ABSTRACT
Chronic liver inflammation (CLI) is a risk factor for development of hepatocellular carcinoma (HCC). Galectin‐1 (Gal1) is involved in the regulation of inflammation, angiogenesis, and ...tumorigenesis, exhibiting multiple anti‐inflammatory and protumorigenic activities. We aimed to explore its regulatory role in CLI and HCC progression using an established model of CLI‐mediated HCC development, Abcb4 multidrug‐resistance 2 (Mdr2)‐knockout (KO) mice, which express high levels of Gal1 in the liver. We generated double‐KO (dKO) Gal1‐KO/Mdr2‐KO mice on C57BL/6 and FVB/N genetic backgrounds and compared HCC development in the generated strains with their parental Mdr2‐KO strains. Loss of Gal1 increased liver injury, inflammation, fibrosis, and ductular reaction in dKO mice of both strains starting from an early age. Aged dKO mutants displayed earlier hepatocarcinogenesis and increased tumor size compared with control Mdr2‐KO mice. We found that osteopontin, a well‐known modulator of HCC development, and oncogenic proteins Ntrk2 (TrkB) and S100A4 were overexpressed in dKO compared with Mdr2‐KO livers. Our results demonstrate that in Mdr2‐KO mice, a model of CLI‐mediated HCC, Gal1‐mediated protection from hepatitis, liver fibrosis, and HCC initiation dominates over its known procarcinogenic activities at later stages of HCC development. These findings suggest that anti‐Gal1 treatments may not be applicable at all stages of CLI‐mediated HCC.—Potikha, T., Pappo, O., Mizrahi, L., Olam, D., Mailer, S. M., Rabinovich, G. A., Galun, E., Goldenberg, D. S. Lack of galectin‐1 exacerbates chronic hepatitis, liver fibrosis, and carcinogenesis in murine hepatocellular carcinoma model. FASEB J. 33, 7995–8007 (2019). www.fasebj.org
Chronic inflammation precedes the majority of hepatocellular carcinoma (HCC) cases. We investigated the chemopreventive potential of S-adenosylmethionine (SAM), an essential donor for all methylation ...reactions in the cell, at the late precancerous stage of HCC development using the Mdr2-knockout (Mdr2-KO, Abcb4
) mice, a model of inflammation-mediated hepatocarcinogenesis. Previously, we revealed down-regulation of the genes regulating SAM metabolism in the liver of these mice at the precancerous stages. Now, we have supplied Mdr2-KO mice at the late precancerous stage with SAM during either a short-term (17 days) or a long-term (51 days) period and explored the effects of such supplementation on tumor development, DNA methylation and gene expression in the liver. The short-term SAM supplementation significantly decreased the number of small tumor nodules, proliferating hepatocytes and the total DNA methylation level, while it increased expression of the tumor suppressor proteins Mat1a and p21. Surprisingly, the long-term SAM supplementation did not affect tumor growth and hepatocyte proliferation, while it increased the total liver DNA methylation. Our results demonstrate that the short-term SAM supplementation in the Mdr2-KO mice inhibited liver tumor development potentially by increasing multiple tumor suppressor mechanisms resulting in cell cycle arrest. The long-term SAM supplementation resulted in a bypass of the cell cycle arrest in this HCC model by a yet unknown mechanism.
Chronic liver inflammation precedes the majority of hepatocellular carcinomas (HCC). Here, we explore the connection between chronic inflammation and DNA methylation in the liver at the late ...precancerous stages of HCC development in Mdr2(-/-) (Mdr2/Abcb4-knockout) mice, a model of inflammation-mediated HCC. Using methylated DNA immunoprecipitation followed by hybridization with "CpG islands" (CGIs) microarrays, we found specific CGIs in 76 genes which were hypermethylated in the Mdr2(-/-) liver compared to age-matched healthy controls. The observed hypermethylation resulted mainly from an age-dependent decrease of methylation of the specific CGIs in control livers with no decrease in mutant mice. Chronic inflammation did not change global levels of DNA methylation in Mdr2(-/-) liver, but caused a 2-fold decrease of the global 5-hydroxymethylcytosine level in mutants compared to controls. Liver cell fractionation revealed, that the relative hypermethylation of specific CGIs in Mdr2(-/-) livers affected either hepatocyte, or non-hepatocyte, or both fractions without a correlation between changes of gene methylation and expression. Our findings demonstrate that chronic liver inflammation causes hypermethylation of specific CGIs, which may affect both hepatocytes and non-hepatocyte liver cells. These changes may serve as useful markers of an increased regenerative activity and of a late precancerous stage in the chronically inflamed liver.
Resection of hepatocellular carcinoma (HCC) tumors by partial hepatectomy (PHx) is associated with promoting hepatocarcinogenesis. We have previously reported that PHx promotes hepatocarcinogenesis ...in the Mdr2-knockout (Mdr2-KO) mouse, a model for inflammation-mediated HCC. Now, to explore the molecular mechanisms underlying the tumor-promoting effect of PHx, we compared genomic and transcriptomic profiles of HCC tumors developing in the Mdr2-KO mice either spontaneously or following PHx. PHx accelerated HCC development in these mice by four months. PHx-induced tumors had major chromosomal aberrations: all were amplifications affecting multiple chromosomes. Most of these amplifications were located near the acrocentric centromeres of murine chromosomes. Four different chromosomal regions were amplified each in at least three tumors. The human orthologs of these common amplified regions are known to be amplified in HCC. All tumors of untreated mice had chromosomal aberrations, including both deletions and amplifications. Amplifications in spontaneous tumors affected fewer chromosomes and were not located preferentially at the chromosomal edges. Comparison of gene expression profiles revealed a significantly enriched expression of oncogenes, chromosomal instability markers and E2F1 targets in the post-PHx compared to spontaneous tumors. Both tumor groups shared the same frequent amplification at chromosome 18. Here, we revealed that one of the regulatory genes encoded by this amplified region, Crem, was over-expressed in the nuclei of murine and human HCC cells in vivo, and that it stimulated proliferation of human HCC cells in vitro. Our results demonstrate that PHx of a chronically inflamed liver directed tumor development to a discrete pathway characterized by amplification of specific chromosomal regions and expression of specific tumor-promoting genes. Crem is a new candidate HCC oncogene frequently amplified in this model and frequently over-expressed in human HCC.
To overcome positional and methylation effects on transgene expression, we developed a universal cloning cassette for in vivo assessment of regulatory elements using the luciferase reporter gene and ...the CCCD camera. Monitoring luciferase expression pattern in live mice enables screening of large numbers of transgenic founders quickly and inexpensively. We demonstrate that in the engineered transgenic mice, the chicken β-globin 5′HS4 insulator did not always provide the desirable expression pattern, and the Island Element, responsible for the demethylation of the surrounding DNA region, was not beneficial. Both tested liver-specific and developmentally regulated promoters exhibited the expected expression pattern in most transgenic founders.
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