Phosphorylation of protein phosphatase 2A facilitated an early stage of chemical carcinogenesis

• Published in: Toxicology and applied pharmacology Vol. 336; pp. 75 - 83
• Main Authors: Ishii, Yuji, Kuroda, Ken, Matsushita, Kohei, Yokoo, Yuh, Takasu, Shinji, Kijima, Aki, Nohmi, Takehiko, Ogawa, Kumiko, Umemura, Takashi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.2017
• Subjects: Animals; Anisoles - toxicity; Apoptosis - drug effects; Cell proliferation; Cell Proliferation - drug effects; Cell Transformation, Neoplastic - chemically induced; Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - metabolism; Cell Transformation, Neoplastic - pathology; DNA adduct; DNA Adducts - genetics; DNA Adducts - metabolism; Dose-Response Relationship, Drug; Estragole; Extracellular Signal-Regulated MAP Kinases - metabolism; Gene mutation; Hepatocytes - drug effects; Hepatocytes - enzymology; Hepatocytes - pathology; Histones - metabolism; Liver Neoplasms - chemically induced; Liver Neoplasms - enzymology; Liver Neoplasms - genetics; Liver Neoplasms - pathology; Male; MAP Kinase Kinase Kinases - metabolism; Mutation; Phosphoproteins - metabolism; Phosphorylation; PP2A; Protein Phosphatase 2 - metabolism; Proto-Oncogene Proteins c-akt - metabolism; Rad51 Recombinase - metabolism; Rats, Inbred F344; Rats, Transgenic; Signal Transduction - drug effects; src-Family Kinases - metabolism; Time Factors; Tumor Suppressor Protein p53 - metabolism; Cell proliferation; dG; Gene mutation; ALP; PME-1; DNA adduct; PP2A; CIP2A; Estragole; ES; LC-MS/MS; DSB; 6-TG; MF; ESI; dA; HE; PCR; ELISA
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1016/j.taap.2017.10.009

Protein phosphatase 2A (PP2A) is a serine-threonine phosphatase that regulates cell signaling pathways. Its inactivation is correlated with tumor malignancy, possibly due to the effects on cell differentiation and malignant cell transformation. Therefore, it has been noted that PP2A could be a promising target for cancer therapy. In our previous study of the hepatocarcinogen estragole (ES), cell proliferation may be required to convert ES-specific DNA adducts to mutations. To explore the trigger for cell proliferation, gpt delta rats were administered ES by gavage at doses of 3, 30 and 300mg/kg/day for 4weeks. ES-induced cell proliferation and gene mutations were observed at only the high dose whereas ES-specific DNA adducts were detected in a dose-dependent manner. Western blot analyses revealed activation of the Akt and ERK pathways without activation of upstream regulators, such as c-Raf, PKC and, PI3K. Phosphorylation of the PP2A C subunit at Tyr307 was found along with phosphorylation of Src. The overall data might imply that PP2A inactivation is responsible for cell cycle progression through activation of the Akt and ERK pathways at high doses of ES. Based on γ-H2AX immunohistochemistry and Western blot analysis for Rad51 protein, the resultant mutation spectra showed large deletion mutations that might result from double strand breaks of DNA. Thus, it is likely that inactivation of PP2A resulted in acceleration and exacerbation of gene mutations. We conclude that PP2A might contribute to an early stage of chemical carcinogenesis, suggesting that PP2A could be a molecular target of primary cancer prevention. •PP2A phosphorylation is proposed as a new pathway in chemical carcinogenesis.•Estragole activates MEK/Erk pathway through the PP2A phosphorylation.•Cell proliferation accelerated gene mutations from estragole-specific DNA adducts.•PP2A affects not only the late stage but also the early stage of carcinogenesis.•PP2A could be targeted in primary cancer prevention.