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Constitutively active signaling by the G protein ??-subunit mediates intrinsically increased phosphodiesterase-4 activity in human asthmatic airway smooth muscle cells.

ABSTRACT: Signaling by the G?? subunit of Gi protein, leading to downstream c-Src-induced activation of the Ras/c-Raf1/MEK-ERK1/2 signaling pathway and its upregulation of phosphodiesterase-4 (PDE4) activity, was recently shown to mediate the heightened contractility in proasthmatic sensitized isolated airway smooth muscle (ASM), as well as allergen-induced airway hyperresponsiveness and inflammation in an in vivo animal model of allergic asthma. This study investigated whether cultured human ASM (HASM) cells derived from asthmatic donor lungs exhibit constitutively increased PDE activity that is attributed to intrinsically upregulated G?? signaling coupled to c-Src activation of the Ras/MEK/ERK1/2 cascade. We show that, relative to normal cells, asthmatic HASM cells constitutively exhibit markedly increased intrinsic PDE4 activity coupled to heightened G??-regulated phosphorylation of c-Src and ERK1/2, and direct co-localization of the latter with the PDE4D isoform. These signaling events and their induction of heightened PDE activity are acutely suppressed by treating asthmatic HASM cells with a G?? inhibitor. Importantly, along with increased G?? activation, asthmatic HASM cells also exhibit constitutively increased direct binding of the small Rap1 GTPase-activating protein, Rap1GAP, to the ?-subunit of Gi protein, which serves to cooperatively facilitate Ras activation and, thereby, enable enhanced G??-regulated ERK1/2-stimulated PDE activity. Collectively, these data are the first to identify that intrinsically increased signaling via the G?? subunit, facilitated by Rap1GAP recruitment to the ?-subunit, mediates the constitutively increased PDE4 activity detected in asthmatic HASM cells. These new findings support the notion that interventions targeted at suppressing G?? signaling may lead to novel approaches to treat asthma.

SUBMITTER: Hu A

PROVIDER: S-EPMC4351001 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Constitutively active signaling by the G protein βγ-subunit mediates intrinsically increased phosphodiesterase-4 activity in human asthmatic airway smooth muscle cells.

Hu Aihua A Diener Barry L BL Josephson Maureen B MB Grunstein Michael M MM

PloS one 20150305 3

Signaling by the Gβγ subunit of Gi protein, leading to downstream c-Src-induced activation of the Ras/c-Raf1/MEK-ERK1/2 signaling pathway and its upregulation of phosphodiesterase-4 (PDE4) activity, was recently shown to mediate the heightened contractility in proasthmatic sensitized isolated airway smooth muscle (ASM), as well as allergen-induced airway hyperresponsiveness and inflammation in an in vivo animal model of allergic asthma. This study investigated whether cultured human ASM (HASM) c ...[more]

PMID: 25742624

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Project description:Asthma is an inflammatory condition for which anti-inflammatory glucocorticoids are the standard of care. However, similar efficacy has not been shown for agents targeting inflammatory cells and pathways. This suggests a noninflammatory cell contributor (e.g., epithelium) to asthmatic inflammation. Herein, we sought to define the intrinsic and glucocorticoid-affected properties of asthmatic airway epithelium compared with normal epithelium. Human primary differentiated normal and asthmatic airway epithelia were cultured in glucocorticoid-free medium beginning at -48 hours. They were pulsed with dexamethasone (20 nM) or vehicle for 2 hours at -26, -2, +22, and +46 hours. Cultures were mechanically scrape-wounded at 0 hours and exposed continuously to bromodeoxyuridine (BrdU). Cytokine secretions were analyzed using cytometric bead assays. Wound regeneration/mitosis was analyzed by microscopy and flow cytometry. Quiescent normal (n = 3) and asthmatic (n = 6) epithelia showed similar minimal inflammatory cytokine secretion and mitotic indices. After wounding, asthmatic epithelia secreted more basolateral TGF-?1, IL-10, IL-13, and IL-1? (P < 0.05) and regenerated less efficiently than normal epithelia (+48 h wound area reduction = [mean ± SEM] 50.2 ± 7.5% versus 78.6 ± 7.7%; P = 0.02). Asthmatic epithelia showed 40% fewer BrdU(+) cells at +48 hours (0.32 ± 0.05% versus 0.56 ± 0.07% of total cells; P = 0.03), and those cells were more dyssynchronously distributed along the cell cycle (52 ± 10, 25 ± 4, 23 ± 7% for G1/G0, S, and G2/M, respectively) than normal epithelia (71 ± 1, 12 ± 2, and 17 ± 2% for G1/G0, S, and G2/M, respectively). Dexamethasone pulses improved asthmatic epithelial inflammation and regeneration/mitosis. In summary, we show that inflammatory/fibrogenic cytokine secretions are correlated with dyssynchronous mitosis upon injury. Intermittent glucocorticoids simultaneously decreased epithelial cytokine secretions and resynchronized mitosis. These data, generated in an airway model lacking inflammatory cells, support the concept that epithelium contributes to asthmatic inflammation.

Project description:Background and objectiveAirway remodeling in asthma refers to numerous structural changes in the airway in asthmatic patients, with thickening of the airway smooth muscle layer as its core feature. However, the nature and sources of the abnormally increased airway smooth muscle cells (ASMCs) in airway remodeling remain unclear. ASMCs play a key role in the pathogenesis of fatal asthma; therefore, it is important to clarify the properties and sources of these ASMCs responsible for asthmatic airway remodeling, which may provide a new direction for the precise treatment for asthma.MethodsWe performed a narrative review of the literature on PubMed, Web of Science, and Google Scholar databases searching for the cellular sources of ASMCs in asthmatic airway remodeling and their clinical relevance.Key content and findingsIt has long been thought that ASMCs are the result of abnormal proliferation of the native ASMCs in asthma; however, increasing evidence suggests that increased "ASMCs" may be due to the differentiation/transdifferentiation of other cells including mesenchymal stem cells (MSCs), myofibroblasts (MYFs), pericytes, and epithelial-mesenchymal transition (EMT). Recently, several pharmacological and biological therapies aimed at "reducing asthmatic ASMCs" have been developed, among which gallopamil, JQ1 [an inhibitor of the bromodomain and extra-terminal domain (BET) protein family], and histone deacetylase (HDAC) inhibitors can alleviate asthma airway remodeling and hyperresponsiveness and improve asthma symptoms in both mouse models and preclinical experiments.ConclusionsAs one of the core features of asthma, ASMCs are an important effector of airway remodeling. It has become extremely important to develop therapies for the reduction and prevention of the "ASMCs" on the basis of the properties and sources of "ASMCs". Many studies have shown that epigenetic regulation is closely related to the abnormal increase of ASMCs in asthma, and interfering with epigenetic regulation factors can reduce the increased smooth muscle cells. Although the epigenetic regulation of asthma is still in its nascent stage, epigenetic therapy targeting "ASMCs" may become another new strategy for asthma prevention and treatment.

Dataset Information

Constitutively active signaling by the G protein ??-subunit mediates intrinsically increased phosphodiesterase-4 activity in human asthmatic airway smooth muscle cells.

Publications

Constitutively active signaling by the G protein βγ-subunit mediates intrinsically increased phosphodiesterase-4 activity in human asthmatic airway smooth muscle cells.

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