Regulation of cyclin D1 expression in the intestine

描述(来自申请人)：细胞周期蛋白D1是一种受到严格调控的细胞周期控制分子，它是细胞外生长刺激和抑制信号的关键传感器，也是进入G1期的关键决定因素。细胞周期蛋白D1的异常表达是人类肿瘤中最常见的异常之一，被认为在肿瘤的发生发展中起着重要作用。因此，了解在正常和病理条件下控制细胞周期蛋白D1积累的潜在机制是至关重要的。我们的研究发现蛋白激酶C a(PKCA)是肠上皮细胞中细胞周期蛋白D1表达的一种新的调节因子。PKCA在肠道具有生长抑制和肿瘤抑制作用，在肠道肿瘤早期表达缺失。基于大量的新数据，提出了解决以下问题的策略 有一种假说认为，PKCA信号在调节肠道细胞中细胞周期蛋白D1的表达中起着关键作用，并且PKCA介导的细胞周期蛋白D1调控的破坏导致了肠道肿瘤的发生。下列主要发现为这一假说提供了基础：(A)PKCA活性通过两种机制抑制未转化的肠道细胞中细胞周期蛋白D1的积聚：(B)PKCA对细胞周期蛋白D1翻译的抑制作用涉及激活翻译抑制因子4E-BP1；(C)PKCA信号的丧失与细胞周期蛋白D1mRNA和蛋白的过度诱导、细胞增殖增加有关；(C)在结肠癌细胞中恢复PKCA可抑制细胞周期蛋白D1mRNA和蛋白的表达，抑制锚定非依赖性生长。为了进一步探索PKCA信号与控制细胞周期蛋白D1在肠道细胞中积累之间的联系，将解决以下具体目标：(1)确定PKCA信号调节PP2A活性和4E-BP1的机制 (2)探讨Id1抑制在PKCA诱导的正常和肿瘤肠细胞周期蛋白D1下调中的作用；(3)探讨细胞周期蛋白D1mRNA高表达与肠上皮细胞PKCA信号丢失相关的机制；(4)探讨PKCA信号在体内调节细胞周期蛋白D1水平和维持肠道内环境稳定中的作用。该项目的长期目标是了解协调肠道上皮细胞更新过程的机制。 在正常情况下，确定肠道细胞如何克服这些控制而产生肿瘤，并确定预防和治疗肠道疾病的新靶点 癌症。 公共卫生相关性：细胞周期蛋白D1在调节细胞生长和存活方面起着关键作用。尽管这种分子的表达增加是 人类癌症，其异常聚集的机制很差 明白了。我们已经鉴定出在肠道肿瘤发生早期丢失的PKCA， 作为一种新的肠道细胞周期蛋白D1水平的抑制因子。对相互作用的理解 PKCA和细胞周期蛋白D1之间的关系可能为预防和/或治疗提供新的线索 肠道肿瘤。

DESCRIPTION (from the applicant): Cyclin D1 is a tightly regulated cell cycle control molecule that functions as a critical sensor of extracellular growth stimulatory and inhibitory signals and a key determinant of progression through G1 phase. Aberrant expression of cyclin D1 is one of the most frequent abnormalities in human cancer, and is believed to play an important role in tumorigenesis. Understanding of the mechanisms underlying control of cyclin D1 accumulation under normal and pathological conditions is, therefore, of key importance. Our studies have identified protein kinase C a (PKCa) as a novel regulator of cyclin D1 expression in intestinal epithelial cells. PKCa exhibits growth inhibitory and tumor suppressor properties in the intestine, and its expression is lost early during intestinal tumor development. Based on extensive new data, strategies are proposed to address the hypothesis that PKCa signaling plays a critical role in regulating the expression of cyclin D1 in intestinal cells, and that disruption of PKCa-mediated cyclin D1 control contributes to intestinal neoplasia. The following key findings provide the foundation for this hypothesis: (a) PKCa activity represses cyclin D1 accumulation in non-transformed intestinal cells by two mechanisms: inhibition of cap-dependent translation initiation and blockade of cyclin D1 mRNA accumulation; (b) inhibitory effects of PKCa on cyclin D1 translation involve activation of the translational repressor 4E-BP1; (c) loss of PKCa signaling is associated with hyperinduction of cyclin D1 mRNA and protein and increased cell proliferation, and (c) restoration of PKCa in colon cancer cells represses cyclin D1 mRNA and protein and inhibits anchorage-independent growth. To explore further the link between PKCa signaling and control of cyclin D1 accumulation in intestinal cells, the following Specific Aims will be addressed: (1) To determine the mechanisms by which PKCa signaling modulates PP2A activity and 4E-BP1 hypophosphorylation/activation to effect cyclin D1 loss in intestinal cells, (2) To explore the role of Id1 suppression in PKCa-induced downregulation of cyclin D1 in normal and neoplastic intestinal cells, (3) To investigate the mechanisms involved in cyclin D1 mRNA hyperinduction associated with loss of PKCa signaling in intestinal epithelial cells, and (4) To explore the role of PKCa signaling in regulation of cyclin D1 levels and maintenance of intestinal homeostasis in vivo. The long-term goals of this project are to understand the mechanisms that orchestrate the process of intestinal epithelial renewal under normal conditions, to determine how intestinal cells overcome these controls to produce tumors, and to identify novel targets for prevention and therapy of intestinal cancer. PUBLIC HEALTH RELEVANCE: Cyclin D1 plays a critical role in regulation of cell growth and survival. Although increased expression of this molecule is one of the most common abnormalities in human cancer, the mechanisms underlying its aberrant accumulation are poorly understood. We have identified PKCa, which is lost early during intestinal tumorigenesis, as a novel repressor of cyclin D1 levels in intestinal cells. Understanding of the interplay between PKCa and cyclin D1 may identify new leads for prevention and/or therapy of intestinal tumors.