B cell antigen receptor (BCR) signaling is initiated by protein kinases and limited by counteracting phosphatases that currently are less well studied in their regulation of BCR signaling. Here, we used the B cell line Ramos to identify and quantify human B cell signaling components. Specifically, a protein tyrosine phosphatase profiling revealed a high expression of the protein tyrosine phosphatase 1B (PTP1B) in Ramos and human naïve B cells. The loss of PTP1B leads to increased B cell activation. Through substrate trapping in combination with quantitative mass spectrometry, we identified 22 putative substrates or interactors of PTP1B. We validated Igα, CD22, PLCγ1/2, CBL, BCAP, and APLP2 as specific substrates of PTP1B in Ramos B cells. The tyrosine kinase BTK and the two adaptor proteins GRB2 and VAV1 were identified as direct binding partners and potential substrates of PTP1B. We showed that PTP1B dephosphorylates the inhibitory receptor protein CD22 at phosphotyrosine 807. We conclude that PTP1B negatively modulates BCR signaling by dephosphorylating distinct phosphotyrosines in B cell-specific receptor proteins and various downstream signaling components.

中文翻译：

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定量蛋白质组学将 PTP1B 鉴定为 B 细胞抗原受体信号传导的调节剂。

B 细胞抗原受体 (BCR) 信号传导由蛋白激酶启动，并通过对抗目前在 BCR 信号传导调节方面研究较少的磷酸酶进行限制。在这里，我们使用 B 细胞系 Ramos 来识别和量化人类 B 细胞信号成分。具体而言，蛋白质酪氨酸磷酸酶分析显示蛋白质酪氨酸磷酸酶 1B (PTP1B) 在 Ramos 和人类幼稚 B 细胞中高表达。PTP1B 的缺失导致 B 细胞活化增加。通过底物捕获结合定量质谱，我们确定了 22 个 PTP1B 的推定底物或相互作用物。我们验证了 Igα、CD22、PLCγ1/2、CBL、BCAP 和 APLP2 作为拉莫斯 B 细胞中 PTP1B 的特异性底物。酪氨酸激酶 BTK 和两个衔接蛋白 GRB2 和 VAV1 被确定为 PTP1B 的直接结合伙伴和潜在底物。我们发现 PTP1B 在磷酸酪氨酸 807 处使抑制性受体蛋白 CD22 去磷酸化。我们得出结论，PTP1B 通过去磷酸化 B 细胞特异性受体蛋白和各种下游信号成分中的不同磷酸酪氨酸来负调节 BCR 信号传导。