Expression of c-jun is not mandatory for mouse hepatocyte proliferation induced by two nuclear receptor ligands: TCPOBOP and T3.

BACKGROUND & AIMS: Mice lacking c-jun in the liver display impaired regeneration after partial hepatectomy (PH), and were reported to be more resistant to chemically-induced hepatocellular carcinoma (HCC). We investigated the role of c-jun in normal and preneoplastic hepatocyte proliferation induced by ligands of nuclear receptors, which cause liver hyperplasia in the absence of cell loss/death. METHODS: The effect of 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) on hepatocyte proliferation was determined in c-jun conditional knockout (c-jun(Δli)) or in mouse liver where c-jun has been silenced. To study the role of c-jun in HCC development, c-jun(Δli) and WT mice were given diethylnitrosamine (DENA) followed by repeated injections of TCPOBOP. RESULTS: Hepatocyte proliferation induced by TCPOBOP was associated with a stronger proliferative response and earlier S phase entry in c-jun(Δli) mice, compared to WT animals. Moreover, silencing of c-jun in the liver of CD-1 mice caused increased hepatocyte proliferation. A stronger hepatocyte proliferative response of c-jun(Δli) mice was observed also following treatment with a ligand of thyroid hormone receptor. Finally, loss of c-jun did not inhibit the development of HCC induced by DENA and promoted by TCPOBOP. CONCLUSIONS: (i) c-jun may, under certain conditions, negatively regulate proliferation of normal hepatocytes, (ii) c-jun is not an absolute requirement for DENA/TCPOBOP-induced HCC formation, suggesting that the therapeutic potential of c-jun/JNK inhibition in liver tumors might be impaired by an increased stimulation of cell growth due to blockade of the c-jun pathway.

Global analysis of estrogen receptor beta binding to breast cancer cell genome reveals an extensive interplay with estrogen receptor alpha for target gene regulation.

BACKGROUND: Estrogen receptors alpha (ERα) and beta (ERß) are transcription factors (TFs) that mediate estrogen signaling and define the hormone-responsive phenotype of breast cancer (BC). The two receptors can be found co-expressed and play specific, often opposite, roles, with ERß being able to modulate the effects of ERα on gene transcription and cell proliferation. ERß is frequently lost in BC, where its presence generally correlates with a better prognosis of the disease. The identification of the genomic targets of ERß in hormone-responsive BC cells is thus a critical step to elucidate the roles of this receptor in estrogen signaling and tumor cell biology. RESULTS: Expression of full-length ERß in hormone-responsive, ERα-positive MCF-7 cells resulted in a marked reduction in cell proliferation in response to estrogen and marked effects on the cell transcriptome. By ChIP-Seq we identified 9702 ERß and 6024 ERα binding sites in estrogen-stimulated cells, comprising sites occupied by either ERß, ERα or both ER subtypes. A search for TF binding matrices revealed that the majority of the binding sites identified comprise one or more Estrogen Response Element and the remaining show binding matrixes for other TFs known to mediate ER interaction with chromatin by tethering, including AP2, E2F and SP1. Of 921 genes differentially regulated by estrogen in ERß+ vs ERß- cells, 424 showed one or more ERß site within 10 kb. These putative primary ERß target genes control cell proliferation, death, differentiation, motility and adhesion, signal transduction and transcription, key cellular processes that might explain the biological and clinical phenotype of tumors expressing this ER subtype. ERß binding in close proximity of several miRNA genes and in the mitochondrial genome, suggests the possible involvement of this receptor in small non-coding RNA biogenesis and mitochondrial genome functions. CONCLUSIONS: Results indicate that the vast majority of the genomic targets of ERß can bind also ERα, suggesting that the overall action of ERß on the genome of hormone-responsive BC cells depends mainly on the relative concentration of both ERs in the cell.

Estrogen receptor alpha controls a gene network in luminal-like breast cancer cells comprising multiple transcription factors and microRNAs.

Luminal-like breast tumor cells express estrogen receptor alpha (ERalpha), a member of the nuclear receptor family of ligand-activated transcription factors that controls their proliferation, survival, and functional status. To identify the molecular determinants of this hormone-responsive tumor phenotype, a comprehensive genome-wide analysis was performed in estrogen stimulated MCF-7 and ZR-75.1 cells by integrating time-course mRNA expression profiling with global mapping of genomic ERalpha binding sites by chromatin immunoprecipitation coupled to massively parallel sequencing, microRNA expression profiling, and in silico analysis of transcription units and receptor binding regions identified. All 1270 genes that were found to respond to 17beta-estradiol in both cell lines cluster in 33 highly concordant groups, each of which showed defined kinetics of RNA changes. This hormone-responsive gene set includes several direct targets of ERalpha and is organized in a gene regulation cascade, stemming from ligand-activated receptor and reaching a large number of downstream targets via AP-2gamma, B-cell activating transcription factor, E2F1 and 2, E74-like factor 3, GTF2IRD1, hairy and enhancer of split homologue-1, MYB, SMAD3, RARalpha, and RXRalpha transcription factors. MicroRNAs are also integral components of this gene regulation network because miR-107, miR-424, miR-570, miR-618, and miR-760 are regulated by 17beta-estradiol along with other microRNAs that can target a significant number of transcripts belonging to one or more estrogen-responsive gene clusters.

Molecular bases of copper and iron deficiency-associated dyslipidemia: a microarray analysis of the rat intestinal transcriptome.

As essential cofactor in many proteins and redox enzymes, copper and iron are involved in a wide range of biological processes. Mild dietary deficiency of metals represents an underestimated problem for human health, because it does not cause clear signs and clinical symptoms, but it is associated to long-term deleterious effects in cardiovascular system and alterations in lipid metabolism. The aim of this work was to study the biological processes significantly affected by mild dietary deficiency of both metals in rat intestine, in order to better understand the molecular bases of the systemic metabolic alterations, as hypercholesterolemia and hypertriglyceridemia observed in copper-deficient rats. A gene-microarray differential analysis was carried out on the intestinal transcriptome of copper- and iron-deficient rats, thus highlighting the biological processes significantly modulated by the dietary restrictions. The gene array analysis showed a down-regulation of genes involved in mitochondrial and peroxisomal fatty acids beta-oxidation and an up-regulation of genes involved in plasmatic cholesterol transport (apoprotein E and lecithin:cholesterol acyltransferase) in copper deficiency. Furthermore, a severe down-regulation of ApoH was pointed out in iron-deficient animals.