A new role for intermediate filaments in the secretory pathway

点击翻译按钮获取中文摘要

Proteins are major building blocks within our cells, and are also secreted from our cells to mediate intercellular communication, as well as generating the extracellular matrix to which cells attach within our bodies. This matrix is vital for tissue formation and maintenance, and provides mechanical strength, which is especially apparent in bone and tendon. Cells therefore constantly make and secrete proteins via a process that can be regulated in response to various external influences, including the mechanical environment of the cell. Approximately one third of all cellular proteins, including those proteins secreted to the cell exterior, are made within the secretory pathway. This pathway is comprised of various compartments through which cargo proteins are sequentially transported, receiving functionally important modifications as they do so. The compartment at the centre of the secretory pathway is the Golgi apparatus, which serves as a hub for transport, as well as being a major site of cargo modification. The organization of the secretory pathway and movement of proteins between secretory compartments, including the Golgi apparatus, is dependent upon a fibrous network, generally referred to as the cytoskeleton. Defects in secretory pathway function and/or cytoskeleton organization can cause disease, highlighting the importance of these processes for human health. The focus of this study is a Golgi resident protein called GORAB, whose mutation causes a skin and bone disorder in humans. We have shown that GORAB forms discrete structures called domains at the Golgi membrane, that this process is important for cargo modification at the Golgi, and that its loss affects assembly of the extracellular matrix. More recently, we have found a novel interaction between GORAB and a type of cytoskeletal structure called cytoplasmic intermediate filaments. Although intermediate filaments are very well studied and known to be important for cell integrity, we know very little about how they might affect the organization or function of the secretory pathway. Our identification of a novel association of the Golgi apparatus with intermediate filaments suggests an important role for this interaction in secretory pathway organization and function. In this proposal we aim to identify how GORAB forms domains at the Golgi membrane, how the assembly of domains is controlled, and how the domains bind to cytoplasmic intermediate filaments. A major goal is then to determine the functional significance of the GORAB-intermediate filament interaction, testing our hypothesis that it is important for Golgi organization and function, with mechanistic experiments to determine how this occurs. Another key aspect will be to determine how the secretory pathway, and the Golgi apparatus in particular, responds to changes in the mechanical environment of the cell, which is vital for the correct production of proteins within the secretory pathway. Because cytoplasmic intermediate filaments play an important mechanical role within cells, we will test the extent to which they directly couple changes in the mechanical environment of cells to the functional organization of the Golgi apparatus, focusing on the interaction with GORAB, but also exploring other possible mechanisms at play. The work will be important for determining how the secretory pathway is organized, how intermediate filaments interact with this pathway, and how the secretory pathway is coupled to its mechanical environment, all of which are fundamentally important for human health.