Non-T cell activation linker (NTAL) proteolytic cleavage as a terminator of activatory intracellular signals

The earliest intracellular signals that occur after T cell activation are local, subsecond Ca2+microdomains. Here, we identified a Ca2+entry component involved in Ca2+microdomain formation in both unstimulated and stimulated T cells. In unstimulated T cells, spontaneously generated small Ca2+microdomains required ORAI1, STIM1, and STIM2. Super-resolution microscopy of unstimulated T cells identified a circular subplasmalemmal region with a diameter of about 300 nm with preformed patches of colocalized ORAI1, ryanodine receptors (RYRs), and STIM1. Preformed complexes of STIM1 and ORAI1 in unstimulated cells were confirmed by coimmunoprecipitation and Förster resonance energy transfer studies. Furthermore, within the first second after T cell receptor (TCR) stimulation, the number of Ca2+microdomains increased in the subplasmalemmal space, an effect that required ORAI1, STIM2, RYR1, and the Ca2+mobilizing second messenger NAADP (nicotinic acid adenine dinucleotide phosphate). These results indicate that preformed clusters of STIM and ORAI1 enable local Ca2+entry events in unstimulated cells. Upon TCR activation, NAADP-evoked Ca2+release through RYR1, in coordination with Ca2+entry through ORAI1 and STIM, rapidly increases the number of Ca2+microdomains, thereby initiating spread of Ca2+signals deeper into the cytoplasm to promote full T cell activation.

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Abstract P193: AMX-818, a novel prodrug HER2-XPAT T-cell engager (TCE) with potent T cell activation, proteolytic cleavage and efficacy in xenograft tumors, and wide safety margins in NHP (Non Human Primate)

10.1158/1535-7163.targ-21-p193 ◽

2021 ◽

Author(s):

Milton To ◽

Pete Yeung ◽

Michael Fox ◽

Mikhail Hammond ◽

Fiore Cattaruzza ◽

...

Keyword(s):

T Cell ◽

T Cell Activation ◽

Cell Activation ◽

Proteolytic Cleavage ◽

Safety Margins ◽

Human Primate

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Glucocorticoids Attenuate T Cell Receptor Signaling

Journal of Experimental Medicine ◽

10.1084/jem.193.7.803 ◽

2001 ◽

Vol 193 (7) ◽

pp. 803-814 ◽

Cited By ~ 78

Author(s):

François Van Laethem ◽

Erika Baus ◽

Lesley A. Smyth ◽

Fabienne Andris ◽

Françoise Bex ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

T Cell Receptor ◽

T Cell Activation ◽

Tyrosine Kinases ◽

Cell Activation ◽

Cell Receptor ◽

Cell Immunity ◽

Intracellular Signals ◽

Membrane Compartmentalization

Glucocorticoids (GCs) affect peripheral immune responses by inhibiting T cell immunity at several stages of the activation cascade, causing impaired cytokine production and effector function. The recent demonstration that the thymic epithelium and possibly thymocytes themselves produce steroids suggests that endogenous GCs also play a role in the control of T cell development. As both peripheral responsiveness and thymic differentiation appear to be regulated by the quantity and quality of intracellular signals issued by antigen–major histocompatibility complex-engaged T cell receptor (TCR) complexes, we investigated the effects of GCs on the signaling properties of T cells stimulated by anti-CD3 monoclonal antibodies or agonist peptides. We demonstrate in this work that dexamethasone, a synthetic GC, inhibits the early signaling events initiated upon TCR ligation, such as tyrosine phosphorylation of several TCR-associated substrates including the ζ chain, the ZAP70 kinase, and the transmembrane adapter molecule linker for activation of T cells. Hypophosphorylation was not a consequence of reduced kinase activity of src protein tyrosine kinases, but was correlated with an altered- membrane compartmentalization of these molecules. These observations indicate that in addition to their well-described ability to interfere with the transcription of molecules involved in peripheral responses, GCs inhibit T cell activation by affecting the early phosphorylating events induced after TCR ligation.

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The Multiple Roles of the Cytosolic Adapter Proteins ADAP, SKAP1 and SKAP2 for TCR/CD3 -Mediated Signaling Events

Frontiers in Immunology ◽

10.3389/fimmu.2021.703534 ◽

2021 ◽

Vol 12 ◽

Author(s):

Nirdosh Dadwal ◽

Charlie Mix ◽

Annegret Reinhold ◽

Amelie Witte ◽

Christian Freund ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

T Cell Activation ◽

Cell Activation ◽

Adaptive Immune Response ◽

Cell Receptor ◽

Cell Interaction ◽

Adapter Proteins ◽

Intracellular Signals ◽

Signaling Events

T cells are the key players of the adaptive immune response. They coordinate the activation of other immune cells and kill malignant and virus-infected cells. For full activation T cells require at least two signals. Signal 1 is induced after recognition of MHC/peptide complexes presented on antigen presenting cells (APCs) by the clonotypic TCR (T-cell receptor)/CD3 complex whereas Signal 2 is mediated via the co-stimulatory receptor CD28, which binds to CD80/CD86 molecules that are present on APCs. These signaling events control the activation, proliferation and differentiation of T cells. In addition, triggering of the TCR/CD3 complex induces the activation of the integrin LFA-1 (leukocyte function associated antigen 1) leading to increased ligand binding (affinity regulation) and LFA-1 clustering (avidity regulation). This process is termed “inside-out signaling”. Subsequently, ligand bound LFA-1 transmits a signal into the T cells (“outside-in signaling”) which enhances T-cell interaction with APCs (adhesion), T-cell activation and T-cell proliferation. After triggering of signal transducing receptors, adapter proteins organize the proper processing of membrane proximal and intracellular signals as well as the activation of downstream effector molecules. Adapter proteins are molecules that lack enzymatic or transcriptional activity and are composed of protein-protein and protein-lipid interacting domains/motifs. They organize and assemble macromolecular complexes (signalosomes) in space and time. Here, we review recent findings regarding three cytosolic adapter proteins, ADAP (Adhesion and Degranulation-promoting Adapter Protein), SKAP1 and SKAP2 (Src Kinase Associated Protein 1 and 2) with respect to their role in TCR/CD3-mediated activation, proliferation and integrin regulation.

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