Van – DNA is spelling out individual words in that instruction manual these sections are called genes and the little ladder steps within the section are a thing called nucleotides. The smallest known component in DNA, in fact, a nucleotide is only one-millionth of a millimeter across the ladder steps or pairs of nucleotides represent the four molecules that make up the letters in the alphabet of genetics the order of these nucleotides on one gene spell out the meaning or function of that gene. here ‘s where the breakthrough comes in scientists have determined that on some jeans a pair of nucleotides is not the correct letter for that regular configuration of that gene. if one of the letters was wrong in genetics this error is called single nucleotide polymorphisms. It’s mean there are many forms of corresponding to a difference at a single nucleotide position such as substitution, deletion or insertion. First and foremost Single nucleotide polymorphisms, frequently called SNPs or pronounced ” snips”, is a DNA sequence variation occurring when a single nucleotide as A, T, C or G in the genome differs between members of a biological species or paired chromosomes in a human. The less common base must have a frequency of SNPs at least 1 % of the population. For example of SNPs is the substitution of a C for a G in the nucleotide sequence AACGAT, therefore producing the sequence AACCAT. When SNPs occur inside a gene they create different variants or alleles of those genes. One of the most striking features of this problem is the SNPs’ region occur in noncoding of the genome as well as in genes specificly in both exons and introns. According to research show that SNPs occur once in every 300 nucleotides on average, so in total there are approximately 10 million SNPs in the human genome. The second thing need to be mentioned is source of polymorphisms. SNPs are created by point mutations normally is any change of single nucleotide at any place in the genome. Some cases can be occur like replacement of one nucleotide with another or delection or addition of a single nucleotide. Single nucleotide polymorphisms are variations in one nucleotide at a very specific locus and mostly have two allles in each locus. SNPs and Genome Wide Association Studies used to determine the functions of genes. Single nucleotide polymorphisms are being very helpful in helping us find that out. These are SNPs which are used to tag specific genotypes. SNPs act as chromosomal tags to specific regions of DNA. Thus, it can be used to identify the location of genes on chromosomes. Non-coding regions that are close to the genome are often the parts that contain the single nucleotide polymorphisms, but it could actually be within a gene also, within a coding region of a gene. Generally, it is right that adjacent to a gene that we are interested in. It is not in the gene itself. Therefore, there are only two varieties of the alleles. SNPs have some influence central nervous system phenotypes contenting susceptibility to neurological disorders. For example, in Alzheimer’s disease have APOE gene that is an important genetic determinant in disease, encoding apolipoprotein E (ApoE). When two SNPs in this gene presence will create three common variants- APOE ?2, ?3 and ?4, which produce the proteins corresponding is ApoE2, E3, and E4 and each variant have a risk with different level of Alzheimer’s disease susceptibility special APOE ?4. We live in a world, in which have much hidden-danger like cancer. Because some reason, right now SNPs in disease-related genes are increasingly being used as candidates in the search for causative variations. Most SNPs have no effect on health or development. Some of these genentic differences have proven to be very important in the study of human health. Researchers have found SNPs that may help predict an individual’s response to certain drugs, susceptibility to environmental factors such as toxins, and risk of developing particular diseases. SNPs can also be used to track the inheritance of disease genes within families. Future studies will work to identify SNPs associated with complex diseases such as heart disease, diabetes, and cancer.
San – Cancer is always a problem that scientists are aiming to address as a result of their high levels of death in human. Because of that, many human bodyís ability was explored with the typical example of miRNA which is a new hope for cancer treatment. Previous studies have demonstrated the roles of miRNA in the diagnosis and treatment of cancer with regulation function in a lot of biological activities includes formation, development, differentiation or by detecting that the miRNA overactive causes cancer cells to live longer instead of apoptosis. This literature review will provide some background knowledge about miRNA, the effects of miRNA on gene that bringing the wonderful signal for cancer treatment and related researches. Cancer is always one of the top killers in the world and there are many causes for this disease. This is the reason why it attracts scientist to constantly explore the therapeutic approach. It has resulted in many advanced treatments including chemotherapy, radiation therapy to fight cancer. However, because of the side effects that these treatment bring so much and can be dangerous to the human body, scientists continue to looking for more optimized and developed treatments. One of them is the discovery of miRNA that has made significant diagnosis and treatment of cancer.
MicroRNA (miRNA) is a small RNA non-coding sequence, about 21-25 nucleotides in length. Each miRNA controls hundreds of gene expression through miRNA ñ mRNA binding. These non-transcriptional genes regulate many biological activities contains the formation, development, differentiation and even cell death. By estimation, miRNA-encoding genes account for 1-5% of the human genome and at least 30% of the total miRNA involved in gene regulation (MarFaclane et al, 2010). The first miRNA was discovered in 1993 by Vitor Ambros et al is called lin-4 in Caenorhabditis elegans. MicroRNA synthesis involves cleavage processes that occur in the nucleus and then in the cytoplasm which are carried out by Drosha and Dicer enzymes in the RNase III group that are essentially endonuclease (MarFaclane et al, 2010). MicroRNA genes tend to be much longer than adult miRNA. Typical animal microRNA is made up of the following steps:
-MicroRNA transcribes by RNA polymerase II form pri-miRNA. Pri-miRNA contains 5ícap and poly tail A.
-Pri-miRNA is processed in the nucleus by a complex formed by RNase III Drosha enzyme and Pasha protein. Pre-miRNA was processed has a length of approximately 70 nucleotides.
-Pre-miRNA is exported to the cytoplasm depend on the Exportin-5 and Ran-GTP complexes.
-In the cytoplasm, pre-miRNA continues to undergo Dicer RNase III enzyme process to produce complete miRNA with a length of 21-25 nucleotides.
Although double miRNA sequences can work, only one sequence can active and form RISC (RNA-induced silencing complex) consisting of miRNA and their target mRNA interacting. The miRNA performs the function by the way that combine with the mRNA molecule follow the complementary rule and this leads to the silencing of the specific sequence in the mRNA molecule through one of the following processes:
-Cutting the mRNA into two sections.
-Making the mRNA unstable by cutting poly tail A.
-Affecting the translation of mRNA into protein.
MiRNA participate in the silent regulation process by attaching to the 3íUTR region of the mRNA, causing the mRNA to decay or the translation of mRNA molecule is blocked (Bartel, 2004). Several recent studies have also shown that miRNAs are capable of binding to the 5í nontranslation region of the mRNA enhancing ribosomal protein translation (Orom et al, 2008). The pairing between central and mRNA base pair may completely or incompletely and determine the relative stability of miRNAs with mRNAs (MacFarlane et al, 2010). There are two mechanisms for explaining the dependence independence of the slicer molecule (Lujambio et al, 2012). For example, when there is complete mating between the central and mRNA sequence, it will spread out 10-11 nucleotides. The products of the decomposition process are decomposed starting with mRNA molecule to remove poly tail A. Following the decomposition of mRNA is made by exosome. Silent regulatory that is not dependent on the slicer is incomplete mating between the miRNA and the mRNA target molecule leading to the inhibition of the cleavage activity of Ago2. Much empirical evidence suggests that in this way miRNA also promote the mRNA to deadenylation process, independent of the activity of the slicer, which inhibits the initiation of translation. Finally, mRNA molecules break down by exosomal pathways.
Since the miRNA was discovered, it has been used as a biomarker for cancer treatment and is aimed at developing effective therapies for this chronic disease. The publication of miRNA studies has focused on the use of miRNA as a potential biomarker for early cancer diagnosis. Reduced expression or loss of miRNA molecules acting as tumor suppressor genes leading to increased cell division results in tumor proliferation. For instant, in chronic lymphoblastic leukemia patients, most of the loss or diminution of two miRNAs was miR-15a and miR-16-1. This reduction leads to the loss or degradation of the BCL12 gene (gene that suppresses cellular apoptosis and high in expression in tumor cells) (Calin et al, 2002). Some other miRNAs act as tumor suppressor genes such as miR-143, miR-145 shown in colorectal cancer, prostate cancer, miR-1, miR-101 and miR-122 shown in hepatocellular carcinoma (Sun et al, 2013). In addition, when miRNAs become active strongly, they can make cancer cells live longer, rather than into apoptosis. An experiment by Andrea Ventura has shown that miR-17-92 can be enhanced in some cancers, especially in the lung cancer and lymphoblastic B cancer. They found that the function of miR-17-92 is damaged in mouse embryos will cause death in mice due to their lung size is too small and all the B cell is death. This suggests that miR-17-92 plays a decisive role in the normal development of lung B cell. In lymphocytes B, miRNA seems to play a role in promoting survival of the cell by blocking the genes of the apoptosis process.
MicroRNA has played a huge role in cancer treatment and has not yet been fully explored. The most difficult is to create a way to get the miRNA to the right place for accurate cancer treatment. That motivates us to constantly create and emanate many achievements contributing to society.
Ha – MiRNAs are short strands of 19 to 22 nucleotides has long been discovered in microbial, animal, plant and human genetics. The different between miRNAs with messenger RNA (mRNA) is not involved in protein biosynthesis, so it has been named non-protein coding RNA. These characteristics make them like a tool that has ability for inhibiting protein transfer. So far, many studies have shown that miRNA is involved in the development of cancer cells. Furthermore, miRNAs as therapeutic tools for cancer management in future. The objective of this review is to discuss the generation, mechanism and function of miRNAs. The treatment base on miRNA strategies is currently being evaluated for use in cancer and the current advantages as well as the challenges of miRNAs in clinical.miRNAs are short RNA fragments has been discovered for a long time, but until 1993 that isolation and qualitative analysis of the lin-4 and let-7 miRNAs of the Caenorhabditis elegans which worm living in the soil, etc. had been completed. The scientists had the proofs that illustrated the present of miRNA related to the increase of tumors and cells. The functionality of a miRNA is based on the catalytic process of miRNAs in the natural, which comprises a 15-22 nt single-stranded RNA that enters the cytoplasmic RNA-induced silencing complex (RISC) to pair with mRNAs carrying complementary sequences consequently, repress gene expression. (D Brown et al., 2011)
In the biological process, the miRNA gene was activated by the enzyme RNA Polymerase II, which converted and produced the original microRNA, called pri-miRNA. This is a long string of thousands of bases, and it carries the 5′-CAP, and the 3 ‘is the Poly A, AAAA. Pri-miRNAs contain at least one or more hairpin loops, each containing about 70 nucleotides. After being affected by the DROSHA in the nucleus, the RNA loop (Stem-Loop) called the pre-miRNA, which is absorbed into the cytoplasm, and then they are cut by DICER into miRNA with 22 nucleotides. If the miRNA is combined with the Antagomir artificial antisense RNA which is capable of binding more strongly to the mRNA, then the original RNA sequence will be generated, and the process will be reversed from the beginning. The combination of miRNA with RNA interference (RNAi) under the presence of RNA-induced silencing complex (RNA) will affect part of mRNA in the form of base-pairing to inhibit the continued reproduction or resolution of mRNAs that appeared in the cell. miRNA can act on nearly 200 RNA transcripts and many miRNAs can exert regulatory effects on a protein-coding gene.
Multivariate expression of the miRNA gene between normal and malignant cells is a complex phenomenon that requires simultaneous co-occurrence of several factors, including control of miRNA expression by oncogenes, Tumor suppression genes, epigenetic mechanisms and the preferred gene position of miRNAs in cancer-related regions (Maitri Y. Shah et al., 2016). The experiments are built in order to identify miRNA abnormalities in human cancers by cutting transcriptional regulators. In addition, the miRNA hypermethylation characteristic of human metastasis was identified which show that somatic mutations in DICER1 and DROSHA impaired biogenesis of tumor suppressive miRNA, including let-7 family, in Wilms tumor (Rakheja et al., 2014). These are only initial steps towards understanding about the cause of the suppression of miRNA that control during metastasis, and new mechanisms will continue to be identified in future. (Maitri Y. Shah et al,. 2016)
The impediment on the RNAs that are not directly related to the process of protein are a new direction for medical research, promising a new drug that will effectively treat genetic diseases. The finding it will change the cancer treated method in humans. Next to miRNAs that promising agents in cancer therapy, however, this studies have not found the best fit therapies for cancer. At the same time, it promotes the later research processes of scientists.
Kieu – MicroRNA has emerged as a potential biomarker for cancer detection and treatment 6. This is because a large number of studies have definitely indicated miRNAs as a key player in pathological mechanism of cancer. This review summarizes two of dysregulatory mechanisms underlying cancer in which miRNAs play a central role including miRNA gene mutation and aberrant miRNA biogenesis as well briefly reporting miRNA biogenesis.
MicroRNAs (abbreviated miRNAs) are firstly identified in C. elegans in 1993, and today people have found miRNAs in most organisms 7,8. MiRNAs are characterized to be non-coding RNAs with a tiny size of about 22 nucleotides 1 and proved to be vital players in negative regulation of gene expression 7. MiRNAs significantly contribute to a variety of biological processes especially cell proliferation, differentiation and apoptosis, in which abnormalities of miRNA functions may cause cancer 7, 9. Additionally, after a breakthrough revealed a correlation between miRNA and cancer in 2003 8, a research of Calin et al. in 2006 showed that the percentage of miRNA genes residing in fragile sites or cancer-related genomic area is up to over 50 percents 2. Another strong evidence of miRNAsí role in cancer is serve dysregulation of miRNAs 6. As a result, miRNAs are concerned as an important target in pathomechanism investigation and therapeutic invention in oncology. This paper reviews previous literatures to answer a research question: How do miRNAs involve in cancer formation? Although cancer-relevant miRNA detects are identified in a range of dysregulatory mechanisms, the review focus on two themes including miRNA gene mutation and aberrant miRNA biogenesis. Furthermore, biological synthesis of miRNAs is briefly reported in the paper.
Synthetic process of miRNAs occurs in both nucleus and cytoplasm with help of various proteins. In the nucleus, pri-miRNAs, large primary transcripts possessing a 5í cap and 3í polyadenylated tail, are transcribed by RNA polymerase II. Then the pri-miRNAs are sliced into a pre-miRNA with stem-loop shape containing about 85 nucleotides by a DGCR8/RNase Drosha III complex. Following exportation of the pre-miRNAs into cytoplasm by a couple-protein complex called RanGTP/Exportin 5, miRNA/miRNA duplex with ~ 20 ñ 22 nucleotides in length is generated through processing the pre-miRNAs by RNase III Dicer and a peer protein TRBP. After that a strand named mature miRNA is separated from miRNA/miRNA duplex and then bind to RISC (RNA ñ induced silencing complex) and orientate RISC to mRNA target Involvement of miRNAs are discovered in two biological processes: gene expression regulation and signaling pathway. Regarding inhibition of gene expression, in a majority of situations, miRNAs are complementary with mRNA target at 6-8 nucleotide region near 5í end of the miRNAs called seed region. Complementarity of mRNA targets and miRNAs at seed region is coined Whatson ñ Crick pairs 10. Consequently, if interaction between miRNAs and mRNA targets is caused by imperfect complemetarity, translation of the target will be repressed. In another case, a perfect base pairing leads to degradation of mRNAs. Turning to miRNA role in the signaling pathway, it is indicated that miRNAs portraying a ligand bind to Toll-like receptors 5
Biogenesis of miRNAs is under a tight control at the levels including miRNA transcription, miRNA processing, miRNA transportation, miRNA function with regulation of a range of enzymes and proteins. MiRNA synthesis experiences a tight control at many levels with involvement of a range of proteins. Through a series of studies over past ten years dysregulation of miRNA expression has clearly known as one of core causes in cancer formation. MiRNA gene mutation and aberrant miRNA biogenesis are two of fundamental mechanisms belong to miRNA dysregulation. As described above, a series of enzymes and proteins such as Dicer, Drosha, DGCR8, exportin 5, Argonaute proteins, etc. enroll apparatus of miRNA genesis to manipulate and regulate a formation of miRNAs as well correcting mistakes during a course from pri-miRNAs to mature miRNAs. Therefore, if any deviant behaviors of components in the machine due to mutation or abnormal expression arise unexpectionally, miRNAs will be expressed aberrantly.
Regardless of Drosha and Dicer, these RNA polymerase III involving in pri-miRNa and pre-miRNA processing are observed to be uncontrolled in several tumors. In particular, Walz et al. discovered that 15% of 534 Wilmsí tumors have Drosha and DGCR8 with substitution or deletion mutations at a single nucleotide, which negatively impacts the expression of mature Let -7a and miR-200 family 4. Furthermore, there is a correlational research of the relationship between the level of Dicer/Drosha and median survival in ovarian cancer. The study identified that if the expression level of Dicer is high, sufferers have higher survival rate 6. Study of Karube et al. also revealed a positive correlation between Dicer content and let-7 expression in lung cancer 6.
Turning to Argonaute (AGO) proteins which catalyze RISC and support RNA-silencing process, lose of Argonaute protein coding EIF2C1/hAgo1 gene often occurs in Wilmsí tumors of the kidney 6. Another example of Argonaute proteinsí impact in cancer, a level of AGO2 gene expression in primary gastric cancer and lymph node metastases is higher than that in control samples 11.
According to a study by Melo et al., exportin 5 (XPO5) which takes responsibility for pre-miRNA transportation to cytoplasm are not expressed due to an inactivating genomic change in XPO5 gene 6. This leads to accumulation of pre-miRNAs in the nucleus and reduces expression of miRNAs.
Deletion of miR-143 and miR-145 gene located on 5q33 area was often observed in lung cancer, causing reduction of these gene expressions 3. Besides of that, miR-17-92 cluster gene is amplified in B cell lymphomas and lung cancer, which leads to overexpression of miRNAs coded by miR-17-92 6. There are not only two above findings but also many evidences of miRNA mutation found in various cancers. This highly frequent miRNA gene mutation was also confirmed by experiment in which 227 specimens loading samples from ovarian cancer, breast cancer, and melanoma were tested by using high-resolution array-based comparative genomic hybridization 6. Further study revealed a half of miRNA genes reside in fragile sites or cancer-related genomic area 2.Overall, miRNA mutation genes cause abnormal expression of miRNA which generally leads to malignancy. Amplification and deletion are two quite popular forms of mutation in miRNA genes and these genomic changes occur high frequently.
Thanks to advanced sequencing technology, abnormal miRNA genes were identified in a variety of malignancies, which is the first clue for a hypothesis of miRNA role in cancer and further researchs of pathomechanic and therapeutic discovery. This paper has answered research question by reporting miRNA gene mutation and misregulation of miRNA biogenesis as well as summarizing how miRNAs are generated and how they function. Based on knowledge gained from this review, I suggest to create a database consist of miRNA mutation sequences, normal miRNA sequences, locations of miRNA, and miRNA-associated cancers. This database could contribute to quicker diagnosis of cause underlying cancer through a three-step process using database after cancer identification: cancer-related miRNA and miRNA location identification, miRNA sequencing, and sequence comparision.