Kruglova N A, Kopylov A T, Filatov A V
Institute of Immunology National Research Center, Federal Medical-Biological Agency, Moscow, 115522 Russia.
Immunology Department, Biological Faculty, Moscow State University, Moscow, 119234 Russia.
Mol Biol (Mosk). 2019 Sep-Oct;53(5):838-848. doi: 10.1134/S0026898419050112.
Lymphocyte phosphatase-associated phosphoprotein (LPAP) is a small transmembrane protein that is found in lymphocytes and is tightly associated with the phosphatase CD45. The function of LPAP is still unknown. Studies of the LPAP interactome may reveal new details of how C45 and lymphocyte signaling in general are regulated. LPAP binding partners were sought using coimmunoprecipitation coupled with mass spectrometry, stabilization of protein complexes with chemical crosslinkers, and Blue Native electrophoresis. In addition to CD45, several proteins were identified as LPAP partners, including CD71, CD98, cytoskeletal proteins, the amino acid transporter SLC1A4, and the cell signaling component HS1. It was confirmed that more than 70% of LPAP molecules were bound with CD45 in a 1 : 1 complex. The effect of CD45 on LPAP was studied in CEM and Jurkat cells with a CD45 knockout. The LPAP levels in the cells were 10% of the level in wild-type cells. In the absence of CD45, LPAP phosphorylation at Ser-153 and Ser-163 was not affected, whereas phosphorylation at Ser-99 and Ser-172 decreased significantly. Based on the results, CD45 was assumed to play a role in regulating LPAP expression and phosphorylation status.
淋巴细胞磷酸酶相关磷蛋白（LPAP）是一种小的跨膜蛋白，存在于淋巴细胞中，与磷酸酶CD45紧密相关。LPAP的功能尚不清楚。对LPAP相互作用组的研究可能会揭示CD45和一般淋巴细胞信号传导如何被调节的新细节。利用免疫共沉淀结合质谱、用化学交联剂稳定蛋白复合物以及蓝色非变性电泳来寻找LPAP结合伴侣。除了CD45外，还鉴定出几种蛋白质作为LPAP的伴侣，包括CD71、CD98、细胞骨架蛋白、氨基酸转运蛋白SLC1A4和细胞信号成分HS1。已证实超过70%的LPAP分子以1:1复合物的形式与CD45结合。在CD45基因敲除的CEM和Jurkat细胞中研究了CD45对LPAP的影响。这些细胞中的LPAP水平是野生型细胞中水平的10%。在没有CD45的情况下，LPAP在Ser-153和Ser-163处的磷酸化不受影响，而在Ser-99和Ser-172处的磷酸化显著降低。基于这些结果，推测CD45在调节LPAP表达和磷酸化状态中起作用。
