Uncoupling and endocytosis of 5-hydroxytryptamine 4 receptors. Distinct molecular events with different GRK2 requirements

Gaël Barthet, Florence Gaven, Bérénice Framery, Katsuhiro Shinjo, Takaaki Nakamura, Sylvie Claeysen, Joël Bockaert, Aline Dumuis
Journal of Biological Chemistry. 2005-07-01; 280(30): 27924-27934
DOI: 10.1074/jbc.m502272200

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Barthet G(1), Gaven F, Framery B, Shinjo K, Nakamura T, Claeysen S, Bockaert J, Dumuis A.

Author information:
(1)CNRS UMR5203, Montpellier, F-34094, France.

The 5-hydroxytryptamine type 4 receptors (5-HT4Rs) are involved in memory,
cognition, feeding, respiratory control, and gastrointestinal motility through
activation of a G(s)/cAMP pathway. We have shown that 5-HT4R undergoes rapid and
profound homologous uncoupling in neurons. However, no significant uncoupling was
observed in COS-7 or HEK293 cells, which expressed either no or a weak
concentration of GRK2, respectively. High expression of GRK2 in neurons is likely
to be the reason for this difference because overexpression of GRK2 in COS-7 and
HEK293 cells reproduced rapid and profound uncoupling of 5-HT4R. We have also
shown, for the first time, that GRK2 requirements for uncoupling and endocytosis
were very different. Indeed, beta-arrestin/dynamin-dependent endocytosis was
observed in HEK293 cells without any need of GRK2 overexpression. In addition to
this difference, uncoupling and beta-arrestin/dynamin-dependent endocytosis were
mediated through distinct mechanisms. Neither uncoupling nor
beta-arrestin/dynamin-dependent endocytosis required the serine and threonine
residues localized within the specific C-terminal domains of the 5-HT4R splice
variants. In contrast, a cluster of serines and threonines, common to all
variants, was an absolute requirement for beta-arrestin/dynamin-dependent
receptor endocytosis, but not for receptor uncoupling. Furthermore,
beta-arrestin/dynamin-dependent endocytosis and uncoupling were dependent on and
independent of GRK2 kinase activity, respectively. These results clearly
demonstrate that the uncoupling and endocytosis of 5-HT4R require different GRK2
concentrations and involve distinct molecular events.

 

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