B Cell Molecular Immunology Section, Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
PLoS One. 2013;8(3):e60139. doi: 10.1371/journal.pone.0060139. Epub 2013 Mar 22.
Germinal centers (GCs) are microanatomic structures that develop in secondary lymphoid organs in response to antigenic stimulation. Within GCs B cells clonally expand and their immunoglobulin genes undergo class switch recombination and somatic hypermutation. Transcriptional profiling has identified a number of genes that are prominently expressed in GC B cells. Among them is Rgs13, which encodes an RGS protein with a dual function. Its canonical function is to accelerate the intrinsic GTPase activity of heterotrimeric G-protein α subunits at the plasma membrane, thereby limiting heterotrimeric G-protein signaling. A unique, non-canonical function of RGS13 occurs following translocation to the nucleus, where it represses CREB transcriptional activity. The functional role of RGS13 in GC B cells is unknown. To create a surrogate marker for Rgs13 expression and a loss of function mutation, we inserted a GFP coding region into the Rgs13 genomic locus. Following immunization GFP expression rapidly increased in activated B cells, persisted in GC B cells, but declined in newly generated memory B and plasma cells. Intravital microscopy of the inguinal lymph node (LN) of immunized mice revealed the rapid appearance of GFP(+) cells at LN interfollicular regions and along the T/B cell borders, and eventually within GCs. Analysis of WT, knock-in, and mixed chimeric mice indicated that RGS13 constrains extra-follicular plasma cell generation, GC size, and GC B cell numbers. Analysis of select cell cycle and GC specific genes disclosed an aberrant gene expression profile in the Rgs13 deficient GC B cells. These results indicate that RGS13, likely acting at cell membranes and in nuclei, helps coordinate key decision points during the expansion and differentiation of naive B cells.
生发中心（GCs）是次级淋巴器官中对抗原刺激产生的微观结构。在 GCs 中，B 细胞克隆扩增，其免疫球蛋白基因发生类别转换重组和体细胞超突变。转录谱分析确定了许多在 GC B 细胞中高度表达的基因。其中包括编码具有双重功能的 RGS 蛋白的 Rgs13。其典型功能是加速质膜上异源三聚体 G 蛋白α亚基的内在 GTPase 活性，从而限制异源三聚体 G 蛋白信号传导。RGS13 的一个独特的、非典型功能发生在易位到核内后，在核内它抑制 CREB 转录活性。RGS13 在 GC B 细胞中的功能作用尚不清楚。为了创建 Rgs13 表达的替代标志物和功能丧失突变，我们将 GFP 编码区插入 Rgs13 基因组座。免疫后，激活的 B 细胞中 GFP 表达迅速增加，在 GC B 细胞中持续存在，但在新生成的记忆 B 和浆细胞中下降。对免疫小鼠腹股沟淋巴结（LN）的活体显微镜检查显示 GFP（+）细胞迅速出现在 LN 滤泡间区以及 T/B 细胞边界，并最终出现在 GC 中。对 WT、敲入和混合嵌合小鼠的分析表明，RGS13 限制了滤泡外浆细胞的生成、GC 大小和 GC B 细胞数量。对选定的细胞周期和 GC 特异性基因的分析揭示了 Rgs13 缺陷 GC B 细胞中异常的基因表达谱。这些结果表明，RGS13 可能在细胞膜和核内发挥作用，有助于协调幼稚 B 细胞扩增和分化过程中的关键决策点。
