MUC4 Mucin and Airway Epithelial Regeneration in COPD

描述（由申请人提供）： 在慢性阻塞性肺疾病如慢性支气管炎和囊性纤维化中，气道上皮不断暴露于中性粒细胞弹性蛋白酶（NE），一种炎性蛋白酶。细胞对NE的反应决定了上皮损伤和修复之间的平衡。这种平衡中的一个关键因素是表皮生长因子受体（EGFR）的激活，EGFR是ErbB受体酪氨酸激酶家族的成员。EGFR的激活需要受体的同源或异源二聚化。气道上皮细胞中的主要EGFR异二聚化伴侣是ErbB 2。迄今为止，已知激活ErbB 2的唯一配体是MUC 4。MUC 4是具有表皮生长因子（EGF）样结构域的主要膜系连的呼吸道粘蛋白。我们已经做了四个关键的观察，支持MUC 4在激活气道上皮对NE的反应中的关键作用：（1）NE作用于气道上皮细胞，以增强MUC 4 mRNA的稳定性和增加MUC 4蛋白水平。 (2)NE诱导EGFR的酪氨酸磷酸化。 (3)NE刺激正常人支气管上皮细胞在无血清和无EGF培养基中的增殖。4. MUC 4、ErbB 2和EGFR在体内共定位于损伤的浅表气道上皮细胞。这些观察结果支持了以下假设：NE通过诱导MUC 4（级联中的关键调节分子）的产生，激活ErbB 2，从而促进EGFR的异源二聚化/激活，在气道上皮细胞中触发分子级联事件。EGFR活化是上皮细胞增殖的关键先决条件。本研究的具体目的是：（1）确定NE是否诱导ErbB 2/EGFR受体酪氨酸激酶级联MUC 4激活，导致上皮细胞增殖。 (2)确定调节NE诱导的MUC 4表达的RNA稳定结构域和RNA结合蛋白，MUC 4是该信号级联反应中的关键分子。 (3)确定这些信号通路在慢性支气管炎和囊性纤维化中介导上皮细胞增殖的相关性。我们的最终目标是利用该项目的信息来确定新的生物靶点，用于合理治疗，以诱导损伤后正常气道上皮细胞的增殖和分化。

DESCRIPTION (provided by applicant): In chronic obstructive pulmonary diseases such as chronic bronchitis, and in cystic fibrosis, the airway epithelium is constantly exposed to neutrophil elastase (NE), an inflammatory protease. The cellular response to NE dictates the balance between epithelial injury and repair. A critical factor in this balance is the activation of the epidermal growth factor receptor (EGFR), a member of the ErbB receptor tyrosine kinase family. Activation of EGFR requires homo- or heterodimerization of the receptor. A major EGFR heterodimerization partner in airway epithelial cells is ErbB2. To date, the only ligand known to activate ErbB2 is MUC4. MUC4 is a major membrane-tethered, respiratory tract mucin with epidermal growth factor (EGF)-like domains. We have made four key observations supporting a critical role for MUC4 in activating the airway epithelial response to NE: (1) NE acts on airway epithelial cells to enhance MUC4 mRNA stability and increase MUC4 protein levels. (2) NE induces tyrosine phosphorylation of EGFR. (3) NE stimulates proliferation of normal human bronchial epithelial cells in serum-free and EGF-free media. 4. MUC4, ErbB2 and EGFR colocalize in injured superficial airway epithelial cells in vivo. These observations support the hypotheses that NE triggers a molecular cascade of events in airway epithelial cells by inducing the production of MUC4, a key regulatory molecule in the cascade, activating ErbB2, and thereby promoting the heterodimerization/activation of EGFR. EGFR activation is a critical prerequisite for epithelial proliferation. The Specific Aims to be tested in this proposal are: (1) To determine whether NE induces MUC4-activation of the ErbB2/EGFR receptor tyrosine kinase cascade, resulting in epithelial cell proliferation. (2) To identify the RNA stability domains and RNA-binding proteins regulating NE-induced expression of MUC4, a key molecule in this signaling cascade. (3) To determine the relevance of these signaling pathways in mediating epithelial proliferation in vivo in chronic bronchitis and cystic fibrosis. Our ultimate goal is to use information from this project to identify new biologic targets for rational therapies to induce normal airway epithelial proliferation and differentiation following injury.