Tryptase is involved in proteinase-activated receptor-2 (PAR-2) mediated up-regulation of IL-8 expression. The present report showed the effects of tryptase on gene expression and activation, including up-regulation IL-8 expression. The expression of mRNA for NF-κB first increased at 1h after tryptase-treatment (1ng/ml) and reached the plateau after 4 h. The NF-κB mRNA increased by 3-fold (n=3, P<0.05), AP-1 by 2-fold (n=3, P<0.05), and PKB by 10-fold (n=3, P<0.05). However, tryptase-treatment did not affect the expression of JNK and p38 MAPK when compared with control cells at mRNA level. Furthermore, in addition to increasing phosphorylation of p38 MAPK, tryptase-treatment also increased phosphorylation of PKB by 2-fold at 15 min following the treatment. The up-regulation and phosphorylation of PKB by tryptase could be abolished by either phosphoinositol-3-kinase (PI3K) inhibitor (LY294002) at 10 μM or antisense PKB cDNA transfection. The up-regulation of NF-κB expression could be inhibited by LY294002 and antisense PKB cDNA. These results indicate that tryptase can activate PI3K-PKB pathway and enhance IL-8 expression.