Casein kinase II sites in the intracellular C-terminal domain of the thyrotropin-releasing hormone receptor and chimeric gonadotropin-releasing hormone receptors contribute to beta-arrestin-dependent internalization
Ac. Hanyaloglu et al., Casein kinase II sites in the intracellular C-terminal domain of the thyrotropin-releasing hormone receptor and chimeric gonadotropin-releasing hormone receptors contribute to beta-arrestin-dependent internalization, J BIOL CHEM, 276(21), 2001, pp. 18066-18074
We have previously shown that the mammalian gonadotropin-releasing hormone
receptor (GnRHR), a unique G-protein-coupled receptor (GPCR) lacking an int
racellular carboxyl tail (C-tail), does not follow a beta -arrestin-depende
nt internalization pathway. However, internalization of a chimeric GnRHR wi
th the thyrotropin-releasing hormone receptor (TRHR) C-tail does utilize be
ta -arrestin, Here, we have investigated the sites within the intracellular
C-tail domain that are important for conferring beta -arrestin-dependent i
nternalization. In contrast to the chimeric GnRHR with a TRHR C-tail, a chi
meric GnRHR with the catfish GnRHR C-tail is not beta -arrestin-dependent.
Sequence comparisons between these chimeric receptors show three consensus
phosphorylation sites for casein kinase II (CKII) in the TRHR C-tail but no
ne in the catfish GnRHR C-tail, We thus investigated a role for CKII sites
in determining GPCR internalization via beta -arrestin. Sequential introduc
tion of three CKII sites into the chimera with the catfish C-tail (H354D,A3
66E,G371D) resulted in a change in the pattern of receptor phosphorylation
and beta -arrestin-dependence, which only occurred when all three sites wer
e introduced. Conversely, mutation of the putative CKII sites (T365A/T371A,
S383A) in the C-tail of a p-arrestin-sensitive GPCR, the TRHR, resulted in
decreased receptor phosphorylation and a loss of beta -arrestin-dependence.
Mutation of all three CKII sites was necessary before a loss of beta -arre
stin-dependence was observed. Visualization of beta -arrestin/GFP redistrib
ution confirmed a loss or gain of beta -arrestin sensitivity for receptor m
utants. Internalization of receptors without C-tail CKII sites was promoted
by a phosphorylation-independent beta -arrestin mutant (R169E), suggesting
that these receptors do not contain the necessary phosphorylation sites re
quired for beta -arrestin-dependent internalization. Apigenin, a specific C
KII inhibitor, blocked the increase in receptor internalization by beta -ar
restin, thus providing further support for the involvement of CKII, This st
udy presents evidence of a novel role for C-tail CKII consensus sites in ta
rgeting these GPCRs to the beta -arrestin-dependent pathway.