Brief Deﬁnitive Report Function of CD3e-mediated Signals in T Cell Development By Connie L. Sommers,* Jan B. Dejarnette,* Kun Huang,* Jan Lee,‡ Dalal El-Khoury,* Elizabeth W. Shores,‡ and Paul E. Love* From the *Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; and the ‡Division of Hematologic Products, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892 Abstract The T cell antigen receptor (TCR) and pre-TCR complexes are composed of multiple signal- transducing subunits (CD3g, CD3d, CD3e, and z) that each contain one or more copies of a semiconserved functional motif, the immunoreceptor tyrosine-based activation motif (ITAM). Although biochemical studies indicate that individual TCR-ITAMs may bind selectively or with different affinity to various effector molecules, data from other experiments suggest that at least some ITAMs are functionally equivalent. In this study, we examined the role of CD3e ITAM-mediated signals in T cell development by genetically reconstituting CD3e-deficient mice with transgenes encoding either wild-type or ITAM-mutant (signaling defective) forms of the protein. The results demonstrate that signals transduced by CD3e are not specifically re- quired for T cell maturation but instead contribute quantitatively to TCR signaling in a man- ner similar to that previously observed for z chain. Unexpectedly, analysis of TCR-transgenic/ CD3e-mutant mice reveals a potential role for CD3e signals in T cell survival. Key words: TCR • CD3epsilon • development • mice • cell survival Introduction Signals transduced by the TCR initiate a broad range of mature T cell responses. Signaling by the TCR and its pre- cursor, the pre-TCR, are also required for thymocyte de- velopment and selection (1–3). The pre-TCR and TCR activate intracellular signaling cascades through semicon- served sequences of amino acids referred to as immuno- receptor tyrosine-based activation motifs (ITAMs). After receptor engagement, phosphorylation of TCR-ITAM tyrosines leads to the recruitment and activation of src ho- mology 2 (SH2) domain–containing kinases (2). The pre- TCR and TCR contain four distinct signal-transducing subunits—CD3g, CD3d, CD3e, and z—assembled as dimers: g/e, d/e, and zz. Each of the CD3 subunits con- tains a single ITAM, whereas z chain contains three ITAMs. Analysis of the function of TCR-ITAMs has revealed that individual motifs bind with different affinities to the same effector (ZAP-70) and bind selectively to other po- Connie L. Sommers’ present address is Laboratory of Cellular and Molec- ular Biology, Division of Basic Sciences, National Cancer Institute, Be- thesda, MD 20892-4255. Address correspondence to Paul E. Love, Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892. Phone: 301-402-4946; Fax: 301-480-6302; E-mail: pel@helix.nih.gov tential effector molecules (4, 5). On the other hand, iso- lated ITAMs have been shown to be independently capable of initiating a broad range of T cell responses, including proliferation and cytokine synthesis (6, 7). Experimental data support the idea that at least some TCR-ITAMs are functionally equivalent with respect to the signaling requirements for T cell development. For ex- ample, mature T cells are still generated in mice that express TCRs lacking the three z chain ITAMs, and these cells ap- pear functionally competent (8–10). In contrast to z chain, the importance of signals transduced by the CD3 subunits has not been as rigorously addressed. Chimeric (Tac/z or Tac/e) transgenes were found to be capable of indepen- dently mimicking pre-TCR signals and some TCR signals; however, it is unknown if endogenous z and CD3e chains contributed to these results (11). Mice lacking CD3g, CD3d, or CD3e exhibit various degrees of developmental arrest, demonstrating a clear role for these proteins in T cell maturation (12–15). However, the importance of the CD3 chains to the TCR signaling response is difficult to assess in knockout mice, as these proteins are also required for TCR assembly and surface expression (12–15). Among the CD3 subunits, CD3e is the most likely can- didate for performing a critical role in the TCR signaling 913 The Journal of Experimental Medicine • Volume 192, Number 6, September 18, 2000 913–919 http://www.jem.org/cgi/content/full/192/6/913