Regulation of plasma cell differentiation by PI3-kinase

描述(申请人提供)：T依赖免疫反应的特征是迅速出现分泌IgM的浆细胞，随后出现毛囊生发中心和同型转换、高亲和力的Ig G、Ig A或Ig E分泌的浆细胞。最近，与浆细胞发育(BLIMP1)和生发中心发育(BCL6和AID，激活诱导胞苷脱氨酶)相关的基因受到了相当大的关注。此外，使用模型T依赖抗原的研究提供了对免疫反应期间B细胞的质和量变化的洞察力。然而，在我们对激活的B细胞分化的理解中，仍然缺乏对促进终末分化为分泌抗体的浆细胞的信号要求的了解，或者相反，促进进入生发中心的信号导致类开关重组(CSR)和体细胞高突变(SHM)。这项拟议的工作涉及磷脂酰肌醇-3激酶(PI3K)在引导激活的B细胞命运决定朝向浆细胞生成或生发中心方向上的作用。我们的初步数据支持这样的假设，即强的PI3K活性促进浆细胞的形成，而弱的PI3K活性促进CSR。我们已经证明，通过降低PI3K活性，无论是化学上还是遗传上，我们都可以促进CSR；这与浆细胞的生成呈负相关，但与增殖无关。我们的数据表明，这种调控在控制AID表达和功能的水平上起作用，并强烈暗示Akt是控制CSR的PI3K激活的下游靶点。此外，我们发现Akt介导的CSR抑制是通过FOXO转录因子家族的失活来实现的。这项建议的具体目的是通过以下步骤确定PI3K信号在激活的B细胞命运决定中的作用：i)鉴定B细胞特异性PTEN缺陷动物、PTEN/CD19双缺陷动物和PTEN/BLIMP1双缺陷动物体内浆细胞和生发中心的发育，ii)评估调节PI3K信号对浆细胞分化相关基因的影响，以及iii)确定调节AID表达和/或功能的PI3K响应元件。相关性：形成浆细胞和进行CSR的能力对抗体介导的免疫反应至关重要。高IgM综合征是一种人类免疫缺陷，其接受CSR的能力存在缺陷，导致抵抗感染的能力严重受损，而浆细胞形成异常最终可导致骨髓瘤。因此，了解调控这些过程的途径是我们了解这些疾病病因的必要步骤。

DESCRIPTION (provided by applicant): T-dependent immune responses are characterized by the rapid appearance of IgM secreting plasma cells followed by the appearance of follicular germinal centers and isotype class switched, high affinity IgG, IgA, or IgE secreting plasma cells. Considerable recent attention has been given to the genes involved in specifying plasma cell development (BLIMP1) and germinal center development (BCL6 and AID, activation induced cytidine deaminase). Additionally, studies using model T-dependent antigens have provided insight into the qualitative and quantitative changes in B cells during an immune response. However, what continues to be lacking in our appreciation of activated B cell differentiation is an understanding of the signaling requirements that promote terminal differentiation into antibody secreting plasma cells or conversely, the signals that promote entry into the germinal center resulting in class switch recombination (CSR) and somatic hypermutation (SHM). The proposed work addresses the role of phosphatidyl inositol-3 kinase (PI3K) in directing the activated B cell fate decision toward plasma cell generation or the germinal center. Our preliminary data support the hypothesis that strong PI3K activity promotes plasma cell formation, whereas weak PI3K activity promotes CSR. We have shown that by reducing PI3K activity, chemically or genetically, we can promote CSR; which is inversely correlated with plasma cell generation but not proliferation. Our data suggest that this regulation operates at the level of controlling the expression and function of AID, and strongly implicate the Akt as the downstream target of PI3K activation that controls CSR. Further, we show that Akt-mediated inhibition of CSR occurs through the inactivation of the Foxo family of transcription factors. The specific aims of this proposal are designed to define the role of PI3K signaling in activated B cell fate decisions by i) characterizing in vivo plasma cell and germinal center development in B cell-specific PTEN-deficient animals, PTEN/CD19 double-deficient animals, and PTEN/BLIMP1 double-deficient animals, ii) assessing the impact of modulating PI3K signaling on genes involved in plasma cell differentiation, and iii) identifying PI3K responsive elements regulating AID expression and/or function. Relevance: The ability to form plasma cells and to undergo CSR is critical for antibody mediated immune responses. Hyper-IgM syndrome is a human immunodeficiency in which the ability to undergo CSR is defective resulting in a severe impairment in the ability to fight infections, whereas dysregulated plasma cell formation can ultimately lead to myeloma. Hence, understanding the pathways regulating these processes is a requisite step towards our ability to understand the etiology of these diseases.