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

Abstract

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.

Differential Impacts on Host Transcription by ROP and GRA Effectors from the Intracellular ParasiteToxoplasma gondii

“…Curiously, this enrichment appeared not to be preserved at 3 hpi, which suggests that the responsible parasite factors exert only a transient influence on host cell cycle-related genes. Of the parasite effectors currently known to modulate the host cell cycle (19, 22, 23, 40, 55), ROP16 is most likely to explain these results: ROP16 phosphorylates ubiquitin-like containing PHD and RING finger domain 1 (UHRF1) in a manner that peaks at 3 hpi, which leads to epigenetic silencing of cyclin B1 (40), a component of the cyclin B1/Cdk1 complex required for the G2/M transition. However, ROP16 is likely not the only ROP to impinge on the host cell cycle, as comparison of G1 phase U-I vs. U-U cells also revealed enrichment in the p53 Pathway and KRAS Signaling Up gene sets (Fig.…”

Toxoplasma GRA16 Inhibits NF-κB Activation through PP2A-B55 Upregulation in Non-Small-Cell Lung Carcinoma Cells

“…We recently reported the anticancer effects of dense granule protein 16 (GRA16) of Toxoplasma gondii in mouse xenograft models of GRA16-stable hepatocellular carcinoma (HCC) [10]. GRA16 increased the nuclear localization of phosphatase, tensin homolog (PTEN), and p53-dependent apoptosis by binding with herpes virus-associated ubiquitin-specific protease (HAUSP) in HCC cells [10].…”

“…We recently reported the anticancer effects of dense granule protein 16 (GRA16) of Toxoplasma gondii in mouse xenograft models of GRA16-stable hepatocellular carcinoma (HCC) [10]. GRA16 increased the nuclear localization of phosphatase, tensin homolog (PTEN), and p53-dependent apoptosis by binding with herpes virus-associated ubiquitin-specific protease (HAUSP) in HCC cells [10]. However, functional studies of GRA16 in host cells revealed its interactions with two host cell enzymes, namely HAUSP and the B55 regulatory subunit of protein phosphatase 2A (PP2A-B55) [10][11][12].…”

“…GRA16 increased the nuclear localization of phosphatase, tensin homolog (PTEN), and p53-dependent apoptosis by binding with herpes virus-associated ubiquitin-specific protease (HAUSP) in HCC cells [10]. However, functional studies of GRA16 in host cells revealed its interactions with two host cell enzymes, namely HAUSP and the B55 regulatory subunit of protein phosphatase 2A (PP2A-B55) [10][11][12]. Therefore, the anticancer mechanisms of GRA16 may be associated with its effects on the HAUSP/PTEN/p53 and PP2A/AKT/NF-κB pathways [10][11][12].…”

“…However, functional studies of GRA16 in host cells revealed its interactions with two host cell enzymes, namely HAUSP and the B55 regulatory subunit of protein phosphatase 2A (PP2A-B55) [10][11][12]. Therefore, the anticancer mechanisms of GRA16 may be associated with its effects on the HAUSP/PTEN/p53 and PP2A/AKT/NF-κB pathways [10][11][12]. T. gondii is an intracellular parasite that infects multiple organs and tissues.…”