Transcription factor activation and mitogenic synergism in airway smooth muscle cells

Abstract

Simultaneous treatment of human airway smooth muscle (HASM) cells with lysophosphatidic acid (LPA) and epidermal growth factor (EGF) leads to strikingly synergistic stimulation of mitogenesis. The purpose of this study was to explore potential sites for signal integration mediating synergism, focusing on extracellular signal-regulated kinase (ERK) and transcription factors involved in proliferation and inflammation as likely candidates.Activation of ERK was analysed by immunoblotting. Transcription factor activation was assessed using HASM cells transduced with luciferase reporter gene constructs.LPA and EGF both activated ERK but had no synergistic effect when combined. LPA and EGF both activated activator protein (AP)-1, cyclic adenosine monophosphate response element-binding protein, nuclear factor of activated T-cells and the serum response element; however, only AP-1 activation exhibited synergism. Activation of the inhibitory guanine nucleotide-binding protein and of ERK signalling pathways were required for most transcription factor responses to LPA. In contrast, nuclear factor (NF)-kB was activated by LPA but not EGF and NF-kB activation was completely blocked only when Rho was inhibited. Rapid activation of Rho was observed in response to LPA but not to EGF. Importantly, inhibition of Rho selectively blocked synergism in both AP-1 activation and mitogenesis.In summary, extracellular signal-regulated kinase activation is required for many transcription factor responses to lysophosphatidic acid and epidermal growth factor, however it is not synergistic. Activation of activator protein-1 is synergistic, and Rho activation by lysophosphatidic acid is required for synergism in both activator protein-1 activation and mitogenesis. Eur Respir J 2003; 21: 759-769.

Endothelin-1 Regulates Proliferative Responses, both alone and Synergistically with PDGF, in Rat Tracheal Smooth Muscle Cells

“…Lysophosphatidic acid-dependent enhancement of EGF-induced proliferation of human airway SMC also does not correlate with ERK 1/2 activation. However, in this case, the low molecular weight G protein, Rho, appears to mediate the synergistic response, whereas p70 S6 kinase does not [49]. The effectors of p70 S6 kinase and Rho that mediate these synergistic proliferative responses have not been identified.…”

Protein Kinase Cδ Mediates Lysophosphatidic Acid-induced NF-κB Activation and Interleukin-8 Secretion in Human Bronchial Epithelial Cells

“…LPA is a potent bioactive lipid that mediates several cellular responses such as proliferation, differentiation, suppression of apoptosis, tumor metastasis, and cytoskeletal reorganization (15,(21)(22)(23)(24)(25)(26)(27)(28). LPA mediates the broad range of cellular responses through the G-protein-coupled receptors LPA 1 /Edg-2, LPA 2 /Edg-4, and LPA 3 /Edg-7 (19).…”

“…In guinea pigs, administration of exogenous LPA into the airway enhances the response to acetylcholine (22) and infiltration of neutrophils (23). Other reports have shown that LPA induces airway smooth muscle contractility (24), proliferation (25), and transcription factor activation (26). In ovarian cancer cells, LPA induces both IL-6 and IL-8 expression (27,28).…”

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

“…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).…”