Protein phosphorylation events in exocytosis and endocytosis

1. Exocytosis and endocytosis are the continuous outward and inward vesicular transports in a cell that occur constantly for intra- and inter-cellular communications. These events are accomplished with the release and uptake of chemical messages fundamental in a variety of cellular functions, such as neurotransmitter release, hormone secretion and receptor internalization. 2. Although the mechanisms underlying these events have not been fully established, it is widely accepted that they are largely mediated and controlled by a number of effector proteins. These proteins can operate individually and in concert to produce specialized machineries in the sequential steps of exocytotic and endocytic transports. 3. Protein phosphorylation, the most common covalent modification of proteins in cells, has been implicated as playing an important role in the regulation of exocytosis and endocytosis. Many proteins involved in these processes have been identified to be phosphorylated under certain conditions. 4. For instance, synapsin I, myristoylated alanine-rich C kinase substrate and dynamin I undergo dynamic phosphorylation and dephosphorylation cycles during exocytosis and endocytosis, implying that protein phosphorylation regulates the functions of these proteins and, thus, exocytosis and endocytosis.