Investigating neurokinin B-NK3R receptor mediated endocytosis as a novel copper trafficking mechanism

Menon R and Jones CE

School of Science and Health, Western Sydney University, Locked bag 1797, Sydney, New South Wales, Australia, 2153.

Neurokinins are a family of neuropeptides which have a broad role in cognition, emotion and reproduction. Several neurokinins are also known to bind copper and one, neurokinin B (NKB), was shown to facilitate copper uptake into astrocytes suggesting a role in copper homeostasis. Copper homeostasis is critical for normal brain function and dyshomeostasis is a feature of several neurodegenerative disorders, including Alzheimer’s disease. Little is known about the mechanisms and pathways by which neurokinin B can traffic copper into astrocytes and participate in cellular responses. To begin to address this, we used fluorescein-labelled NKB (FNKB) to track the peptide in the cell, and immunofluorescence to follow the NKB receptor (NK3R) after activation by NKB and copper-bound NKB. We show that FNKB is taken into the cell and localises to perinuclear vesicles. Intracellular concentrations are increased in the presence of the recycling inhibitor monensin, suggesting that NKB is actively recycled in these cells. FNKB and the NKB receptor do co-localise, but only in vesicles close to the plasma membrane. The addition of copper as [CuII(NKB2)] causes an increase in cellular copper that rises in the presence of monensin. We predict that receptor mediated endocytosis accounts for the increased copper concentration. This mechanism has not previously been observed for any metal other than iron.