MicroRNA - Volume 7, Issue 1, 2018

MicroRNAs (miRNAs), as a major player in post-transcriptional regulation of gene expression, have been reported to regulate a broad variety of key biological processes, including growth, development and stress responses in both plants and animals. While the biogenesis and regulatory abilities of miRNAs have been extensively studied, the evolutionary history of miRNAs still needs more exploration. So far, several models explain the origination of plant and animal MIRNA (MIR) genes. Both inter-species and intra-species conservation and divergence of miRNAs exhibits functional adaptation to changing environments in evolution. Here we summarize recent progress in how these similarities and differences contribute to the characteristic features of miRNA evolution in the two kingdoms.

Background: Late blight is a serious disease in potato caused by Phytophthora infestans. To date only few miRNA have been discovered which are related to late blight disease of potato during host pathogen interaction. Recent studies showed that miRNA, an important gene expression regulator, plays a very important role in host-pathogen interaction by silencing genes either by destructing or blocking of translation of mRNA. Method: Homology search was performed between non-redundant mature miRNA sequences from miRBase database and Solanum tuberosum EST sequences from NCBI database. Screening of the potential miRNA was done after secondary structure prediction. The target related to late blight disease of respective miRNA was functionally annotated. To identify the relationship between the predicted and mature miRNAs, multiple sequence alignment and evolutionary relationships were established. Results and Conclusion: 34 Candidate miRNA related to late blight disease of potato were identified which were associated to five target genes. These miRNAs were linked with Avr3a, INF1, INF2b genes which are elicitin like protein and triggers a hypersensitive response to host cell. Mapping of target sequences showed similarity with Solanum lycopersicum NRC1 gene of chr.1, which are reported as a casual protein required for Pto-mediated cell death and resistance in N. benthamiana. NRC1 are considered as a RX-CC_like domain-containing protein which shows similarity with coiledcoil domain of the potato virus X resistance protein (RX) in Solanum tuberosum. RX recognizes pathogen effector proteins and triggers a response that may be as severe as localized cell death thereby providing resistance against potato virus X.

Background: microRNAs (miRNAs) are small noncoding segments of RNA that negatively regulate gene expression at the post-transcriptional level and fine-tune gene functions. A global repression in miRNA expression is a phenomenon observed in different types of cancer. In this study we aimed to reveal a possible association of miRNAs downregulation in cancer, with the guanine (G) content in the terminal loop (TL) sequences of their precursors. Methods: Lists of most significantly downregulated miRNAs in different tumor types, obtained from previously published microarray experiments, were selected for bioinformatics analysis. The complete precursor, TL, and mature miRNA sequences, were analyzed for evaluation of nucleotide composition and motif enrichment. Results: Herein, we show an association of miRNAs downregulation in cancer, with G enrichment in the TL sequences of their precursors. High G (and GG) content was mostly found in repressed miRNAs of breast, lung and ovary cancers, predominantly in poorly differentiated tumors. The mature sequences of repressed miRNAs had significantly low G content and were enriched with an ACA motif. Conclusion: This study suggests a new link between G enrichment of precursor miRNAs TLs and carcinogenesis, and the possible association of specific sequence motifs with the regulation of their expression.

Background: Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers with high mortality rate. Cigarette smoke and chewing tobacco are well known risk factors associated with ESCC. However, molecular mechanisms associated with development of ESCC among smokers and chewers are poorly understood. MicroRNAs play an important role in regulating physiological and disease processes including esophageal cancer. Objective and Methods: In this study, we developed an in vitro model by treating non-neoplastic Het- 1A esophageal cell line with cigarette smoke and chewing tobacco. We carried out miRNA sequencing on Illumina HiSeq 2500 platform and compared miRNA expression pattern across cigarette smoke and chewing tobacco treated Het-1A cells with untreated cells. Results: We identified and quantified 433 miRNAs in both smoke exposed and chewing tobacco treated cells, of which 13 miRNAs showed significantly altered expression in cigarette smoke exposed cells while 25 miRNAs showed significantly altered expression in chewing tobacco treated cells. In addition, we predicted novel miRNAs from these data-sets. We evaluated miRNAs that showed selective or context dependent expression pattern in cigarette smoke exposed or chewing tobacco treated cells. Conclusion: In this study, we have comprehensively mapped miRNA expression pattern in response to cigarette smoke and chewing tobacco in Het-1A cells. We identified miRNAs that show altered expression in these cell models.

Background: Dysregulation of miRNAs is associated with the development of non-small cell lung cancer (NSCLC). It is imperative to study the dysregulation of miRNAs by cigarette smoke which will affect their targets, either leading to the overexpression of oncoproteins or downregulation of tumor suppressor proteins. Objective and Methods: In this study, we carried out miRNA sequencing and SILAC-based proteomic analysis of H358 cells chronically exposed to cigarette smoke condensate. Using bioinformatics analysis, we mapped the dysregulated miRNAs to differentially expressed target proteins identified in our data. Gene ontology-based enrichment and pathway analysis was performed using the deregulated targets to study the role of cigarette smoke-mediated miRNA dysregulation in NSCLC cell line. Results: miRNA sequencing resulted in the identification of 208 miRNAs, of which 6 miRNAs were found to be significantly dysregulated (2 fold, Log Base 2; p-value ≤ 0.05) in H358-Smoke cells. Proteomic analysis of the smoke exposed cells compared to the untreated parental cells resulted in the quantification of 2,610 proteins, of which 690 proteins were found to be differentially expressed (fold change ≥ 2). Gene ontology based analysis of target proteins revealed enrichment of proteins driving metabolism and a decrease in expression of proteins associated with immune response in the cells exposed to cigarette smoke. Pathway study using Ingenuity Pathway Analysis (IPA) revealed activation of NRF2-mediated oxidative stress response and actin-cytoskeleton signaling, and repression of protein kinase A signaling in H358-Smoke cells. We also identified 5 novel miRNAs in H358-Smoke cells using unassigned reads of small RNA-Seq dataset. Conclusion: In summary, this study indicates that chronic exposure to cigarette smoke leads to widespread dysregulation of miRNAs and their targets, resulting in signaling aberrations in NSCLC cell line. The miRNAs and their targets identified in the study need to be further investigated to explore their role as potential therapeutic targets and/or molecular markers in NSCLC especially in smokers.

Background: Aberrant miRNA expression is associated with the development of several diseases including cervical cancer. Dysregulation of miR-125a-5p is present in a plethora of tumors, but its role in cervical cancer is not well understood. Objective: The aim was to analyze the expression profile of miR-125a-5p in tumor and immortal cell lines with further target prediction, validation and function analysis. Methods: MiR-125a-5p expression was determined by real-time RT-PCR from nine cervical cell lines. In silico tools were used to find target transcripts with an miR-125-5p complementary site within the 3'UTR region. Further target selection was based on gene ontology annotation and ΔG analysis. Target validation was performed by transfection of synthetic miR-125a-5p mimics and luciferase assays. Functional evaluation of miR-125a-5p on migration was performed by transwell migration assays. Results: Differential miR-125a-5p expression was observed between immortal and tumor cells regardless of the human papillomavirus (HPV) content. Thermodynamic and ontological analyses showed Microtubule-Affinity-Regulating Kinase1 (MARK1) as a putative target for miR-125a-5p. An inverse correlation was observed among miR-125a-5p expression and MARK1 protein levels in tumor but not in immortal cells. Luciferase assays showed direct miR-125a-5p regulation over MARK1 through recognition of a predicted target site within the 3'-UTR. HeLa and C-33A cervical tumor cells enhanced migration after transfection with miR-125a-5p mimics and stimulation of cell migration was reproduced by siRNA-mediated inhibition of MARK1. Conclusion: The results showed MARK1 as a novel functional target for miR-125a-5p with implications on cell migration of tumor cervical cancer cells.

Background: The let-7 microRNAs (miRNAs) are frequently dysregulated in carcinogenic processes, including cervical cancer. LIN28 proteins regulate let-7 biogenesis by binding to conserved sequences within the pre-miRNA structure. Nevertheless, recent research has shown that some let-7 miRNAs may escape LIN28 regulation. Objective: Correlate pre-let-7 miRNAs and LIN28B levels in cervical cell lines with different malignancy and HPV content. Methods: Pre-let-7 levels were determined by RTqPCR. LIN28B and other let-7 targets were analyzed by immunoblot. In silico tools were used to correlate let-7 and LIN28B expression and to analyze prelet- 7 sequences and structures. Results: Lin28B protein was detected in all tested cell lines although it was more expressed in tumor cell lines. High levels of pre-let-7c/f-1 and pre-miR-98 were present in almost all cell lines regardless malignancy and LIN28B expression. Pre-let-7g/i were mainly expressed in tumor cell lines, pre-let-7e and pre-let-7-a3 were absent in all cell lines and pre-let-7a-2 showed indistinct expression. LIN28B showed positive correlation with pre-let-7i/g/f-1 and pre-miR-98 in tumor cell lines, suggesting escape from regulation. Sequence alignment and analysis of pre-let-7 miRNAs showed distinctive structural features within the preE region that may influence the ideal pre-let-7 structuring for LIN28B interaction. Short preE-stems were present in pre-let-7 that may escape LIN28B regulation, but long preEstems were mostly associated with high-level pre-let-7 miRNAs. Conclusion: The observed differences of pre-let-7 levels in cervical cell lines may be the result of alternative preE structuring affecting interaction with LIN28B thus resulting in differential let-7 regulation.