An essential role for constitutive endocytosis, but not activity, in the axonal targeting of the CB1 cannabinoid receptor

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

VL - 71

SP - 976

EP - 984

JO - Molecular Pharmacology

JF - Molecular Pharmacology

SN - 0026-895X

IS - 4

ER -