In the present study, the function and the mechanism of action of RGS4, a member of a
family of proteins called Regulators of G protein Signalling (RGS) was investigated.
A C-terminal fluorescent tag on RGS4 confirmed that transiently transfected RGS4 was
predominantly cytosolic and underwent translocation to the plasma membrane of
HEK293T cells following co-expression of Gi1, the 2A-adrenoceptor, or agonist activated
2A-adrenoceptor. This translocation of RGS4 to the plasma membrane was most
pronounced with the co-expression of the constitutively active GTPase deficient Gi1
Q204L.
High-affinity GTPase experiments indicated that RGS4S30C had enhanced GAP activity
towards Go1 compared to wild type RGS4. This approach also demonstrated a
simultaneous significant decrease in potency of both adrenaline and UK14304 to increase
2A-arenoceptor-activated high-affinity GTPase activity of Go1 in the presence of RGS4
and a further significant decrease in potency of both ligands in the presence of RGS4S30C.
This enhanced GAP activity and observed decrease in agonist potency was also
transferable to RGS16, an RGS protein closely related to RGS4. The selectivity of the G
subunit was also investigated. The enhanced GAP activity and simultaneous significant
decrease in potency of adrenaline and UK14304 to increase 2A-arenoceptor-activated
high-affinity GTPase activity of RGS4S30C and RGS16S30C was selective for Go1 over
Gi1. RGS4S30K and RGS4S30F also demonstrated higher GAP activity than wild type
RGS4 but no consensus side chain could be identified that conferred a specific
enhancement or loss of GAP activity.
The ability to inhibit intracellular calcium release by an activated 1b-adrenoceptor-G11
fusion protein was used in order to investigate the GAP activity of RGS4N88S, RGS4N128A
and RGS4N88S,N128A. All three mutants had ablated GAP activity towards G11 and
therefore failed to inhibit intracellular calcium release.
A novel role for the RGS insensitive mutation G188S was also observed when despite
similar expression, G11
G188S significantly reduced agonist-stimulated [35S]GTPS binding
compared to wild type G11.
RGS4 represents a novel target for pharmaceutical drug development and the study of its
regulation of signal transduction is an important area of investigation. These results
highlight specific areas of RGS4 research with great pharmaceutical potential
