THROMBIN ACTIVATION OF THE 9E3 CEF4 CHEMOKINE INVOLVES TYROSINE KINASES INCLUDING C-SRC AND THE EPIDERMAL GROWTH-FACTOR RECEPTOR/

The 9E3/CEF4 gene codes for a chemokine that is highly homologous to h uman interleukin-8 and melanoma growth-stimulating activity/gro alpha. These chemokines belong to a family of molecular mediators that are i mportantly involved in inflammation, wound healing, tumor development, and viral entry into cells. On the chorioallantoic membrane the 9E3 p rotein is chemotactic for monocyte/macrophages and lymphocytes and is angiogenic. In cultured chicken embryo fibroblasts, which have many of the properties of wound fibroblasts, the gene is stimulated by a vari ety of agents including oncogenes, growth factors, phorbol esters, and thrombin, The strong stimulation of 9E3 by thrombin in culture correl ates well with the observation that in young chicks this gene is stimu lated to very high levels in fibroblasts upon wounding and remains hig h throughout wound repair, Activation of 9E3 by thrombin: (i) occurs v ery rapidly, one minute exposure to thrombin is sufficient to initiate the signals necessary for gene activation; (ii) is independent of mit ogenesis; (iii) operates through the proteolytically activated recepto r for thrombin; (iv) is mediated by tyrosine kinases, including c-src and the epidermal growth factor (EGF) receptor, rather than Ser/Thr ki nases such as protein kinase C and protein kinase A. Inhibition of eit her c-src or the EGF receptor tyrosine kinase inhibits the stimulation of 9E3 by thrombin. We show here for the first time that activation o f the EGF receptor through a cell-surface receptor that does not have tyrosine kinase activity can lead to expression of an immediate early response gene which encodes for a secreted protein, a chemokine. This rapidly activated tyrosine kinase pathway may be a general stress resp onse by which in vivo a localized cell population reacts to emergency situations such as viral infection, wounding, or tumor growth.