The function and activity of membrane-associated proteins are often acutely regulated via various signalling molecules and hormones via alterations in protein post-translational modification (PTM). The overall effects of their regulated function are to maintain and modulate the homeostasis of the epithelial cell the proteins are expressed in. Our research focuses on examining how various PTMs exert their effects on membrane proteins to modulate their function. In particular, we are interested in the interplay between PTMs and the role of the membrane lipid bilayer for modulating the overall effects. In this talk I will focus on our studies of a water channel (AQP2) and a sodium-chloride cotransporter (NCC). The vasopressin-regulated water channel AQP2 is expressed in kidney collecting duct principal cells where its apical plasma membrane abundance is the rate-limiting step for controlling the reabsorption of water. A regulated balance of exocytosis and endocytosis of AQP2 determines the levels of apical membrane AQP2 and thus water reabsorption. PTMs of AQP2, in particular phosphorylation and ubiquitylation, are essential mechanisms for modulating AQP2 subcellular sorting and distribution, degradation, and protein:protein interactions. Site-specific phosphorylation of AQP2 can determine the rate of its exocytosis and endocytosis, whereas ubiquitylation of AQP2 can mediate its endocytic retrieval from the plasma membrane. Phosphorylation of AQP2 does not appear to affect the transport capacity of the channel. Our recent data suggests that site specific phosphorylation of AQP2 is able to over-ride the internalization signal mediated by K63-linked polyubiquitylation, providing a novel cell biological concept for membrane protein regulation. Lipid-rich domains within the plasma membrane play a pivotal role in determining the phosphorylation/ubiquitylation ratio. In contrast phosphorylation of NCC does not alter its exocytic trafficking, but modulates NCC activity in the plasma membrane. We recently determined that phosphorylation of NCC modulates NCC plasma membrane abundance by limiting NCC ubiquitylation and thus endocytic retrieval. In conclusion, PTM of membrane-associated proteins is a diverse mechanism for modulation of protein function. Interplay or ‘cross-talk’ between the PTMs increase the complexity of the system – with one particular type of PTM often influencing the likelihood that neighboring amino acids undergo further PTM to modulate protein function.