Cite this as: M. Kawaguchi, J. Fujita, F. Kokubu, G. Ohara, S-K Huang, S. Matsukura, Y. Ishii, M. Adachi, H. Satoh and N. Hizawa, Clinical & Experimental Allergy, 2010 (40) 1036–1043.
Background Increased expression of IL-17F has been noted in the airway of asthmatic patients, but its role in asthma has not been fully elucidated. Insulin-like growth factor-I (IGF-I) is known to be involved in airway remodelling and inflammation, while its regulatory mechanisms remain to be defined.
Objective To further clarify the biological function of IL-17F, we investigated whether IL-17F is able to regulate the expression of IGF-I in bronchial epithelial cells.
Methods Bronchial epithelial cells were stimulated with IL-17F in the presence or absence of T-helper type 2 cytokines. Various kinase inhibitors were added to the culture to identify the key signalling events leading to the expression of IGF-I, in conjunction with the use of short interfering RNAs (siRNAs) targeting mitogen- and stress-activated protein kinase (MSK) 1, p90 ribosomal S6 kinase (p90RSK), and cyclic AMP response element-binding protein (CREB).
Results IL-17F significantly induced IGF-I gene and protein expression, and co-stimulation with IL-4 and IL-13 augmented its production. MAP kinase kinase (MEK) inhibitors and the Raf1 kinase inhibitor significantly inhibited IGF-I production, and the combination of PD98059 and Raf1 kinase inhibitor showed further inhibition. Overexpression of Raf1 and Ras dominant-negative mutants inhibited its expression. MSK1 inhibitors significantly blocked IL17F-induced IGF-I expression. Moreover, transfection of the siRNAs targeting MSK1, p90RSK, and CREB blocked its expression.
Conclusions In bronchial epithelial cells, IL-17F is able to induce the expression of IGF-I via the Raf1–MEK1/2–ERK1/2–MSK1/p90RSK–CREB pathway in vitro.