Suppression of Cellular Invasion by Activated G-Protein Subunits Gαo, Gαi1, Gαi2, and Gαi3 and Sequestration of Gβγ

Abstract

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 Galphao, Galphai1, Galphai2, Galphai3 (AGalphao/i), two Gbetagamma sequestering proteins [C-terminal end of beta-adrenergic receptor kinase (ct-betaARK) and the Galphat subunit of retinal G-protein transducin], and Gbeta1-Ggamma2 subunits alone or in combination. Cellular invasion induced by src, Met, and leptin was abrogated by the AGalphao/i, ct-betaARK, and Galphat-positive clones, but was induced by coexpression of Gbeta1gamma2. In contrast, invasion stimulated by the trefoil factors (TFFs) pS2 and intestinal trefoil factor in MDCKts.src cells or human colonic epithelial cells PCmsrc and HCT8/S11 was insensitive to PAF, AGalphao, AGalphai1, and AGalphai2, but was abolished by AGalphai3 and the protease-activated receptor-1 (PAR-1) agonist thrombin receptor-activating peptide. Depletion of free Gbetagamma heterodimers by ct-betaARK resulted in a remarkable decrease of cellular adhesion and spreading on collagen matrix. Our data demonstrate the following: 1) PAF-Rs impair cellular invasion induced by src, Met, and leptin via the activation of Galphao and Galphai1 to -3; 2) invasion induced by TFFs is selectively inhibited by PAR-1 receptors and Galphai3 activation; and 3) Gbetagamma dimers are required as positive effectors of invasion pathways induced by oncogenes and epigenetic factors. Thus, redistribution of Galphao/Galphai and Gbeta/gamma heterotrimeric G-proteins by PAF-R and PAR-1 exert differential functions on positive and negative signaling pathways involved in cellular invasion and may serve as potential targets for anticancer therapy.

Gβγ Signaling Promotes Breast Cancer Cell Migration and Invasion

“…Instead, disruption of G␤␥ signaling inhibits neutrophil chemotaxis (Lehmann et al, 2008). In addition, sequestration of G␤␥ subunits or using constitutively activated G i ␣ subunit suppress cellular invasion of Madin-Darby canine kidney cells, suggesting that only G␤␥ signaling is responsible for cell invasion (Faivre et al, 2001). Thus, we hypothesized that G␤␥ signaling is important for breast cancer metastasis.…”

Anticancer Activity of BIM-46174, a New Inhibitor of the Heterotrimeric Gα/Gβγ Protein Complex

“…Cancer cell invasion assays were done using collagen type I gels and parental or stably transfected colorectal, kidney, and lung cell lines as described previously (18,29,30). This assay is based on counting the percentage of invasive cells in collagen type I versus total number of viable cells in the same field.…”

“…Zeiger et al (16) first showed in vivo that constitutive activation of Ga by a transgene expressing the cholera toxin A1 subunit in normal cells induced the mitotic activity, infiltration of skeletal muscle, and lung metastases. Recent research shows that Ghg dimers are also involved in cancer transformation and invasive tumor growth because forced expression of Ghg-sequestering agents, such as the COOH terminus of G-protein-coupled receptor kinase 2 (ct-hARK), obliterates multiple oncogenic pathways (17,18). Conversely, overexpression of Ghg subunits and constitutively active mutants of Ga subunits stimulates mitogen-and stress-activated protein kinase cascades p42/p44, p38, and c-Jun NH 2 -terminal kinase, which regulate promoter activity of immediate response genes involved in cell proliferation, apoptosis, and transformation (19).…”

Role of tissue stroma in cancer cell invasion

“…Cancer cell invasion is facilitated by myofibroblastderived proteinases, which also serve structural remodelling of the ECM and so excitation of nociceptors. Remarkably, both stimulation of cancer cell invasion and pain signalling by nociceptors involve signalling pathways that are activated by heterotrimeric guanine nucleotide-binding protein (G-protein)-coupled receptors [151,152]. Such receptors, of which more than 100 are known in mammalian cells, are targets for hormones, neurotransmitters, chemokines, local mediators, and sensory stimuli.…”