MicroRNAs are emerging as a hot topic in research, and rightfully so. They show great promise as targets of treatment and as markers for common human diseases, such as cancer and metabolic diseases. In this review, we address some of the basic questions regarding microRNA function in human disease and the clinical significance of microRNAs. Specifically, microRNAs in epigenetics, cancer, and metabolic diseases are discussed, with examples taken from cholangiocarcinoma and nonalcoholic fatty liver disease.

MicroRNAs are small, endogenously expressed, single-stranded, noncoding RNAs about 19-24 nucleotides in length [1]. Found throughout the human genome, microRNAs work to fine-tune gene expression [2,3]. This leads to the following question: are microRNAs epigenetic? Many factors need to be carefully considered before answering this question. What we know for certain is that microRNAs, or more specifically their aberrant expression, are linked to all human cancers. The current review specifically looks at the aberrant expression of a multitude of microRNAs implicated in cholangiocarcinoma, tabulating microRNAs known to be dysregulated in malignant cells and tumors, as compared to normal cells and tissue. Additionally, microRNAs play a major regulatory role in metabolic diseases, such as nonalcoholic fatty liver disease. Much like in cancer, an aberrant expression of microRNAs has been reported in patients with metabolic disease. Since microRNAs can be easily found in tissue and biological fluids such as serum [4], cerebrospinal fluid [5], aqueous humor [6], milk [7], bile [8], peritoneal fluid [7], ovarian follicular fluid [9], and urine [10], the measurement of microRNA expression levels can be used to detect diseases. In addition to disease detection, successful treatment can result in a return to normal levels of microRNAs, suggesting a role in disease monitoring and prognosis. Unfortunately, we cannot provide a comprehensive review of the state of microRNA research, due in no small part to the rapid proliferation of microRNA studies; we hope to provide a few illustrative examples because microRNAs will have an important role in both the diagnosis and treatment of human diseases.

MicroRNAs are expressed from a dedicated gene (termed intergenic with reference to protein-coding genes) or are processed from the RNA of a host gene (whereby both the mRNA and microRNA are products of the same primary transcript). The mature microRNA sequence can be derived from either introns or exons. MicroRNAs can be grouped into larger microRNA families which share conserved sequences. Within the genome, microRNAs are found clustered together or single, and clusters can contain related family members or disparate microRNAs. Once expressed, microRNAs are incorporated into the RNA-induced silencing complex and direct repression of a target mRNA by base complementarity within a 6- to 8-nucleotide sequence, the ‘seed' sequence, of the microRNA [11,12]. This leads to either degradation or repression of the target mRNA, impacting proliferation, apoptosis, and differentiation of cells. MicroRNAs act on several oncogenes or tumor suppressors, contributing to cancer formation and progression. Importantly, aberrant expression of microRNAs has been linked to all human cancers. In addition to cancer biology, microRNAs target a high proportion of cellular mRNAs (estimated as high as 60% of genes) and can impact normal physiology and nonmalignant disease. On the clinical level, microRNAs are surfacing as a novel diagnostic tool for the early detection, classification, and perhaps treatment of human disease.

Should gene regulation by microRNAs always be considered an epigenetic process? There is controversy concerning the exact definition of epigenetics and whether it is necessary for an epigenetic effect to be heritable through either a meiotic or mitotic cell division [13,14]. Indeed, there are arguably cases where the same molecular change in one circumstance is heritable and in another is transient. Fittingly, there is also difficulty in determining if the effects of microRNAs to fine-tune gene expression should be considered epigenetic. If the heritability standard is enforced, then microRNAs would generally be considered regulatory. However, note that in the absence of microRNAs, the development of the zebrafish is impaired (e.g., gastrulation, brain formation, somitogenesis, and heart development), but injection of miR-430 into the single-cell fertilized embryo resulted in phenotypic rescue of these later-stage processes. Further, the model embryos had to be deficient in microRNAs and derived from an egg lacking microRNAs (maternal-zygotic deletion), because the maternal contribution was sufficient to allow development. The rescue of later-stage developmental processes by either maternally derived or injected miR-430 is consistent with this microRNA acting in daughter cells after several rounds of division, for example a heritable effect [15]. This does not indicate that miR-430 expression was self-reinforcing, but only that some microRNAs are stable enough to maintain a functional concentration in a daughter cell even after numerous cell divisions. To complicate matters, microRNAs are regulated by classic imprinting [reviewed in [16,17,18]] and can target proteins mechanistically involved in epigenetic DNA methylation, for example DNMT3 and DNMT1 [19,20] and methyl CpG binding protein 2 [21]. Thus, it may be better to ask whether a specific microRNA is acting in an epigenetic manner rather than broadly trying to classify all microRNA effects as epigenetic.

Early in the study of microRNAs in human disease, it became clear that microRNAs were involved in cancer. For instance, a minimally deleted region of chromosome 13 in chronic lymphocytic leukemia contained the related microRNAs, miR-15a and miR-16-1, and these microRNAs were lost or decreased in cancerous cells [22]. Separately, the analysis of small RNAs cloned and sequenced from colorectal adenocarcinoma tissues revealed decreased levels of miR-143 and miR-145, with levels of both reduced versus nontumor colonic tissues [23]. Since these early studies, there has been a marked expansion in microRNA research. Altered microRNA expression is now well recognized in human malignancies, including examples where microRNAs are expressed at abnormally high levels in tumor cells or at significantly reduced levels. Because there is far more information on microRNAs in cancer than can be covered in a single short review, we have chosen to discuss microRNAs in the biliary tract cancer cholangiocarcinoma, an area of active research in our lab, as an illustrative example.

Cholangiocarcinoma is a relatively rare but highly malignant cancer of the biliary tree that shares a number of features with other cancers, including the risk factors for chronic inflammation and injury [24]. Aberrant microRNA expression has been implicated in cholangiocarcinoma progression, though our understanding is still incomplete. Table 1 lists 47 microRNAs whose expression is increased in cholangiocarcinoma. It is organized to group microRNAs from the same family that share sequence similarity, and presumably function, with other family members. Not all members of the family are included in table 1, but only those with altered levels in disease. The 47 increased microRNAs represent 34 microRNA families. On the other hand, 53 microRNAs are decreased in cholangiocarcinoma (table 2) that belong to 42 microRNA families. There is some overlap, with 5 microRNAs, miR-22-3p, miR-122-5p, miR-200c-3p, miR-221-3p, and miR-424-5p, having been measured at increased and decreased levels in different studies. Whether this reflects differences in disease etiology, stage, or behavior is not yet known. Note that the expression changes - either up or down - have been linked with a functional target in the minority of cases. Studies in other tumor types as well as future studies in cholangiocarcinoma will help determine the functional role of each of the altered microRNAs.

Table 1

Upregulated microRNAs in cholangiocarcinoma

Upregulated microRNAs in cholangiocarcinoma
Upregulated microRNAs in cholangiocarcinoma
Table 2

Downregulated microRNAs in cholangiocarcinoma

Downregulated microRNAs in cholangiocarcinoma
Downregulated microRNAs in cholangiocarcinoma

Metabolic syndrome is defined as three or more of the following: abdominal obesity, hypertriglyceridemia, low HDL cholesterol, hypertension, and elevated blood glucose. Metabolic syndrome has an estimated prevalence of up to 34% of all adults in the USA [25]. Diseases associated with metabolic disease, including obesity, coronary artery disease, type 2 diabetes, nonalcoholic fatty liver disease, and polycystic ovarian syndrome, each have been reported to have altered microRNA expression and function [9,26,27,28,29,30,31,32,33,34,35,36]. MicroRNAs are involved in a number of metabolic processes, such as maintenance of cellular glucose, cholesterol, triglyceride, and fatty acid metabolism [37].

A pathologic contribution of microRNAs to metabolic syndrome seems likely, including a role in inflammation. For example, decreased expression of miR-132 and miR-155 in adipose tissue is associated with increased expression of the proinflammatory cytokine IL-6 in obese individuals [38]; studies in patients with nonalcoholic fatty liver disease have revealed a similar increase in hepatic and circulating levels of IL-6 [39,40]. For additional information regarding altered expression of microRNAs in adipocyte differentiation, inflammation, adipogenesis, and insulin signaling in obese individuals, we refer the reader to excellent recent reviews [38,41]. Here, we will further discuss microRNA signaling in nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease is a spectrum of liver disease including simple steatosis, nonalcoholic steatohepatitis (NASH), advanced hepatic fibrosis, liver cirrhosis, and hepatocellular carcinoma [42]. Aberrant expression of various microRNAs has been reported in patients with NASH [26,43]. NASH patients, for example, had elevated levels of miR-34a and miR-146 and decreased levels of miR-122 in the liver [26], and increasing miR-34a expression in the liver was found to correlate with increasing severity of NASH [44,45]. Free fatty acid-induced lipotoxicity is due, in part, to an increase in miR-34a expression in hepatocytes resulting in repression of the antiapoptotic protein, Sirt1 (a protein deacetylase). Decreased Sirt1 expression caused by miR-34a results in an increase in acetylation of p53 and activates the expression of p53 targets such as PUMA, a proapoptotic BH3-containing protein, promoting the induction of hepatocyte lipoapoptosis [44]. Indeed, PUMA dysregulation appears to be important in nonalcoholic fatty liver disease, as levels of PUMA mRNA and protein were elevated in patients with NASH compared with patients with simple steatosis and control population [46]. Separately, PUMA expression in nonalcoholic fatty liver disease was controlled by miR-296-5p, which was downregulated in patients with NASH [47].

MicroRNAs can be detected in diseased tissue as well as in biological fluids. Some of the mechanisms of microRNA release from the cell of origin are diagrammed in figure 1[48,49,50,51,52], and microRNAs can communicate between cells [53]. Thus, the measurement of altered microRNAs can be performed from tissue biopsies or from relevant biological fluids. In the latter case, detection of microRNAs in biological fluids still leaves a question as to their cell of origin [54]. If the diseased tissue is releasing more microRNAs, it may be a reflection of cellular injury or increased synthesis and export. If another cellular source is responsible, the increased extracellular microRNA may reflect injury to a secondary tissue or recruitment of an inflammatory cell, for instance. This ambiguity should be considered when altered microRNAs in fluids are observed, but also may allow for the detection of related pathologic processes.

Fig. 1

MicroRNAs are released from cells. MicroRNAs have been detected in many extracellular fluids, and are potentially released by regulated processes such as exosome-mediated release or as part of lipid particles (not shown). Alternatively, injury (either necrotic or apoptotic) can result in the release of intracellular microRNAs into the extracellular compartment. Note that endogenous microRNAs detected in biological fluids are consistently more stable than exogenous microRNAs spiked into the same sample. This is consistent with protection of endogenous microRNAs in ribonucleoprotein complexes, in membrane-bound vesicles, or in another stabilizing complex. RISC = RNA-induced silencing complex.

Fig. 1

MicroRNAs are released from cells. MicroRNAs have been detected in many extracellular fluids, and are potentially released by regulated processes such as exosome-mediated release or as part of lipid particles (not shown). Alternatively, injury (either necrotic or apoptotic) can result in the release of intracellular microRNAs into the extracellular compartment. Note that endogenous microRNAs detected in biological fluids are consistently more stable than exogenous microRNAs spiked into the same sample. This is consistent with protection of endogenous microRNAs in ribonucleoprotein complexes, in membrane-bound vesicles, or in another stabilizing complex. RISC = RNA-induced silencing complex.

Close modal

In addition to a correlation between microRNA expression and disease, successful treatment can result in a return to normal microRNA levels. In the case of obesity, for example, the circulating levels of miR-140-5p and miR-142-3p progressively increased in nonobese (BMI <30) to obese (BMI 30-40) to morbidly obese (BMI >40) patients. After bariatric surgery, the circulating levels of miR-140-5p and miR-142-3p were markedly decreased [55]. Of potential importance, miR-140-5p and miR-142-3p are both highly expressed in blood neutrophils [56]. It is not clear whether increased circulating miR-140-5p and miR-142-3p in obese individuals originated from blood cells, such as neutrophils (potentially reflecting the inflammatory component of obesity), or from a tissue more traditionally associated with obesity.

MicroRNAs, whether considered epigenetic or regulatory, play a major role in human diseases. Aberrant expression of microRNAs has been reported in all cancers. Altered also in metabolic diseases, it is clear that microRNAs and their significance in clinical medicine should be looked into more closely. The ability to detect microRNAs in tissue and biological fluids makes them highly useful for early diagnosis of disease. Perhaps even more significant would be the ability to use microRNAs to treat human disease through the return of normal microRNA levels. It is evident that microRNAs will play a major role in the future diagnosis and treatment of human disease.

1.
Bartel DP: MicroRNAs: genomics, biogenesis, mechanism, and function. Cell 2004;116:281-297.
2.
Baek D, Villen J, Shin C, Camargo FD, Gygi SP, Bartel DP: The impact of microRNAs on protein output. Nature 2008;455:64-71.
3.
Selbach M, Schwanhausser B, Thierfelder N, Fang Z, Khanin R, Rajewsky N: Widespread changes in protein synthesis induced by microRNAs. Nature 2008;455:58-63.
4.
Mitchell PS, Parkin RK, Kroh EM, Fritz BR, Wyman SK, Pogosova-Agadjanyan EL, Peterson A, Noteboom J, O'Briant KC, Allen A, Lin DW, Urban N, Drescher CW, Knudsen BS, Stirewalt DL, Gentleman R, Vessella RL, Nelson PS, Martin DB, Tewari M: Circulating microRNAs as stable blood-based markers for cancer detection. Proc Natl Acad Sci USA 2008;105:10513-10518.
5.
Cogswell JP, Ward J, Taylor IA, Waters M, Shi Y, Cannon B, Kelnar K, Kemppainen J, Brown D, Chen C, Prinjha RK, Richardson JC, Saunders AM, Roses AD, Richards CA: Identification of miRNA changes in Alzheimer's disease brain and CSF yields putative biomarkers and insights into disease pathways. J Alzheimers Dis 2008;14:27-41.
6.
Dunmire JJ, Lagouros E, Bouhenni RA, Jones M, Edward DP: MicroRNA in aqueous humor from patients with cataract. Exp Eye Res 2013;108:68-71.
7.
Weber JA, Baxter DH, Zhang S, Huang DY, Huang KH, Lee MJ, Galas DJ, Wang K: The microRNA spectrum in 12 body fluids. Clin Chem 2010;56:1733-1741.
8.
Shigehara K, Yokomuro S, Ishibashi O, Mizuguchi Y, Arima Y, Kawahigashi Y, Kanda T, Akagi I, Tajiri T, Yoshida H, Takizawa T, Uchida E: Real-time PCR-based analysis of the human bile microRNAome identifies miR-9 as a potential diagnostic biomarker for biliary tract cancer. PLoS One 2011;6:e23584.
9.
Sang Q, Yao Z, Wang H, Feng R, Wang H, Zhao X, Xing Q, Jin L, He L, Wu L, Wang L: Identification of microRNAs in human follicular fluid: characterization of microRNAs that govern steroidogenesis in vitro and are associated with polycystic ovary syndrome in vivo. J Clin Endocrinol Metab 2013;98:3068-3079.
10.
Hanke M, Hoefig K, Merz H, Feller AC, Kausch I, Jocham D, Warnecke JM, Sczakiel G: A robust methodology to study urine microRNA as tumor marker: microRNA-126 and microRNA-182 are related to urinary bladder cancer. Urol Oncol 2010;28:655-661.
11.
Lewis BP, Burge CB, Bartel DP: Conserved seed pairing, often flanked by adenosines, indicates that thousands of human genes are microRNA targets. Cell 2005;120:15-20.
12.
Grimson A, Farh KK, Johnston WK, Garrett-Engele P, Lim LP, Bartel DP: MicroRNA targeting specificity in mammals: determinants beyond seed pairing. Mol Cell 2007;27:91-105.
13.
Ptashne M: On the use of the word ‘epigenetic'. Curr Biol 2007;17:R233-R236.
14.
Bird A: Perceptions of epigenetics. Nature 2007;447:396-398.
15.
Giraldez AJ, Cinalli RM, Glasner ME, Enright AJ, Thomson JM, Baskerville S, Hammond SM, Bartel DP, Schier AF: MicroRNAs regulate brain morphogenesis in zebrafish. Science 2005;308:833-838.
16.
Girardot M, Cavaille J, Feil R: Small regulatory RNAs controlled by genomic imprinting and their contribution to human disease. Epigenetics 2012;7:1341-1348.
17.
Baer C, Claus R, Plass C: Genome-wide epigenetic regulation of miRNAs in cancer. Cancer Res 2013;73:473-477.
18.
Wang Z, Yao H, Lin S, Zhu X, Shen Z, Lu G, Poon WS, Xie D, Lin MC, Kung HF: Transcriptional and epigenetic regulation of human microRNAs. Cancer Lett 2013;331:1-10.
19.
Garzon R, Liu S, Fabbri M, Liu Z, Heaphy CE, Callegari E, Schwind S, Pang J, Yu J, Muthusamy N, Havelange V, Volinia S, Blum W, Rush LJ, Perrotti D, Andreeff M, Bloomfield CD, Byrd JC, Chan K, Wu LC, Croce CM, Marcucci G: MicroRNA-29b induces global DNA hypomethylation and tumor suppressor gene reexpression in acute myeloid leukemia by targeting directly DNMT3A and 3B and indirectly DNMT1. Blood 2009;113:6411-6418.
20.
Braconi C, Huang N, Patel T: MicroRNA-dependent regulation of DNA methyltransferase-1 and tumor suppressor gene expression by interleukin-6 in human malignant cholangiocytes. Hepatology 2010;51:881-890.
21.
Volkmann I, Kumarswamy R, Pfaff N, Fiedler J, Dangwal S, Holzmann A, Batkai S, Geffers R, Lother A, Hein L, Thum T: MicroRNA-mediated epigenetic silencing of Sirtuin1 contributes to impaired angiogenic responses. Circ Res 2013;113:997-1003.
22.
Calin GA, Dumitru CD, Shimizu M, Bichi R, Zupo S, Noch E, Aldler H, Rattan S, Keating M, Rai K, Rassenti L, Kipps T, Negrini M, Bullrich F, Croce CM: Frequent deletions and down-regulation of micro-RNA genes miR15 and miR16 at 13q14 in chronic lymphocytic leukemia. Proc Natl Acad Sci USA 2002;99:15524-15529.
23.
Michael MZ, O'Connor SM, van Holst Pellekaan NG, Young GP, James RJ: Reduced accumulation of specific microRNAs in colorectal neoplasia. Mol Cancer Res 2003;1:882-891.
24.
de Groen PC, Gores GJ, LaRusso NF, Gunderson LL, Nagorney DM: Biliary tract cancers. N Engl J Med 1999;341:1368-1378.
25.
Ervin RB: Prevalence of metabolic syndrome among adults 20 years of age and over, by sex, age, race and ethnicity, and body mass index: United States, 2003-2006. Natl Health Stat Rep 2009;13:1-7.
26.
Cheung O, Puri P, Eicken C, Contos MJ, Mirshahi F, Maher JW, Kellum JM, Min H, Luketic VA, Sanyal AJ: Nonalcoholic steatohepatitis is associated with altered hepatic MicroRNA expression. Hepatology 2008;48:1810-1820.
27.
Hilton C, Karpe F: Circulating microRNAs: what is their relevance? Clin Chem 2013;59:729-731.
28.
Xie H, Lim B, Lodish HF: MicroRNAs induced during adipogenesis that accelerate fat cell development are downregulated in obesity. Diabetes 2009;58:1050-1057.
29.
Kloting N, Berthold S, Kovacs P, Schon MR, Fasshauer M, Ruschke K, Stumvoll M, Bluher M: MicroRNA expression in human omental and subcutaneous adipose tissue. PLoS One 2009;4:e4699.
30.
Wang GK, Zhu JQ, Zhang JT, Li Q, Li Y, He J, Qin YW, Jing Q: Circulating microRNA: a novel potential biomarker for early diagnosis of acute myocardial infarction in humans. Eur Heart J 2010;31:659-666.
31.
Contu R, Latronico MV, Condorelli G: Circulating microRNAs as potential biomarkers of coronary artery disease: a promise to be fulfilled? Circ Res 2010;107:573-574.
32.
Fichtlscherer S, De Rosa S, Fox H, Schwietz T, Fischer A, Liebetrau C, Weber M, Hamm CW, Roxe T, Muller-Ardogan M, Bonauer A, Zeiher AM, Dimmeler S: Circulating microRNAs in patients with coronary artery disease. Circ Res 2010;107:677-684.
33.
D'Alessandra Y, Devanna P, Limana F, Straino S, Di Carlo A, Brambilla PG, Rubino M, Carena MC, Spazzafumo L, De Simone M, Micheli B, Biglioli P, Achilli F, Martelli F, Maggiolini S, Marenzi G, Pompilio G, Capogrossi MC: Circulating microRNAs are new and sensitive biomarkers of myocardial infarction. Eur Heart J 2010;31:2765-2773.
34.
Poy MN, Eliasson L, Krutzfeldt J, Kuwajima S, Ma X, Macdonald PE, Pfeffer S, Tuschl T, Rajewsky N, Rorsman P, Stoffel M: A pancreatic islet-specific microRNA regulates insulin secretion. Nature 2004;432:226-230.
35.
Lovis P, Roggli E, Laybutt DR, Gattesco S, Yang JY, Widmann C, Abderrahmani A, Regazzi R: Alterations in microRNA expression contribute to fatty acid-induced pancreatic beta-cell dysfunction. Diabetes 2008;57:2728-2736.
36.
Chen YH, Heneidi S, Lee JM, Layman LC, Stepp DW, Gamboa GM, Chen BS, Chazenbalk G, Azziz R: miRNA-93 inhibits GLUT4 and is overexpressed in adipose tissue of polycystic ovary syndrome patients and women with insulin resistance. Diabetes 2013;62:2278-2286.
37.
Rottiers V, Naar AM: MicroRNAs in metabolism and metabolic disorders. Nat Rev Mol Cell Biol 2012;13:239-250.
38.
Hulsmans M, De Keyzer D, Holvoet P: MicroRNAs regulating oxidative stress and inflammation in relation to obesity and atherosclerosis. FASEB J 2011;25:2515-2527.
39.
Dogru T, Ercin CN, Erdem G, Sonmez A, Tapan S, Tasci I: Increased hepatic and circulating interleukin-6 levels in human nonalcoholic steatohepatitis. Am J Gastroenterol 2008;103:3217-3218.
40.
Wieckowska A, Papouchado BG, Li Z, Lopez R, Zein NN, Feldstein AE: Increased hepatic and circulating interleukin-6 levels in human nonalcoholic steatohepatitis. Am J Gastroenterol 2008;103:1372-1379.
41.
Williams MD, Mitchell GM: MicroRNAs in insulin resistance and obesity. Exp Diabetes Res 2012;2012:484696.
42.
Michelotti GA, Machado MV, Diehl AM: NAFLD, NASH and liver cancer. Nat Rev Gastroenterol Hepatol 2013;10:656-665.
43.
Cheung O, Sanyal AJ: Role of microRNAs in non-alcoholic steatohepatitis. Curr Pharm Des 2010;16:1952-1957.
44.
Castro RE, Ferreira DM, Afonso MB, Borralho PM, Machado MV, Cortez-Pinto H, Rodrigues CM: miR-34a/SIRT1/p53 is suppressed by ursodeoxycholic acid in the rat liver and activated by disease severity in human non-alcoholic fatty liver disease. J Hepatol 2013;58:119-125.
45.
Fu T, Choi SE, Kim DH, Seok S, Suino-Powell KM, Xu HE, Kemper JK: Aberrantly elevated microRNA-34a in obesity attenuates hepatic responses to FGF19 by targeting a membrane coreceptor beta-Klotho. Proc Natl Acad Sci USA 2012;109:16137-16142.
46.
Cazanave SC, Mott JL, Elmi NA, Bronk SF, Werneburg NW, Akazawa Y, Kahraman A, Garrison SP, Zambetti GP, Charlton MR, Gores GJ: JNK1-dependent PUMA expression contributes to hepatocyte lipoapoptosis. J Biol Chem 2009;284:26591-26602.
47.
Cazanave SC, Mott JL, Elmi NA, Bronk SF, Masuoka HC, Charlton MR, Gores GJ: A role for miR-296 in the regulation of lipoapoptosis by targeting PUMA. J Lipid Res 2011;52:1517-1525.
48.
Zernecke A, Bidzhekov K, Noels H, Shagdarsuren E, Gan L, Denecke B, Hristov M, Koppel T, Jahantigh MN, Lutgens E, Wang S, Olson EN, Schober A, Weber C: Delivery of microRNA-126 by apoptotic bodies induces CXCL12-dependent vascular protection. Sci Signal 2009;2:ra81.
49.
Kosaka N, Iguchi H, Ochiya T: Circulating microRNA in body fluid: a new potential biomarker for cancer diagnosis and prognosis. Cancer Sci 2010;101:2087-2092.
50.
Zhu H, Fan GC: Extracellular/circulating microRNAs and their potential role in cardiovascular disease. Am J Cardiovasc Dis 2011;1:138-149.
51.
Zhou Q, Li M, Wang X, Li Q, Wang T, Zhu Q, Zhou X, Gao X, Li X: Immune-related microRNAs are abundant in breast milk exosomes. Int J Biol Sci 2012;8:118-123.
52.
Rayner KJ, Hennessy EJ: Extracellular communication via microRNA: lipid particles have a new message. J Lipid Res 2013;54:1174-1181.
53.
Valadi H, Ekstrom K, Bossios A, Sjostrand M, Lee JJ, Lotvall JO: Exosome-mediated transfer of mRNAs and microRNAs is a novel mechanism of genetic exchange between cells. Nat Cell Biol 2007;9:654-659.
54.
Pritchard CC, Kroh E, Wood B, Arroyo JD, Dougherty KJ, Miyaji MM, Tait JF, Tewari M: Blood cell origin of circulating microRNAs: a cautionary note for cancer biomarker studies. Cancer Prev Res (Phila) 2012;5:492-497.
55.
Ortega FJ, Mercader JM, Catalan V, Moreno-Navarrete JM, Pueyo N, Sabater M, Gomez-Ambrosi J, Anglada R, Fernandez-Formoso JA, Ricart W, Fruhbeck G, Fernandez-Real JM: Targeting the circulating microRNA signature of obesity. Clin Chem 2013;59:781-792.
56.
Gantier MP: The not-so-neutral role of microRNAs in neutrophil biology. J Leukoc Biol 2013;94:575-583.
57.
Meng F, Henson R, Lang M, Wehbe H, Maheshwari S, Mendell JT, Jiang J, Schmittgen TD, Patel T: Involvement of human micro-RNA in growth and response to chemotherapy in human cholangiocarcinoma cell lines. Gastroenterology 2006;130:2113-2129.
58.
Meng F, Henson R, Wehbe-Janek H, Smith H, Ueno Y, Patel T: The MicroRNA let-7a modulates interleukin-6-dependent STAT-3 survival signaling in malignant human cholangiocytes. J Biol Chem 2007;282:8256-8264.
59.
Mott JL, Kobayashi S, Bronk SF, Gores GJ: mir-29 regulates Mcl-1 protein expression and apoptosis. Oncogene 2007;26:6133-6140.
60.
Meng F, Wehbe-Janek H, Henson R, Smith H, Patel T: Epigenetic regulation of microRNA-370 by interleukin-6 in malignant human cholangiocytes. Oncogene 2008;27:378-386.
61.
Chen L, Yan HX, Yang W, Hu L, Yu LX, Liu Q, Li L, Huang DD, Ding J, Shen F, Zhou WP, Wu MC, Wang HY: The role of microRNA expression pattern in human intrahepatic cholangiocarcinoma. J Hepatol 2009;50:358-369.
62.
Selaru FM, Olaru AV, Kan T, David S, Cheng Y, Mori Y, Yang J, Paun B, Jin Z, Agarwal R, Hamilton JP, Abraham J, Georgiades C, Alvarez H, Vivekanandan P, Yu W, Maitra A, Torbenson M, Thuluvath PJ, Gores GJ, LaRusso NF, Hruban R, Meltzer SJ: MicroRNA-21 is overexpressed in human cholangiocarcinoma and regulates programmed cell death 4 and tissue inhibitor of metalloproteinase 3. Hepatology 2009;49:1595-1601.
63.
Kawahigashi Y, Mishima T, Mizuguchi Y, Arima Y, Yokomuro S, Kanda T, Ishibashi O, Yoshida H, Tajiri T, Takizawa T: MicroRNA profiling of human intrahepatic cholangiocarcinoma cell lines reveals biliary epithelial cell-specific microRNAs. J Nippon Med Sch 2009;76:188-197.
64.
Razumilava N, Bronk SF, Smoot RL, Fingas CD, Werneburg NW, Roberts LR, Mott JL: miR-25 targets TNF-related apoptosis inducing ligand (TRAIL) death receptor-4 and promotes apoptosis resistance in cholangiocarcinoma. Hepatology 2012;55:465-475.
65.
Liu CZ, Liu W, Zheng Y, Su JM, Li JJ, Yu L, He XD, Chen SS: PTEN and PDCD4 are bona fide targets of microRNA-21 in human cholangiocarcinoma. Chin Med Sci J 2012;27:65-72.
66.
Li B, Han Q, Zhu Y, Yu Y, Wang J, Jiang X: Down-regulation of miR-214 contributes to intrahepatic cholangiocarcinoma metastasis by targeting Twist. FEBS J 2012;279:2393-2398.
67.
Yamanaka S, Campbell NR, An F, Kuo SC, Potter JJ, Mezey E, Maitra A, Selaru FM: Coordinated effects of microRNA-494 induce G(2)/M arrest in human cholangiocarcinoma. Cell Cycle 2012;11:2729-2738.
68.
Zhang J, Han C, Wu T: MicroRNA-26a promotes cholangiocarcinoma growth by activating beta-catenin. Gastroenterology 2012;143:246-256.e8.
69.
Zeng B, Li Z, Chen R, Guo N, Zhou J, Zhou Q, Lin Q, Cheng D, Liao Q, Zheng L, Gong Y: Epigenetic regulation of miR-124 by hepatitis C virus core protein promotes migration and invasion of intrahepatic cholangiocarcinoma cells by targeting SMYD3. FEBS Lett 2012;586:3271-3278.
70.
Oishi N, Kumar MR, Roessler S, Ji J, Forgues M, Budhu A, Zhao X, Andersen JB, Ye QH, Jia HL, Qin LX, Yamashita T, Woo HG, Kim YJ, Kaneko S, Tang ZY, Thorgeirsson SS, Wang XW: Transcriptomic profiling reveals hepatic stem-like gene signatures and interplay of miR-200c and epithelial-mesenchymal transition in intrahepatic cholangiocarcinoma. Hepatology 2012;56:1792-1803.
71.
Huang Q, Liu L, Liu CH, You H, Shao F, Xie F, Lin XS, Hu SY, Zhang CH: MicroRNA-21 regulates the invasion and metastasis in cholangiocarcinoma and may be a potential biomarker for cancer prognosis. Asian Pac J Cancer Prev 2013;14:829-834.
72.
Karakatsanis A, Papaconstantinou I, Gazouli M, Lyberopoulou A, Polymeneas G, Voros D: Expression of microRNAs, miR-21, miR-31, miR-122, miR-145, miR-146a, miR-200c, miR-221, miR-222, and miR-223 in patients with hepatocellular carcinoma or intrahepatic cholangiocarcinoma and its prognostic significance. Mol Carcinog 2013;52:297-303.
73.
Chusorn P, Namwat N, Loilome W, Techasen A, Pairojkul C, Khuntikeo N, Dechakhamphu A, Talabnin C, Chan-On W, Ong CK, Teh BT, Yongvanit P: Overexpression of microRNA-21 regulating PDCD4 during tumorigenesis of liver fluke-associated cholangiocarcinoma contributes to tumor growth and metastasis. Tumour Biol 2013;34:1579-1588.
74.
Collins AL, Wojcik S, Liu J, Frankel WL, Alder H, Yu L, Schmittgen TD, Croce CM, Bloomston M: A differential microRNA profile distinguishes cholangiocarcinoma from pancreatic adenocarcinoma. Ann Surg Oncol 2013, E-pub ahead of print.
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