The metabotropic glutamate receptor 4 is internalized and desensitized upon protein kinase C activation

TY - JOUR

T1 - The metabotropic glutamate receptor 4 is internalized and desensitized upon protein kinase C activation

AU - Mathiesen, Jesper Mosolff

AU - Ramirez, M. Teresa

PY - 2006/6/1

Y1 - 2006/6/1

N2 - 1. The metabotropic glutamate receptor 4 (mGluR4) is a Gα i-coupled receptor that modulates glutamatergic neurotransmission. As mGluR4 expression and activation have been implicated in a number of pathological conditions and because the internalization and desensitization properties of this receptor are poorly understood, studies were designed to investigate these aspects of mGluR4 biology. 2. Neither agonist activation by L-(+)-2-amino-4-phosphonobutyric acid (L-AP4) nor L-glutamate caused mGluR4 internalization when cmyc-tagged mGluR4 was expressed in a human embryonic kidney 293 cell line as assessed by cell surface enzyme-linked immunosorbent and immunostaining assays. Instead, a modest increase in mGluR4 surface expression was observed and found to be receptor specific as the competitive antagonist α-cyclopropyl-4-phosphonophenylglycine (CPPG) blocked this effect. 3. In contrast, mGluR4 internalized when the protein kinase C (PKC) pathway was activated either by phorbol-12-myristate-13-acetate (PMA) or by the activation of the Gα q-coupled, neurokinin 3 receptor (NK3R) when co-expressed. This process was PKC-dependent as the specific PKC inhibitor GF 109203X inhibited PMA and NK3R-mediated internalization. 4. PKC activation by PMA caused desensitization of mGluR4 as measured by forskolin-stimulated cAMP inhibition, whereas agonist activation had no effect on desensitization. 5. When mGluR4's coupling was redirected from adenylyl cyclase to phospholipase C by coexpression of a chimeric Gα qo5 protein, mGluR4 both internalized and desensitized in response to its agonists. 6. These findings demonstrate that mGluR4 internalization and desensitization are agonist-independent unless pathways leading to the activation of PKC are induced.

AB - 1. The metabotropic glutamate receptor 4 (mGluR4) is a Gα i-coupled receptor that modulates glutamatergic neurotransmission. As mGluR4 expression and activation have been implicated in a number of pathological conditions and because the internalization and desensitization properties of this receptor are poorly understood, studies were designed to investigate these aspects of mGluR4 biology. 2. Neither agonist activation by L-(+)-2-amino-4-phosphonobutyric acid (L-AP4) nor L-glutamate caused mGluR4 internalization when cmyc-tagged mGluR4 was expressed in a human embryonic kidney 293 cell line as assessed by cell surface enzyme-linked immunosorbent and immunostaining assays. Instead, a modest increase in mGluR4 surface expression was observed and found to be receptor specific as the competitive antagonist α-cyclopropyl-4-phosphonophenylglycine (CPPG) blocked this effect. 3. In contrast, mGluR4 internalized when the protein kinase C (PKC) pathway was activated either by phorbol-12-myristate-13-acetate (PMA) or by the activation of the Gα q-coupled, neurokinin 3 receptor (NK3R) when co-expressed. This process was PKC-dependent as the specific PKC inhibitor GF 109203X inhibited PMA and NK3R-mediated internalization. 4. PKC activation by PMA caused desensitization of mGluR4 as measured by forskolin-stimulated cAMP inhibition, whereas agonist activation had no effect on desensitization. 5. When mGluR4's coupling was redirected from adenylyl cyclase to phospholipase C by coexpression of a chimeric Gα qo5 protein, mGluR4 both internalized and desensitized in response to its agonists. 6. These findings demonstrate that mGluR4 internalization and desensitization are agonist-independent unless pathways leading to the activation of PKC are induced.

KW - cAMP

KW - Chimeric G protein

KW - Desensitization

KW - Inositol phosphate

KW - Internalization

KW - mGluR4

KW - PMA

KW - Protein kinase C

UR - http://www.scopus.com/inward/record.url?scp=33744473559&partnerID=8YFLogxK

U2 - 10.1038/sj.bjp.0706733

DO - 10.1038/sj.bjp.0706733

M3 - Journal article

C2 - 16582932

AN - SCOPUS:33744473559

SN - 0007-1188

VL - 148

SP - 279

EP - 290

JO - British Journal of Pharmacology

JF - British Journal of Pharmacology

IS - 3

ER -