Ubiquitin mediated intracellular trafficking is required for Jam-C function

Endothelial cells form a barrier between the components present in the blood and the underlying tissue. Essential to formation of this barrier are junctional complexes present between cells. These complexes are dynamic, tightly regulated and remodel during key physiological processes such as inflammation, angiogenesis and development to allow passage of molecules, cells and movement of endothelial cells. One such junctional protein, Jam-C, is involved in the pathology of a number of inflammatory disease states and its inhibition in vitro and in vivo results in aberrant forms of leukocyte migration, dysregulated angiogenesis and inhibition of cell migration. Intracellular trafficking has been shown to be a general means of regulating the function of junctional proteins but its role in Jam-C function is unclear. Using a combination of receptor mutagenesis, HRP and APEX-2 proximity labelling alongside light and electron microscopy, we here characterise the dynamics and route of Jam-C trafficking. Rather than trafficking with junctional proteins associated with the inflammatory process, Jam-C co-traffics with receptors associated with changes in permeability such as VE-Cadherin, NRP-1 and 2. We show that Jam-C becomes ubiquitylated by the E-3 ligase CBL and that this post translational modification controls the likelihood of its degradation in the lysosomes or its recycling back to the cell surface. Finally, we show that Jam-C trafficking is essential for some of the endothelial functions of Jam-C.