Cooperative mitogenic signaling by G protein‐coupled receptors and growth factors is dependent on G_q/11

Abstract

Previously we reported that the G protein-coupled receptor (GPCR) agonist thrombin potentiated the mitogenic effect of epidermal growth factor (EGF) on human airway smooth muscle (ASM) by promoting sustained late-phase activation of PI3K and p70S6K via a pathway dependent on Gbetagamma subunits of heterotrimeric G proteins. Here, we provide additional mechanistic insight and reveal the robustness of this phenomenon by demonstrating that H1 histamine and thromboxane receptors utilize the same mechanism to augment ASM growth via specific activation of the heterotrimeric G protein G(q/11). Thrombin, histamine, and U46619 all enhanced EGF-stimulated [3H]-thymidine incorporation as well as late-phase Akt and p70S6K phosphorylation in ASM cultures. Heterologous expression of Gbetagamma sequestrants (GRK2CT-GFP or Galpha(i)G203A), as well as GRK2NT-GFP (an RGS protein for G(q/11)) but neither p115RhoGEFRGS-GFP (an RGS for G(12/13)) nor pertussis toxin pretreatment (inactivating G(i/o)), attenuated the effects on both signaling and growth. Inhibition of Rho, Rho kinase, or Src, or modulation of arrestin expression did not significantly affect the cooperative signaling by EGF and any of the GPCR agonists. Thus, G(q/11)-coupled receptors are the principal GPCR subfamily mediating cooperative mitogenic signaling in ASM, acting through Gbetagamma-dependent, and Src/arrestin-independent activation of PI3K and p70S6K.

Antimitogenic effect of bitter taste receptor agonists on airway smooth muscle cells

“…6). Previous studies have demonstrated that p70S6 kinase is a critical effector of mitogenic signaling mediated by receptor tyrosine kinases, GPCRs, and PI3K in ASM (3,29,32). As previously demonstrated, PDGF and EGF stimulation resulted in increased activation of p70S6 kinase.…”

“…Stable expression of green fluorescent protein (GFP), protein kinase A inhibitory peptide (PKI)-GFP, and RevAB-GFP was achieved by retroviral infection, as described previously (15,20,29,55). Briefly, retrovirus for the expression of each was produced by cotransfecting GP2-293 cells with pVSV-G vector (encoding the pantropic VSV-G envelope protein) and either pLNCX2-GFP, or pLNCX2-PKI-GFP, and viral particles were harvested from supernatant.…”

Adenosine A1 receptor-mediated transactivation of the EGF receptor produces a neuroprotective effect on cortical neurons in vitro

“…In human airway smooth muscle cells, various GPCR agonists, which are often weak mitogens themselves, have been shown to promote the synergistic stimulation of cell proliferation when combined with growth factors such as EGF www.nature.com/aps Xie KQ et al Acta Pharmacologica Sinica npg or platelet-derived growth factor (PDGF) [9] . Previous reports have shown that the GPCR agonist thrombin can potentiate the mitogenic effects of EGF in human airway smooth muscle [10] . EGFR has been recognized as a convergence point for diverse signal transduction pathways [11] .…”

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

“…Activation of the G i -coupled pathway reduces cAMP and thus indirectly promotes contractility. Although much of the previous work in this area has focused on expression and function of different GPCRs (typically G q , G i , and G s ) in the context of ASM contractility/relaxation, there is increasing recognition that GPCRs acting alone, or in conjunction with other pathways such as receptor tyrosine kinases (18,20,59,155,162), can contribute to the "synthetic function" of ASM via cell proliferation/growth and secretion of growth factors and inflammatory mediators, thus influencing airway remodeling and the local inflammatory milieu (e.g., see Refs. 20 and 59 for review).…”

“…However, there is also some suggestion that "normal" stimuli such as bronchoconstrictor agonists (114,233,341) and other locally produced factors (5,53,75) could trigger increased proliferation under certain conditions, leading to the asthmatic phenotype. In this regard, interactions between GPCRs and RTKs may be important (18,67,68,155,162,303). For example, M 2 muscarinic receptors can potentiate TGF-␤-induced enhancement of proliferation (216).…”