PI3-kinase p85α is a target molecule of proline-rich antimicrobial peptide to suppress proliferation of ras-transformed cells

Abstract

PR-39, which is an endogenous antimicrobial peptide, can bind to Src homology 3 domains of the NADPH complex protein p47phox and the signaling adapter protein p130Cas. Recently, we have reported that PR-39 gene transduction altered invasive activity and actin structure of human hepatocellular carcinoma cells, suggesting that this peptide affects cellular signaling due to its proline-rich motif. In order to clarify the mechanism of the PR-39 functions, we transfected the PR-39 gene into mouse NIH3T3 cells which had already been transformed with human activated k-ras gene. The PR-39 gene transfectant showed a reorganization of actin structure and suppression of cell proliferation both in vitro and in vivo. Decreases of MAP (mitogen-activated protein) kinase activity, cyclin D1 expression and JNK activity were observed in the PR-39 gene transfectant. Co-immunoprecipitation analysis revealed that PR-39 binds to P13-kinase p85α, which is a regulatory subunit of P13-kinase and one of the effectors by which ras induces cytoskeletal changes and stimulates mitogenesis. The P13-kinase activity of the PR-39 gene transfectant was decreased compared with that of the ras transformant. These results suggest that PR-39 alters actin structure and cell proliferation rate by binding to P13-kinase p85α and suppressing the P13-kinase activity.