Adaptor Protein-1 Complex Affects the Endocytic Trafficking and Function of Peptidylglycine α-Amidating Monooxygenase, a Luminal Cuproenzyme

J Biol Chem. 2015 Aug 28;290(35):21264-79. doi: 10.1074/jbc.M115.641027. Epub 2015 Jul 13.


The adaptor protein-1 complex (AP-1), which transports cargo between the trans-Golgi network and endosomes, plays a role in the trafficking of Atp7a, a copper-transporting P-type ATPase, and peptidylglycine α-amidating monooxygenase (PAM), a copper-dependent membrane enzyme. Lack of any of the four AP-1 subunits impairs function, and patients with MEDNIK syndrome, a rare genetic disorder caused by lack of expression of the σ1A subunit, exhibit clinical and biochemical signs of impaired copper homeostasis. To explore the role of AP-1 in copper homeostasis in neuroendocrine cells, we used corticotrope tumor cells in which AP-1 function was diminished by reducing expression of its μ1A subunit. Copper levels were unchanged when AP-1 function was impaired, but cellular levels of Atp7a declined slightly. The ability of PAM to function was assessed by monitoring 18-kDa fragment-NH2 production from proopiomelanocortin. Reduced AP-1 function made 18-kDa fragment amidation more sensitive to inhibition by bathocuproine disulfonate, a cell-impermeant Cu(I) chelator. The endocytic trafficking of PAM was altered, and PAM-1 accumulated on the cell surface when AP-1 levels were reduced. Reduced AP-1 function increased the Atp7a presence in early/recycling endosomes but did not alter the ability of copper to stimulate its appearance on the plasma membrane. Co-immunoprecipitation of a small fraction of PAM and Atp7a supports the suggestion that copper can be transferred directly from Atp7a to PAM, a process that can occur only when both proteins are present in the same subcellular compartment. Altered luminal cuproenzyme function may contribute to deficits observed when the AP-1 function is compromised.

Keywords: AtT-20; Atp7a; PAM; adaptor protein; amidation; copper; peptide biosynthesis; pituitary gland; secretion.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Protein Complex 1 / analysis
  • Adaptor Protein Complex 1 / metabolism*
  • Adenosine Triphosphatases / analysis
  • Adenosine Triphosphatases / metabolism
  • Animals
  • Cation Transport Proteins / analysis
  • Cation Transport Proteins / metabolism
  • Cell Line
  • Cells, Cultured
  • Copper / metabolism*
  • Copper-Transporting ATPases
  • Endocytosis*
  • HeLa Cells
  • Humans
  • Mice
  • Mixed Function Oxygenases / analysis
  • Mixed Function Oxygenases / metabolism*
  • Multienzyme Complexes / analysis
  • Multienzyme Complexes / metabolism*
  • Pituitary Gland / cytology
  • Pituitary Gland / metabolism
  • Protein Transport
  • Rats


  • Adaptor Protein Complex 1
  • Atp7a protein, mouse
  • Cation Transport Proteins
  • Multienzyme Complexes
  • Copper
  • Mixed Function Oxygenases
  • peptidylglycine monooxygenase
  • Adenosine Triphosphatases
  • Atp7a protein, rat
  • Copper-Transporting ATPases