SCF Complexes: Key to Understanding Cochlear Homeostasis

描述(申请人提供)：哺乳动物听觉器官的感觉毛细胞终末分化，不能分裂，必须持续一生。这一挑战在任何组织中都是令人望而生畏的，但在Corti(OC)器官中，由于缺乏血管系统、高度正的电势和持续的“沉默的”K+电流，这一挑战变得更加复杂。在这种情况下，即使是短暂的偏离生理标准，也会导致毛细胞死亡和随之而来的听力损失。具有讽刺意味的是，最常见的与遗传性耳聋疾病相关的基因(连接蛋白26，Cx26)并不在感觉细胞中表达，而是在支持细胞群体或上皮支持复合体(ESC)中表达。两个共同的特征将ESC的不同细胞类型结合在一起--一个复杂的上皮缝隙连接系统(EGJS)和OCP1和OCP2的高水平表达。缝隙连接由连接蛋白分子的六角形排列形成，有助于低分子化合物-营养物质、代谢物、信号分子-在相邻细胞之间的移动。正如Cx26表型的严重程度所表明的那样，这种运输系统的中断对感觉细胞的生存具有灾难性的影响。令人信服的初步证据将OCP1和OCP2与EGJS的监管联系起来。OCP1和OCP2是OC中含量最丰富的两种蛋白，它们与SCF E3泛素连接酶的亚基具有同源性。这些多组分、多功能的复合体调节广泛的生物过程，通常是通过靶向泛素化的关键蛋白质。根据泛素信号的确切分子细节，修饰后的蛋白质将经历几种潜在的命运之一，包括蛋白质分解破坏或亚细胞重新定位。OCP1-OCP2的表达与EGJS边界的一致性提示OCP1-OCP2复合体可能参与了一种或多种连接蛋白亚型的泛素化。这一假说得到了最近OCP1在体外与Cx2.6结合的证据的支持。拟议研究的目的是研究OCP1-OCP2复合体的功能意义，特别是它与EGJS的相互关系。这项多学科的项目包括有针对性地破坏OCP1基因，鉴定其他OCP1靶蛋白，以及OCP1-OCP2复合体和OCP1-靶标复合体的生化/生物物理特性。这项工作将为毛细胞功能保存的生理过程提供洞察力。这将促进我们对最常见的先天性遗传性听力损失的系统(Cx26)的理解。最终，该项目的数据可能会为听力障碍的遗传和药物干预提供基础。

DESCRIPTION (provided by applicant): Terminally differentiated, incapable of dividing, the sensory hair cells of the mammalian auditory organ must last a lifetime. This challenge, daunting in any tissue, is further complicated in the organ of Corti (OC) by the absence of vasculature, a highly positive electrical potential, and the continuous "silent" K+ current. In this setting, even transient departures from the physiological norm result in hair cell death and consequent hearing loss. Ironically, the gene most commonly linked to hereditary deafness disorders (connexin 26, Cx26) is not expressed in the sensory cell, but rather in the supporting cell population, or epithelial support complex (ESC). Two common features unite the diverse cell types of the ESC - an elaborate epithelial gap-junction system (EGJS) and high-level expression of OCP1 and OCP2. Formed by hexagonal arrays of connexin molecules, gap-junctions facilitate movement of low molecular weight compounds - nutrients, metabolites, signaling molecules - between adjacent cells. As the severity of the Cx26 phenotype illustrates, disruption of this transport system has disastrous implications for sensory cell survival. Compelling preliminary evidence links OCP1 and OCP2 to regulation of the EGJS. The two most abundant proteins in the OC, OCP1 and OCP2 display homology to subunits of SCF E3 ubiquitin ligases. These multi-component, multi-functional complexes regulate a broad spectrum of biological processes, typically by targeting critical proteins for ubiquitination. Depending on the precise molecular details of the ubiquitin signal, the modified protein will experience one of several potential fates, including proteolytic destruction or sub-cellular relocation. The coincidence of OCP1-OCP2 expression with the boundaries of the EGJS suggests that the OCP1-OCP2 complex may participate in the ubiquitination of one or more connexin isoforms. This hypothesis is bolstered by the recent demonstration that OCP1 binds to Cx2.6 in vitro. The objective of the proposed research is to examine the functional significance of the OCP1-OCP2 complex and, in particular, its interrelationship with the EGJS. The multi-disciplinary project includes targeted disruption of the OCP1 gene, identification of additional OCP1 target proteins, and biochemical/biophysical characterization of the OCP1-OCP2 complex and OCPl-target complexes. This work will furnish insight into the physiological processes underlying preservation of hair cell function. It will advance our understanding of the system (Cx26) most commonly responsible for congenital hereditary hearing loss. Ultimately, the data from this project could provide a foundation for genetic and pharmacologic intervention in hearing disorders.