The Molecular Regulation of Gli2 in Hedgehog Signaling

描述(由申请人提供)：Hedgehog(HH)分泌信号蛋白家族在胚胎器官发生和模式形成中发挥重要作用。HH信号的缺失会导致严重的发育缺陷，而HH通路的异常激活与几种常见的人类癌症类型有关。深入了解HH信号转导的分子机制对于预防和治疗与HH通路相关的异常至关重要。在小鼠中，HH信号主要由Gli2和Gli3转录因子介导。Gli2通常被认为是一种转录激活因子，而Gli3在很大程度上是一种抑制因子，尽管它也具有较弱的激活功能。Gli2和Gli3的不同功能主要归因于它们固有的分子特性，也是因为在没有HH信号的情况下，大部分全长Gli3蛋白经历了蛋白酶体介导的C端截短阻遏蛋白的加工，而只有一小部分Gli2被加工。这两种蛋白质的加工都是由六个蛋白激酶A(PKA)C末端的前四个位点的磷酸化诱导的。HH信号抑制Gli2和Gli3的加工，并产生全长Gli2和Gli3蛋白。然而，全长Gli2本身不足以激活HH靶基因，因此必须转换为激活剂；这种转换也依赖于HH信号。到目前为止，Gli2激活剂的产生机制和分子性质尚不清楚。我们的初步研究表明，翻译后修饰在Gli2转录活性的调节中起着关键作用。因此，我们假设HH信号通过调节其翻译后修饰来激活全长Gli2蛋白。我们将通过仔细研究两个具体目标来检验这一假设。目的1.了解PKA磷酸化抑制Gli2活性的生物学意义和机制；2.了解SUMO修饰在Gli2活性调节中的作用及其分子机制。这项研究的完成将极大地促进我们对HH信号调节Gli2转录活性的分子机制的理解。这也可能使我们深入了解与异常HH信号相关的人类出生缺陷和癌症的分子机制。公共卫生相关性：Hedgehog(HH)分泌信号蛋白家族在细胞命运指定以及细胞增殖和分化中发挥重要作用。HH信号的丢失会导致广泛的出生缺陷，而HH通路的异常激活会导致几种类型的人类癌症。了解HH信号转导的分子机制可能有助于设计治疗药物来调节HH信号通路的活性，从而预防或治疗由于HH信号转导活性的错误调节而导致的出生缺陷和癌症。

DESCRIPTION (provided by applicant): The Hedgehog (Hh) family of secreted signaling proteins plays important roles in organogenesis and patterning of the embryo. Loss of the Hh signaling results in severe developmental defects, whereas aberrant activation of the Hh pathway is associated with several common types of human cancer. A thorough understanding of the molecular mechanism of Hh signal transduction is crucial for prevention and remedy of the abnormalities related to the Hh pathway. In mice, Hh signaling is primarily mediated by the Gli2 and Gli3 transcription factors. Gli2 is generally considered to be a transcriptional activator, while Gli3 acts largely as a repressor, though it also has a weak activator function. The distinct functions of Gli2 and Gli3 is primarily attributed to their intrinsic molecular properties, and is also due to the fact that in the absence of Hh signaling, the majority of the full-length Gli3 protein undergoes the proteasome-mediated processing to a C-terminally truncated repressor, while only a small fraction of Gli2 is processed. The processing of both proteins is induced by the phosphorylation of the first four of the six protein kinase A (PKA) sites at their C-termini. Hh signaling inhibits Gli2 and Gli3 processing and generates the full-length Gli2 and Gli3 proteins. However, full- length Gli2 itself is not sufficient to activate Hh target genes and thus has to be converted into an activator; this conversion is also dependent on Hh signaling. To date, the mechanism of production and molecular nature of the Gli2 activator are unknown. Our preliminary studies indicate that post-translational modification plays a critical role in the regulation of Gli2 transcriptional activity. We thus hypothesize that Hh signaling activates full-length Gli2 protein by regulating its post-translational modification. We will test this hypothesis by perusing two specific aims. Aim 1. To understand the biological significance and mechanism of PKA phosphorylation- mediated suppression of Gli2 activity; Aim 2. To understand the role of SUMO modification in the regulation of Gli2 activity and the molecular mechanism underlying it. The completion of the proposed study will significantly advance our understanding of the molecular mechanisms by which Hh signaling regulates Gli2 transcriptional activity. It may also give us insight into the molecular mechanisms of the human birth defects and cancer associated with abnormal Hh signaling. PUBLIC HEALTH RELEVANCE: The Hedgehog (Hh) family of secreted signaling proteins plays fundamental roles in cell fate specification and cell proliferation and differentiation. Loss of Hh signaling results in a wide range of birth defects, whereas aberrant activation of the Hh pathway causes several types of human cancer. Understanding the molecular mechanism of Hh signaling may provide insights into the design of therapeutic agents to modulate Hh pathway activity and therefore prevent or treat birth defects and cancers caused by misregulation of the Hh signaling activity.