Role of Shc in T-cell development and function

Structure-functional implications of longevity protein p66Shc in health and disease

ShcA (Src homologous- collagen homologue), family of adapter proteins, consists of three isoforms which integrate and transduce external stimuli to different signaling networks. ShcA family consists of p46Shc, p52Shc and p66Shc isoforms, characterized by having multiple protein-lipid and protein-protein interaction domains implying their functional diversity. Among the three isoforms p66Shc is structurally different containing an additional CH2 domain which attributes to its dual functionality in cell growth, mediating both cell proliferation and apoptosis. Besides, p66Shc is also involved in different biological processes including reactive oxygen species (ROS) production, cell migration, ageing, cytoskeletal reorganization and cell adhesion. Moreover, the interplay between p66Shc and ROS is implicated in the pathology of various dreadful diseases. Accordingly, here we discuss the recent structural aspects of all ShcA adaptor proteins but are highlighting the case of p66Shc as model isoform. Furthermore, this review insights the role of p66Shc in progression of chronic age-related diseases like neuro diseases, metabolic disorders (non-alcoholic fatty liver, obesity, diabetes, cardiovascular diseases, vascular endothelial dysfunction) and cancer in relation to ROS. We finally conclude that p66Shc might act as a valuable biomarker for the prognosis of these diseases and could be used as a potential therapeutic target.

ShcA regulates late stages of T cell development and peripheral CD4+ T cell numbers

T cell development in the thymus is a highly regulated process that critically depends upon productive signaling via the preTCR at the β-selection stage, as well as via the TCR for selection from the CD4(+)CD8(+) double-positive stage to the CD4 or CD8 single-positive stage. ShcA is an adapter protein expressed in thymocytes, and it is required for productive signaling through the preTCR, with impaired signaling via ShcA leading to a developmental block at the β-selection checkpoint. However, the role of ShcA in subsequent stages of T cell development has not been addressed. In this study, we generated transgenic mice (CD4-Cre/ShcFFF mice) that specifically express a phosphorylation-defective dominant-negative ShcA mutant (ShcFFF) in late T cell development. Thymocytes in CD4-Cre/ShcFFF mice progressed normally through the β-selection checkpoint, but displayed a significant reduction in the numbers of single-positive CD4(+) and CD8(+) thymocytes. Furthermore, CD4-Cre/ShcFFF mice, when bred with transgenic TCR mouse strains, had impaired signaling through the transgenic TCRs. Consistent with defective progression to the single-positive stage, CD4-Cre/ShcFFF mice also had significant peripheral lymphopenia. Moreover, these CD4-Cre/ShcFFF mice develop attenuated disease in CD4(+) T cell-dependent experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis. Collectively, these data identify an important role for the adapter protein ShcA in later stages of thymic T cell development and in peripheral T cell-dependent events.

Unexpected phenotype of mice lacking Shcbp1, a protein induced during T cell proliferation

T cell development and activation are highly regulated processes, and their proper execution is important for a competent immune system. Shc SH2-domain binding protein-1 (Shcbp1) is an evolutionarily conserved protein that binds to the adaptor protein ShcA. Studies in Drosophila and in cell lines have strongly linked Shcbp1 to cell proliferation, embryonic development, growth factor signaling, and tumorigenesis. Here we show that Shcbp1 expression is strikingly upregulated during the β-selection checkpoint in thymocytes, and that its expression tightly correlates with proliferative stages of T cell development. To evaluate the role for Shcbp1 during thymic selection and T cell function in vivo, we generated mice with global and conditional deletion of Shcbp1. Surprisingly, the loss of Shcbp1 expression did not have an obvious effect during T cell development. However, in a mouse model of experimental autoimmune encephalomyelitis (EAE), which depends on CD4⁺ T cell function and mimics multiple features of the human disease multiple sclerosis, Shcbp1 deficient mice had reduced disease severity and improved survival, and this effect was T cell intrinsic. These data suggest that despite the striking upregulation of Shcbp1 during T cell proliferation, loss of Shcbp1 does not directly affect T cell development, but regulates CD4⁺ T cell effector function in vivo.

The G protein-coupled estrogen receptor-1, GPER-1, promotes fibrillogenesis via a Shc-dependent pathway resulting in anchorage-independent growth

The G protein-coupled estrogen receptor-1, GPER-1, coordinates fibronectin (FN) matrix assembly and release of heparan-bound epidermal growth factor (HB-EGF). This mechanism of action results in the recruitment of FN-engaged integrin α5β1 to fibrillar adhesions and the formation of integrin α5β1-Shc adaptor protein complexes. Here, we show that GPER-1 stimulation of murine 4 T1 or human SKBR3 breast cancer cells with 17β-estradiol (E2β) promotes the formation of focal adhesions and actin stress fibers and results in increased cellular adhesion and haptotaxis on FN, but not collagen. These actions are also induced by the xenoestrogen, bisphenol A, and the estrogen receptor (ER) antagonist, ICI 182, 780, but not the inactive stereoisomer, 17α-estradiol (E2α). In addition, we show that GPER-1 stimulation of breast cancer cells allows for FN-dependent, anchorage-independent growth and FN fibril formation in "hanging drop" assays, indicating that these GPER-1-mediated actions occur independently of adhesion to solid substrata. Stable expression of Shc mutant Y317F lacking its primary tyrosyl phosphorylation site disrupts E2β-induced focal adhesion and actin stress fiber formation and abolishes E2β-enhanced haptotaxis on FN and anchorage-dependent growth. Collectively, these data demonstrate that E2β action via GPER-1 enhances cellular adhesivity and FN matrix assembly and allows for anchorage-independent growth, cellular events that may allow for cellular survival, and tumor progression.

Neddylation pathway regulates T-cell function by targeting an adaptor protein Shc and a protein kinase Erk signaling

NEDD8 (neural precursor cell expressed, developmentally down-regulated 8) is a ubiquitin-like molecule whose action on modifying protein substrates is critical in various cellular functions but whose importance in the immune system is not well understood. Here we investigated the role of protein neddylation in regulating T-cell function using an in vivo knockdown technique. We found that reduced expression of Ubc12 in CD4(+) T cells led to impaired T-cell receptor/CD28-induced proliferation and cytokine production both in vitro and in vivo, accompanied by reduced Erk activation. These findings were recapitulated by treatment with MLN4924, an inhibitor of NEDD8-activating enzyme. Furthermore, Shc, an adaptor molecule between antigen receptors and the Ras/Erk pathway, was identified as a target for neddylation. Importantly, mice adoptively transferred with Ubc12 knockdown CD4(+) T cells showed markedly ameliorated allergic responses. This study thus identifies an important role for protein neddylation in T-cell function, which may serve as a therapeutic target for inflammatory diseases.

TCR-mediated Erk activation does not depend on Sos and Grb2 in peripheral human T cells

Sos proteins are ubiquitously expressed activators of Ras. Lymphoid cells also express RasGRP1, another Ras activator. Sos and RasGRP1 are thought to cooperatively control full Ras activation upon T-cell receptor triggering. Using RNA interference, we evaluated whether this mechanism operates in primary human T cells. We found that T-cell antigen receptor (TCR)-mediated Erk activation requires RasGRP1, but not Grb2/Sos. Conversely, Grb2/Sos—but not RasGRP1—are required for IL2-mediated Erk activation. Thus, RasGRP1 and Grb2/Sos are insulators of signals that lead to Ras activation induced by different stimuli, rather than cooperating downstream of the TCR.

The adaptor protein Shc integrates growth factor and ECM signaling during postnatal angiogenesis

Angiogenesis requires integration of cues from growth factors, extracellular matrix (ECM) proteins, and their receptors in endothelial cells. In the present study, we show that the adaptor protein Shc is required for angiogenesis in zebrafish, mice, and cell-culture models. Shc knockdown zebrafish embryos show defects in intersegmental vessel sprouting in the trunk. Shc flox/flox; Tie2-Cre mice display reduced angiogenesis in the retinal neovascularization model and in response to VEGF in the Matrigel plug assay in vivo. Functional studies reveal a model in which Shc is required for integrin-mediated spreading and migration specifically on fibronectin, as well as endothelial cell survival in response to VEGF. Mechanistically, Shc is required for activation of the Akt pathway downstream of both integrin and VEGF signaling, as well as for integration of signals from these 2 receptors when cells are grown on fibronectin. Therefore, we have identified a unique mechanism in which signals from 2 critical angiogenic signaling axes, integrins and VEGFR-2, converge at Shc to regulate postnatal angiogenesis.

Stromal cell-derived factor 1α and CXCR4: newly defined requirements for efficient thymic β-selection

The progressive maturation of T cells is accompanied by their migration through the thymus, with each selection stage occurring in distinct microenvironments. Many specialized receptor-ligand pairs have been defined that drive T cell differentiation, but our understanding of the complex relationship between T cells and the thymic stroma is incomplete. Recent reports have identified a role for the chemokine stromal cell-derived factor 1α and its receptor CXC chemokine receptor 4 in β-selection. This review explores these findings in detail.

Positive and negative regulation of antigen receptor signaling by the Shc family of protein adapters

The Shc adapter family includes four members that are expressed as multiple isoforms and participate in signaling by a variety of cell-surface receptors. The biological relevance of Shc proteins as well as their variegated function, which relies on their highly conserved modular structure, is underscored by the distinct and dramatic phenotypic alterations resulting from deletion of individual Shc isoforms both in the mouse and in two model organisms, Drosophila melanogaster and Caenorhabditis elegans. The p52 isoform of ShcA couples antigen and cytokine receptors to Ras activation in both lymphoid and myeloid cells. However, the recognition of the spectrum of activities of p52ShcA in the immune system has been steadily expanding in recent years to other fundamental processes both at the cell and organism levels. Two other Shc family members, p66ShcA and p52ShcC/Rai, have been identified recently in T and B lymphocytes, where they antagonize survival and attenuate antigen receptor signaling. These developments reveal an unexpected and complex interplay of multiple Shc proteins in lymphocytes.

The molecular basis of IL-21-mediated proliferation

Interleukin-21 (IL-21) is a type I cytokine that modulates functions of T, B, natural killer (NK), and myeloid cells. The IL-21 receptor (IL-21R) is closely related to the IL-2 receptor beta chain and is capable of transducing signals through its dimerization with the common cytokine receptor gamma chain (gamma(c)), the protein whose expression is defective in humans with X-linked severe combined immunodeficiency. To clarify the molecular basis of IL-21 actions, we investigated the role of tyrosine residues in the IL-21R cytoplasmic domain. Simultaneous mutation of all 6 tyrosines greatly diminished IL-21-mediated proliferation, whereas retention of tyrosine 510 (Y510) allowed full proliferation. Y510 efficiently mediated IL-21-induced phosphorylation of Stat1 and Stat3, but not of Stat5, and CD8(+) T cells from Stat1/Stat3 double knock-out mice exhibited decreased proliferation in response to IL-21 + IL-15. In addition, IL-21 weakly induced phosphorylation of Shc and Akt, and consistent with this, specific inhibitors of the MAPK and PI3K pathways inhibited IL-21-mediated proliferation. Collectively, these data indicate the involvement of the Jak-STAT, MAPK, and PI3K pathways in IL-21 signaling.

Lck regulates the threshold of activation in primary T cells, while both Lck and Fyn contribute to the magnitude of the extracellular signal-related kinase response

The src family kinases p56lck (Lck) and p59fyn (Fyn) are the most proximal signaling molecules to be activated downstream of the T-cell receptor. Using an inducible transgenic model, we can regulate the expression of Lck in primary T cells and ask how the signaling cascade and differentiation potential are affected by the absence or the presence of reduced levels of Lck. We show that in naïve T cells, Lck controls the threshold of activation by preferentially regulating multiple signaling pathways that result in the mobilization of Ca2+ through activation of phospholipase C-gamma and protein kinase C as well as activation of the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway. Fyn is also able to stimulate the ERK/MAPK pathway in primary T cells but has little influence on the mobilization of Ca2+. Only Lck efficiently stimulates production of diacylglycerol and therefore RasGRP1 recruitment to the plasma membrane and phosphorylation of Shc, suggesting that Fyn activates ERK via a different upstream signaling route. Finally, we show that signals through Lck are essential for the development of T-cell-effector potential, particularly for effective cytokine transcription.

Activation of the lutropin/choriogonadotropin receptor in MA-10 cells stimulates tyrosine kinase cascades that activate ras and the extracellular signal regulated kinases (ERK1/2)

We show that activation of the recombinant lutropin/choriogonadotropin receptor (LHR) in mouse Leydig tumor cells (MA-10 cells) leads to the tyrosine phosphorylation of Shc (Src homology and collagen homology) and the formation of complexes containing Shc and Sos (Son of sevenless), a guanine nucleotide exchange factor for Ras. Because a dominant-negative mutant of Shc inhibits the LHR-mediated activation of Ras and the phosphorylation of ERK1/2, we conclude that the LHR-mediated phosphorylation of ERK1/2 is mediated, at least partially, by the classical pathway used by growth factor receptors. We also show that the endogenous epidermal growth factor receptor (EGFR) present in MA-10 cells is phosphorylated upon activation of the LHR. The LHR-mediated phosphorylation of the EGFR and Shc, the activation of Ras, and the phosphorylation of ERK1/2 are inhibited by expression of a dominant-negative mutant of Fyn, a member of the Src family kinases (SFKs) expressed in MA-10 cells and by PP2, a pharmacological inhibitor of the SFKs. These are also inhibited, but to a lesser extent, by AG1478, an inhibitor of the EGFR kinase. We conclude that the SFKs are responsible for the LHR-mediated phosphorylation of the EGFR and Shc, the formation of complexes containing Shc and Sos, the activation of Ras, and the phosphorylation of ERK1/2.

CEACAM1: contact-dependent control of immunity

The carcinoembryonic-antigen-related cell-adhesion molecule (CEACAM) family of proteins has been implicated in various intercellular-adhesion and intracellular-signalling-mediated effects that govern the growth and differentiation of normal and cancerous cells. Recent studies show that there is an important role for members of the CEACAM family in modulating the immune responses associated with infection, inflammation and cancer. In this Review, we consider the evidence for CEACAM involvement in immunity, with a particular emphasis on CEACAM1, which functions as a regulatory co-receptor for both lymphoid and myeloid cell types.

Adaptors and linkers in T and B cells

By mediating non-covalent protein-protein interactions, adaptors organize and assemble the multimolecular signalling complexes that coordinate intracellular programs leading to the activation and differentiation of lymphocytes. The co-ordinated interaction between adaptor and effector molecules is required for the propagation and dynamic modification of externally applied signals. Recent advances have been made regarding our understanding of how adaptors regulate signalling within lymphocytes. An unexpected function has been revealed for the well-known adaptor protein LAT in pre-B-cell receptor signalling. In addition, the adaptors BCAP, Bcl10, CARMA1 and Malt1 seem to regulate the development of particular B-cell subsets. In contrast to Shc, c-Cbl and LAT, which are involved in early signalling events, BCAP, Bcl10, CARMA1 and Malt1 seem to act more distally, by controlling NF-kappaB activation. Additional transmembrane adaptors, such as NTAL/LAB and LIME, have been identified and partially characterized. Finally, an involvement of the cytosolic adaptors ADAP, SKAP-55 and Cbl-b in the regulation of lymphocyte adhesion and migration has been demonstrated.