Regulation of plasma cell differentiation by PI3-kinase

描述（由申请人提供）：t依赖性免疫反应的特征是IgM分泌浆细胞的快速出现，随后出现滤泡生发中心和同型转换，高亲和力的IgG， IgA或IgE分泌浆细胞。近年来，参与浆细胞发育的基因（BLIMP1）和生发中心发育的基因（BCL6和AID，激活诱导胞苷脱氨酶）引起了相当大的关注。此外，使用模型t依赖性抗原的研究提供了对免疫反应期间B细胞定性和定量变化的见解。然而，在我们对活化B细胞分化的认识中，仍然缺乏对促进最终分化为分泌抗体的浆细胞的信号要求的理解，或者相反，促进进入生发中心导致类开关重组（CSR）和体细胞超突变（SHM）的信号要求的理解。提出的工作解决了磷脂酰肌醇-3激酶（PI3K）在指导激活的B细胞命运决定浆细胞生成或生发中心的作用。我们的初步数据支持强PI3K活性促进浆细胞形成的假设，而弱PI3K活性促进CSR。我们已经证明，通过化学或基因方式降低PI3K的活性，我们可以促进CSR；这与浆细胞的产生呈负相关，但与增殖无关。我们的数据表明，这种调控在控制AID的表达和功能水平上起作用，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家族转录因子的失活发生的。该提案的具体目的是通过以下方式来确定PI3K信号在活化B细胞命运决定中的作用：1)在B细胞特异性PTEN缺陷动物、PTEN/CD19双缺陷动物和PTEN/BLIMP1双缺陷动物的体内浆细胞和生发中心发育特征；2)评估调节PI3K信号对参与浆细胞分化的基因的影响。iii)鉴定调节AID表达和/或功能的PI3K应答元件。相关性：形成浆细胞和经历CSR的能力对抗体介导的免疫反应至关重要。Hyper-IgM综合征是一种人类免疫缺陷，在这种情况下，进行CSR的能力存在缺陷，导致抵抗感染的能力严重受损，而浆细胞形成失调最终会导致骨髓瘤。因此，了解调节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.