S. Faivre et al., Suppression of cellular invasion by activated G-protein subunits G alpha o, G alpha i1, G alpha i2, and G alpha i3 and sequestration of G beta gamma, MOLEC PHARM, 60(2), 2001, pp. 363-372
It was shown previously that platelet-activating factor receptors (PAF-Rs)
inhibit invasiveness of colonic and kidney epithelial cells induced by the
src and Met oncogenes via a pertussis toxin-sensitive mechanism. Therefore,
Madin-Darby canine kidney (MDCKts.src) cells were stably transfected with
constitutively activated forms of G alphao, G alpha i1, G alpha i2, G alpha
i3 (AG alphao/i), two G beta gamma sequestering proteins [C-terminal end o
f beta -adrenergic receptor kinase (ct-beta ARK) and the Gat subunit of ret
inal G-protein transducin], and G beta1-G gamma2 subunits alone or in combi
nation. Cellular invasion induced by src, Met, and leptin was abrogated by
the AG alphao/i, ct-beta ARK, and Gat-positive clones, but was induced by c
oexpression of G alpha1 gamma2. In contrast, invasion stimulated by the tre
foil factors (TFFs) pS2 and intestinal trefoil factor in MDCKts.src cells o
r human colonic epithelial cells PCmsrc and HCT8/S11 was insensitive to PAF
, AG alphao, AG alpha i1, and AG alpha i2, but was abolished by AG alpha i3
and the protease-activated receptor-1 (PAR-1) agonist thrombin receptor-ac
tivating peptide. Depletion of free G beta gamma heterodimers by ct-beta AR
K resulted in a remarkable decrease of cellular adhesion and spreading on c
ollagen matrix. Our data demonstrate the following: 1) PAF-Rs impair cellul
ar invasion induced by src, Met, and leptin via the activation of G alphao
and G alpha i1 to -3; 2) invasion induced by TFFs is selectively inhibited
by PAR-1 receptors and G alpha i3 activation; and 3) G beta gamma dimers ar
e required as positive effectors of invasion pathways induced by oncogenes
and epigenetic factors. Thus, redistribution of G alphao/G alphai and G bet
a/gamma heterotrimeric G-proteins by PAF-R and PAR-1 exert differential fun
ctions on positive and negative signaling pathways involved in cellular inv
asion and may serve as potential targets for anticancer therapy.