubiquitin ligases in T‐cell tolerance

Paolino

Penninger

2009

Eur J Immunol

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The immune system uses several mechanisms of central and peripheral tolerance in order to prevent the activation of T lymphocytes toward self-antigens. Although the importance of immune self-tolerance has been established for a long time, some essential cellular and molecular mechanisms of T-cell tolerance have only been recently revealed. Once thought to be a recycling system, protein ubiquitylation by E3 ligases has now emerged as a regulated and crucial modulator of immune responses, and more importantly as a key signaling pathway involved in T-cell tolerance. In this review, we highlight our current understanding of the transcriptional and molecular signaling mechanisms involved in ubiquitylation-mediated T-cell tolerance.Key words: Autoimmunity . Cbl-b . E3 ligase . T-cell tolerance . Ubiquitylation IntroductionUpon activation, the immune system orchestrates robust and potentially destructive responses intended to eliminate the immunogenic antigen. Thus, immune system activation is under stringent control to prevent a detrimental immune response against self-antigens. The processes that ensure unresponsiveness toward self-antigens are known as immunological tolerance and, in their absence or failure, autoimmunity occurs [1]. Central tolerance mechanisms operate in the thymus to eliminate potentially self-reactive thymocytes and generate (T reg ) suppressor cells [2]. In addition, several peripheral tolerance mechanisms act to prevent self-reactivity once mature T cells have reached the periphery. These peripheral mechanisms of tolerance include the following: (i) immunological ignorance to selfantigens expressed at low levels or in immunoprivileged sites; (ii) active immunosuppression by Foxp31 T reg cells; (iii) activation-induced cell death of autoreactive T cells and (iv) induction of a state of unresponsiveness known as T-cell anergy [3].During the past few years, extensive research has revealed new insights into the cellular and molecular mechanisms necessary to induce and maintain T-cell tolerance. In particular, ubiquitylation of proteins by E3 ligases has emerged as a novel and indispensable signaling pathway that regulates T-cell tolerance toward self-antigens [4][5][6]. The ubiquitylation processUbiquitylation is an important mechanism of post-translational modification of proteins by which the 76-aa polypeptide ubiquitin, Ub, is covalently attached to a substrate protein. This process occurs in a stepwise manner, requiring the participation of three enzymes: a ubiquitin-activating enzyme E1, responsible for the first binding and activation of the Ub; a second ubiquitinconjugating enzyme E2, which receives the activated Ub from the E1; and a third ubiquitin-ligase E3 that catalyzes the final covalent transfer of the Ub from the E2 enzyme to the protein substrate [7]. Once thought to only mediate proteosomal degradation, the ubiquitylation of a protein can have multiple effects, including altered subcellular localization, regulation of protein-protein interactions, and functional modulation. The fa...

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Cbl-b regulates the CD28 dependence of T-cell activation

Cited by 562 publications

References 25 publications

Reduced Cbl phosphorylation and degradation of the ζ‐chain of the T‐cell receptor/CD3 complex in T cells with low Lck levels

Reduced Cbl phosphorylation and degradation of the ζ‐chain of the T‐cell receptor/CD3 complex in T cells with low Lck levels

CYFIP2 is highly abundant in CD4⁺ cells from multiple sclerosis patients and is involved in T cell adhesion

E3 ubiquitin ligases in T‐cell tolerance

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Cbl-b regulates the CD28 dependence of T-cell activation

Cited by 562 publications

References 25 publications

Reduced Cbl phosphorylation and degradation of the ζ‐chain of the T‐cell receptor/CD3 complex in T cells with low Lck levels

Reduced Cbl phosphorylation and degradation of the ζ‐chain of the T‐cell receptor/CD3 complex in T cells with low Lck levels

CYFIP2 is highly abundant in CD4+ cells from multiple sclerosis patients and is involved in T cell adhesion

E3 ubiquitin ligases in T‐cell tolerance

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CYFIP2 is highly abundant in CD4⁺ cells from multiple sclerosis patients and is involved in T cell adhesion