The role of adherens junction proteins in the regulation of insulin secretion

In healthy individuals, any rise in blood glucose levels is rapidly countered by the release of insulin from the beta-cells of the pancreas which in turn promotes the uptake and storage of the glucose in peripheral tissues. The beta-cells possess exquisite mechanisms regulating the secretion of insulin to ensure that the correct amount of insulin is released. These mechanisms involve tight control of the movement of insulin containing secretory vesicles within the beta-cells, initially preventing most vesicles being able to move to the plasma membrane. Elevated glucose levels trigger an influx of Ca2+ that allows fusion of the small number of insulin containing vesicles that are pre-docked at the plasma membrane but glucose also stimulates processes that allow other insulin containing vesicles located further in the cell to move to and fuse with the plasma membrane. The mechanisms controlling these processes are complex and not fully understood but it is clear that the interaction of the beta-cells with other beta-cells in the islets is very important for their ability to develop the appropriate machinery for proper regulation of insulin secretion. Emerging evidence indicates one factor that is key for this is the formation of homotypic cadherin mediated adherens junctions between beta-cells. Here, we review the evidence for this and discuss the mechanisms by which these adherens junctions might regulate insulin vesicle trafficking as well as the implications this has for understanding the dysregulation of insulin secretion seen in pathogenic states.