AP180 binds to the C-terminal SH2 domain of phospholipase C-gamma1 and inhibits its enzymatic activity

The Tyrosine Phosphatase Activity of PTPN22 Is Involved in T Cell Development via the Regulation of TCR Expression

The protein tyrosine phosphatase PTPN22 inhibits T cell activation by dephosphorylating some essential proteins in the T cell receptor (TCR)-mediated signaling pathway, such as the lymphocyte-specific protein tyrosine kinase (Lck), Src family tyrosine kinases Fyn, and the phosphorylation levels of Zeta-chain-associated protein kinase-70 (ZAP70). For the first time, we have successfully produced PTPN22 CS transgenic mice in which the tyrosine phosphatase activity of PTPN22 is suppressed. Notably, the number of thymocytes in the PTPN22 CS mice was significantly reduced, and the expression of cytokines in the spleen and lymph nodes was changed significantly. Furthermore, PTPN22 CS facilitated the positive and negative selection of developing thymocytes, increased the expression of the TCRαβ-CD3 complex on the thymus cell surface, and regulated their internalization and recycling. ZAP70, Lck, Phospholipase C gamma1(PLCγ1), and other proteins were observed to be reduced in PTPN22 CS mouse thymocytes. In summary, PTPN22 regulates TCR internalization and recycling via the modulation of the TCR signaling pathway and affects TCR expression on the T cell surface to regulate negative and positive selection. PTPN22 affected the development of the thymus, spleen, lymph nodes, and other peripheral immune organs in mice. Our study demonstrated that PTPN22 plays a crucial role in T cell development and provides a theoretical basis for immune system construction.

p104 binds to Rac1 and reduces its activity during myotube differentiation of C2C12 cell

The p104 protein inhibits cellular proliferation when overexpressed in NIH3T3 cells and has been shown to associate with p85α, Grb2, and PLCγ1. In order to isolate other proteins that interact with p104, yeast two-hybrid screening was performed. Rac1 was identified as a binding partner of p104 and the interaction between p104 and Rac1 was confirmed by immunoprecipitation. Using a glutathione S-transferase (GST) pull-down assay with various p104 fragments, the 814–848 amino acid residue at the carboxyl-terminal region of p104 was identified as the key component to interact with Rac1. The CrkII which is involved in the Rac1-mediated cellular response was also found to interact with p104 protein. NIH3T3 cells which overexpressed p104 showed a decrease of Rac1 activity. However, neither the proline-rich domain mutant, which is unable to interact with CrkII, nor the carboxy-terminal deletion mutant could attenuate Rac1 activity. During the differentiation of myoblasts, the amount of p104 protein as well as transcript level was increased. The overexpression of p104 enhanced myotube differentiation, whereas siRNA of p104 reversed this process. In this process, more Rac1 and CrkII were bound to increased p104. Based on these results, we conclude that p104 is involved in muscle cell differentiation by modulating the Rac1 activity.

Genome-wide association of mood-incongruent psychotic bipolar disorder

Mood-incongruent psychotic features (MICP) are familial symptoms of bipolar disorder (BP) that also occur in schizophrenia (SZ), and may represent manifestations of shared etiology between the major psychoses. In this study we have analyzed three large samples of BP with imputed genome-wide association data and have performed a meta-analysis of 2196 cases with MICP and 8148 controls. We found several regions with suggestive evidence of association (P<10(-6)), although no marker met genome-wide significance criteria. The top associations were on chromosomes: 6q14.2 within the PRSS35/SNAP91 gene complex (rs1171113, P=9.67 × 10(-8)); 3p22.2 downstream of TRANK/LBA1 (rs9834970, P=9.71 × 10(-8)); and 14q24.2 in an intron of NUMB (rs2333194, P=7.03 × 10(-7)). These associations were present in all three samples, and both rs1171113 and rs2333194 were found to be overrepresented in an analysis of MICP cases compared with all other BP cases. To test the relationship of MICP with SZ, we performed polygenic analysis using the Psychiatric GWAS Consortium SZ results and found evidence of association between SZ polygenes and the presence of MICP in BP cases (meta-analysis P=0.003). In summary, our analysis of the MICP phenotype in BP has provided suggestive evidence for association of common variants in several genes expressed in the nervous system. The results of our polygenic analysis provides support for a modest degree of genetic overlap between BP with MICP and SZ, highlighting that phenotypic correlations across syndromes may be due to the influence of polygenic risk factors.

Effect of clathrin assembly lymphoid myeloid leukemia protein depletion on clathrin coat formation

The endocytic accessory clathrin assembly lymphoid myeloid leukemia protein (CALM) is the ubiquitously expressed homolog of the neuron-specific protein AP180 that has been implicated in the retrieval of synaptic vesicle. Here, we show that CALM associates with the alpha-appendage domain of the AP2 adaptor via the three peptide motifs 420DPF, 375DIF and 489FESVF and to a lesser extent with the amino-terminal domain of the clathrin heavy chain. Reducing clathrin levels by RNA interference did not significantly affect CALM localization, but depletion of AP2 weakens its association with the plasma membrane. In cells, where CALM levels were reduced by RNA interference, AP2 and clathrin remained organized in somewhat enlarged bright fluorescent puncta. Electron microscopy showed that the depletion of CALM drastically affected the clathrin lattice structure. Round-coated buds, which are the predominant features in control cells, were replaced by irregularly shaped buds and long clathrin-coated tubules. Moreover, we noted an increase in the number of very small cages that formed on flat lattices. Furthermore, we noticed a redistribution of endosomal markers and AP1 in cells that were CALM depleted. Taken together, our findings indicate a critical role for CALM in the regulation and orderly progression of coated bud formation at the plasma membrane.

Identification of p115 as a PLCgamma1-binding protein and the role of Src homology domains of PLCgamma1 in the vesicular transport

In order to gain further insight into the function(s) of PLCgamma1, we tried to identify the binding partners that can interact with the SH223 domains of PLCgamma1. Immunoscreening was performed with the purified antisera that are specific to SH223-binding proteins. Several immunoreactive clones were identified as the putative binding proteins and one of them was identified as p115. p115 was reported to be required for transcytotic fusion and subsequent binding of the vesicles to the target membrane. The interaction between PLCgamma1 and p115 was specific to carboxyl-terminal SH2 domain and SH3 domain of PLCgamma1, and also confirmed by biochemical approaches such as co-immunoprecipitation, pull-down assay, and glycerol gradient fractionation. To further characterize the role of SH domains of PLCgamma1 in the vesicle transport pathway, secreted form of alkaline phosphatase (SEAP) reporter assay was carried out. When the SH2 and/or SH3 domains of PLCgamma1 were deleted, the secretion of SEAP was significantly reduced. These findings indicate that the SH2 and SH3 domains of PLCgamma1 may play a role(s) in the process of the vesicle transport via interaction with other vesicle-associated proteins such as p115.