赖氨酸氧化酶的调控与功能研究

The microenvironment of cells plays fundamental roles in physiological processes, including cell fate determination, establishment and maintenance of tissue architecture. The importance of microenvironment in pathogenesis is becoming much more recognized during inflammation, tissue fibrosis and cancer. Extracellular matrix (ECM) is an important component of microenvironment. Dynamic ECM remodeling is pivotal to development, tissue homeostasis and maintenance of proper tissue function. Aberrant change in ECM remodeling is one of the most significant events in disease progression, including tissue fibrosis and cancer. Lysyl Oxidase (LOX) functions as ECM remodeling enzyme involved in the regulation of ECM rigidity and many physiopathological processes. Abnormality in LOX expression and/or activity results in connective tissue disorders and fibrotic diseases. Recent studies, including ours, have highlighted the roles of LOX in promoting cancer progression and metastasis. However, the expression regulation and functions of LOX remain to be more comprehensively elucidated. The endoplasmic reticulum (ER) is the cellular organelle where membrane and secreted protein folding and lipid synthesis occur. Physiologic stress, such as increased secretory load, or pathological stress, such as the hypoxic or hypoglycemic microenvironment in tumors, can lead to disruption of proper ER function, thereby causing ER stress. ER stress is a self-protective mechanism of cells in responding to extreme environment, by utilizing three branches of signaling pathways, including ATF4, ATF6 and XBP1. Our preliminary studies have demonstrated ER stress signal can upregulate LOX expression. However, it remains unclear how LOX is regulated by ER stress signals. It is also not clear whether upregulated LOX expression has any physiological or pathological significance. ER stress frequently occurs in pathological conditions, including cancer and tissue fibrosis. ER stress regulators have been implicated to promote the progression of these pathological conditions. By using cell model we will investigate the molecular mechanism how LOX expression is regulated by ER stress signals, and whether LOX is directly involved in the regulation of cellular response to ER stress inducers. By using cancer mouse model and lung fibrosis mouse model, we will further investigate whether and how LOX is participated in the progression of cancer and lung fibrosis that is promoted by the ER stress. By addressing above scientific questions, we intend to understand the functions of LOX in regulating cellular response to microenvironmental stress.

微环境在细胞命运决定、组织发育及肿瘤等病理过程中发挥重要作用。胞外基质是微环境的重要组成部分，对其动态变化的研究有着重要的科学意义及潜在的应用前景。赖氨酰氧化酶（Lysyl Oxidase, LOX）参与调节胞外基质的刚性，并作为胞外基质重塑的重要蛋白参与调控多种生理、病理过程。但其表达如何被调控，并通过何种机制发挥功能还有待进一步阐明。内质网应激反应作为细胞的应急反应机制，在细胞存活、凋亡调控及肿瘤、纤维化等疾病的发生发展中发挥重要作用。我们的初步研究表明LOX受到内质网应激反应的调控。本课题将利用现有的细胞模型及肿瘤与肺纤维化小鼠模型，系统研究肿瘤和组织纤维化中缺氧等病理微环境诱发的内质网应激反应调控LOX表达的分子机制；探讨LOX是否参与调控细胞的内质网应激反应；及内质网应激反应促肿瘤与肺纤维化发展中LOX的功能与作用机制。进而深入理解LOX在细胞应对外部压力过程中的功能和作用机制。

胞外基质是微环境的重要组成部分，在细胞命运决定、组织发育及肿瘤等病理过程中发挥重要作用。对其动态变化的研究有着重要的科学意义及潜在的应用前景。赖氨酰氧化酶（Lysyl Oxidase, LOX）作为胞外基质重塑的重要蛋白参与调控多种生理、病理过程。但其表达如何被调控，并通过何种机制发挥功能还有待进一步阐明。内质网负责分泌型蛋白及膜蛋白合成和加工折叠。在组织纤维化、肿瘤等病理过程中，细胞处于压力环境之下，从而诱发细胞发生内质网应激反应。我们的工作发现在乳腺癌细胞中内质网应激反应上调LOX的表达。内质网应激反应通过IRE1-XBP1和PERK-ATF4两条信号通路来共同上调LOX的表达。转录因子XBP1s和ATF4分别结合到LOX的启动子和内含子区域直接调控LOX的转录，过表达XBP1s和ATF4都能显著上调LOX的表达。在应激条件下，LOX与整合素、受体酪氨酸激酶等形成新的复合体，调控整合素介导的细胞粘附和对生长因子的响应。在组织纤维化过程中，胞外基质蛋白合成的需求大大增加，从而诱发细胞发生内质网应激反应。我们的工作发现LOX的表达上调及其氧化酶活力是肺纤维化发生的必要条件。抑制LOX的表达或其氧化酶活力显著抑制博来霉素诱导的肺纤维化，而过表达LOX则大大升高小鼠对博来霉素诱导肺纤维化的敏感性。进一步的研究发现，抑制LOX活力显著减弱炎症细胞，特别是巨噬细胞向肺部的浸润，进而影响了TGF-信号、肌成纤维细胞的活化，以及胞外基质的过量沉积，及肺纤维化的发展。