Imamura Yasuhiro, Katahira Takashi, Kitamura Daisuke
Research Institute for Biological Sciences, Tokyo University of Science, 2669 Yamazaki, Noda-city, Chiba 278-0022, Japan.
J Biol Chem. 2004 Jun 18;279(25):26425-32. doi: 10.1074/jbc.M403685200. Epub 2004 Apr 15.
A B cell-specific adaptor protein, BASH (also known as BLNK or SLP-65), is crucial for B cell receptor (BCR) signaling. BASH binds to various signaling intermediates, such as Btk, PLCgamma2, Vav, and Grb2, through its well defined motifs. Although functional significance of such interactions has been documented, BASH-mediated signal transduction mechanism is not fully understood. Using the yeast two-hybrid system, we have identified a novel protein that binds to a conserved N-terminal domain of BASH, which we named BNAS2 (BASH N terminus associated protein 2). From its deduced amino acid sequence, BNAS2 is presumed to contain four transmembrane domains, which are included in a central MARVEL domain, and to localize to endoplasmic reticulum. BNAS2 was co-precipitated with BASH as well as Btk and ERK2 from a lysate of mouse B cell line. In the transfected cells, the exogenous BNAS2 was localized in a mesh-like structure in the cytoplasm resembling that of endoplasmic reticulum (ER) and nuclear membrane. BASH was co-localized with BNAS2 in a manner dependent on its N-terminal domain. RT-PCR analysis indicated that BNAS2 mRNA is expressed ubiquitously except for plasma cells. In chicken B cell line DT40, overexpression of BNAS2 resulted in an enhancement of BCR ligation-mediated transcriptional activation of Elk1, but not of NF-kappaB, in a manner dependent on the dose of BNAS2. Thus BNAS2 may serve as a scaffold for signaling proteins such as BASH, Btk, and ERK at the ER and nuclear membrane and may facilitate ERK activation by signaling from cell-surface receptors.
一种B细胞特异性衔接蛋白BASH（也称为BLNK或SLP-65）对B细胞受体（BCR）信号传导至关重要。BASH通过其明确的基序与各种信号中间体结合，如Btk、PLCγ2、Vav和Grb2。尽管此类相互作用的功能意义已有文献记载，但BASH介导的信号转导机制尚未完全了解。利用酵母双杂交系统，我们鉴定出一种与BASH保守的N端结构域结合的新型蛋白质，我们将其命名为BNAS2（BASH N端相关蛋白2）。从其推导的氨基酸序列推测，BNAS2含有四个跨膜结构域，这些结构域包含在一个中央MARVEL结构域中，并定位于内质网。BNAS2与BASH以及Btk和ERK2从小鼠B细胞系裂解物中共沉淀。在转染细胞中，外源性BNAS2定位于细胞质中类似内质网（ER）和核膜的网状结构中。BASH与BNAS2以依赖于其N端结构域的方式共定位。RT-PCR分析表明，除浆细胞外，BNAS2 mRNA在各处均有表达。在鸡B细胞系DT40中，BNAS2的过表达导致BCR连接介导的Elk1转录激活增强，但不影响NF-κB，且呈剂量依赖性。因此，BNAS2可能在内质网和核膜上作为BASH、Btk和ERK等信号蛋白的支架，并可能通过细胞表面受体的信号促进ERK激活。
