Novel unconventional myosins in B cell homeostasis

摘要 无法治愈的自身免疫性疾病折磨着数百万美国人，导致疼痛和多器官的持续损伤。 系统，并对患者的健康，福祉和生活质量产生重大影响。B细胞数量增加， 更强的B细胞活化和向浆细胞的分化以及自身抗体的产生通常表征 自身免疫，表明失调的B细胞存活和分化是自身免疫的关键步骤， 发病机制鉴定调节B细胞存活、活化和增殖的蛋白质和分子事件。 因此，分化对于更好地理解自身免疫性疾病的机制至关重要 发展Myo 18 A是一种具有独特结构域组织的支架蛋白， 在非免疫细胞的各种亚细胞区室中的多蛋白复合物。我们报道了B细胞 表达Myo 18 A，并且其在B细胞中的条件性缺失（Myo 18 A BKO）导致成熟B细胞中Myo 18 A的增加， 细胞和浆细胞、脾肿大、高丙种球蛋白血症和自身抗体的产生。 有趣的是，这一特征与过度表达的转基因小鼠中报告的自身免疫表现重叠， B细胞存活因子BAFF，以及基因缺失参与mRNA衰变的蛋白质的小鼠。在 根据初步数据，我们观察到Myo 18 A缺陷型B细胞显示出更大的BAFF反应性特征， 包括增加线粒体大小和基因表达，以及更强的促生存Akt信号传导，表明 Myo 18 A负调节B细胞对BAFF的应答。此外，B细胞中Myo 18 A的缺失增加了 降低了B细胞中关键转录因子Blimp-1 mRNA的基础表达并减少了其降解 分化此外，B细胞中的Myo 18 A与Blimp 1 mRNA结合并与亚细胞mRNA共定位 降解位点，表明Myo 18 A参与转录后调控和Blimp的表达。 1.我们发表的和初步的数据表明，Myo 18 A是一个重要的，以前未被认识到的， B细胞免疫中的决定簇。我们的具体目的是检验以下假设：（1）Myo 18 A限制BCR （2）Myo 18 A通过抑制mRNA的稳定性来调控B细胞基因表达， Myo 18 A通过控制B细胞转录组限制B细胞分化。拟议 这项研究是创新的，因为它将为非传统的肌球蛋白家族蛋白Myo 18 A建立一个新的作用。 防止不受控制的B细胞活化和分化。具体来说，我们的研究将确定一个新的 通过调节B细胞抗原在Myo 18 A和B细胞存活和分化之间的功能联系 以及BAFF反应性和转录后mRNA稳定性。这项研究预计将有 重要的影响，因为它将使更好地了解分子过程的机制， 防止过度的抗体产生。

ABSTRACT Incurable autoimmune diseases afflict millions of Americans, cause pain and persistent damage to multiple organ systems, and have a major impact on patient health, well-being and quality of life. Increased B cell numbers, greater B cell activation and differentiation into plasma cells, and autoantibody production often characterize autoimmunity, signifying that dysregulated B cell survival and differentiation are critical steps in autoimmune pathogenesis. Identification of proteins and molecular events that regulate B cell survival, activation and differentiation is therefore critical for better mechanistic understanding of autoimmune disease development. Myo18A is a scaffolding protein with a unique domain organization that enables assembly of multiprotein complexes in various subcellular compartments of non-immune cells. We reported that B cells express Myo18A, and that its conditional deletion in B cells (Myo18A BKO) leads to an increase in mature B cells and plasma cells, splenomegaly, hypergammaglobulinemia, and development of autoantibodies. Interestingly, this profile overlaps with autoimmune manifestations reported in transgenic mice overexpressing the B cell survival factor BAFF, and in mice with genetic deletion of proteins involved in mRNA decay. In preliminary data, we observed that Myo18A-deficient B cells display features of greater BAFF responsiveness, including increased mitochondrial size and gene expression, and stronger pro-survival Akt signaling, indicating that Myo18A negatively regulates B cell response to BAFF. Additionally, deletion of Myo18A in B cells increased the basal expression and reduced the decay of mRNA encoding Blimp-1, a key transcription factor in B cell differentiation. Further, Myo18A in B cells bound to Blimp1 mRNA and co-localized with subcellular mRNA degradation sites, indicating that Myo18A is involved in post-transcriptional regulation and expression of Blimp- 1. Our published and preliminary data suggest that Myo18A is an important and previously unrecognized determinant in B cell immunity. Our specific aims are to test the hypotheses that (1) Myo18A restricts BCR and BAFF-R signaling to control B cell homeostasis, (2) Myo18A inhibits mRNA stability to inform B cell gene expression, and (3) Myo18A limits B cell differentiation by controlling the B cell transcriptome. The proposed research is innovative because it will establish a novel role for the unconventional myosin family protein Myo18A in preventing uncontrolled B cell activation and differentiation. Specifically, our research will identify a novel functional connection between Myo18A and B cell survival and differentiation through regulation of B cell antigen and BAFF responsiveness and post-transcriptional mRNA stability. This research is expected to have significant impact because it will enable better mechanistic understanding of the molecular processes that prevent exaggerated antibody development.