ABSTRACT
Nucleosomes are the basic structural units of eukaryotic chromatin. In recent years, it has become evident that nucleosomes and their position, in concert with other epigenetic mechanisms (such as DNA methylation, histone modifications, changes in histone variants, as well as small noncoding regulatory RNAs) play essential roles in the control of gene expression. Here, we discuss the mechanisms and factors that regulate nucleosome position and gene expression in normal and cancer cells.
Subject(s)
Chromatin/genetics , Gene Expression Regulation, Neoplastic , Neoplasms/genetics , Neoplasms/pathology , Nucleosomes/genetics , Animals , HumansABSTRACT
GRP78, a major endoplasmic reticulum chaperone and signaling regulator, is commonly overexpressed in cancer. Moreover, induction of GRP78 by a variety of anti-cancer drugs, including histone deacetylase inhibitors, confers chemoresistance to cancer, thereby contributing to tumorigenesis. Thus, therapies aimed at decreasing GRP78 levels, which results in the inhibition of tumor cell proliferation and resensitization of tumor cells to chemotherapeutic drugs may hold promise for cancer treatment. Despite advances in our understanding of GRP78 actions, little is known about endogenous inhibitors controlling its expression. As endogenous regulators, microRNAs (miRNAs) play important roles in modulating gene expression; therefore, we sought to identify miRNA(s) that target GRP78, under the hypothesis that these miRNAs may serve as therapeutic agents. Here, we report that three miRNAs (miR-30d, miR-181a, miR-199a-5p) predicted to target GRP78 are down-regulated in prostate, colon and bladder tumors, and human cancer cell lines. We show that in C42B prostate cancer cells, these miRNAs down-regulate GRP78 and induce apoptosis by directly targeting its 3' untranslated region. Importantly, we demonstrate that the three miRNAs act cooperatively to decrease GRP78 levels, suggesting that multiple miRNAs may be required to efficiently control the expression of some genes. In addition, delivery of multiple miRNAs by either transient transfection or lentivirus transduction increased the sensitivity of cancer cells to the histone deacetylase inhibitor, trichostatin A, in C42B, HCT116 and HL-60 cells. Together, our results indicate that the delivery of co-transcribed miRNAs can efficiently suppress GRP78 levels and GRP78-mediated chemoresistance, and suggest that this strategy holds therapeutic potential.
Subject(s)
Gene Expression Regulation, Neoplastic , Heat-Shock Proteins/biosynthesis , MicroRNAs/physiology , RNA, Messenger/physiology , 3' Untranslated Regions , Adenocarcinoma/genetics , Adenocarcinoma/pathology , Animals , Apoptosis , Cell Line, Tumor/drug effects , Cell Line, Tumor/metabolism , Colonic Neoplasms/genetics , Colonic Neoplasms/pathology , Drug Resistance, Neoplasm/genetics , Endoplasmic Reticulum Chaperone BiP , Genes, Reporter , Genetic Vectors , HL-60 Cells/drug effects , HL-60 Cells/metabolism , Heat-Shock Proteins/genetics , Histone Deacetylase Inhibitors/pharmacology , Humans , Hydroxamic Acids/pharmacology , Lentivirus/genetics , Male , Mice , Mice, Nude , MicroRNAs/genetics , Neovascularization, Pathologic , Prostatic Neoplasms/genetics , Prostatic Neoplasms/pathology , RNA/pharmacology , RNA, Messenger/genetics , Thapsigargin/pharmacology , Transcription, Genetic , Transfection , Tumor Stem Cell Assay , Urinary Bladder Neoplasms/genetics , Urinary Bladder Neoplasms/pathology , Xenograft Model Antitumor AssaysABSTRACT
It has been proposed that gonadotropin-releasing hormone (GnRH) plays an autocrine/paracrine regulatory role in mammalian and fish ovaries. The marine teleost gilthead seabream is an interesting model since, during the life span of the fish, gonadal tissues develop first as testes, which then regress allowing the development of ovarian follicles. Recent studies carried out in ovaries of the gilthead seabream have demonstrated that various GnRH transcripts as well as GnRH splicing variants are expressed. The mRNA level of several GnRH forms in the female and male areas of the switching gonad, and their possible role in this process, were further investigated. The results here reported show that sGnRH, cGnRH-II, and sbGnRH transcripts are locally expressed during gilthead seabream gonadal differentiation; the expression of the three GnRH forms was found to differ among the morphologically defined areas of the switching gonad, as demonstrated by applying reverse transcription-polymerase chain reaction (RT-PCR), together with in situ hybridization, and semiquantitative PCR analyses. Moreover, the hypothesis that GnRH forms may regulate testicular regression via an apoptotic mechanism was investigated by analyzing the different areas of switching gonads for caspase-3 activity as a measure of apoptosis. Our results showed a marked increase of caspase-3 activity in the area corresponding to the regressing testes in which a significant decrease of testosterone production was also found. The present findings demonstrate that the changes in the endogenous GnRH transcripts could be related with the gonadal differentiation in gilthead seabream, and that exogenous GnRH plays a role by stimulating apoptosis in the degenerating testis.
Subject(s)
Genes, Switch , Gonadotropin-Releasing Hormone/physiology , Gonads/growth & development , Sea Bream/growth & development , Sex Differentiation/genetics , Alternative Splicing , Animals , Female , Gonadotropin-Releasing Hormone/genetics , Gonadotropin-Releasing Hormone/pharmacology , Gonads/drug effects , Gonads/metabolism , Male , Ovarian Follicle/drug effects , Ovarian Follicle/metabolism , RNA, Messenger/analysis , RNA, Messenger/metabolism , Sea Bream/anatomy & histology , Sea Bream/genetics , Testosterone/biosynthesis , Transcription, GeneticABSTRACT
Apoptosis is a form of cell death, characterized by morphological and biochemical changes. Apoptosis occurs in the normal testis and in response to different agents. In this study, we investigated the effect of gonadotropin-releasing hormone (GnRH) in testicular apoptosis in the goldfish. GnRH is a decapeptide that is expressed in different tissues, including gonads in mammalian and non-mammalian species. While GnRH is considered to be a paracrine mediator of ovarian follicular atresia, the role of GnRH in the testis is less clear. In the present study, treatments with native salmon GnRH and chicken GnRH-II increased DNA fragmentation (a hallmark of apoptosis) in the mature goldfish testis. On the other hand, gonadotropin hormone was found to act as survival factor, by decreasing spontaneous and GnRH-induced DNA fragmentation in the goldfish testis. The results demonstrate that GnRH plays an important paracrine role in the control of apoptosis in the goldfish testis.
Subject(s)
Apoptosis/drug effects , Chickens , Goldfish/physiology , Gonadotropin-Releasing Hormone/analogs & derivatives , Gonadotropin-Releasing Hormone/pharmacology , Salmon , Testis/drug effects , Animals , Cells, Cultured , Chorionic Gonadotropin/pharmacology , Male , Testis/cytologyABSTRACT
Apoptosis is a form of programmed cell death that is essential for the development of the embryo and adult tissue plasticity. In adults, it is observed mainly in those tissues undergoing active differentiation such as the hematopoietic system, testis, ovary, and intestinal epithelium. Apoptosis can be triggered by many factors, such as hormones, cytokines, and drugs, depending on the type of the cell. While the intracellular signaling mechanisms may vary in different cells, they all display similar morphological and biochemical features at the later stages of the apoptotic process. This review focuses on the factors controlling ovarian apoptosis, emphasizing observations made on GnRH-induced apoptotic process in goldfish follicles.
