Cysteinyl leukotrienes synergize with growth factors to induce proliferation of human bronchial fibroblasts

Background: Cysteinyl leukotrienes (cys-LTs) are potent asthma-related mediators that function through their G protein-coupled,receptors, cys-LT receptor type 1 (CysLT1R) and cys-LT receptor type 2 (CysLT2R). Objective: Because many G protein-coupled receptors transactivate the epidermal growth factor receptor (EGFR) through metalloprotease-mediated ligand shedding, we investigated the effects of cys-LTs on signal transduction and proliferation of bronchial fibroblasts. Methods: Human bronchial fibroblasts were grown from biopsy specimens of healthy subjects. Mitogenesis was assessed on the basis of tritiated methylthymidine incorporation. Results: Leukotriene (LT) D-4 alone did not increase mitogenesis but dose-dependently increased thymidine incorporation and cell proliferation in the presence of epidermal growth factor (EGF). The enhancement was not prevented by CysLT1R antagonists (MK-571 and montelukast) or by a dual antagonist (BAY u9773), which is consistent with the lack of detectable mRNA for CysLT1R and CysLT2R in bronchial fibroblasts. LTD4 did not cause EGFR transphosphoryiation nor was the synergism blocked by the metalloprotease inhibitor GM6001. The EGFR-selective kinase inhibitor AG1478 suppressed the synergy between LTD4 and EGF but had no effect on synergistic interactions of LTD4 with other receptor tyrosine kinase growth factors. The effect of LTD4 involved a pertussis toxin-sensitive and protein kinase C-mediated intracellular pathway, leading to sustained growth factor-dependent phosphorylation of extracellular signal-regulated kinase 1/2 and protein kinase B (PKB/Akt). Conclusion: Cys-LTs do not transactivate EGFR but have a broader capability to synergize with receptor tyrosine kinase pathways. Clinical implications: This study implies a critical role of cys-LTs in airway fibrosis in asthma and other chronic airway diseases, which might not be blocked by therapy with current LT receptor antagonists.