MicroRNA (miRNA)
In the history, the two scientists shared Noble Prize in 2006 for their invention of RNA interference which is the regulatory influence on gene expression by RNA degradation process. MiRNA is initially discovered from Caenorhabditis elegans that free-living, transparent nematode (roundworm), later found in a wide variety of mammals, including humans. According to the latest researches, approximately 2300 human mature miRNAs had discovered by scientists and biologists.
In the cell, numerous categories of small endogenous RNA molecule populations, including small interfering RNA, microRNA, small transfer RNA, ribosomal RNA, small nucleolar RNA, repeat-associated small RNA, and tiny non-coding RNA. In this thesis is emphasized miRNA among these small RNAs. They are originated from the different sources, interestingly, biochemical structure and function of MiRNA and siRNA almost same. Both of them have phosphorylated 5’ and hydroxylated 3’ terminals with an identical length roughly 20-30 nucleotides, associate with RNA-induced silencing complexes (RISC) to suppress gene expression particularly. As I mentioned earlier, double-stranded RNA hairpin precursor is the origin of miRNA, on contrary long double-stranded RNA is the origin of siRNA. MicroRNAs are short, small, single-stranded, 21-23 nucleotides long and non-coding RNA sequences that produced by the cleavage of Dicer from a longer hairpin structure double-stranded RNA.
Origination of miRNA initiates in the cell nucleus with the generation of primary miRNA involved by polymerase II or polymerase III enzyme. Primary miRNA cleaved by RNase III endonuclease enzyme and microprocessor protein complex concerning to create more shorter, hairpin structured and 70 nucleotides in length precursor miRNA. Afterward, precursor miRNA has changed a position to the cytoplasm from the cell nucleus through messenger containing two proteins called Exportin 5 and Ran-GPT. Functions of Exportin 5 and Ran-GPT are avoiding nuclear destruction and assisting the movement of pre-miRNA in the cytosol. In the cytosol precursor miRNA split by endonuclease Dicer to establish miRNA duplex (miRNA: miRNA*) which containing the mature double-stranded miRNA
Maturation of miRNA involved by RNA induced silencing complex which consists of Dicer and a large number of integrated proteins including AGO2, Protein Kinase R-activating protein and human immunodeficiency virus transactivating response RNA-binding protein.
Unique protein has slicer activity of messenger RNA is the AGO2 protein. The function of PACT and TRBP are regulated Protein Kinase R(PKR) phosphorylation which operates components of miRNA functional pathway. The active site of RISC is consisting of Argonaute family proteins including AGO1, AGO2, AGO3 and AGO4 proteins that are associated with the silencing mechanism.
Active RISC binds mRNA through incomplete base pairing within the 3’- untranslated region and the seed sequence where located in 5’ end of miRNA, around 2-7 nucleotides long. This sequence of miRNA is a conserved heptametrical region usually sufficient for meticulousness and capability of miRNA. As claimed by the studies, there is somewhere about 60 percent of protein-coding genes of humans are predicted to include 3’-untranslated terminals of miRNA binding sites.
Mature intracellular miRNA could regulate the gene silencing by two post-transcriptional mechanisms: mRNA cleavage or translation repression.
The RISC could localize in the cell following two ways, disseminated in the cytosol or exit in P-bodies. P-bodies are dense cytosolic structure contains various kinds of enzymes and factors. It is the main place for regulating mRNAs stability which undergoes decapping, deadenylation, RNA degradation compartmentalization, and translational repression.
Extracellular miRNA (mature miRNA) exists and circulates in blood plasma and serum only Ago protein-associated type, encapsulated into microvesicles, high density lipoprotein particles, and programmed cell death body
According to the tendency by previous researches, the function of these extracellular vesicles to convey genetic information through transporting genetic material and tumorigenic proteins to spread cancer.
Many different kinds of cells, including immunogenic cells such as macrophages, mast cells, T cells, B cells, dendritic cells, and cancer cells release extracellular vesicles. For instance, microRNAs which includes, lin-4, let7, miR-1, miR-15, miR-16, miR-17, miR-18, miR-181, and miR-375 were revealed within their released extracellular vesicles from the mast cell lines. Other miRNAs have been indicated in extracellular vesicles from common cells such as IL-4-activated macrophages express miR223, dendritic cells express miR451 and T cells express miR335, respectively.
miRNA regulates miscellaneous of vital life actions including resolution of cell fate, cell cycle progress, distinction, programmed cell death. Additionally, miRNA as well as associated with initiation, proliferation, metastasis of cancer cells. Thus, these assumptions for miRNAs considering as a relevant biomarker allow us to diagnose in an early stage of cancer as possible, to predict prognosis of patients, and how successful is the treatment.
Breast cancer
Breast cancer is the one of the widespread cancers and the mortality rate is high out of the women. In the preceding year, 2.1 million new occurrences of breast cancer diagnosed across the globe. The incidence of breast cancer has been increasing worldwide and varies by race and ethnicity. According to the Global cancer statistics in 2018, the prevalence of breast cancer in over a great distance of the globe are as followings: in Australia/New Zealand: 94.2, Northern Europe (the United Kingdom, Sweden, Finland, and Denmark ect.): 90.1, Western Europe (Belgium, Netherlands, and France): 92.6, Southern Europe (Italy): 80.3, Northern America: 84.8, Northern and Southern Africa: 48.9 and 46.2, Eastern Asia: 39.2, and South Central Asia: 25.9.
Regarding the mortality rate of breast cancer demonstrated less discrepancy, with the highest mortality rate calculated in Melanesia, Fiji: 25.5 has the highest number of deaths across the globe, in African and Asian countries have more breast cancer mortality rate compared to Europe and American countries
There are various risk factors affect the occurrence of breast cancer, of which genetic factors such as patients have family history of breast cancer, genetic mutations in the Breast cancer gene 1 and Breast cancer gene 2, environmental factors (air pollution), lifestyle (obesity, utilization of alcohol and coffee, usage of tobacco and cigarette, diet, physical activity, quality and period of sleep, vitamin D intake), demographic factor (gender, age, blood type), reproductive factors (the first occurrence of menstruation and menopause, full-term pregnancy, abortion), hormonal factors (contraceptive methods, postmenopausal hormone therapy), breast-related factors (lactation, breast density, benign breast disorders) others such as socioeconomic status, night shift, diabetes, and radiation.
Hereditary mutations in Breast cancer gene 1, Breast cancer gene 2, other breast cancer susceptibility genes and person who has individual or family history of breast or ovarian cancer, these are genetic factors and constitute of five to ten percent of all breast cancer occurrences.
Breast cancer evolves in five different phases 0-4 on a macroscopic level. In phase 0, a small tumor starts to develop in the ductal, lobular site, or nipple cells of the breast. During phases, 1–3, the tumor grows continuously in its dimensions and spreads to the lymphatic system through lymphatic vessels. In phase 4, the tumor has metastasized to farthest parts of the body including the brain, liver, bones, and lungs through the bloodstream and the lymphatic system from original cancer.
In microscopically, breast cancer development is detailed by 3 definite stages: initiation, progression, and metastasis of the tumor. Breast cancer initiation could take place in many different passages inside somatic cells and cancer cells acquire self-renewing capabilities. Throughout the cancer progression, cancer cells start to grow quickly and keep away from programmed cell death. Cancer metastasis takes places when cancer cells separated from the original tumor, enter the bloodstream, and spread to other tissues and organs, called a secondary tumor and it is connected with the epithelial-mesenchymal transition (EMT) which is the mislay of apicobasal polarity and rise of mesenchymal protein of epithelial cells.
