Novel membrane traffic steps regulate the exocytosis of the Menkes disease ATPase

The Menkes disease protein (ATP7A or MNK) is a P-type transmembrane ATPase that regulates translocation of cytosolic copper ions across intracellular membranes of compartments along the secretory pathway. In this study, we show that endogenous MNK in cultured cell lines is localized to the distal Golgi apparatus and translocates to the plasma membrane in response to exogenous copper ions. This transport event is not blocked by expression of a dominant-negative mutant protein kinase D, an enzyme implicated in regulating constitutive trafficking from the trans-Golgi network (TGN) to the plasma membrane, whereas constitutive transport of CD4 is inhibited. In contrast, protein kinase A inhibitors block copper-stimulated MNK delivery to the plasma membrane. Expression of constitutively active Rho GTPases such as Cdc42, Rac1 and RhoA reveals a requirement for Cdc42 in the trafficking of MNK, to the cell surface. Furthermore, overexpression of WASp inhibits anterograde transport of MNK, further supporting regulation by the Cdc42 GTPase. These findings define a novel step in TGN-to-plasma membrane traffic required to export MNK to the cell surface.