Protection of epithelial cells by keratinocyte growth factor signaling.

Oxidative injury to the lung is associated with widespread injury to the alveolar epithelium, which can be fatal unless the process is controlled and repaired. Keratinocyte growth factor (KGF), a member of the fibroblast growth factor family, has been shown to protect the lung from a variety of oxidative insults. The mechanism(s) underlying the protective effects of KGF in lung injury is being investigated in many laboratories. Although KGF has potent mitogenic effects on epithelial cells, the proliferative effect of KGF was shown to be abolished in oxygen-breathing animals, but KGF was still able to inhibit alveolar damage. This demonstrates that the protective effect of KGF cannot simply be explained by the ability of KGF to stimulate type II cell proliferation. To identify the mechanisms involved in the protective effects of KGF, we used an inducible lung-specific transgenic approach to overexpress KGF in murine lungs, since constitutive overexpression of KGF in the mouse affects lung development. The transgenic system allowed us to identify the pro-survival Akt pathway as an important mediator of the protective effects of KGF both in vivo and in vitro. In addition, use of a yeast two-hybrid system led to the identification two proteins p90RSK and PAK4 that associate with the KGF receptor and are important for the protective functions of KGF. Experiments are underway to determine whether the different pathways triggered by KGF all converge on the Akt pathway, or whether they independently induce protective mechanisms that along with Akt are crucial for cell survival.