circulating-microrna-quantification-using-dna-binding-dye-chemistry

Circulating MicroRNA Quantification Using DNA-binding Dye Chemistry and Droplet Digital PCR

Circulating (of cell-free) microRNAs (miRNAs) are released from cells into the blood stream. The amount of specific microRNAs in the circulation has been ...

University of ferrara

MicroRNA-221 (miR-221) is one of the most frequently and consistently up-regulated microRNAs (miRNAs) in human cancer. It has been hypothesized that miR-221 may act as a tumor promoter. To demonstrate this, we developed a transgenic (TG) mouse model that exhibits an inappropriate overexpression of miR-221 in the liver. Immunoblotting and immunostaining confirmed a concomitant down-regulation of miR-221 target proteins. This TG model is characterized by the emergence of spontaneous nodular liver lesions in approximately 50% of male mice and by a strong acceleration of tumor development in 100% of mice treated with diethylnitrosamine. Similarly to human hepatocellular carcinoma, tumors are characterized by a further increase in miR-221 expression and a concomitant inhibition of its target protein-coding genes (i.e., cyclin-dependent kinase inhibitor [Cdkn]1b/p27, Cdkn1c/p57, and B-cell lymphoma 2-modifying factor). To validate the tumor-promoting effect of miR-221, we showed that in vivo delivery of anti-miR-221 oligonucleotides leads to a significant reduction of the number and size of tumor nodules.

Liver tumorigenicity promoted by microRNA-221 in a mouse transgenic model.

hsa-mir-483 is located within intron 2 of the IGF2 locus. We found that the mature microRNA (miRNA) miR-483-3p is overexpressed in 100% of Wilms' tumors. In addition, colon, breast, and liver cancers exhibit high or even extremely high levels of miR-483-3p in approximately 30% of the cases. A coregulation with IGF2 mRNA was detected, although some tumors exhibited high expression of miR-483-3p without a concomitant increase of IGF2. These findings suggested that miR-483-3p could cooperate with IGF2 or act as an autonomous oncogene. Indeed, here we prove that an anti-miRNA oligonucleotide against miR-483-3p could inhibit the miRNAs without affecting IGF2 mRNA and it could suppress tumorigenicity of HepG2 cells, a cell line that overexpresses miR-483-3p and IGF2. Conversely, no antitumor effect was elicited by inhibition of IGF2. The oncogenic mechanism of miR-483-3p was at least partially clarified by the finding that it could modulate the proapoptotic protein BBC3/PUMA and miR-483-3p enforced expression could protect cells from apoptosis. Our results indicate that miR-483-3p could function as an antiapoptotic oncogene in various human cancers and reveal a new, potentially important target for anticancer therapy.

Oncogenic role of miR-483-3p at the IGF2/483 locus.

Fludarabine, is one of the most active single agents in the treatment of chronic lymphocytic leukemia (CLL). Over time, however, virtually all CLL patients become fludarabine-refractory. To elucidate whether microRNAs are involved in the development of fludarabine resistance, we analyzed the expression of 723 human miRNAs before and 5-days after fludarabine mono-therapy in 17 CLL patients which were classified as responder or refractory to fludarabine treatment based on NCI criteria.

MicroRNAs involvement in fludarabine refractory chronic lymphocytic leukemia.

hsa-mir-483 is located within intron 2 of the IGF2 gene. We have previously shown oncogenic features of miR-483-3p through cooperation with IGF2 or by independently targeting the proapoptotic gene BBC3/PUMA. Here we demonstrate that expression of miR-483 can be induced independently of IGF2 by the oncoprotein β-catenin through an interaction with the basic helix-loop-helix protein upstream stimulatory transcription factor 1. We also show that β-catenin itself is a target of miR-483-3p, triggering a negative regulatory loop that becomes ineffective in cells harboring an activating mutation of β-catenin. These results provide insights into the complex regulation of the IGF2/miR-483 locus, revealing players in the β-catenin pathway.

Mutated beta-catenin evades a microRNA-dependent regulatory loop.

The recently discovered mitochondrial calcium uniporter (MCU) promotes Ca(2+) accumulation into the mitochondrial matrix. We identified in silico miR-25 as a cancer-related MCU-targeting microRNA family and demonstrate that its overexpression in HeLa cells drastically reduces MCU levels and mitochondrial Ca(2+) uptake, while leaving other mitochondrial parameters and cytosolic Ca(2+) signals unaffected. In human colon cancers and cancer-derived cells, miR-25 is overexpressed and MCU accordingly silenced. miR-25-dependent reduction of mitochondrial Ca(2+) uptake correlates with resistance to apoptotic challenges and can be reversed by anti-miR-25 overexpression. Overall, the data demonstrate that microRNA targeting of mitochondrial Ca(2+) signaling favors cancer cell survival, thus providing mechanistic insight into the role of mitochondria in tumorigenesis and identifying a novel therapeutic target in neoplasia.

Downregulation of the mitochondrial calcium uniporter by cancer-related miR-25.

BCR/ABL1-positive acute lymphoblastic leukemia relapsing as BCR/ABL1-negative acute lymphoblastic leukemia.

microRNA miR-221 is frequently over-expressed in a variety of human neoplasms. Aim of this study was to identify new miR-221 gene targets to improve our understanding on the molecular tumor-promoting mechanisms affected by miR-221. Gene expression profiling of miR-221-transfected-SNU-398 cells was analyzed by the Sylamer algorithm to verify the enrichment of miR-221 targets among down-modulated genes. This analysis revealed that enforced expression of miR-221 in SNU-398 cells caused the down-regulation of 602 mRNAs carrying sequences homologous to miR-221 seed sequence within their 3'UTRs. Pathways analysis performed on these genes revealed their prominent involvement in cell proliferation and apoptosis. Activation of E2F, MYC, NFkB, and β-catenin pathways was experimentally proven. Some of the new miR-221 target genes, including RB1, WEE1 (cell cycle inhibitors), APAF1 (pro-apoptotic), ANXA1, CTCF (transcriptional repressor), were individually validated as miR-221 targets in SNU-398, HepG2, and HEK293 cell lines. By identifying a large set of miR-221 gene targets, this study improves our knowledge about miR-221 molecular mechanisms involved in tumorigenesis. The modulation of mRNA level of 602 genes confirms the ability of miR-221 to promote cancer by affecting multiple oncogenic pathways.

miR-221 affects multiple cancer pathways by modulating the level of hundreds messenger RNAs.

The microRNA 125b is a double-faced gene expression regulator described both as a tumor suppressor gene (in solid tumors) and an oncogene (in hematologic malignancies). In human breast cancer, it is one of the most down-regulated miRNAs and is able to modulate ERBB2/3 expression. Here, we investigated its targets in breast cancer cell lines after miRNA-mimic transfection. We examined the interactions of the validated targets with ERBB2 oncogene and the correlation of miR-125b expression with clinical variables.

miR-125b targets erythropoietin and its receptor and their expression correlates with metastatic potential and ERBB2/HER2 expression.

The majority of patients with chronic lymphocytic leukemia (CLL) and favorable prognostic features live for long periods without treatment. However, unexpected disease progression is observed in some cases. In a cohort of untreated CD38- CLL patients with normal FISH or isolated 13q- we found that, by fluorescence in situ hybridization (FISH), 16/28 cases presented, within immunomagnetic sorted CD38+ cells, genetic lesions undetectable in the CD38- fraction. These patients showed a shorter time to first treatment (TTFT, p=0.0162) in comparison to cases without FISH lesions in CD38+ cells. Patients with FISH abnormalities in CD38+ cells showed a distinctive microRNA profile, characterized by the down-regulation of miR-125a-5p both in the CD38- and CD38+ populations. In an independent cohort of 71 consecutive untreated CD38- CLL with normal FISH or isolated 13q-, a lower miR125a-5p expression was associated with a shorter TTFT both in univariate and multivariate analysis (p=0.003 and 0.016, respectively) and with a higher prevalence of mutations (7/12 vs 0/8, p=0.015) as assessed by next-generation sequencing. In conclusion, our data showed previously unrecognized subclonal heterogeneity within the CD38+ fraction of CD38- CLL patients with low-risk FISH findings and suggested an association between down-regulated miR-125a-5p expression, genetic complexity and worse outcome.

Genetic subclonal complexity and miR125a-5p down-regulation identify a subset of patients with inferior outcome in low-risk CLL patients.

We evaluated the capability of "microRNA sponges" in sequestering and inhibiting the over-expressed miR-221 in HCC cell lines.

Inhibiting the oncogenic mir-221 by microRNA sponge: toward microRNA-based therapeutics for hepatocellular carcinoma.

Droplet digital PCR (ddPCR) has been successfully used with TaqMan assays to assess gene expression through the quantification of mRNA and miRNA. Recently, a new ddPCR system that can also run DNA-binding dye-based assays has been developed but it has not yet been tested for miRNA. We tested and compared the feasibility of quantifying miRNA with the new QX200 Droplet Digital PCR system when used with EvaGreen dye- and TaqMan probe-based assays. RNA from plasma and serum of 28 patients with cancer and healthy persons was reverse-transcribed and quantified for two circulating miRNAs and one added exogenous miRNA, with both EvaGreen dye-based miRCURY LNA miRNA assays and TaqMan assays. Amplification and detection of target miRNAs were performed on the QX200 ddPCR system. Conditions required to run miRCURY LNA miRNA assays were optimized. The EvaGreen-based assay was precise, reproducible over a range of concentrations of four orders of magnitude, and sensitive, detecting a target miRNA at levels down to 1 copy/μL. When this assay was compared with TaqMan assays, high concordance was obtained for two endogenous miRNAs in serum and plasma (Pearson r > 0.90). EvaGreen dye-based and TaqMan probe-based assays can be equally used with the ddPCR system to quantify circulating miRNAs in human plasma and serum. This study establishes the basis for using EvaGreen dye-based assays on a ddPCR system for quantifying circulating miRNA biomarkers and potentially other low-abundance RNA biomarkers in human biofluids. See all the articles in this CEBP Focus section, "Biomarkers, Biospecimens, and New Technologies in Molecular Epidemiology."

Quantification of circulating miRNAs by droplet digital PCR: comparison of EvaGreen- and TaqMan-based chemistries.

The hypothesis to use microRNAs (miRNAs) circulating in the blood as cancer biomarkers was formulated some years ago based on promising initial results. After some exciting discoveries, however, it became evident that the accurate quantification of cell-free miRNAs was more challenging than expected. Difficulties were linked to the strong impact that many, if not all, pre- and post- analytical variables have on the final results. In this study, we used currently available high-throughput technologies to identify miRNAs present in plasma and serum of patients with breast, colorectal, lung, thyroid and melanoma tumors, and healthy controls. Then, we assessed the absolute level of nine different miRNAs (miR-320a, miR-21-5p, miR-378a-3p, miR-181a-5p, miR-3156-5p, miR-2110, miR-125a-5p, miR-425-5p, miR-766-3p) in 207 samples from healthy controls and cancer patients using droplet digital PCR (ddPCR) technology. We identified miRNAs specifically modulated in one or more cancer types, according to tissue source. The significant reduction of miR-181a-5p levels in breast cancer patients serum was further validated using two independent cohorts, one from Italy (n = 70) and one from US (n = 90), with AUC 0.66 and 0.73 respectively. This study finally powers the use of cell-free miRNAs as cancer biomarkers and propose miR-181a-5p as a diagnostic breast cancer biomarker.

Absolute quantification of cell-free microRNAs in cancer patients.

To clarify whether karyotype aberrations (KA) involving regions not covered by the standard fluorescence in situ hybridization (FISH) panel have independent prognostic relevance, we evaluated KA by conventional cytogenetics in a learning cohort (LC; n = 166) and a validation cohort (VC; n = 250) of untreated chronic lymphocytic leukemia (CLL) patients. In the VC, novel mitogens were used to improve metaphase generation and TP53, NOTCH1, and SF3B1 mutations were assessed. KA undetected by FISH were found in 35 and 35% of the cases in the LC and VC, respectively. In addition to FISH, KA allowed reclassification of 23 and 26% of cases in the LC and VC, respectively, into a higher cytogenetic risk group. By multivariate analysis, both in the LC and VC, KA other than isolated 13q deletion correlated with a shorter time to first treatment (TFT; P < 0.001 and 0.003, respectively), while a complex karyotype predicted a worse overall survival (OS, P = 0.015 and 0.010, respectively). In the VC, where a comprehensive biologic assessment was performed, a shorter TFT was also predicted by stage (P < 0.001), IGHV mutational status (P = 0.05), and del(17p)/TP53 mutations (P = 0.033) while stage (P = 0.023) and del(17p)/TP53 mutations (P = 0.024) independently predicted a shorter OS. FISH results did not independently impact on TFT and OS, in the LC and VC cohorts; this was also the case for NOTCH1 and SF3B1 mutations in the VC. We suggest that in CLL, conventional karyotyping with novel mitogens could be more effective than FISH for the detection of KA allowing for a more precise refinement of prognosis.

Chromosome aberrations detected by conventional karyotyping using novel mitogens in chronic lymphocytic leukemia: Clinical and biologic correlations.

The anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (moAbs) cetuximab or panitumumab are administered to colorectal cancer (CRC) patients who harbor wild-type RAS proto-oncogenes. However, a percentage of patients do not respond to this treatment. In addition to mutations in the RAS genes, mutations in other genes, such as BRAF, PI3KCA, or PTEN, could be involved in the resistance to anti-EGFR moAb therapy.

Prediction of response to anti-EGFR antibody-based therapies by multigene sequencing in colorectal cancer patients.

The miR-145-5p, which induces TP53-dependent apoptosis, is down-regulated in several tumors, including hepatocellular carcinomas (HCCs), but some HCCs show physiological expression of this miR. Here we demonstrate that in HCC cells carrying wild-type TP53 the steady activation of the miR-145 signaling selects clones resistant to apoptosis via up-regulation of the oncogenic miR-483-3p. Expression of the miR-145-5p and of the miR-483-3p correlated negatively in non-neoplastic liver (n=41; ρ=-0.342, P=0.028), but positively in HCCs (n=21; ρ=0.791, P<0.0001), which we hypothesized to be due to impaired glucose metabolism in HCCs versus normal liver. In fact, when liver cancer cells were grown in low glucose, miR-145-5p lowered miR-483-3p expression, allowing apoptosis, whereas when cells were grown in high glucose the levels of miR-483-3p increased, reducing the apoptotic rate. This indicates that depending on glucose availability the miR-145-5p has double effects on the miR-483-3p, either inhibitory or stimulatory. Moreover, resistance to apoptosis in clones overexpressing both miR-145-5p and miR-483-3p was abrogated by silencing the miR-483-3p. Our data highlight a novel mechanism of resistance to apoptosis in liver cancer cells harbouring wild type TP53 and suggest a potential role of miR-145-5p and miR-483-3p as druggable targets in a subset of HCCs.

Article	Year
Liver tumorigenicity promoted by microRNA-221 in a mouse transgenic model. Hepatology (Baltimore, Md.)\| PubMed ID: 22473819	2012
Oncogenic role of miR-483-3p at the IGF2/483 locus. Cancer research\| PubMed ID: 20388800	2010
MicroRNAs involvement in fludarabine refractory chronic lymphocytic leukemia. Molecular cancer\| PubMed ID: 20504344	2010
Mutated beta-catenin evades a microRNA-dependent regulatory loop. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 21383185	2011
Downregulation of the mitochondrial calcium uniporter by cancer-related miR-25. Current biology : CB\| PubMed ID: 23246404	2013
BCR/ABL1-positive acute lymphoblastic leukemia relapsing as BCR/ABL1-negative acute lymphoblastic leukemia. Leukemia & lymphoma\| PubMed ID: 23323950	2013
miR-221 affects multiple cancer pathways by modulating the level of hundreds messenger RNAs. Frontiers in genetics\| PubMed ID: 23630541	2013
miR-125b targets erythropoietin and its receptor and their expression correlates with metastatic potential and ERBB2/HER2 expression. Molecular cancer\| PubMed ID: 24165569	2013
Genetic subclonal complexity and miR125a-5p down-regulation identify a subset of patients with inferior outcome in low-risk CLL patients. Oncotarget\| PubMed ID: 24334759	2014
Inhibiting the oncogenic mir-221 by microRNA sponge: toward microRNA-based therapeutics for hepatocellular carcinoma. Gastroenterology and hepatology from bed to bench\| PubMed ID: 25436097	2014
Quantification of circulating miRNAs by droplet digital PCR: comparison of EvaGreen- and TaqMan-based chemistries. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology\| PubMed ID: 25472671	2014
Absolute quantification of cell-free microRNAs in cancer patients. Oncotarget\| PubMed ID: 26036630	2015
Chromosome aberrations detected by conventional karyotyping using novel mitogens in chronic lymphocytic leukemia: Clinical and biologic correlations. Genes, chromosomes & cancer\| PubMed ID: 26355802	2015
Prediction of response to anti-EGFR antibody-based therapies by multigene sequencing in colorectal cancer patients. BMC cancer\| PubMed ID: 26508446	2015
Over-expression of the miR-483-3p overcomes the miR-145/TP53 pro-apoptotic loop in hepatocellular carcinoma. Oncotarget\| PubMed ID: 27120784	2016

Laura Lupini

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