Dissertation committee:
Ε. Φραγκούλης Καθηγητής (Επιβλέπων), Ζ. Γεωργούση Διευθύντρια Ερευνών, Δ. Βασιλακοπούλου Αναπληρώτρια Καθηγήτρια
Summary:
Opioid receptors belong to the superfamily of G protein coupled receptors
(GPCRs) and regulate analgesia and tolerance-dependence to narcotic drugs. A
new family of proteins, RGS proteins (Regulators of G protein Signalling), are
involved in the signalling of GPCRs by accelerating the rate of GTP hydrolysis
from Gα subunits, thus terminating signal transduction. The aim of the research
was to study the interactions of μ- and δ-opioid receptors (μ-OR, δ-OR) with
RGS4 protein and the role of RGS4 in receptor signalling. In vitro pulldown
experiments using GST-/MBP-fusion peptides demonstrated that RGS4 binds to the
third intracellular loop and the conserved region of the carboxyl tails of
opioid receptors (μ-CT, δ-CT). RGS4 functions as a scaffold protein and
promotes the binding of Gα subunit to the μ-CT, forming a RGS4–Gα–μ-CT ternary
complex. Co-immunoprecipitation experiments showed that RGS4 promotes
interaction of μ-OR, δ-OR with specific Gα subunit subtypes, depending on
receptor activation. Functional experiments demonstrated that RGS4 a) increases
intracellular cAMP accumulation by reducing opioid receptor adenyl cyclase
inhibition, b) inhibits ERK phosphorylation, c) colocalizes with activated
receptors. The N terminal of RGS4 is responsible for the protein’s functional
activity. The results of this study indicate that RGS4 protein is a key element
for the regulation and specificity of opioid receptor signalling.
Keywords:
opioid receptors, RGS proteins, protein interaction, protein complexes, signalling specificity
