Prss16 Is Not Required for T-Cell Development

Abstract

PRSS16 is a serine protease expressed exclusively in cortical thymic epithelial cells (cTEC) of the thymus, suggesting that it plays a role in the processing of peptide antigens during the positive selection of T cells. Moreover, the human PRSS16 gene is encoded in a region near the class I major histocompatibility complex (MHC) that has been linked to type 1 diabetes mellitus susceptibility. The mouse orthologue Prss16 is conserved in genetic structure, sequence, and pattern of expression. To study the role of Prss16 in thymic development, we generated a deletion mutant of Prss16 and characterized T-lymphocyte populations and MHC class II expression on cortical thymic epithelial cells. Prss16-deficient mice develop normally, are fertile, and show normal thymic morphology, cellularity, and anatomy. The total numbers and frequencies of thymocytes and splenic T-cell populations did not differ from those of wild-type controls. Surface expression of MHC class II on cTEC was also similar in homozygous mutant and wild-type animals, and invariant chain degradation was not impaired by deletion of Prss16. These findings suggest that Prss16 is not required for quantitatively normal T-cell development.Peptide fragments, which are processed from self-proteins within the thymus and presented to developing thymocytes, shape the selection of T-cell receptors (TCR). Positive selection, mediated by cortical thymic epithelial cells (cTEC), selects TCR clones that are capable of engaging peptides bound to self-major histocompatibility complex (MHC) (1,11,16). Evidence that a diverse array of self-peptides is required for normal positive selection of the CD4 ϩ -TCR repertoire comes from mice in which a single peptide is bound to nearly all MHC class II molecules. In the H2-M-deficient mouse, the class II-associated invariant chain peptide fragment (CLIP) fails to be removed; in the A b EpIi Ϫ transgenic mouse, MHC class II molecules are covalently linked to the MHC class II peptide E␣ 52-68 (5, 13, 31). Although both of these strains select a surprisingly large number of T cells, the T-cell repertoire is altered. Further evidence of the role of self-peptide diversity in positive selection comes from mice expressing transgenic TCR ␤ chains. Nearly all T cells in these mice express the transgenic ␤ chain, but the ␣ chain locus undergoes normal rearrangement and selection (4,6,28). Sequence analysis of the parenteral ␣ chains has demonstrated a bias that is severely restricted when selected against a limited diversity of selfpeptides (4, 12).The cellular machinery generating self-peptides in cTEC is unique and likely plays an important role in the selection of the TCR repertoire (25). Unlike professional antigen-presenting cells (APC) and medullary thymic epithelial cells, cTEC efficiently process endogenous antigens but poorly process exogenous antigens (22,24). In addition, the MHC class II compartment in which peptides are generated and loaded occurs in early stages of endosome formation in cTEC as opposed to late stages of endosom...

Thymus-specific serine protease controls autoreactive CD4 T cell development and autoimmune diabetes in mice

“…In agreement with previous reports (10,11), Tssp° NOD mice showed normal T cell development and no global defect in positive or negative T cell selection in the thymus (Supplemental Figure 2). Furthermore, the Vβ-segment usage by mature peripheral CD4 and CD8 was similar in Tssp° and WT control mice (Supplemental Figure 3).…”

“…Mice were immunized with the corresponding Ag in CFA, and their recall response was analyzed in vitro. Quite unexpectedly in light of the foremost role of insulin in diabetes development (31,32), we found that the frequency of IL-2-producing CD4 T cells specific for Ins [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and Ins [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66] was comparable in Tssp° and WT NOD mice ( Figure 6). Likewise WT and Tssp° NOD mice responded similarly to the GAD 206-220 peptide and the known IGRP immunodominant epitopes ( Figure 6).…”

“…Expression in the endosomal compartment of cTECs and homology with endosomal proteases led to the hypothesis that TSSP might contribute to the generation of the peptide repertoire presented by MHC class II molecules in the thymus and consequently to T cell repertoire selection (8,9). Tssp-deficient (Tssp°) B6 mice showed normal CD4 T cell development in the thymus and normal numbers of peripheral CD4 T cells expressing polyclonal TCRs, indicating that Tssp, in contrast to cathepsin L, has no quantitative impact on T cell repertoire selection (10,11). However, the thymic development of CD4 T cells expressing I-A b -restricted TCR transgenes (OT-II and Marilyn) is impaired in Tssp° B6 mice, while the development of TCR transgenic CD8 T cells (OT-I) proceeded normally (11).…”

Gene expression profiling of precursor T-cell lymphoblastic leukemia/lymphoma identifies oncogenic pathways that are potential therapeutic targets

“…The overexpressed genes included several known to be involved in protein synthesis (Eef2, eEF-Tu and Mrpl38), Notch signaling (Dtx1) and Ccl8. Several classes of genes were commonly underexpressed in the pre-T LBL samples, including apoptotic pathway genes (Cox8b and Cidea), 16 genes involved in T-cell differentiation (Prss16, Ccl25, CD83, Spatial, Fkbp6 and Tcrd), [17][18][19][20] a group of fatty acid-binding proteins (Fabp3, Fabp4 and Fabp9), 21 and Bop1 22 and Rb1cc1, 23 two genes whose overexpression is linked to decreased cell proliferation. The Fabp proteins are typically expressed in adipocytes, 21 and their underexpression in pre-T LBL relative to normal thymus may reflect a decreased proportion of adipocytes in the pre-T LBL tumor samples compared to normal thymus.…”

Association analysis in type 1 diabetes of the PRSS16 gene encoding a thymus-specific serine protease

“…Furthermore, development of autoreactive diabetogenic T cells has been suggested to result from inordinate positive selection [11,12]. The function of PRSS16 is still largely unknown, but murine studies of Prss16-deficient mice revealed that Prss16 is not required for quantitatively normal T-cell development or normal surface expression of MHC class II molecules on thymic cortical epithelial cells [13]. However, in human beings, PRSS16 and its splice variants have been shown to be differentially expressed in thymus from myasthenia gravis patients with thymoma compared with myasthenia gravis patients with thymic hyperplasia, suggesting a role in the thymus pathology [14].…”