HGF- and KGF-induced activation of PI-3K/p70 S6 kinase pathway in corneal epithelial cells: its relevance in wound healing

In this study we have investigated the involvement of PI-3K and its downstr eam target p70 S6K in the signaling response of corneal epithelial cells af ter HGF and KGF stimulation. HGF induced three- to fivefold increase in PI- 3K activity in 5-10 min, whereas KGF stimulation resulted in two- to three- fold increase in activity in 2-10 min. Both growth factors also caused the phosphorylation of p70 S6K and stimulation of its activity. HGF increased p 70 S6K activity by 300 % and KGF by about 200 %. Protein kinase C (PKC) act ivator TPA also induced the phosphorylation of p70 S6K. Both the PI-3K inhi bitor wortmannin and PKC inhibitor calphostin C blocked the phosphorylation of p70 S6K mediated by the growth factors, However, the mitogen-activated protein kinase (p42/44 MAPK) cascade inhibitor PD98059 had no effect on p70 S6K activation. Furthermore, HGF and KGF increased the rate of corneal epi thelial wound healing in an organ culture model, and wortmannin and rapamyc in (the p70 S6K inhibitor) blocked corneal epithelial wound healing promote d by the growth factors. These studies suggest that PI-3K and p70 S6K are i mportant signal transducers in the stimulation of corneal epithelial cells by HGF and KGF. PKC is involved in the PI-3K-dependent activation of p70 S6 K but not MAPK. Inhibition of wound closure by PT-3K and p70 S6K inhibitors suggests these enzymes play a significant role in corneal wound repair sti mulated by HGF and K GF. (C) 2001 Academic Press.