He description in LYP of a single nucleotide polymorphism (SNP) [9,10] associated to several autoimmune diseases such as type 1 diabetes, systemic lupus erytematosus and rheumatoid arthritis [11] indicates that this phosphatase plays a critical role in the regulation of the immune response. This SNP, C1858T, changes into a Trp the Arg620 present in the P1 PRM that binds to CSK SH3 domain [9,12]. Based on data obtained in T lymphocytes, LYPW has been proposed to be a gain-of-function Title Loaded From File variant with increased phosphatase activity that reduces early Tcell signaling parameters such as Ca2+ mobilization and LCK phosphorylation [13]. Nevertheless, it is not fully clear how these changes in early signaling affect T cell physiology. A recent work has proposed that a reduced interaction with CSK leads to a lower tyrosine phosphorylation of LYP in a negative regulatory site, responsible for the increase in the activity of LYP [14]. Although the gain-of-function phenotype has received support from several studies, there is no agreement on this point; and recent reports have claimed that LYPW is a loss of function variant [15,16]. Furthermore, knockout mice deficient in Pep phosphatase did not develop any autoimmune disease [17], despite augmented LCK activity in re-stimulated T-lymphocytes and an increase in the number of germinal centers. Current knowledge about LYP/CSK binding is mainly based on the study of Csk interaction with Pep [6,8,12]. However, no detailed study has been yet reported on the association of LYP with CSK to determine the validity of this model in human cells, which is relevant to the pathogenesis of autoimmune diseases. Therefore, to determine how the R620W polymorphism modifies the function of this complex and contributes to the induction ofRegulation of TCR Signaling by LYP/CSK Complexautoimmunity, in this work we have analyzed LYP/CSK interaction and its relevance for TCR signaling.Materials and Methods Antibodies and ReagentsTissue culture reagents were from Lonza (Verviers, Belgium). The anti-hemagglutinin (HA) mAb was from Covance (Berkely, CA, USA). The anti-LCK mouse Ab (3A5), anti-GST Ab, antimyc Ab (9E10), anti-Erk2 Ab (C154), anti-Fyn Ab (6A406) and anti-CSK rabbit polyclonal Ab (C-20) were from Santa Cruz Biotechnology Inc. (Santa Cruz, CA, USA). The anti-CD3 (UCHT1), anti-CD28 (clone CD28.2), anti-Abl and anti-CSK mouse Ab were from BD Pharmingen (Franklin Lakes, NJ, USA). The anti-phosphotyrosine 4G10 mAb was from Millipore (Billerica, MA, USA).The anti-LYP goat polyclonal Ab was from R D Systems, Inc. (Minneapolis, MN, USA). The GW-0742 cost anti-phospho-p38 Ab was from Cell Signaling Technology Inc., (Beverly, MA, USA).The anti-phospho-Erk Ab was from Promega (Fitchburg, WI, USA).Pull-down of GST fusion proteins was done with Glutathion sepharose beads (GE Healthcare, Buckinghamshire, UK.) incubated with the clarified lysates for 2 h. The complexes were then washed and processed as explained above for the IP. Blots were scanned with the GS-800 Densitometer (Bio-Rad Laboratories, CA, USA) and analyzed with the image analysis software Quantity One (Bio-Rad Laboratories, CA, USA). Data are reported as arbitrary units.Luciferase AssaysTransfection of Jurkat T cells and assays for LUC activity were performed as described previously [19,20]. Briefly, 206106 Jurkat cells were transfected with 20 mg empty pEF vector or the indicated plasmids, along with 3 mg of NFAT/AP-1-luc (or other reporters) and 0.5 mg of a Renilla luciferase r.He description in LYP of a single nucleotide polymorphism (SNP) [9,10] associated to several autoimmune diseases such as type 1 diabetes, systemic lupus erytematosus and rheumatoid arthritis [11] indicates that this phosphatase plays a critical role in the regulation of the immune response. This SNP, C1858T, changes into a Trp the Arg620 present in the P1 PRM that binds to CSK SH3 domain [9,12]. Based on data obtained in T lymphocytes, LYPW has been proposed to be a gain-of-function variant with increased phosphatase activity that reduces early Tcell signaling parameters such as Ca2+ mobilization and LCK phosphorylation [13]. Nevertheless, it is not fully clear how these changes in early signaling affect T cell physiology. A recent work has proposed that a reduced interaction with CSK leads to a lower tyrosine phosphorylation of LYP in a negative regulatory site, responsible for the increase in the activity of LYP [14]. Although the gain-of-function phenotype has received support from several studies, there is no agreement on this point; and recent reports have claimed that LYPW is a loss of function variant [15,16]. Furthermore, knockout mice deficient in Pep phosphatase did not develop any autoimmune disease [17], despite augmented LCK activity in re-stimulated T-lymphocytes and an increase in the number of germinal centers. Current knowledge about LYP/CSK binding is mainly based on the study of Csk interaction with Pep [6,8,12]. However, no detailed study has been yet reported on the association of LYP with CSK to determine the validity of this model in human cells, which is relevant to the pathogenesis of autoimmune diseases. Therefore, to determine how the R620W polymorphism modifies the function of this complex and contributes to the induction ofRegulation of TCR Signaling by LYP/CSK Complexautoimmunity, in this work we have analyzed LYP/CSK interaction and its relevance for TCR signaling.Materials and Methods Antibodies and ReagentsTissue culture reagents were from Lonza (Verviers, Belgium). The anti-hemagglutinin (HA) mAb was from Covance (Berkely, CA, USA). The anti-LCK mouse Ab (3A5), anti-GST Ab, antimyc Ab (9E10), anti-Erk2 Ab (C154), anti-Fyn Ab (6A406) and anti-CSK rabbit polyclonal Ab (C-20) were from Santa Cruz Biotechnology Inc. (Santa Cruz, CA, USA). The anti-CD3 (UCHT1), anti-CD28 (clone CD28.2), anti-Abl and anti-CSK mouse Ab were from BD Pharmingen (Franklin Lakes, NJ, USA). The anti-phosphotyrosine 4G10 mAb was from Millipore (Billerica, MA, USA).The anti-LYP goat polyclonal Ab was from R D Systems, Inc. (Minneapolis, MN, USA). The anti-phospho-p38 Ab was from Cell Signaling Technology Inc., (Beverly, MA, USA).The anti-phospho-Erk Ab was from Promega (Fitchburg, WI, USA).Pull-down of GST fusion proteins was done with Glutathion sepharose beads (GE Healthcare, Buckinghamshire, UK.) incubated with the clarified lysates for 2 h. The complexes were then washed and processed as explained above for the IP. Blots were scanned with the GS-800 Densitometer (Bio-Rad Laboratories, CA, USA) and analyzed with the image analysis software Quantity One (Bio-Rad Laboratories, CA, USA). Data are reported as arbitrary units.Luciferase AssaysTransfection of Jurkat T cells and assays for LUC activity were performed as described previously [19,20]. Briefly, 206106 Jurkat cells were transfected with 20 mg empty pEF vector or the indicated plasmids, along with 3 mg of NFAT/AP-1-luc (or other reporters) and 0.5 mg of a Renilla luciferase r.