Increase in the nuclear localization of PTEN by the Toxoplasma GRA16 protein and subsequent induction of p53-dependent apoptosis and anticancer effect.

This study investigated the efficacy of Toxoplasma GRA16, which binds to herpes virus-associated ubiquitin-specific protease (HAUSP), in anticancer treatment, and whether the expression of GRA16 in genetically modified hepatocellular carcinoma (HCC) cells (GRA16-p53-wild HepG2 and GRA16-p53-null Hep3B) regulates PTEN because alterations in phosphatase and tensin homologue (PTEN) and p53 are vital in liver carcinogenesis and the abnormal p53 gene appears in HCC. For this purpose, we established the GRA16 cell lines using the pBABE retrovirus system, assessed the detailed mechanism of PTEN regulation in vitro and established the anticancer effect in xenograft mice. Our study showed that cell proliferation, antiapoptotic factors, p-AKT/AKT ratio, cell migration and invasive activity were decreased in GRA16-stable HepG2 cells. Conversely, the apoptotic factors PTEN and p53 and apoptotic cells were elevated in GRA16-stable HepG2 cells but not in Hep3B cells. The change in MDM2 was inconspicuous in both HepG2 and Hep3B; however, the PTEN level was remarkably elevated in HepG2 but not in Hep3B. HAUSP-bound GRA16 preferentially increased p53 stabilization by the nuclear localization of PTEN rather than MDM2-dependent mechanisms. These molecular changes appeared to correlate with the decreased tumour mass in GRA16-stable-HepG2 cell-xenograft nude mice. This study establishes that GRA16 is a HAUSP inhibitor that targets the nuclear localization of PTEN and induces the anticancer effect in a p53-dependent manner. The efficacy of GRA16 could be newly highlighted in HCC treatment in a p53-dependent manner.