SHP1‐ing thymic selection

Abstract

The development of conventional T cells in the thymus is highly dependent on parsing small differences in TCR affinity for self MHC-peptide, and responding with the induction of cell-survival and differentiation signals (positive selection) or with activationinduced cell death (negative selection). Regulation of TCR signal strength is important in defining the boundary between positive and negative selection [1,2]. TCR ligation leads to phosphorylation of ITAMs on the CD3 complex by Lck kinase, resulting in recruitment and tyrosine phosphorylation of the tyrosine kinase ZAP70. Activated ZAP70 can then phosphorylate the scaffold proteins LAT and SLP76, resulting in activation of multiple downstream signalling pathways [2]. As the initiation and maintenance of TCR signalling pathways are critically dependent on protein Correspondence: Dr. Nicholas R.J. Gascoigne e-mail: micnrjg@nus.edu.sg tyrosine phosphorylation, counteraction by tyrosine phosphatases plays a major role in negative regulation of TCR signal strength. SHP1 (Src homology region 2 domain-containing phosphatase-1), or PTPN6, is a tyrosine phosphatase that has been suggested to control TCR signalling in the thymus and periphery [3]. However, the precise role of SHP1 in thymic development has been the subject of controversy, with reports suggesting either a major [4] Early studies of SHP1-deficient "motheaten" mice showed that this phosphatase is important for TCR signalling and specifically, in setting the threshold for positive and negative selection [4,[7][8][9]. However, the complete loss of SHP1 expression leads to systemic inflammation in SHP1-deficient mice, influencing thymocyte differentiation, and calling into question the validity of the interpretation of data from these mice. A recent study looked at the role of SHP1 in thymic differentiation using CD4-Cre-mediated conditional knockout of SHP1 only in the T-cell lineage, prior to positive selection. They did not see any defect in positive or negative selection [5]. The work of Martinez et al. re-examines this question in mice of the same genotype, but performing a more in-depth analysis of thymocyte development [6].Thymocyte development proceeds along a set of well-defined developmental stages (Fig. 1A) after stimulation with weak peptide ligands, suggesting that SHP1 acts to set the positive versus negative selection threshold by dampening TCR signal strength [6]. This enhanced TCR signalling leading to negative selection in response to relatively weak peptide MHC ligands is similar to the phenotype of mice that are deficient for Themis [11]. Themis is a protein that is important at the positive selection checkpoint [12][13][14][15][16], which interacts with SHP1 [11,17,18]. Both proteins, Themis and SHP1, bind to the adapter protein GRB2, allowing their recruitment to the LAT signalosome [17,19]. Themisdeficient thymocytes show reduced levels of SHP1 tyrosine phosphorylation [11], suggesting that Themis controls SHP1 phosphatase activity in thymocytes. Analysis of themis-deficiency in mou...

THEMIS is a priming substrate of non-receptor tyrosine phosphatase PTPN6/SHP1 and plays dual roles during T cell development

“…THEMIS (Thymocyte-expressed molecule involved in selection) is a T cell-specific protein which is critical for T cell development, especially CD4SP thymocytes maturation (Allen, 2009; Fu et al ., 2009; Johnson et al ., 2009; Kakugawa et al ., 2009; Lesourne et al ., 2009; Patrick et al ., 2009). Furthermore, it is reported that the interplay between SHP1 and THEMIS is important to regulate the threshold of TCR signal transduction for positive and negative selection during T cell development (Choi et al ., 2017a; Choi et al ., 2017b; Fu et al ., 2013; Gascoigne and Acuto, 2015; Gascoigne et al ., 2016a; Gascoigne et al, 2016b; Mehta et al ., 2018; Paster et al ., 2015). To verify this interaction, immunoprecipitation experiments were performed in both Jurkat and HEK293T cell lines with co-expression of THEMIS and SHP1 WT or DA mutant, respectively.…”

“…Actually, one debate regarding the function of THEMIS in T cell development during positive selection is focused on its role in regulating the phosphatase activity of SHP1. Although several groups agree on the essentiality of THEMIS during T cell development through its interaction with SHP1, two contradictory models have been proposed regarding the positive or negative role of THEMIS in moderating the phosphatase activity of SHP1, which leads to a decrease or increase of TCR signaling response accordingly (Choi et al, 2017a; Choi et al, 2017b; Fu et al, 2013; Gascoigne and Acuto, 2015; Gascoigne et al, 2016a; Mehta et al, 2018; Paster et al, 2015). Thus, there is an urgent need to develop a systematic platform to profile the whole spectrum of potential substrates for any given PTP and to further characterize the molecular function of these PTPs within a physiological context.…”

Themis-associated phosphatase activity controls signaling in T cell development

“…The role of Shp1 in the development of thymocytes is not yet clear. There have been contradictory studies regarding the involvement of this phosphatase in thymic development ( 23 , 24 , 27 ). As Themis regulates Shp1 activity in the thymus, we initially predicted the phenotype of Shp1-deficient thymocytes to be similar to that of Themis KO mice.…”

“…Previous work using mice conditionally deficient for Shp1 in the T cell lineage, CD4-Cre, Ptpn6 fl/fl (Shp1 cKO), reported a lack of any significant defect in thymocyte development ( 23 ). However, a more recent study has identified some relatively subtle changes in thymic selection ( 24 , 27 ). We tested the Themis-associated PTP activity in Shp1 cKO thymocytes, finding that in the absence of Shp1, Themis interacts with Shp2 and retains most of the associated phosphatase activity.…”