Lysophosphatidic acid upregulates the epidermal growth factor receptor in human airway smooth muscle cells

Abstract

Human airway smooth muscle cells treated with lysophosphatidic acid (LPA) and epidermal growth factor (EGF) exhibit synergistic stimulation of mitogenesis (Ediger TL and Toews ML. J Pharmacol Exp Ther 294: 1076-1082, 2000). The effects of LPA treatment of human airway smooth muscle cells on EGF receptor (EGFR) regulation have now been investigated. LPA treatment for 12-24 h resulted in a twofold increase in (125)I-EGF binding and EGFR protein levels as assessed by Western blot analysis. Competition binding assays indicated single-site binding with an affinity of 3 nM, and the affinity was not changed by LPA treatment. EGFR upregulation was blocked by cycloheximide and actinomycin D, suggesting that LPA influences transcriptional regulation of EGFR expression. Inhibitor studies revealed a prominent role for activation of mitogen-activated protein kinase and p70 ribosomal S6 kinase. Both synergism and EGFR upregulation increased with increased cell density, whereas EGFR expression in control cells decreased. The similar requirements for exposure time, LPA concentrations, and cell confluence suggest that EGFR upregulation may be one contributing factor to the synergistic stimulation of mitogenesis seen with LPA plus EGF.

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).…”

Lysophosphatidic Acid Decreases Epidermal Growth Factor Receptor Binding in Airway Epithelial Cells

“…Because of the rapid time course in the epithelial cells, it is unlikely that the initial decrease in binding is a result of transcriptional inhibition of EGFR synthesis, but rather results from more rapid mechanisms such as transactivation, internalization, and perhaps degradation of EGFRs. Several studies have found that transactivation of the EGFR by LPA and other GPCR agents does not occur in HASM cells (Rakhit et al, 1999;Krymskaya et al, 2000;Ediger et al, 2002;Capra et al, 2003), and the lack of this response may be critical to the differences between regulation of EGFRs by LPA in epithelial versus mesenchymal cells. For both the differences among epithelial cell lines and the differences between epithelial versus mesenchymal cells, it is possible that one LPA receptor subtype and signaling pathway mediates one response, whereas a different subtype and signaling pathway mediates the other response.…”

Autotaxin Production of Lysophosphatidic Acid Mediates Allergic Asthmatic Inflammation

“…ATX is present in plasma, saliva, follicular fluid, and malignant effusions (1,2). Through engagement with distinct high-affinity cell-surface G-protein-coupled receptors, LPA exhibits a wide range of effects on a variety of cell types, including bronchial epithelium, smooth muscle cells, fibroblasts, and lymphocytes (3)(4)(5). LPA augments cytokine synthesis and chemotaxis in lymphocytes (6)(7)(8)(9), induces contractility and proliferation of airway smooth muscle cells (10), and modulates inflammatory signaling in bronchial epithelial cells (10)(11)(12), suggesting a possible role in the molecular pathogenesis of asthma.…”