Downregulation of UBE2E2 in rat liver cells after hepatocarcinogen treatment facilitates cell proliferation and slowing down of DNA damage response in GST-P-expressing preneoplastic lesions.

Abstract

We previously found downregulation of ubiquitin-conjugating enzyme E2E 2 (UBE2E2) in GST-P-positive (+) proliferative lesions produced by tumor promotion from early hepatocarcinogenesis stages in rats. Here we investigated the role of UBE2E2 downregulation in preneoplastic lesions of the liver and other target organs produced by tumor promotion in rats. Increased number of UBE2E2-related ubiquitination target proteins, phosphorylated c-MYC, KDM4A and KMT5A, was found in the UBE2E2-downregulated GST-P+ foci, compared with GST-P+ foci expressing UBE2E2. However, p21WAF1/CIP1, another UBE2E2 target protein, did not increase in the positive cells. Furthermore, the numbers of PCNA+ cells and γH2AX+ cells were increased in UBE2E2-downregulated foci. These results suggest sustained activation of c-MYC and stabilization of KMT5A to result in c-MYC-mediated transcript upregulation and following KMT5A-mediated protein stabilization of PCNA in GST-P+ foci, as well as KDM4A stabilization resulting in slowing down of DNA damage response in these lesions. Similar results were also observed in GST-P+ foci produced by repeated treatment of rats with a hepatocarcinogen, thioacetamide, for 90days. Hepatocarcinogen treatment for 28 or 90days also increased the numbers of liver cells expressing UBE2E2-related ubiquitination target proteins, as well as PCNA+ or γH2AX+ cells. Conversely, UBE2E2 downregulation was lacking in PPARα agonist-induced hepatocarcinogenesis, as well as in carcinogenic processes targeting other organs, suggestive of the loss of UBE2E2-related ubiquitination limited to hepatocarcinogenesis producing GST-P+ proliferative lesions. Our results suggest that repeated hepatocarcinogen treatment of rats causes stabilization of UBE2E2-related ubiquitination target proteins in liver cells to promote carcinogenesis.

• Authors: Sayaka Mizukami, Yousuke Watanabe, Yukie Saegusa, Kota Nakajima, Yuko Ito, Yasunori Masubuchi, Toshinori Yoshida, Makoto Shibutani
• Journal: Toxicology and applied pharmacology (Toxicol Appl Pharmacol) Vol. 334 Pg. 207-216 (11 01 2017) ISSN: 1096-0333 [Electronic] United States
• PMID: 28899750 (Publication Type: Journal Article)
• Copyright: Copyright © 2017 Elsevier Inc. All rights reserved.

Chemical References

• Carcinogens
• UBE2E2 protein, rat
• Ubiquitin-Protein Ligases
• Glutathione S-Transferase pi
• Gstp1 protein, rat

Topics

• Animals
• Apoptosis
• Carcinogens (toxicity)
• Cell Proliferation (drug effects)
• DNA Damage (drug effects)
• DNA Repair
• Down-Regulation
• Gene Expression Regulation
• Glutathione S-Transferase pi (genetics, metabolism)
• Hepatocytes (drug effects)
• Precancerous Conditions (chemically induced)
• Random Allocation
• Rats
• Ubiquitin-Protein Ligases (genetics, metabolism)