Is an ATPase involved in uncoating of plasma membrane adaptor complex AP-2?

Evidence on differential role for alpha 1 and alpha 2 subtypes of AP-2 adaptin in the Central Nervous System

Two subtypes of alpha (α)subunits , α1and α2, belonging to AP-2 complex have been described in the central nervous system (CNS). The specific role of each subtype is still unclear. In this study, we evaluated the expression and interaction with cell membranes of both subtypes in the postnatal developing cerebral cortex and cerebellum in two rat strains that display distinct developmental features. We observed that α2 displays higher variations than α1 during development, and at lesser extent in the rats with delayed rate of development. Additionally, by in vitro binding assays we evaluated the interaction of α subunits with bovine brain membranes. Both subtypes displayed clear differences in their performance, maximum binding of α1 was higher and α2 reached it faster than α1. In addition, both subtypes displayed different binding to membranes when bivalent cations or nucleotides were added. We conclude that both subtypes interact differently with membranes and that they may play different roles in clathrin-mediated endocytosis in the CNS.

Binding of AP-2 adaptor complex to brain membrane is regulated by phosphorylation of proteins

Phosphorylation of proteins appears as a key process in early steps of clathrin coated vesicle formation. Here, we report that treatment of post-nuclear fraction with alkaline phosphatase induced redistribution of alpha subunits of AP-2 adaptor complex to cytosol and this effect was higher in the alpha2 subunit. A high serine phosphorylation status of alpha subunits correlated with the higher affinity of AP-2 to membranes. Using a simple binding assay, where membranes were incubated with either purified adaptors or cytosols, we observed an inhibitory effect of tyrphostin, a tyrosine kinase inhibitor, on the binding of AP-2 to membranes, but also an unexpected decrease induced by the phosphatase inhibitor cyclosporine. We also show an inhibitory effect of ATP mediated by cytosolic proteins, although it could not be related to the phosphorylation of AP-2, suggesting an action upstream a cascade of phosphorylations that participate in the regulation of the assembly of AP-2 to membranes.