The insect peptide CopA3 enhances hepatocyte proliferation by directly binding to PTEN and inhibiting its activity

Phosphatase and tensin homolog (PTEN) is a tumor suppressor that negatively regulates the PI3K/AKT signaling pathway, effectively preventing cell growth. Because PTEN-mediated regulation of cell growth is also closely associated with tissue regeneration, controlled inhibition of PTEN could be a therapeutic strategy for mitigating abnormal tissue regeneration, such as in liver fibrosis. In this study, we investigated the ability of the insect-derived peptide CopA3, which specifically inhibits caspase through direct binding, also interacts with PTEN and modulates its activity, potentially influencing cell proliferation. Consistent with direct binding to PTEN, polyacrylamide gel electrophoresis of CopA3 with PTEN revealed a distinct migratory band shift, a pattern like that observed for CopA3 and caspases. Surface plasmon resonance analysis and experiments utilizing cysteine-substituted mutants of CopA3 further demonstrated that this direct interaction is dependent on internal cysteine residues. Functional assays revealed that interaction with CopA3 markedly reduced the activity of PTEN immunoprecipitated from HepG2 liver cells as well as recombinant human PTEN. Moreover, both in vitro and in vivo studies confirmed that binding of CopA3 to PTEN promoted liver cell proliferation. These findings suggest that inhibition of PTEN by CopA3 is a potential therapeutic strategy in conditions where promoting hepatocyte proliferation is beneficial, such as liver injury.