LncRNA-OIS1 regulates DPP4 activation to modulate senescence induced by RAS.

Oncogene-induced senescence (OIS), provoked in response to oncogenic activation, is considered an important tumor suppressor mechanism. Long non-coding RNAs (lncRNAs) are transcripts longer than 200 nt without a protein-coding capacity. Functional studies showed that deregulated lncRNA expression promote tumorigenesis and metastasis and that lncRNAs may exhibit tumor-suppressive and oncogenic function. Here, we first identified lncRNAs that were differentially expressed between senescent and non-senescent human fibroblast cells. Using RNA interference, we performed a loss-function screen targeting the differentially expressed lncRNAs, and identified lncRNA-OIS1 (lncRNA#32, AC008063.3 or ENSG00000233397) as a lncRNA required for OIS. Knockdown of lncRNA-OIS1 triggered bypass of senescence, higher proliferation rate, lower abundance of the cell-cycle inhibitor CDKN1A and high expression of cell-cycle-associated genes. Subcellular inspection of lncRNA-OIS1 indicated nuclear and cytosolic localization in both normal culture conditions as well as following oncogene induction. Interestingly, silencing lncRNA-OIS1 diminished the senescent-associated induction of a nearby gene (Dipeptidyl Peptidase 4, DPP4) with established role in tumor suppression. Intriguingly, similar to lncRNA-OIS1, silencing DPP4 caused senescence bypass, and ectopic expression of DPP4 in lncRNA-OIS1 knockdown cells restored the senescent phenotype. Thus, our data indicate that lncRNA-OIS1 links oncogenic induction and senescence with the activation of the tumor suppressor DPP4.

Evaluation of fluorescence in situ hybridization techniques to study long non-coding RNA expression in cultured cells.

Deciphering the functions of long non-coding RNAs (lncRNAs) is facilitated by visualization of their subcellular localization using in situ hybridization (ISH) techniques. We evaluated four different ISH methods for detection of MALAT1 and CYTOR in cultured cells: a multiple probe detection approach with or without enzymatic signal amplification, a branched-DNA (bDNA) probe and an LNA-modified probe with enzymatic signal amplification. All four methods adequately stained MALAT1 in the nucleus in all of three cell lines investigated, HeLa, NHDF and T47D, and three of the methods detected the less expressed CYTOR. The sensitivity of the four ISH methods was evaluated by image analysis. In all three cell lines, the two methods involving enzymatic amplification gave the most intense MALAT1 signal, but the signal-to-background ratios were not different. CYTOR was best detected using the bDNA method. All four ISH methods showed significantly reduced MALAT1 signal in knock-out cells, and siRNA-induced knock-down of CYTOR resulted in significantly reduced CYTOR ISH signal, indicating good specificity of the probe designs and detection systems. Our data suggest that the ISH methods allow detection of both abundant and less abundantly expressed lncRNAs, although the latter required the use of the most specific and sensitive probe detection system.

Contribution of Hfe expression in macrophages to the regulation of hepatic hepcidin levels and iron loading.

Hereditary hemochromatosis (HH), an iron overload disease associated with mutations in the HFE gene, is characterized by increased intestinal iron absorption and consequent deposition of excess iron, primarily in the liver. Patients with HH and Hfe-deficient (Hfe-/-) mice manifest inappropriate expression of the iron absorption regulator hepcidin, a peptide hormone produced by the liver in response to iron loading. In this study, we investigated the contribution of Hfe expression in macrophages to the regulation of liver hepcidin levels and iron loading. We used bone marrow transplantation to generate wild-type (wt) and Hfe-/- mice chimeric for macrophage Hfe gene expression. Reconstitution of Hfe-deficient mice with wt bone marrow resulted in augmented capacity of the spleen to store iron and in significantly decreased liver iron loading, accompanied by a significant increase of hepatic hepcidin mRNA levels. Conversely, wt mice reconstituted with Hfe-deficient bone marrow had a diminished capacity to store iron in the spleen but no significant alterations of liver iron stores or hepcidin mRNA levels. Our results suggest that macrophage Hfe participates in the regulation of splenic and liver iron concentrations and liver hepcidin expression.

Hfe deficiency increases susceptibility to cardiotoxicity and exacerbates changes in iron metabolism induced by doxorubicin.

The clinical use of doxorubicin (DOX), an anthracycline chemotherapeutic agent, is limited by cardiotoxicity. The possible involvement of iron in DOX-induced cardiotoxicity became evident from studies in which iron chelators were shown to be cardioprotective. Iron overload is found in hereditary hemochromatosis, a genetic disorder prevalent in individuals of European descent. We hypothesized that Hfe deficiency may increase susceptibility to DOX-induced toxicity. Acute cardiotoxicity and iron changes were studied after treatment with DOX in Hfe knock-out (Hfe-/-) mice and wild-type mice. DOX-induced iron metabolism changes were intensified in Hfe-/- mice, which accumulated significantly more iron in the heart, liver, and pancreas, but less in the spleen compared with wild-type mice. In addition, Hfe-deficient mice exhibited significantly greater sensitivity to DOX-induced elevations in serum creatine kinase and aspartate aminotransferase. Increased mortality after chronic DOX treatment was observed in Hfe-/- mice and Hfe+/-mice compared with wild-type mice. DOX-treated Hfe-/- mice had a higher degree of mitochondrial damage and iron deposits in the heart than did wild-type mice. These data demonstrate that Hfe deficiency in mice increases susceptibility to DOX-induced cardiotoxicity and suggest that genetic mutations related to defects in iron metabolism may contribute to its cardiotoxicity in humans.