The role of CD3 delta interacting proteins in T-Cell receptor assembly and signaling

Official URL: http://risc01.sabanciuniv.edu/record=b1301512 (Table of Contents)

The signals initiated from the T cell receptor (TCR)-CD3 complex receptors are not only important for the correct functioning but also for the differentiation and survival of T cells. While CD3 chains play an essential role in the assembly of and signaling by the TCR and preTCR complexes, the logic behind the redundancy of these signaling subunits has not been addressed. In this study, we aimed to identify novel proteins that interact with the CD3delta subunit of the TCR complex. We performed a membrane based split ubiquitin yeast two hybrid screen. This novel genetic screening system allows the identification of interaction partners of membrane-associated proteins. We used the CD3delta chain as bait and screened a Jurkat cell cDNA library to identify CD3 interacting proteins. We confirmed the in-vivo relevance of these interactions by co-immunoprecipitation in human tissue culture cell lines. We further examined the functional significance of two CD3delta interacting proteins: BCAP31 and CD81.We demonstrate that BCAP31, previously shown to associate with B cell receptor, interacts with CD3delta in the endoplasmic reticulum (ER) and plays a role in TCR assembly. We also identified the tetraspanin superfamily member CD81, previously shown to have a role in early T cell development, as a CD3delta interaction partner. In order to investigate the functional significance of this interaction, we silenced CD81 expression in T lymphocyte cell lines by shRNA mediated expression arrest and performed functional assays. We demonstrate that CD81 is important for TCR/CD4 co-receptor mediated signaling of T lymphocytes, possibly inhibiting the initiation of TCR signals.