Downregulation of low-density lipoprotein receptor class A domain-containing protein 4 (Ldlrad4) in the liver of rats treated with nongenotoxic hepatocarcinogen to induce transforming growth factor ß signaling promoting cell proliferation and suppressing apoptosis in early hepatocarcinogenesis.

We previously found downregulation of low-density lipoprotein receptor class A domain-containing protein 4 (LDLRAD4), a negative regulator of transforming growth factor (TGF)-ß signaling, in glutathione S-transferase placental form (GST-P) expressing (+ ) pre-neoplastic lesions produced by treatment with nongenotoxic hepatocarcinogens for up to 90 days in rats. Here, we investigated the relationship between LDLRAD4 downregulation and TGFß signaling in nongenotoxic hepatocarcinogenesis. The transcripts of Tgfb and Hb-egf increased after ≥28 days of treatment. After 84 or 90 days, Snai1 increased transcripts and the subpopulation of GST-P+ foci downregulating LDLRAD4 co-expressed TGFß1, phosphorylated EGFR, or phosphorylated AKT2, and downregulated PTEN, showing higher incidences than those in GST-P+ foci expressing LDLRAD4. The subpopulation of GST-P+ foci downregulating LDLRAD4 also co-expressed caveolin-1 or TACE/ADAM17, suggesting that disruptive activation of TGFß signaling through a loss of LDLRAD4 enhances EGFR and PTEN/AKT-dependent pathways via caveolin-1-dependent activation of TACE/ADAM17 during nongenotoxic hepatocarcinogenesis. The numbers of c-MYC+ cells and PCNA+ cells were higher in LDLRAD4-downregulated GST-P+ foci than in LDLRAD4-expressing GST-P+ foci, suggesting a preferential proliferation of pre-neoplastic cells by LDLRAD4 downregulation. Nongenotoxic hepatocarcinogens markedly downregulated Nox4 after 28 days and later decreased cleaved caspase 3+ cells in LDLRAD4-downregulated GST-P+ foci, suggesting an attenuation of apoptosis by LDLRAD4 downregulation through activation of the EGFR pathway. At the late hepatocarcinogenesis stage in a two-stage model, LDLRAD4 downregulation was higher in adenoma and carcinoma than in pre-neoplastic cell foci, suggesting a role of LDLRAD4 downregulation in tumor development. Our results suggest that nongenotoxic hepatocarcinogens cause disruptive activation of TGFß signaling through downregulating LDLRAD4 toward carcinogenesis in the rat liver.

Expression Characteristics of Genes Hypermethylated and Downregulated in Rat Liver Specific to Nongenotoxic Hepatocarcinogens.

This study examined hypermethylated and downregulated genes specific to carbon tetrachloride (CCl4) by Methyl-Seq analysis combined with expression microarray analysis in the liver of rats treated with CCl4 or N-nitrosodiethylamine (DEN) for 28 days, by excluding those with DEN. Among 52 genes, Ldlrad4, Proc, Cdh17, and Nfia were confirmed to show promoter-region hypermethylation by methylation-specific quantitative PCR analysis on day 28. The transcript levels of these 4 genes decreased by real-time reverse transcription-PCR analysis in the livers of rats treated with nongenotoxic hepatocarcinogens for up to 90 days compared with untreated controls and genotoxic hepatocarcinogens. Immunohistochemically, LDLRAD4 and PROC showed decreased immunoreactivity, forming negative foci, in glutathione S-transferase placental form (GST-P)+ foci, and incidences of LDLRAD4- and PROC- foci in GST-P+ foci induced by treatment with nongenotoxic hepatocarcinogens for 84 or 90 days were increased compared with those with genotoxic hepatocarcinogens. In contrast, CDH17 and NFIA responded to hepatocarcinogens without any relation to the genotoxic potential of carcinogens. All 4 genes did not respond to renal carcinogens after treatment for 28 days. Considering that Ldlrad4 is a negative regulator of transforming growth factor-ß signaling, Proc participating in p21WAF1/CIP1 upregulation by activation, Cdh17 inducing cell cycle arrest by gene knockdown, and Nfia playing a role in a tumor-suppressor, all these genes may be potential in vivo epigenetic markers of nongenotoxic hepatocarcinogens from the early stages of treatment in terms of gene expression changes. LDLRAD4 and PROC may have a role in the development of preneoplastic lesions produced by nongenotoxic hepatocarcinogens.

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.

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.

Downregulation of TMEM70 in Rat Liver Cells After Hepatocarcinogen Treatment Related to the Warburg Effect in Hepatocarcinogenesis Producing GST-P-Expressing Proliferative Lesions.

We previously observed downregulation of mitochondrial oxidative phosphorylation-related protein, TMEM70, which is suggestive of disrupted cellular senescence, in GST-P-expressing (+) proliferative lesions from early hepatocarcinogenesis stages in rats. The present study investigated the immunohistochemical relationship between TMEM70 downregulation and cellular metabolic changes in carcinogenic processes, as well as the onset of the liver cell respiratory changes after repeated hepatocarcinogen treatment in rats. At the early hepatocarcinogenesis stage in a 2-stage model, GST-P+ preneoplastic lesions showing TMEM70 downregulation also downregulated the mitochondrial ATPase, ATPB, but upregulated glycolysis-related glucose transporter member 1 (GLUT1) and glucose-6-phosphate dehydrogenase, suggesting a metabolic shift from oxidative phosphorylation to glycolysis, known as the Warburg effect. Combined downregulation of TMEM70 and ATPB increased proliferation activity in GST-P+ preneoplastic lesions, suggesting cell proliferation facilitation by reducing mitochondrial respiration. Concurrent GLUT1-upregulation and TMEM70-downregulation increased nuclear phosphorylated c-MYC+ cells in GST-P+ preneoplastic lesions, suggesting c-MYC-mediated transcription facilitation to promote glycolysis and cell proliferation. The TMEM70-related metabolic shift was enhanced in GST-P+ neoplastic lesions, suggesting a contribution to tumor progression. Conversely, the TMEM70-related metabolic shift was lacking in peroxisome proliferator-activated receptor-α agonist-induced hepatocarcinogenesis, as well as in carcinogenic processes targeting other organs. Transcript expression analysis following 28- and 90-day repeated hepatocarcinogen treatment showed downregulation of Tmem70 from day 28 and upregulation of Pkm and Myc at day 90, suggesting early onset of a catastrophic cellular senescence-related metabolic shift beginning from depressed mitochondrial respiration in the liver. These results suggest a contribution of TMEM70 downregulation to the Warburg effect, which directs tumor promotion and progression in GST-P+-linked hepatocarcinogenesis in rats.

The NADPH Oxidase Inhibitor Apocynin Suppresses Preneoplastic Liver Foci of Rats.

Reactive oxygen species (ROS) have been revealed to be important factors for carcinogenesis and tumor progression. Therefore, we focused on an ROS-generating protein, nicotinamide adenine dinucleotide phosphate oxidase, and evaluated whether its inhibitor, apocynin, could suppress hepatocarcinogenesis in a medium-term rat liver bioassay. The number and size of glutathione S-transferase placental form (GST-P)-positive foci were significantly reduced by apocynin in a dose-dependent manner. The reduction of ROS generation by apocynin was confirmed by dihydroethidium staining. Apocynin treatment also significantly reduced Ki-67 positivity, downregulated cyclooxygenase 2, and suppressed the activation of the c-Myc pathway. Meanwhile, ROS generation was not different between GST-P-positive foci and surrounding GST-P-negative areas of the liver. In conclusion, the present data suggest that apocynin possesses a potential antihepatocarcinogenic property.

Promoter-region hypermethylation and expression downregulation of Yy1 (Yin yang 1) in preneoplastic liver lesions in a thioacetamide rat hepatocarcinogenesis model.

Thioacetamide (TAA) has been used to develop a rodent model for hepatocarcinogenesis. To determine the genes with epigenetic modifications in early hepatocarcinogenesis, we did a genome-wide scan for hypermethylated promoter regions using CpG island microarrays in TAA-promoted rat liver tissue. Eight genes were selected based on the microarray profile; of these, Yy1 and Wdr45b were confirmed to be hypermethylated by methylation-specific polymerase chain reaction (PCR) and pyrosequencing and downregulated by real-time reverse transcription PCR. Non-neoplastic liver cells had nuclear Yy1 immunoreactivity, while preneoplastic foci with glutathione S-transferase placental form (GST-P) immunoreactivity had decreased Yy1 immunoreactivity. The incidence of these foci was proportional to the dose of TAA administered. Co-expression analysis of gene products downstream of Yy1 revealed increased nuclear phospho-c-Myc(+) foci as well as nuclear and cytoplasmic p21(Cip1+) foci in Yy1(-) or GST-P(+) foci in response to TAA-promotion dose. Although the absolute number of cells was low, the incidence of death receptor 5(-) foci was increased in Yy1(-) foci in proportion to the TAA dose. Yy1(-)/GST-P(+) foci revealed a higher number of proliferating cell nuclear antigen (PCNA)-immunoreactive cells than Yy1(+)/GST-P(+) foci, while cleaved caspase-3(+) cells were unchanged between Yy1(-)/GST-P(+) and Yy1(+)/GST-P(+) foci. In the case of Wdr45b, most GST-P(+) foci were Wdr45b(-) and were not increased by TAA promotion. These results suggest involvement of Yy1 in the epigenetic gene regulation at the early stages of TAA promoted cell proliferation and concomitant cell cycle arrest in preneoplastic lesions.

Cancer promoting effects of N-nitrosodiethylamine (DEN) and 2-acetylaminofluorene (2-AAF) with medium term rat liver bioassay / 中国药理学通报

AIM To study the cancer promoting effects of N nitrosodiethylamine (DEN) and 2 Acetylaminofluorene (2 AAF). METHODS Medium Term Rat Liver Bioassay (MTRLB). Male SD rats were initially given a single dose (200 mg?kg -1 ) of DEN ip and starting 2 weeks later, were treated with 10, 33 and 100 ppm DEN in drinking water, or with 2 2, 6 6 and 22 mg?kg -1 2 AAF by gavage for 6 weeks. All rats were subjected to two thirds partial hepatectomy at week 3 and killed at the end of week 8. Carcinogenic potential was scored by comparing the numbers and areas in induced glutathione S transferase placental form (GST P) positive foci in the liver with those of corresponding control group given DEN alone. RESULTS Both DEN and 2 AAF caused the increases of the numbers and areas of GST P positive foci in the liver, and showed dose response relationship. CONCLUSION Both DEN and 2 AAF shows cancer promoting effects, and MTRLB was a convenient, economical and effective tool to study the cancer promoting effects of test chemicals.