Infection of mice with Listeria monocytogenes results in a strong T-cell response that is critical for an efficient defense. Here, we demonstrate that the adapter protein SLy1 (SH3-domain protein expressed in Lymphocytes 1) is essential for the generation of a fully functional T-cell response. The lack of SLy1 leads to reduced survival rates of infected mice. The increased susceptibility of SLy1 knock-out (KO) mice was caused by reduced proliferation of differentiated T cells. Ex vivo analyses of isolated SLy1 KO T cells displayed a dysregulation of Forkhead box protein O1 shuttling after TCR signaling, whichresulted in an increased expression of cell cycle inhibiting genes, and therefore, reduced expansion of the T-cell population. Forkhead box protein O1 shuttles to the cytoplasm after phosphorylation in a protein complex including 14-3-3 proteins. Interestingly, we observed a similar regulation for the adapter protein SLy1, where TCR stimulation results in SLy1 phosphorylation and SLy1 export to the cytoplasm. Moreover, immunoprecipitation analyses revealed a binding of SLy1 to 14-3-3 proteins. Altogether, this study describes SLy1 as an immunoregulatory protein, which is involved in the generation of adaptive immune responses during L. monocytogenes infection, and provides a model of how SLy1 regulates T-cell proliferation.Keywords: Foxo1 r Infection r Proliferation r SLy1 r T cells Additional supporting information may be found in the online version of this article at the publisher's web-site
IntroductionInfection with the intracellular bacterium Listeria monocytogenes (LM) induces strong immune responses, which makes it ideally suited as a model to analyze the innate and adaptive immune responses in mice. Following infection, the innate immune system is quickly activated and serves as a first line defense to control Correspondence: Dr. Sandra Beer-Hammer e-mail: sandra.beer-hammer@uni-tuebingen.de the spreading of the bacteria. Neutrophils, macrophages, and NK cells have been shown to be part of this early response [1][2][3]. The importance of the innate immune system was further demonstrated by a significantly increased susceptibility of mice lacking , , , or IFNR-γ [7], and also by studies with SCID mice that develop chronic listeriosis, but are protected through the innate response from early death [8,9]. In contrast, the adaptive immune system requires several days to get fully activated and to generate Ag-specific T cells that resolve the infection and provide a long-lasting immunity [10].C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 3088 Daniel Schäll et al. Eur. J. Immunol. 2015. 45: 3087-3097 SLy1 (SH3-domain protein expressed in Lymphocytes 1) is exclusively expressed in lymphocytes and is part of a family of adapter proteins comprising three members, SLy1 [11], SLy2 [12], and SASH1 (SAM-and SH3-domain containing protein 1) [13]. SLy1 and SLy2 are highly homologous, as both express a bipartite nuclear localization sequence as well as an SH3 and an SAM domain [11,14]. SL...