CRTC2 in Cellular Development, Function, and Neoplasia

描述（由申请人提供）：大多数淋巴细胞恶性肿瘤是由生发中心（GC）经历的B细胞转化引起的。在之前的两个资助期内，我们发现TCL1原癌基因在三种主要GC B细胞淋巴瘤（包括滤泡性（FL）、伯基特（BL）和弥漫性大B细胞（DLBCL）淋巴瘤）的样本中异常表达。两组特异性目标阐述了在GC B细胞转化过程中TCL1异常表达的致病作用，以及在人B细胞恶性肿瘤中调节和失调TCL1表达的机制。资助我们的小组发表了66篇同行评议的出版物。现在，我们建议从逻辑上扩展TCL1之外的先前成功工作的范围，进入一个令人兴奋的新方向。在免疫应答过程中，B细胞经历快速增殖和GCs内免疫球蛋白（IG）基因的重塑，以产生记忆B细胞和浆细胞。不幸的是，与这种“GC反应”相关的DNA损伤也促进了大多数B细胞恶性肿瘤。我们最近发现，在GC B细胞的IG类开关重组（CSR）过程中，由AID依赖性DNA双链断裂（dsb）激活的ATM通过LKB1发出信号，使CRTC2失活，CRTC2是一种已知的CREB转录共激活因子。通过全基因组定位分析，我们确定CRTC2失活意外地抑制了控制GC B细胞增殖、自我更新和向抗体（Ab）分泌浆细胞分化的遗传程序，同时反对淋巴瘤形成（见附录- Sherman等人，Molecular cell, in press, 2010）。通过ATM或LKB1抑制，或最近发现的CRTC2体细胞突变或遗传多态性，在人类B细胞淋巴瘤的初步研究中发现了这一途径的缺陷。关于CRTC2作为葡萄糖代谢的调节因子，我们已经知道了很多，现在我们已经证明dsb激活了GC B细胞中的一条途径，使CRTC2失活。然而，到目前为止，CRTC2在细胞分化或癌症中的作用尚未被描述。在新的初步研究中，我们在GC - B细胞中发现了一组来自ChIP-chip的CRTC2结合基因，当CRTC2失活时，这些基因的表达增加而不是减少，这表明CRTC2在其CREB共激活子功能之外还具有转录抑制活性。作为细胞分化和癌症的候选调节因子，我们提出了三个新的特异性目标来研究CRTC2在控制B细胞命运和功能中的作用。在Aim 1中，我们将确定CRTC2是否参与转录抑制。在Aim 2中，我们将在GC B细胞中组构激活CRTC2，并在体内评估其对B细胞分化和体液免疫的影响。在目标3中，我们将确定一个新的激活CRTC2改变是体细胞突变还是种系多态性，我们将研究CRTC2失活以避免淋巴瘤发生的必要性。总的来说，我们的研究将CRTC2的作用扩展到代谢之外，并描述了一种意想不到的B细胞发育和功能的新调节剂。

DESCRIPTION (provided by applicant): Most lymphoid malignancies arise by transformation of germinal center (GC) experienced B cells. In two prior funding periods we showed that the TCL1 proto-oncogene was abnormally expressed in samples from three major GC B cell lymphoma categories, including follicular (FL), Burkitt (BL), and diffuse large B cell (DLBCL) lymphomas. Two sets of Specific Aims addressed a causative role for aberrant TCL1 expression in the transformation of GC B cells and the mechanism(s) for regulating and dysregulating TCL1 expression in human B cell malignancies. Funding supported our group for 66 peer-reviewed publications. Now, we propose to logically expand the scope of prior successful work beyond TCL1 into an exciting new direction. During an immune response, B cells undergo rapid proliferation and remodeling of immunoglobulin (IG) genes within GCs to generate memory B and plasma cells. Unfortunately, DNA damage associated with this "GC reaction" also promotes most B cell malignancies. We recently discovered that ATM, activated by AID- dependent DNA double-stranded breaks (DSBs) during IG class switch recombination (CSR) in GC B cells, signals through LKB1 to inactivate CRTC2, a known transcriptional co-activator of CREB. Using genome-wide location analysis, we determined that CRTC2 inactivation unexpectedly repressed a genetic program that controls GC B cell proliferation, self-renewal, and differentiation into antibody (Ab)-secreting plasma cells while opposing lymphomagenesis (see Appendix- Sherman, et al., Molecular Cell, in press, 2010). Defects in this pathway were identified in pilot studies of human B cell lymphomas by ATM or LKB1 repression, or by a recently identified somatic mutation or genetic polymorphism in CRTC2. Much is known about CRTC2 as a regulator of glucose metabolism, and we have now shown that DSBs activate a pathway in GC B cells that inactivates CRTC2. However, no role for CRTC2 in cell differentiation or cancer has been described to date. In new preliminary studies, we discovered a set of CRTC2 bound genes from ChIP-chip in GC B cells that increase rather than decrease in expression with CRTC2 inactivation, suggesting that CRTC2 also has transcriptional repression activity beyond its CREB co-activator function. As a candidate regulator of cell differentiation and cancer, we propose Three New Specific Aims to investigate the role of CRTC2 in controlling B cell fate and function. In Aim 1, we will determine whether CRTC2 participates in transcriptional repression. In Aim 2, we will constitutively activate CRTC2 in GC B cells and evaluate effects on B cell differentiation and humoral immunity in vivo. In aim 3, we will determine whether a new activating CRTC2 alteration is a somatic mutation or germline polymorphism and we will investigate the necessity for CRTC2 inactivation to avoid lymphomagenesis. Overall, our studies expand the role for CRTC2 beyond metabolism and characterize an unexpected new regulator of B cell development and function.