A THEMIS : SHP 1 complex promotes T‐cell survival

Abstract

THEMIS is critical for conventional T-cell development, but its precise molecular function remains elusive. Here, we show that THEMIS constitutively associates with the phosphatases SHP1 and SHP2. This complex requires the adapter GRB2, which bridges SHP to THEMIS in a Tyr-phosphorylation-independent fashion. Rather, SHP1 and THEMIS engage with the N-SH3 and C-SH3 domains of GRB2, respectively, a configuration that allows GRB2-SH2 to recruit the complex onto LAT. Consistent with THEMIS-mediated recruitment of SHP to the TCR signalosome, THEMIS knock-down increased TCR-induced CD3-ζ phosphorylation, Erk activation and CD69 expression, but not LCK phosphorylation. This generalized TCR signalling increase led to augmented apoptosis, a phenotype mirrored by SHP1 knock-down. Remarkably, a KI mutation of LCK Ser59, previously suggested to be key in ERK-mediated resistance towards SHP1 negative feedback, did not affect TCR signalling nor ligand discrimination in vivo. Thus, the THEMIS:SHP complex dampens early TCR signalling by a previously unknown molecular mechanism that favours T-cell survival. We discuss possible implications of this mechanism in modulating TCR output signals towards conventional T-cell development and differentiation.

Themis1 enhances T cell receptor signaling during thymocyte development by promoting Vav1 activity and Grb2 stability

“…Some in vitro studies have proposed that Themis1 acts as a negative regulator of TCR signaling (10,11); however, this is inconsistent with the developmental defect observed in Themis1 −/− mice, which supports a positive role for Themis1 in TCR signaling (2,3,5,9). To analyze the effect of Themis1 on the TCR signaling response to endogenous selecting ligands in developing thymocytes, we took advantage of the previously reported Nur77-green fluorescent protein (GFP) transgenic mouse model in which GFP abundance correlates with the intensity of TCR signals transmitted during positive or negative selection (16).…”

“…It was shown in that study that the loss of Themis1 results in enhanced calcium (Ca 2+ ) flux and increased phosphorylation of Lck, LAT, and ERK in preselected DP thymocytes that are stimulated by low-affinity pMHCs. Themis1 binds to the inhibitory protein tyrosine phosphatases SHP-1 (Src homology 2 domain-containing phosphatase-1) and SHP-2 in thymocytes (10) and Jurkat cells (11). The tyrosine phosphorylation of SHP-1 and its recruitment to LAT are reduced in Themis1 −/− thymocytes, which suggests that Themis1 inhibits early signaling events by controlling the activity and localization of SHP-1.…”

Grb2 Is Important for T Cell Development, Th Cell Differentiation, and Induction of Experimental Autoimmune Encephalomyelitis

“…However, the role of SOS in Ras activation in T cells is controversial (30-32). Alternatively, but not mutually exclusively, the role of Grb2 in T cell selection might be explained by its ability to recruit a THEMISGrb2-SHP1/2 complex to LAT in the immunological synapse, where THEMIS and SHP1/2 set the threshold for positive selection (6,7). In the absence of THEMIS or if the THEMIS binding site for Grb2 is mutated, positive selection is drastically impaired (5,7,33,34).…”

“…It was reported recently that Grb2 recruits THEMIS and SHP1 via its SH3 domains to phosphorylated LAT after TCR stimulation (5,6). Thereby, it directs them to the immunological synapse where, in turn, the complex with THEMIS and SHP1 sets the threshold for selection processes (6,7). When the Grb2-dependent recruitment of THEMIS is abrogated, T cell development is impaired; this highlights the importance of Grb2 in thymocyte development (5).…”

“…As a consequence of impaired selection processes, Grb2 fl/fl Lckcre tg mice show reduced T cell numbers in the periphery (2). It was reported recently that Grb2 recruits THEMIS and SHP1 via its SH3 domains to phosphorylated LAT after TCR stimulation (5,6). Thereby, it directs them to the immunological synapse where, in turn, the complex with THEMIS and SHP1 sets the threshold for selection processes (6,7).…”