TY - JOUR
T1 - An essential role for constitutive endocytosis, but not activity, in the axonal targeting of the CB1 cannabinoid receptor
AU - McDonald, Neil A.
AU - Henstridge, Christopher M.
AU - Connolly, Christopher N.
AU - Irving, Andrew J.
N1 - dc.publisher: American Society for Pharmacology and Experimental Therapeutics (ASPET)
dc.description.sponsorship: The Anonymous Trust (Dundee)
Medical Research Council
Tenovus (Scotland)
University of Dundee
PY - 2007
Y1 - 2007
N2 - In central neurons, the cell-surface distribution of cannabinoid receptor subtype-1 (CB1) is highly polarized toward axons and is associated with synaptic terminals, in which it is well-positioned to modulate neurotransmitter release. It has been suggested that high levels of constitutive activity mediate CB1 receptor axonal targeting, leading to domain-specific endocytosis. We have investigated further the mechanisms that underlie CB1 receptor axonal polarization in hippocampal neurons and found that constitutive activity is not an essential requirement for this process. We demonstrate that the cell-surface distribution of an N-terminally tagged, fluorescent CB1 receptor fusion-protein is almost exclusively localized to the axon when expressed in cultured hippocampal neurons. Inhibition of endocytosis by cotransfection with a dominant-negative dynamin-1 (K44A) mutant traps both recombinant and endogenous CB1 receptors at the somatodendritic cell surface. However, this effect could not be mimicked by inhibiting constitutive activity or receptor activation, either by expressing mutant receptors that lack these properties or by treatment with CB1 receptor antagonists possessing inverse agonist activity. These data are consistent with a revised model in which domain-specific endocytosis regulates the functional polarization of CB1 receptors, but this process is distinct from constitutive activity.
AB - In central neurons, the cell-surface distribution of cannabinoid receptor subtype-1 (CB1) is highly polarized toward axons and is associated with synaptic terminals, in which it is well-positioned to modulate neurotransmitter release. It has been suggested that high levels of constitutive activity mediate CB1 receptor axonal targeting, leading to domain-specific endocytosis. We have investigated further the mechanisms that underlie CB1 receptor axonal polarization in hippocampal neurons and found that constitutive activity is not an essential requirement for this process. We demonstrate that the cell-surface distribution of an N-terminally tagged, fluorescent CB1 receptor fusion-protein is almost exclusively localized to the axon when expressed in cultured hippocampal neurons. Inhibition of endocytosis by cotransfection with a dominant-negative dynamin-1 (K44A) mutant traps both recombinant and endogenous CB1 receptors at the somatodendritic cell surface. However, this effect could not be mimicked by inhibiting constitutive activity or receptor activation, either by expressing mutant receptors that lack these properties or by treatment with CB1 receptor antagonists possessing inverse agonist activity. These data are consistent with a revised model in which domain-specific endocytosis regulates the functional polarization of CB1 receptors, but this process is distinct from constitutive activity.
KW - Axons chemistry
KW - Endocytosis physiology
KW - Hippocampus cytology
KW - Receptors
KW - Cannabinoid
KW - CB1 analysis
U2 - 10.1124/mol.106.029348
DO - 10.1124/mol.106.029348
M3 - Article
SN - 1521-0111
VL - 71
SP - 976
EP - 984
JO - Molecular Pharmacology
JF - Molecular Pharmacology
IS - 4
ER -