B-lymphocytes recognize antigen via B cell antigen receptors (BCR). This binding induces signaling leading to B cell activation, proliferation and differentiation. Early events of BCR signaling include reorganization of actin, and membrane spreading for increased antigen gathering. We have previously shown that the gap junction protein connexin43 (Cx43) is phosphorylated upon BCR signaling, and its carboxyl tail (CT) is important for BCR-mediated spreading. Here, specific serines in the Cx43 CT that are phosphorylated following BCR stimulation were identified. A chimeric protein containing the extracellular and transmembrane domains of CD8 fused to the Cx43 CT was sufficient to support cell spreading. Cx43 CT truncations showed that the region between amino acids 246-307 was necessary for B cell spreading. Site-specific serine to alanine mutations, S255A, S262A, S279A and S282A, resulted in differential effects on both BCR signaling, and BCR-mediated spreading. These serines can serve as potential binding sites for actin remodeling mediators and/or BCR signaling effectors; therefore, our results may reflect unique roles for each of these serines in terms of linking the Cx43 CT to actin remodeling.

中文翻译：

---

鉴定 connexin43 羧基尾中的丝氨酸残基对于 BCR 介导的 B 淋巴细胞扩散很重要。

B 淋巴细胞通过 B 细胞抗原受体 (BCR) 识别抗原。这种结合诱导导致 B 细胞激活、增殖和分化的信号传导。BCR 信号传导的早期事件包括肌动蛋白重组和膜扩散以增加抗原聚集。我们之前已经证明间隙连接蛋白 connexin43 (Cx43) 在 BCR 信号传导时被磷酸化，其羧基尾 (CT) 对于 BCR 介导的扩散很重要。在此，鉴定了 Cx43 CT 中在 BCR 刺激后磷酸化的特定丝氨酸。含有与 Cx43 CT 融合的 CD8 胞外和跨膜结构域的嵌合蛋白足以支持细胞扩散。Cx43 CT 截短表明氨基酸 246-307 之间的区域对于 B 细胞扩散是必需的。位点特异性丝氨酸至丙氨酸突变（S255A、S262A、S279A 和 S282A）对 BCR 信号传导和 BCR 介导的扩散产生不同的影响。这些丝氨酸可以作为肌动蛋白重塑介质和/或 BCR 信号传导效应器的潜在结合位点；因此，我们的结果可能反映了这些丝氨酸在连接 Cx43 CT 与肌动蛋白重塑方面的独特作用。